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  • 1995-1999  (706)
  • 1990-1994  (1,081)
  • 1996  (706)
  • 1994  (1,081)
  • Organic Chemistry  (1,471)
  • crystal structure
  • 1
    Electronic Resource
    Electronic Resource
    Structure of 1-(2′-tosyloxyethoxy)-8-tosyloxy-9,10-anthraquinone (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 677-681 
    Details
    ISSN: 1572-8854
    Keywords: Anthraquinone ; crystal structure ; intramolecular hindrance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound crystallizes in the monoclinic space group, P21/c;a=12.938(1),b=11.041(1),c=19.285(2) Å, β=104.314(8)°,Z=4. Refinement based on 1660 unique observed reflections converged toR=0.054. The anthraquinone moiety is distorted due to intramolecular steric hindrance from the tosylate groups.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01991963
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  • 2
    Electronic Resource
    Electronic Resource
    Synthesis and crystal structure of a dinuclear organometallic phosphonium ylid complex, [(η5-C5H5(CO)C2(ε-CO)(ε-CHP(C6H5)3)+][PF – 6 ] (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 683-690 
    Details
    ISSN: 1572-8854
    Keywords: Organoiron complex ; dinuclear complex ; crystal structure ; phosphonium ylid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound crystallizes in the centrosymmetric monoclinic space group P21/n withZ=4. The cation consists of two (η5-C5h5)Fe(CO) units which are linked via a metal-metal bond (Fe(1)−Fe(2)=2.530(1) Å), a bridging carbonyl ligand (Fe(1)−C(4)=1.912(8) Å. Fe(2)−C(4)=1.940(9) Å) and a bridging phosphonium ylid ligand (Fe(1)−C(1)=1.991(6) Å, Fe(2)−C(1)=1.985(6) Å and C(1)−P(1)=1.781(6) Å).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01991964
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  • 3
    Electronic Resource
    Electronic Resource
    Crystal and molecular structure of [(C6H5)2P(=0)(CH2CH2N(CH3)3 +][I−] (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 747-752 
    Details
    ISSN: 1572-8854
    Keywords: Phosphine oxide ; quaternary ammonium ; water-soluble phosphine ; crystal structure ; hydrogen bonding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound crystallizes in the centrosymmetric triclinic space group $$P\bar 1$$ withZ=4. The crystallographic asymmetric unit contains two independent cations; interatomic distances within these include P=O=1.47(1) and 1.47(1) Å, P−C6H5=1.78(2)–1.81(1)Å and P−CH2CH2NMe3 +=1.80(1) and 1.81(1) Å. The phosphine oxide moiety is involved in intermolecular hydrogen bonding ()...H−C, with O...H≥2.42Å) and the iodide is involved in I...H−C contacts with I...H≥3.10Å.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01664651
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  • 4
    Electronic Resource
    Electronic Resource
    Solid-state formation of an inclusion compound of cholic acid withp-toluidine (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 185-189 
    Details
    ISSN: 1572-8854
    Keywords: Solid-solid reaction ; inclusion compound ; p-toluidine ; cholic acid ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Cholic acid undergoes solid-solid reactions with some aromatic molecules to form inclusion compounds. Simple shaking of a mixture of powdered cholic acid andp-toluidine results in formation of the 1∶1 (host:guest) inclusion compound which has the same structure as that formed by conventional crystallization methods: monoclinic space groupP21 witha=13.577(4),b=8.078(2),c=14.182(6) Å, β=114.42(3)°,Z=2 andR 1=0.061 for 2680 unique reflections.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01673668
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  • 5
    Electronic Resource
    Electronic Resource
    Synthesis ofcis-[Ru{4,4′-(t-Bu)2bpy}2(PPh3)Cl+][ClO 4 − ] and the crystal structure of its disordered hemiacetonitrile, hemitoluene solvate (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 267-275 
    Details
    ISSN: 1572-8854
    Keywords: Ruthenium(II) complex ; disordered structure ; crystal structure ; solvate ; triphenylphosphine ; bipyridyl
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The complexcis-[Ru{4,4′-(t-Bu)2bpy}2(PPh3)Cl+][ClO 4 − ·0.5(toluene)·0.5(MeCN), where 4,4′-(t-Bu)2bpy=4,4′-di(t-butyl)-2,2′-bipyridyl crystallizes with an ordered racemic mixture of the chiral cations in the centrosymmetric triclinic space group $$P\bar 1$$ (No. 2). The structure was refined toR=4.42% for those 6426 reflections with 20=5–50o and |F o|〉6σ(F). Ruthenium ligand distances are Ru−Cl=2.423(2)Å, Ru−PPh3=2.346(2)Å and Ru−N=2.056(4)–2.098(4)Å. Both the Ru(II)-containing cation and the perchlorate anion are ordered, but the toluene and acetonitrile exhibit an interesting type of scrambled disorder about the inversion center atx=1,y=1/2,z=0.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01677780
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  • 6
    Electronic Resource
    Electronic Resource
    Reactions of the dirhenium(II) complexes Re2X4(dppm)2 (X= Cl, Br; dppm = Ph2PCH2PPh2) with isocyanides. Part IX. New isomeric forms of the mixed carbonyl-isocyanide dirhenium(II) Complexes Re2 Cl4(dppm)2(CO)(CNxyl) and [Re2Cl3(dppm)2(CO)(CNxyl)2]O3SCF3 The X-ray crystal structure of [(xyl NC)2ClRe(μ-dppm)2ReCl2(CO)] O3SCF3 (1996)
    Springer
    Journal of cluster science 7 (1996), S. 155-166 
    Details
    ISSN: 1572-8862
    Keywords: Rhenium ; dirhenium complexes ; rhenium-rhenium multiple bonds ; isocyanide ligands ; carbonyl ligand ; structural isomers ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The monocarbonyl complex Re2Cl4(µ-dppm)2(CO) reacts with xylyl isocyanide in acetonitrile to afford the bioctahedral complex (CO)Cl2Re(µ-dppm)2 ReCl2(CNxyl), 2b. This is a different structural isomer from the edge-sharing bioctahedral complex Cl2Re(µ-Cl)(µ-dppm)2ReCl(CNxyl) or this same stoichiometry which A formed when acetone is be reaction solvent. The complex2b reacts with a further equivalent of xylNC in the presence of TlO3SCF3 in dichloromethane to form a red complex of composition [Re2Cl3(µ-dppm)2 (CO)(CNxyl)2]O3SCF3. 3, which has the open bioctahedral structure [(xylNC)2ClRe(µ-dppm)2ReCl2(CO)]O3SCF3. This is a third isomeric form of this dirhenium cation: the previously isolated green and yellow forms have edge-sharing bioctahedral structures. Crystal data for3 at 295 K: orthorhombic space group Pbca (No. 61) witha=22.654(5) Å,b=22.717(4) Å,c=27.324(4) A,V= 14061(7) Å3, andZ = 8. The structure was refined to R = 0.059 (R, = 0.134 ) for 14164 data. The Re-Re distance is 2.3833(8) Å.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01166054
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  • 7
    Electronic Resource
    Electronic Resource
    A hydrogen-bonded dichloromethane-perchlorate-water channel in the crystal structure ofcis-[Ru(bpy)2{PPh-(o-tolyl)2}Cl+][ClO4 −]·CH2Cl2·H2O (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 67-73 
    Details
    ISSN: 1572-8854
    Keywords: Ruthenium(II) ; bipyridyl ; phenyldi(o-tolyl)phosphine ; solvate ; hydrogen bonding ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The complexcis-[Ru(bpy)2{PPh(o-tolyl)2}Cl+][ClO4 −] crystallized from a solution in dichloromethane as the dichloromethane-water solvate. The structure was refined toR=4.5% for those 2433 reflections with |F o|〉6σ(|F o|). The octahedral Ru(II) cation is associated with metal-ligand distances as follows: Ru−Cl=2.434(3)Å, Ru-PPh(o-tol)2=2.382(2)Å, and Ru−N=2.037(7)–2.088(7)Å. The structure is stabilized by a hydrogen-bonded CH2Cl2...ClO4 −...H2O channel which incorporates adventitious water of crystallization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02018700
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  • 8
    Electronic Resource
    Electronic Resource
    The molecular structure of [bis-triphenylphosphine-silver(I) stearate], [((C6H5)3P)2Ag(O2C(CH2)16CH3)], solubilization of long alkyl chain silver carboxylates (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 99-105 
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    ISSN: 1572-8854
    Keywords: Silver ; stearate ; triphenylphosphine ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The crystal and molecular structure of [bis-triphenylphosphine-silver(I) stearate], [((C6H5)3P)2Ag(O2C(CH2)16CH3)], has been determined by single crystal X-ray analysis: the space group is PT witha=12.021(4),b=13.916(5)1,c=14.678(5) Å, α=95.952(5), β=101.249(6), γ=93.259(5)°,V=2388(2) Å3, andD calc=1.293 g/cm3 forZ=2. The silver is four coordinate: the carboxylate symmetrically chelates the silver while the triphenylphosphine ligands occupy the third and fourth coordination sites. The strong bonding nature of the phosphine ligands, as indicated by the Ag−P bond lengths, 2.446(3) and 2.424(3) Å, dominates the coordination sphere of the silver and forces the initial carboxylate ligand to rearrange from bridging to chelating resulting in weaker Ag−O bonds, as indicated by the extended Ag−O bond lengths, 2.399(8) and 2.449(8) Å. Unlike the free acid, the long hydrocarbon chain is not linear, and exhibits disorder in the lattice. The structure of the title complex explains the dramatic shift in solubility properties compared to the starting phosphine free silver carboxylate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01669724
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  • 9
    Electronic Resource
    Electronic Resource
    Crystal structure of the methanol solvate of (η5-cyclopentadienyl)[1,2-bis(diphenylphosphino)ethane] nitroruthunium(II) Ru(η5-C5H5)dppe)(NO2)·CH3OH (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 489-495 
    Details
    ISSN: 1572-8854
    Keywords: Ruthenium(II) complex ; organoruthenium compound ; bis(1,2-diphenylphosphino)ethane ligand ; ruthenium-nitro complex ; crystal structure ; cyclopentadienyl derivative ; methanol solvate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title complex crystallizes in the centrosymmetric monoclinic space group C2/c (No. 15) withZ=8. The structure was refined toR=4.49% for those 2745 independent reflections with 2θ=5–50o and |F σ|〉6σ(F). Ruthenium-ligand distances are as follows: Ru-P=2.284(2) and 2.286(2) Å, Ru-NO2=2.049(6) Å and Ru-C(Cp)=2.210(10)-2.246(9) Å. Bond lengths within the nitro ligand are N(1)-O(1)=1.226(10) Å and N(1)-O(2)=1.244(10) Å. The methanol of solvation is ordered but is subject to large thermal vibrational motions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01668310
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  • 10
    Electronic Resource
    Electronic Resource
    Crystal structure and molecular dynamics simulation of tri-o-thymotide clathrates with thiophene as guest molecule (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 461-465 
    Details
    ISSN: 1572-8854
    Keywords: Molecular dynamics ; crystal structure ; TOT clathrate ; thiophene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Tri-o-thymotide (TOT) forms a cage-type clathrate with the thiophene guest molecule in a host:guest ratio of 2∶1. This clathrate crystallizes in the trigonal system (space groupP3121). The unit cell, of dimensionsa=b=13.585(4),c=29.914(12)Å, contains 6 TOT and one thiophene molecule. The crystal structure, established by direct methods (R=0.053), indicates that the host cavity has an oblate-ellipsoid shape with a crystallographic twofold axis parallel to the largest dimension of the cage. The guest molecule within the cavity is disordered. Molecular dynamics simulations have been performed and indicate that the guest molecules have hindered molecular freedom around the shortest ellipsoid axis of the cavity, and may produce a dynamic disorder in the cage of the TOT clathrate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01668305
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  • 11
    Electronic Resource
    Electronic Resource
    Crystal structure ofmer,trans-[Ru(NO2)(trpy)(PPr3) 2 + ][ClO 4 − ], a species with disordered PPr3 and NO2 ligands (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 543-551 
    Details
    ISSN: 1572-8854
    Keywords: Ruthenium(II) complex ; tri-n-propylphosphine ; terpyridine ; ruthenium-nitro complex ; crystal structure ; disordered ligands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The complexmer,trans-[Ru(NO2)(trpy)(PPr3) 2 + ][ClO 4 − ]crystallizes in the centrosymmetric orthorhombic space group Pnma withZ=4. Both the ruthenium(II) cation and the perchlorate ligand lie about crystallographic mirror planes. The nitro ligand is not coplanar with the Ru(trpy) moiety and suffers from two fold disorder about its Ru−N bond such that the two sets of oxygen atoms have symmetry-related sites above or below the crystallographic mirror plane. The n-propyl groups within the PPr3 ligands suffer from disorder of their C(α) and C(β) atoms but share common C(γ) sites. Ruthenium-ligand distances are: Ru−PPr3=2.398(2)Å, Ru−NO2=2.053(7) Å, Ru−N(trpy, outer)=2.078(6) and 2.092(6) Å and Ru−N(trpy, central) =1.965(6) Å.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01668413
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  • 12
    Electronic Resource
    Electronic Resource
    Structures of 355-1355-1355-1tricarbonyl: structural evidence for the near-electroneutrality of the dialkylacetal substituent (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 355-360 
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    ISSN: 1572-8854
    Keywords: Chromium ; carbonyl ; arene ; acetal ; crystal structure ; conformation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The structures of the (benzene dialkylacetal)tricarbonyl chromium complexes [η6-C6H5-CH(OR)2]Cr(CO)6 (R=Me,1; Et,2), are reported. The compounds were examined as part of a study of the conformations of the tripodal tricarbonylchromium group. For [η6-C6H5-CH(OMe)2]Cr(CO)3,1, monoclinic,P21/c (# 14),a=15.235(1) Å,b=6.5304(5) Å,c=12.702 Å, β=103.197(1)o,Z=4. For [η6-C6H5-CH(OEt)2]Cr(CO)3,2, monoclinic,P21/c (# 14),a=9.859(3) Å,b=10.547(3) Å,c=15.138(3) Å, β=108.42(2)o,Z=4. The data show that the molecules adopt the expected “three-legged piano stool” structure. The carbonyl ligands in1 adopt an eclipsed arrangement with respect to the arene ring and its substituent, while those in2 are staggered. These conformations are consistent with the notion that the acetal substituent behaves largely as an electroneutral group, or at most as a weak electronic acceptor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01677100
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  • 13
    Electronic Resource
    Electronic Resource
    Structure of (Z)-1-p-methoxyphenyltelluro-1,4-diphenyl but-1-en-3-yne (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 389-392 
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    ISSN: 1572-8854
    Keywords: p-Methoxyphenyltelluro ; x-ray diffraction ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract C23H18TeO,M r=437.97, $$P\bar 1$$ ,a=9.940(2),b=13.664(3),c=7.895(2) Å, α=80.60(1), β=69.71(2), γ=75.95(1)°,V=972.0(4) Å3,Z=2,R=0.041 for 2668 observed reflections. The Te−C bond distances are 2.109(5)Å and the C−Te−C angle is 96.0(2)°. The phenyl rings are planar to within experimental accuracy, making dihedral angles of 64.6(2), 65.3(2) and 31.1(3)°.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01665816
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  • 14
    Electronic Resource
    Electronic Resource
    Crystal structure of (diphenyl)(morpholino)phosphiniminocyclotrithiazene (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 403-406 
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    ISSN: 1572-8854
    Keywords: Cyclotrithiazene ; arylaminophospine ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound (C6H5)2(OC4H8N)P=N−S3N3 crystallizes in the space group $$P\bar 1$$ with unit cell parametersa=9.3900(2),b=9.4747(1),c=11.3850(3) Å, α=95.73(4), β=96.85(6), γ=104.26(2)o, and Z=2. The tricoordinated sulfur of the cyclotrithiazene ring deviates from the mean plane of other skeletal atoms by 0.683(4) Å. The angle at this atom is the smallest in the ring and is enclosed by the longest S−N bonds observed in the ring.
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    URL: http://dx.doi.org/10.1007/BF01665819
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  • 15
    Electronic Resource
    Electronic Resource
    Formation of copper(II) coordination polymers by a flexible double betaine: [{Cu(L)X2(H2O)} n ]·2nH2O [X=Cl, Br] and [{Cu(L)(H2O)4} n ](ClO4)2n ·2nH2O [L=−O2CCH (Me3N+)CH2CH2CH(Me3N+)CO 2 − ] (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 471-477 
    Details
    ISSN: 1572-8854
    Keywords: Copper(II) complex ; crystal structure ; coordination polymer ; betaine ; dicarboxylate ligand
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Three polymeric copper(II) complexes of a flexible double betaine, namely, [{Cu(L)Cl2(H2O)} n ]·2 n H2O (1), [{Cu(L)Br2(H2O)} n ]·2nH2O (2), and [{Cu(L)(H2O)4} n ](ClO4)2n ·2nH2O (3) [L=−O2CCH(Me3N+)CH2CH2CH(Me3N+CO2], have been prepared and characterized by singlecrystal X-ray analysis. Isomorphous complexes (1) and (2) crystallize in space groupC2/c (No. 15) witha=17.725(3),b=5.958(2),c=19.077(3) Å, β=110.70(1)o,V=1881.4(4) Å3, Z=4 anda=18.268(4),b=5.948(3),c=19.166(5) Å, β=109.08(2)o,V=1964.7(9) Å3, Z=4, respectively. Complex (3) belongs to space groupPĪ (No. 2) witha=6.203(1),b=9.293(2),c=12.035(2) Å, α=86.56(2), β=87.33(3), γ=71.23(2)o,V=655.4(2) Å3 and Z=1. The crystal structure of (1) and (2) features an infinite zigzag chain composed of an alternate arrangement of metal atoms and double betaines ligands, with each Cu(II) atom in a distorted CuX2O3 [X-Cl, Br] square-pyramidal geometry, and hydrogen bonding between adjacent chains leads to a layer structure concentrated the (200) family of planes. Complex (3) exhibits a layer structure corresponding to the (001) family of planes, in which neighboring chains constructed from the metal atoms and the double betaine ligands are cross-linked by hydrogen bonding between the aqua ligands. The Cu(II) atom is coordinated in a CuO6 octahedral geometry with Jahn-Teller distortion.
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    URL: http://dx.doi.org/10.1007/BF01668307
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  • 16
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    Electronic Resource
    Crystal structure of aquo (hydroxo) (ethylenediaminetetraacetato) sodium(I) tin(IV), NaSn(OH)(edta)(H2O) (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 503-508 
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    ISSN: 1572-8854
    Keywords: Tin(IV) sodium(I) complex ; ethylenediaminetetraacetic acid ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract NaSn(OH)(edta)(H2O) is monoclinic, space groupP21/c, witha=9.747(3)Å,b=9.121(3)Å,c=16.430(6)Å, β=98.69(4)°, Å3, andZ=4. The coordination environment of Sn(IV) is a capped octahedron. Sn−O distances range from 1.990(6)Å to 2.351(7)Å. Na(I) is five coordinated to three different edta molecules. Na−O distances range from 2.283(9)Å to 2.414(7)Å. The edta ligand presents the E, G/R conformation. The crystal structure is composed of sheets parallel to (001): inside a sheet Sn(OH)(edta) molecules are connected to each other by the Na(I) interactions.
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    URL: http://dx.doi.org/10.1007/BF01668312
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  • 17
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    Electronic Resource
    Geometry of lidocaine-like molecules. 1. Crystal structure of tocainide (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 515-518 
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    ISSN: 1572-8854
    Keywords: Antiarrhythmic agent ; crystal structure ; absolute configuration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound crystallizes in the orthorhombic space groupP212121, withZ=4,a=4.770(1)Å,b=6.620(1)Å,c=37.550(7)Å,R=0.04. The most important factors affecting conformation of the molecules are: the protonation state of the N(9) atom andortho-substitution of the benzene ring in the acetanilide system. Protonation promotes an extended form of the molecule and 2,6-substitution forces a twist of at least 60° between the benzene ring and amide group planes. The resulting separation of lipophilic (xylidine) and amine groups, being two important pharmacophores, equals about 5Å in tocainide and all other structures comprising the amino-2,6-dimethylacetanilide system.
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    URL: http://dx.doi.org/10.1007/BF01668314
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  • 18
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    Electronic Resource
    Structure of a binuclear silver(I) complex [Ph3PAg(O2CCH2Ph)]2 (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 553-557 
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    ISSN: 1572-8854
    Keywords: Silver(I) complex ; synthesis ; crystal structure ; spectroscopic properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The reaction of [Ph3PAgI]4 with sodium phenylacetate in MeOH and CH2Cl2 at room temperature gave rise to a binuclear silver complex with triphenylphosphine and phenylacetate mixed ligands, [Ph3PAg(O2CCH2Ph)]2. The crystal and molecular structure of the complex has been determined by single crystal X-ray diffraction analysis. The space group is $$P\bar 1$$ witha=9.198(2),b=9.516(2),c=13.842(3) Å, α=102.00(3), β=108.34(3), γ=93.58(3)°,Z=1, andDc=1.506 g cm−3. The silver atoms are each coordinated by one phosphorus atom from triphenylphosphine and two oxygen atoms from the carboxylate groups in a T-shape. The complex is further characterized by its IR,1H, and31P NMR spectra.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01668414
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  • 19
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    Electronic Resource
    Crystal structure of the hemitoluene solvate of racemiccis-bis(bipyridyl)chloro(tri-n-propylphosphine)ruthenium(II) perchlorate, a species with disordered PPr3 and toluene moieties (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 667-675 
    Details
    ISSN: 1572-8854
    Keywords: Ruthenium(II) complex ; tri-n-propylphosphine ; bipyridyl ; crystal structure ; disorder
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The complexcis-[Ru(bpy)2(PPr3)Cl+][ClO 4 − ] · 0.5 (toluene) crystallizes as a racemate in the monoclinic space group P21/n. Both the PPr3 ligand and the toluene of crystallization are subject to disorder. Ruthenium—ligand distances are: Ru−PPr3=2.348(2) Å, Ru−Cl=2.426(2) Å and Ru−N(bpy)=2.035(6)–2.112(5) Å.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01991962
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  • 20
    Electronic Resource
    Electronic Resource
    Crystal structure ofmer,trans-[Ru(NO2)(trpy) (PPh3) 2 + ][PF 6 − ]: a “problem structure” (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 853-859 
    Details
    ISSN: 1572-8854
    Keywords: Ruthenium(II) complex ; terpyridine ; triphenylphosphine ; ruthenium-nitro complex ; crystal structure ; pseudo-lattice
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The complexmer,trans-[Ru(NO2)(trpy)(PPh3) 2 + ][PF 6 − ] crystallizes in the centrosymmetric monoclinic space groupP21/n withZ=4; the ruthenium atom lies close toy=1/4 and all data withh+l=2n+1 are systematically weak. The trpy ligand is not strictly planar, but has a “dish-like” geometry. The nitro ligand is rotated from the plane of the Ru(trpy) moiety, the N3Ru/NO2 interplanar angle being 32.5o. Ruthenium-ligand distances are: Ru−PPh3=2.418(4) Å and 2.429(4) Å, Ru−NO2=2.063(12) Å, Ru−N(trpy, outer)=2.100(12) Å and 2.116(12) Å and Ru−N(trpy, central)=2.004(11) Å.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01670319
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  • 21
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    Electronic Resource
    The structure of N,N′-bis(2-hydroxyphenyl)butanediamide (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 661-665 
    Details
    ISSN: 1572-8854
    Keywords: N,N′-bis(2-hydroxyphenyl)butanediamide ; crystal structure ; hydrolysis product
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The structure of N,N′-bis(2-hydroxyphenyl)butanediamide has been determined. The molecule consists of two 2-hydroxyphenyl moieties which are attached (at the 2 position) to the two nitrogens of the butanediamide. The compound C16H16N2O4 crystallizes in the monoclinic space group P21/c witha=5.576(1),b=4.8853(6),c=25.397(6) Å and β=90.58(1)°.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01991961
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  • 22
    Electronic Resource
    Electronic Resource
    The 1∶1-adduct of chlorotriphenyltin with 2′,6′-dimethoxyflavone: a potential fungicide (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 691-694 
    Details
    ISSN: 1572-8854
    Keywords: Organotin ; crystal structure ; flavone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The 1∶1 adduct of chlorotriphenyltin with 2′,6′-dimethoxyflavone, (C35H29O4ClSn)Mr=667.78, crystallizes in the triclinic space groupP1 with the following data:a-9.094(2),b=12.369(3),c=14.674(3) Å, α=74.78(2), β=77.00(2), γ=73.06(3)°,V=1503.8(4) Å3,Z=2, Mo-Kα, μ=9, 8 cm−1,Dc=1.475 g cm−3, F(000)=676,T=293K. The structure was solved by direct-methods and has been refined to a finalR value (l〉3σ(I)) of 0.0301. The flavone coordinates to the tin atom through the carbonyl oxygen atom. The metal center exhibits a trigonal bipyramidal configuration with the three phenyl groups in equatorial positions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01991965
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  • 23
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    Electronic Resource
    Molecular structure and hydrogen bonding of 4-dimethylaminopyridinioacetate in its crystalline dihydrate and hydrochloride trihydrate, L·2H2O and [L2H]Cl·3H2O (L=p-Me2NC5H4N+CH2CO2 −) (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 133-139 
    Details
    ISSN: 1572-8854
    Keywords: Betaine ; 4-dimethylaminopyridinioacetate ; hydrogen bonding ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The crystalline dihydrate and hydrochloride trihydrate of a new betaine, namely, L·2H2O (1) and [L2H]Cl·3H2O(2) (L=p-Me2NC5H4N+CH2CO2), have been synthesized and characterized by X-ray crystallography. Molecule L in compound1 [space groupPbcn, witha=15.732(3),b=7.894(2),c=18.304(4) Å, andZ=8] possesses approximateC s symmetry. The formation of hydrogen bonds by water molecules bridging neighboring carboxy oxygen atoms leads to an infinite two-dimensional network composed of a packing of two different kinds of 12-membered rings. In compound2 [space group PT witha=7.341(2),b=9.543(2),c=17.010(4) Å, α=82.43(2)°, δ=80.34(2)°, λ=74.05(2)°, andZ=2], the carboxylate groups of a pair of betaine molecules are bridged by a proton to form a dimeric cation L2H+ with a very strong asymmetric hydrogen bond of length 2.464(7) Å. The crystal structure features a hydrogen-bonded corrugated ribbon comprising an alternate arrangement of edge-sharing centrosymmetric (H2O)4(Cl−)2 and (H2O)4 rings running parallel to thea axis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01669730
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  • 24
    Electronic Resource
    Electronic Resource
    Crystal and molecular structure of the bidentate ligand 2,2-di(1-pyrazolyl)propane, CH3C(C3N2H3)2CH3 (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 179-183 
    Details
    ISSN: 1572-8854
    Keywords: Bidentate ligand ; crystal structure ; pyrazolyl group ; hydrogen bonding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound lies on a site of C2 symmetry, with the two planar pyrazolyl moieties oriented at 86.1° to one another. The hydrogen atoms were located and refined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01673667
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  • 25
    Electronic Resource
    Electronic Resource
    Synthesis and structure determination of 3α-triphenylstannyl-cholest-5-ene (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 219-222 
    Details
    ISSN: 1572-8854
    Keywords: Steroid ; organometallic ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract 3α-Triphenylstannylcholest-5-ene (1) has been synthesised and its molecular structure has been determined by single crystal X-ray diffraction. Refinement in the triclinic space groupP1 witha=7.805(6),b=7.862(5),c=32.351(10)Å, α=90.87(8), β=94.77(8) and γ=101.15(4)o converged atR=0.063. One of the two crystallographically independent molecules in the unit cell has a patially disordered side chain. The bond lengths and valency angles about tin indicate some steric hindrance due to the proximity of one of the phenyl rings with the B ring of the steroid nucleus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01673674
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  • 26
    Electronic Resource
    Electronic Resource
    Crystal and molecular structure of β-resorcylidene aminoguanidine copper(II) complex (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 841-846 
    Details
    ISSN: 1572-8854
    Keywords: Cu(II) resorcylidene aminoguanidine ; synthesis ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The tridentate Schiff base, β-resorcylidene aminoguanidine (RAG)1 was synthesized from 2,4-dihydroxybenzaldehyde and aminoguanidine and complexed with copper(II) to form a copper(II)-β-resorcylidene aminoguanidine (Cu-RAG)2 complex. X-ray diffraction analysis of compound2 (orthorhombic, Pnma,a=11.674(1);b=6.7198(7);c=17.836(2) Å) revealed a square-planar copper(II) cation with a tridentate·ligand bound through two nitrogen atoms (N1 and N3) of the aminoguanidine moiety and an oxygen (O1) of the monodeprotonated dihydroxybenzaldehyde function. The remaining coordination site was occupied by chloride and the structure was rigidly planar as demanded by the restrictions of the crystallographic space group. The unit cell contents exhibited an extended sheet-like structure constructed via hydrogen bonds both intermolecularly and involving two water molecules (O3 and O4) also restricted by the same mirror symmetry. The remaining water (O5) provided for interlayer hydrogen bonding.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01670317
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  • 27
    Electronic Resource
    Electronic Resource
    Crystal and molecular structure of di(1-pyrazolyl)methane, CH2(C3N2H3)2 (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 93-97 
    Details
    ISSN: 1572-8854
    Keywords: Pyrazolyl group ; crystal structure ; bidentate ligand ; hydrogen bonding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound consists of two planar pyrazolyl fragments oriented at 73.0° to each other and linked to a common carbon atom. All hydrogen atoms were located unambiguously and their positions were refined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01669723
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  • 28
    Electronic Resource
    Electronic Resource
    Crystal structure ofcis-[Ru(bpy)2{PPh2(o-tol)}Cl][ClO4]·1.5(CH2Cl2), a structure containing both ordered and disordered dichloromethane molecules of crystallization (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 111-116 
    Details
    ISSN: 1572-8854
    Keywords: Ruthenium(II) complex ; bipyridyl ; diphenyl(o-tolyl)phosphine ; dichloromethane solvate ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The complexcis-[Ru(bpy)2 {PPh2(o-tol)}Cl][ClO4] crystallizes from dichloromethane as the sesqui-dichloromethane solvate. The complex crystallizes in the monoclinic space group P21/n with Z=4. The structure was refined toR=5.50% for those 2552 independent reflections with |F 0|〉6σ(|F 0|) The octahedral Ru(II) cation is associated with the following bond lengths: Ru-PPh2(o-tol)=2.360(3)Å. Ru−Cl=2.433(2)Å and Ru−N(bpy)=2.041(8)–2.095(8)Å. Both the perchlorate anion and the dichloromethane molecules of solvation exhibit large amplitudes of vibration. One dichloromethane molecule lies in a general position, the other lies about an inversion center and suffers from disorder.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01669726
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  • 29
    Electronic Resource
    Electronic Resource
    Trifluoromethyl group disorder in crystalline 2,8-bis(trifluoromethyl)-4-hydroxymethylquinoline (1996)
    Springer
    Journal of chemical crystallography 26 (1996), S. 615-619 
    Details
    ISSN: 1572-8854
    Keywords: Disordered trifluoromethyl group ; quinoline ; crystal structure ; AM1 calculation ; mefloquine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound crystallized in space groupPna21 with lattice constantsa=13.406(1),b=18.799 (4), andc=4.785(1). The molecule is essentially flat with only fluorine atoms, methylene hydrogen atoms, and the hydroxyl hydrogen atom out of the plane of the quinoline ring. Only one of the trifluoromethyl groups of the title compound is disordered following a pattern observed in other crystal structures. Quantum chemical calculations at the AM1 level are consistent with this phenomenon. Although the carbon atom of the fixed trifluoromethyl group is further from the quinoline nitrogen atom than the carbon atom of the disordered trifluoromethyl group, the fluorine atoms of the fixed trifluoromethyl group more closely approach the quinoline nitrogen atom by 0.3 Å if the C(8)−C(10) bond in the crystal structure is freely rotated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01668622
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  • 30
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    Electronic Resource
    A double-bonded niobium(III) compound with a formamidinate core: Nb2(μ-SMe)2(μ-DTolF)2 (η2-DTolF)2.2 toluene, DToIF= di-p-tolylformamidinate (1996)
    Springer
    Journal of cluster science 7 (1996), S. 655-662 
    Details
    ISSN: 1572-8862
    Keywords: Niobium(III) ; edge-sharing bioctahedra ; di-p-tolylformamidinato ; thiomethoxide ; double-bond ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The reaction of NaEt3BH with Nb2(μ-SMe2)3Cl6 results in the transfer of a hydride ion to dimethylthioether with concomitant production of methane. Further reaction with potassium di-p-tolylformamidinate, KDTolF, yields Nb2(μ-SMe)2(μ-DTolF)2η2-DTolF:)2.2 toluene, 1. In the latter, two thiomethoxide ions and two DTolF groups bridge the trivalent niobium atoms. Each of the other two DTolF groups chelate a metal atom to give the molecule an edge-sharing bioctahedral structure, The niobium-niobium distance of 2.655(2) A is consistent with the presence of a double bond between the metal atoms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01165807
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  • 31
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    Electronic Resource
    Ligand displacement reactions from the coordination sphere of cobalt complexes. Part II: The displacement of ligands of [cis-Co(en)2Cl2]Cl by potassium squarate. The crystal and molecular structure of a compound with idealized formula of [cis-Co(en)2(H2O)Br]2[trans-(C2O4 2−(C2O4H−)Co-trans-(H2O)2(OH)2]Br2 (I) (1996)
    Springer
    Structural chemistry 7 (1996), S. 233-240 
    Details
    ISSN: 1572-9001
    Keywords: Cobalt complexes ; potassium squarate ; crystal structure ; molecular structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Compound (I), idealized as Br4Co3O14N8C16H41 (see text), crystallizes in the triclinic space groupP¯ 1 (No. 2) with cell constants ofa=7.4470(7),b=7.9648(4),c=15.2223(8),α=96.338(4)ℴΒ=93.504(6)ℴ,γ=112.894(6)ℴ,V=821.328 å3, and d(calc; MW=1065.97,z=1)=2.155 gm-cm−3. Data (3880 total reflections) were collected over the range 2ℴ ≤ 2θ ≤ 55ℴ and corrected for absorption (Μ=63.69 cm−1) using data from Psi scans. The unexpectedly isolated compound contains a [cis-Co(en)2Br(OH)]+ cation, while the anion contains a central Co(III) surrounded by two mondentate,trans-squarato ligands, twotrans-hydroxo, and two waters. The waters and hydroxy ligands were identified by determining, experimentally, the presence and positions of their respective hydrogens. Given the need for overall electroneutrality, one squarato ligand must be a dianion (Sq2−) and the other a monoanion (SqH−); however, since the ion bearing the squarato ligands sits at an inversion center, the hydrogen of the latter must be disordered. Refinement of the heavy atoms with anisotropic thermal parameters and fixed hydrogen positions (B's fixed at) led to the finalR(F) andR W(F) factors of 0.036 and 0.042, respectively. (I) was obtained during efforts to prepare [Co(en)2(squarate)]Br by the displacement of two chloro ligands from the coordination sphere of [cis-Co(en)2Cl2]Cl by K2 (squarate) followed by addition of NaBr. Compound (I) appears to be the first example of a coordination compound in which squarate2− and squarate H− anions are present as ligands to a transition metal ion. A search of the Cambridge file (to 1992) produced no known examples of Co(III) squarates. Thus, (I) appears to also be the first example of its kind.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02281234
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  • 32
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    Electronic Resource
    Tryptophan-derived peptides. 1: Crystal structure and solution conformation of Boc-Gly-Trp-Ala-OtBu (1996)
    Springer
    Structural chemistry 7 (1996), S. 103-110 
    Details
    ISSN: 1572-9001
    Keywords: Protected tripeptide ; solution structure ; crystal structure ; X-ray analysis ; NMR analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The solid-state structure of Boc-Gly-Trp-Ala-OBut was determined by single-crystal X-ray diffraction analysis. The tripeptide gave crystals belonging to the orthorhombic systemP212121 and at 122.0(5) K:a=11.0663(12),b=14.107(2),c=17.275(2) Å,V=2697.0(5) Å3Z=4,R(F)=0.0259, andR w(F)=0.0695. The peptide adopts a type-Iβ-turn in the solid state with a single, rather weak, intramolecular hydrogen bond between the Boc-CO and Ala-NH groups (N⋯O 3.082(1) Å, 〈NH⋯O 167(1)°). The conformation of the Boc-Gly-Trp-Ala-OBut peptide has also been studied by1H NMR spectroscopy. The solvent and temperature dependencies of NH chemical shifts suggests that this hydrogen bond is broken and that all amide protons are solvent exposed in CDCl3 and (CD3)2SO.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02278735
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  • 33
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    Electronic Resource
    The crystal structures and thermal shrinkage properties of aromatic polyimide fibers (1996)
    Springer
    Journal of thermal analysis and calorimetry 46 (1996), S. 719-731 
    Details
    ISSN: 1572-8943
    Keywords: aromatic polyimide fiber ; as-spun fiber ; crystallization ; crystal structure ; crystal unit cell ; draw ratio ; dry-jet wet spinning ; isotropic solution ; modulus ; self-elongation ; tensile strength ; thermal shrinkage stress ; thermal shrinkage strain ; thermomechnical analysis ; triclinic ; wide angle X-ray diffraction ; zone drawing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Three aromatic polyimides based on 3,3′,4,4′-biphenyl-tetracarboxylic dianhydride (BPDA) and three different diamines 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (PFMB), 2,2′-dimethyl-4, 4′-diaminophenyl (DMB) or 3,3′-dimethylbenzidine (OTOL) have been synthesized. These polyimides are soluble in hotp-chlorophenol,m-cresol or other phenolic solvents. Fibers have been spun from isotropic solutions using a dry-jet wet spinning method. The as-spun fibers generally exhibit low tensile properties, and can be drawn at elevated temperatures (〉380° C) up to a draw ratio of 10 times. Remarkable increases in tensile strength and modulus are achieved after drawing and annealing. The crystal structures of highly drawn fibers were determinedvia wide angle X-ray diffraction (WAXD). The crystal unit cell lattices have been determined to be monoclinic for BPDA-PFMB and triclinic for both BPDA-DMB and BPDA-OTOL. Thermomechanical analysis (TMA) was used to measure thermal shrinkage stress and strain. A selfelongation has been found in the temperature region around 450°C. This phenomenon can be explained as resulting from the structural development in the fibers as evidencedvia WAXD observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01983598
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  • 34
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    Electronic Resource
    Formation of various polymeric frameworks by dicarboxylate-like ligands: Synthesis and crystal structures of polymeric complexes of sodium perchlorate with flexible double betaines (1996)
    Springer
    Structural chemistry 7 (1996), S. 91-101 
    Details
    ISSN: 1572-9001
    Keywords: Betaine ; sodium perchlorate ; crystal structure ; polymeric framework
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Three crystalline complexes of sodium perchlorate with different flexible double betaines [Na 2(L1)(ClO4)(H2O) n ](ClO4) n (1), [Na 3(L2)(ClO4)3(H2O)2 n ] (2), and [Na(L 3)(CH3OH)n]-(ClO4) n ·xnH2O (x=0.25) (3) [−O2CCH2N+Me2−(CH2) n -N+Me2CH2CO2 −,n=2 L1;n=3 L2;n=4 L3] have been synthesized and characterized by single-crystal X-ray structure analysis. Complex (1) comprises tetranuclear sodium units consolidated by betaine and aqua ligands, which are bridged by half of the ClO4 − anions to form layers matching the (200) planes, the remaining uncoordinated ClO4 − anions being accommodated between adjacent layers. Complex (2) possesses a double-layer polymeric structure with the sodium atoms bridged by ligand oxygen atoms to form columns running parallel to thea axis, which are interconnected by double-betaine ligands lying parallel to theac plane. All of the ClO4 − groups and water molecules are coordinated to the metal atoms. In complex (3) the chains composed of alternating eight-membered and four-membered metallocycles are cross-linked by the betaine ligands, which lie in the (020) and (01/1) families of planes, to yield a three-dimensional network. All of the ClO4 − groups and water molcules fill the resulting infinite channels running parallel to thea axis. Two unusual carboxylate coordination modes are identified, namelyμ 3-O andhapto-3-O plushapto-2-O′ in (1) and (2), respectively.
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    URL: http://dx.doi.org/10.1007/BF02278734
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  • 35
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    Electronic Resource
    Crystal and molecular structure of organic semiconductor (ET)8[Hg4Cl12] · 2C6H6 (1996)
    Springer
    Russian chemical bulletin 45 (1996), S. 370-375 
    Details
    ISSN: 1573-9171
    Keywords: organic conductors ; bis(ethylenedithio)tetrathiafuIvalene ; mercury halides ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A new organic semiconductor, (ET)8[Hg4C112] · 2C6H6, obtained in the ET+-HgCl 3 − -PhF system has been studied by X-ray structural analysis. Radical cations of bis(ethylenedithio)tctrathiafulvalene (ET) in the organic layer of the structure are packed in stacks ofa-type. The average angle between the planes of ET cations from adjacent stacks is 50.1°. The anionic layer is formed by four-charge centrosymmetric [Hg4Cl12]4− complexes and benzene solvate molecules. A comparative crystal-chemical study of the salts obtained by the reaction in the ET+-HgX 3 − -PhY system (where X = Cl, Br, and I; Y = F, Cl, and Br) made it possible to reveal a substantial effect of the sizes of the X and Y atoms on the composition of the salts and on the structural characteristics of the layers, which are responsible for the various conductivities of these salts.
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    URL: http://dx.doi.org/10.1007/BF01433975
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  • 36
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    Tetramethyl(2-methylthioethyl)cyclopentadienyl complexes of zirconium(iv): synthesis, crystal structure, and dynamic behavior in solutions (1996)
    Springer
    Russian chemical bulletin 45 (1996), S. 940-949 
    Details
    ISSN: 1573-9171
    Keywords: substituted sulfur-containing cyclopentadienes ; cyclopentadienyl zirconium complexes ; dynamic behavior ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Chelating sulfur-containing cyclopentadienyl ligand tetramethyl(2-methylthioethyl)cyclopentadiene (1), was synthesized for the first time. Its sodium (2a) and lithium (2b) derivatives were isolated in the crystalline state. Starting from compound1 some novel ZrIV complexes were prepared: [tetramethyl(2-methylthioethyl)cyclopentadienylltriclllorozirconium (3), bis[tetramethyl(2-methylthioethyl)cyclopentadienylldichlorozirconium (4), and [pentamethylcyclopentadienyll [tetramethyl(2-methylthioethyl)cyclopentadienylldichlorozirconium (5). The crystal structures of3 and5 were determined by X-ray diffraction analysis. The dynamic behavior of complex3 in various solvents was investigated by1H and13C N MR spectroscopy. The S→Zr coordination bond was shown to exist in complex3 both in the crystalline state and in solution. No coordination of this type was found in compounds4 and5.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01431329
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    Tetramethyl(2-methoxyethyl)cyclopentadienyl complexes of zirconium(iv). Crystal structure of [η5:η1−C5(CH3)4(CH2CH2OCH3)]ZrCl3 (1996)
    Springer
    Russian chemical bulletin 45 (1996), S. 1740-1744 
    Details
    ISSN: 1573-9171
    Keywords: cyclopentadienes with oxygen-containing substituents ; cyclopentadienyl zirconium complexes ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Several novel zirconium(iv) complexes with the chelating oxygen-containing cyclopentadienyl ligand, tetramethyl(2-methoxyethyl)cyclopentadiene, have been synthesized. [η5:η1-Tetra-methyl(2-methyl)cyclopentadienyl]trichlorozirconium (2), bis[η5-tetramethyl(2-methoxyethyl)cyclopentadienyl]dichlorozirconium (3), [η5-pentamethylcyclopentadienyl][η5-tetra-methyl(2-methoxyethyl)cyclopentadienyl]dichlorozirconium (4), and [η5-tetra-methyl(2-methylthioethyl)cyclopentadienyl][η5-tetramethyl(2-methoxyethyl)-cyclopentadienyl]dichlorozirconium (5) have been prepared from the corresponding lithium cyclopentadienide (l). The crystal structure of cyclopentadienyl complex2 has been established by X-ray analysis. The coordination O→Zr bond in compound2 exists both in the crystalline state and in solutions. No coordination of this type was observed in complexes3–5. Synthesized complexes2–5 are discussed in comparison with their sulfur-containing analogs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01431817
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  • 38
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    Computer Simulation of Crystal-liquid Interface: Application to Wettability of Solids (1996)
    Springer
    Pharmaceutical research 13 (1996), S. 1003-1007 
    Details
    ISSN: 1573-904X
    Keywords: molecular simulation ; interfacial energy ; wettability ; crystal structure ; Monte Carlo method ; potential energy calculations ; contact angle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. This study describes the development and application of a molecular simulation technique for investigating the solid-liquid interface. It attempts to relate the molecular and crystal structure to the observed wettability of solids. Methods. Molecular simulations have been carried out for the crystal-water interface of a series of N-n-alkyl-D-gluconamide crystals using the Monte Carlo technique. The molecular system simulated consisted of a layer of water bounded by two crystal slabs. The interfacial potential energies were calculated for the crystal-water interactions and compared with experimental enthalpy values obtained from contact angle measurements. Results. The simulations clearly reveal the distinct hydrophilic and hydrophobic nature of the respective (010) and (010) faces of these compounds. The distribution of water at the interface observed in the simulations is in accord with the nature of the crystal faces. The calculated interfacial potential energies are in the right ball park, but consistently higher than the experimental values. The disparity, however, is justifiable, resulting from the highly simplified model simulated. Conclusions. Using the developed molecular simulation technique one can calculate the wettability of a solid given the crystal structure. This approach represents an important step towards the goal of engineering crystals with desired wettability characteristics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016094204888
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  • 39
    Electronic Resource
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    On the crystallization behavior of cold-drawn syndiotactic polypropylene (1996)
    Springer
    Colloid & polymer science 274 (1996), S. 1006-1011 
    Details
    ISSN: 1435-1536
    Keywords: Syndiotactic polypropylene ; cold stretching ; chain conformation ; crystal structure ; crystallization behavior
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The influence of the chain conformation on the crystallization behavior of cold-drawn syndiotactic polypropylene (sPP) has been investigated. The conformational and structural changes depending on drawing conditions and thermal treatments has been observed by x-ray diffraction, infra-red spectroscopy and modulated differential scanning calorimetry. A nucleation and crystal growth model is introduced, which explains the low crystallinity of cold-drawn sPP.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00656632
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  • 40
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    Structural variation and recovery of superconductivity by Ca substitution in Y0.4Pr0.6Bs2−x Ca x Cu3 (1996)
    Springer
    Journal of superconductivity 9 (1996), S. 89-91 
    Details
    ISSN: 1572-9605
    Keywords: Y0.4Pr0.6Ba2−xCaxCu3O7−δ ; superconductivity ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Y0.4Pr0.6Ba2−xCaxCu3O7−δ polycrystalline samples were prepared and investigated. The Ca substitution led to a structural variation toward tetragonal symmetry, possibly due to the structural modification within the Cu(1)O layer. Superconductivity and metallic conduction were recovered whenx≥0.2, giving one more evidence for the existence of the ion-size effect at the Ba site.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00728431
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  • 41
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    Fullerene-Acetylene Molecular Scaffolding: Chemistry of 2-functionalized 1-ethynylated C60, oxidative homocoupling, hexakis-adduct formation, and attempted synthesis of C1242- (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 6-20 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: On the way to the fullerene-acetylene hybrid carbon allotropes 2 and 6, the oxidative homocoupling of the 2-functionalized 1-ethynylated C60 derivatives 11, 12, 14, and 15 was investigated. Under Glaser-Hay conditions, the two soluble dumbbell-shaped bisfullerenes 17 and 18, with two C60 moieties linked by a buta-1,3-diynediyl bridge, were formed in 52 and 82% yield, respectively (Scheme 2). Cyclic-voltammetric measurements revealed that there is no significant electronic communication between the two fullerene spheres via the buta-1,3-diynediyl linker. Removal of the 3,4,5,6-tetrahydro-2H-pyran-2-yl (Thp) protecting groups in 18 gave in 80% yield the highly insoluble dumbbell 19 with methanol groups in the 2,2′-positions of the buta-1,3-diynediyl-bridged carbon spheres. Attempted conversion of 19 to the all-carbon dianion 6 (C1242-) via base-induced elimination of formaldehyde was not successful presumably due to exo-dig cyclization of the formed alkoxides. The occurrence of this cyclization under furan formation was proven for 2-[4-(trimethylsilyl)buta-1,3-diyn-1-yl][60]fullerene-1-methanol (21), a soluble model compound for 19 (Scheme 3). To compare the properties of ethynylated fullerene mono-adducts to those of corresponding higher adducts, hexakis-adducts 26 and 28 with an octahedral functionalization pattern resulting from all-e (equatorial) additions were prepared by the reversible-template method of Hirsch (Scheme 4). Reaction of the ethynylated mono-adducts 25 or 13 with diethyl 2-bromomalonate/1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in the presence of 1,9-dimethylanthracene (DMA) as reversible template led to 26 and 28 in 28 and 22% yield, respectively. Preliminary experiments indicated a significant change in reactivity and NMR spectral properties of the fullerene addends with increasing degree of functionalization.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19960790103
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  • 42
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    Oligonucleotide Synthesis on Polystyrene-Grafted Poly(tetrafluoroethylene) Support (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 137-150 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Supports consisting of a thin layer (2-10%) of polystyrene (PS) grafted onto a poly(tetrafluoroethylene) (PTFE) core are an interesting alternative to controlled pore glass (CPG) carriers in oligonucleotide synthesis. The beads are mechanically stable, do not show significant swelling, and allow effective removal of substrates by short washing steps with organic solvents. PTFE-PS as an organic polymer has generally more hydrophobic properties than inorganic polymer supports and, therefore, is well compatible with organic solvents such as anhydrous MeCN. We found PTFE with a content of 2-3% PS graft to be a very good support for the synthesis of oligonucleotides of extended length. In comparison, PTFE with 5-10% grafted PS is especially useful for large-scale syntheses. Functionalization procedures minimized in the extent of side reactions are described as well as examples for the use of the supports in syntheses of oligonucleotides both on large scale and of extended chain length.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790115
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  • 43
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    Säure-Additionen an ‘Push-Pull’-Enine. Erste Beobachtung einer Umlagerung von 5-Chloro-5-(dialkylamino)pentadienalen30. Mitteilung über Aminoacryl-Derivate. 29. Mitteilung: [1]. (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 192-202 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of ‘Push-Pull’ Enynes with Acids. First Observation of a Rearrangement of 5-Chloro-5-(dialkylamino)pentadienals‘Push-pull’-enynes 7 react easily with HCl as well as with AcOH to give 5-amino-5-chloropentadienals 8 and 5-(acetoxy)-5-aminopentadienals 13 as well as the corresponding ketones. In view of a postulated rearrangement of compounds 8 and 13 (Scheme 2), both types of compounds have been treated with traces of acid. While no definite reaction is observed in case of 13, HCl-addition products 8 easily and quantitatively rearrange to give 2H-pyran-2-iminium chlorides 10 which are the postulated intermediates of the rearrangement 8→12 (Scheme 2).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790119
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  • 44
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    The Self-Recognition and Self-Assembly of Folic Acid Salts in Isotropic Water Solution (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 220-234 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The self-assembly of alkaline folates in isotropic water solutions, with or without added salts, has been investigated by small-angle neutron-scattering, circular-dichroism, and NMR techniques. The assembled species are chiral, cylindrical aggregates of finite length, composed of stacked tetramers; each tetramer is formed by Hoogsteen-bonded folate residues. The assembly process is more efficient in the presence of an excess of NaI ions, leading to longer aggregates with stronger tetramer-tetramer-tetramer interaction. In pure water, the rods are shorter and the tetramer-tetramer interaction weaker. Association between folates can be detected by circular-dichroism spectroscopy starting from a concentration of 6· 10-4 mol l-1, well below the critical concentration for the formation of the cholesteric mesophase (ca. 0.5 mol l-1).
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790123
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  • 45
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    Oligosaccharide Analogues of Polysaccharides. Part 6. Orthogonal protecting/activating groups in an improved binomial synthesis of ‘acetyleno-oligosaccharides’ (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 255-268 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bromination of the monosilylated dialkynylated monomer 1a (Scheme 1), dimer 3 and tetramer 5 by N-bromosuccinimide (NBS) in the presence of CF3COOAg gave 2, 4, and 6, respectively, in over 93%. Similar conditions led to bromodesilylation. Either silyl group of the diprotected monomer 1c was selectively removed by bromolysis. On the one hand, bromodesilylation of 1c gave 2 in yields varying between 80 and 99%. On the other hand, bromodesilylation of 7, obtained from 1c by hydrolytic removal of the tetrahydro-2H-pyran-2-yl (Thp) group, yielded 91% of 8. Mechanistic considerations suggested that the deprotective bromination should be improved by replacing the Me3Si by a Me3Ge group. Indeed, bromodegermylation of 1b was quantitative and ca. 60 times faster than bromodesilylation of 1c. The Me3Si and Me3Ge groups can be used for an orthogonal protection/activation of dialkynes. This was shown by desilylating 12 to 11 (Scheme 2), while bromination yielded 13. Both reactions proceeded in high yields; 9 was isolated as a minor by-product of 13. The reactivity towards bromolysis decreases in the series H-DOPS 〉 Me3Ge ≈ H 〉 Me3Si 〉 Thp-DOPS (DOPS = [dimethyl(oxy)-p ropyl]dimethylsilyl). Orthogonal bromolysis of DOPS- and Me3Ge-substituted dialkynes is slightly more selective than the one of Me3Si- and Me3Ge-substituted analogues. Coupling of 7 with the bromoalkyne 2 gave the dimer 15 (76%), 14 (2%), and 16 (4%) (Scheme 3). The binomial synthesis was optimized so that each cycle, doubling the size of the precursor, requires the minimal number of transformations (Scheme 4). The orthogonally protected monomer 1b, dimer 19, and tetramer 22 were, on the one hand, hydrolyzed to the alcohols 18 (95%), 21 (91%), and 24(91%), respectively, and, on the other hand, bromodegermylated to 2 (99%), 4 (97%), and 6(93%). Cross-coupling of 18 with 2, 21 with 4, and 24 with 6 gave the orthogonally protected dimer 19 (73%), tetramer 22 (87%), and octamer 25 (83%), respectively.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19960790126
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  • 46
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    Novel Thiazole-Containing Complexing Agents and Luminescence of Their Europum(III) and Terbium(III) Chelates (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 295-306 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of novel thiazole-containing complexing agents and their luminescence properties with EuIII and TbIII ions are reported. One of these terpyridine analogues was also tested as an EuIII labelling reagent, and its luminescence properties as an antibody conjugate were studied.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790129
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  • 47
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    Masthead (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996) 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790201
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  • 48
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    Corniculoside, a New Biosidic Ester Secoiridoid from Halenia corniculata (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 363-370 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chemical screening of the secondary metabolites from Halenia corniculata L. (CORNAZ), by LC/UV,LC/TSP-MS (thermospray), and LC/ES-MS (electrospray) was used for the targeted isolation of corniculoside (1), a new biosidic ester secoiridoid. The structure was established as 7-β-[(E)-4′-O-(β-D-glucopyranosyl)caffeoyloxy]-sweroside by 1D- and 2D-NMR, LC/UV, LC/MS, and FAB-MS data, in combination with chemical reactions.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790205
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  • 49
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    New Addition Reactions of Organometal Compounds with 4,4-Dimethyl-1,3-thiazole-5(4H)-thionesDedicated to Professor H. Suschitzky on the occasion of his 80th birthday (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 371-384 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Addition reactions of organometallic reagents with 4,4-disubstituted 1,3-thiazole-5(4H)-thiones were studied. Whereas the reactions with alkyllithium and alkyl Grignard reagents occurred in the thiophilic manner, the carbophilic addition was observed with allyllithium and allyl Grignard reagents. A radical reaction mechanism is proposed for rationalizing these observations (Scheme 5). A radical cyclization of the prepared 5-allyl-4,5-dihydro-1,3-thiazole-5-thiol derivatives yielded 1,6-dithia-3-azaspiro[4.4]non-2-enes (Table 4).
    Additional Material: 4 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19960790206
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  • 50
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    Synthesis of Highly Fluorinated Di-O-alk(en)yl-glycerophospholipids and Evaluation of Their Biological Tolerance (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 405-425 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The syntheses of various fluorocarbon/fluorocarbon and fluorocarbon/hydrocarbon rac-1,2- and 1,3-di-O-alk(en)ylglycerophosphocholines and rac-1,2-di-O-alkylglycerophosphoethanolamines (see Fig.2), which may be used as components for drug-carrier and delivery systems, are described together with some results concerning their biological tolerance. They were obtained by phosphorylation of perfluoroalkylated rac-di-O-alk(en)ylgly-cerols using POCl3, then condensation with choline tosylate or N-Boc-ethanolamine (2-[(tert-butoxy)carbonyl-amino]ethanol) followed by Boc-deportection (Schemes 6-8). The fluorcarbon/fluorocarbon 1,2-di-O-alkylgly-cerols were prepared by O-alkylation of rac-1-O-benzylglycerol using perfluoroalkylated mesylates, then hydrogenolysis for benzyl deprotection (Scheme 1). The two different hydrophobic chains in the mixed fluorocarbon/fluorocarbon and fluorocarbon/hydrocarbon 1,2-di-O-alk(en)ylglycerols were introduced starting from 1,2-O-iso-propylidene- then O-trityl-protected glycerols or from 1,3-O-benzylidene-glycerol (Schemes 3 and 4). The perfluoroalkylated O-alkenylglycerols were obtained by O-alkylation of a glycerol derivative using an ω-unsaturated alkenyl reagent, the perfluoroalkyl segment being connected onto the double bond in a subsequent step (Schemes 1) and 3. The perfluoroalkylated symmetrical and mixed 1,3-di-O-alkylglycerols were synthesized by displacement of the Cl-atom in epichlorohydrin by perfluoroalkylated alcohols, then catalytic (SnCl4) opening of the oxirane ring of the resulting alkyl glycidyl ethers in neat alcohols (Scheme 5). When injected intravenously into mice, acute maximum tolerated doses higher than 1500 and 2000 mg/kg body weight were observed for the fluorinated glycerophosphocholines, indicating a very promising in vivo tolerance.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19960790209
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    Diazoaldehyde Chemistry. Part 3Part 1: [1a]; Part 2: [1b].. Synthesis of 4-acyl-1H-1,2,3-triazole derivatives (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 449-453 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ten new α-diazo-β-oxoaldehydes were condensed with aniline, ammonia, hydroxylamine, and semicarbazide to yield new 4-acyl-(1-substituted)-1H-1,2,3-triazoles in moderate-to-good yields. The method is simple and regiospecific. The latter feature makes this method superior to the widely used acylacetylene + azide approach.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19960790212
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  • 52
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    N7-DNA: Synthesis and Base Pairing of Oligonucleotides Containing N7-(2-Deoxy-β-D-erythro-pentofuranosyl)guanine (N7Gd) (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 477-487 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of oligonucleotides containing N7-(2-deoxy-β-D-erythro-pentofuranosyl)guanine (N7Gd; 1) is described. Compound 1 was prepared by nucleobase-anion glycosylation of 2-amino-6-methoxypurine (5) with 2-deoxy-3,5-di-O-(4-toluoyl)-α-D-erythro-pentofuranosyl chloride (6) followed by detoluoylation and displacement of the MeO group (8→10→1). Upon base protection with the (dimethylamino)methylidene residue (→11) the 4,4-dimethoxytrityl group was introduced at OH—C(5′) (→12). The phosphonate 3 and the phosphoramidite 4 were prepared and used in solid-phase oligonucleotide synthesis. The self-complementary dodecamer d(N7G—C)6 shows sigmoidal melting. The Tm of the duplex is 40°. This demonstrates that guanine residues linked via N(7) of purine to the phosphodiester backbone are able to undergo base pairing with cytosine.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790215
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  • 53
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    Studied Directed toward the Synthesis of Phomenoic Acid. Part 2Part 1: [1].. Stereocontrolled Synthesis of the C(7)-to-C(14) Segment (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 518-526 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Starting from the esters (2E,4S)-6 and (2E,4R)-6, bromo aldehydes (S)-9 and (R)-9 as well as bromo alcohols (S)-10 and (R)-10, respectively, were prepared. Bromo alcohol (R)-8 was converted to the diol (2E,4R)-16. Ozonolysis of the latter led to aldehyde (R)-17, which was transformed, by a Wittig reaction, to (2R,4E,6R)-18, corresponding to the C(7)-to-C(14) segment of phomenoic acid (1). Attempts to improve the yields by applying a Julia coupling of (R)-23, which was prepared from (2E,4R)-7, with (R)-24 were unsuccessful. Finally, the coupling of the iodo derivative (2E,4S)-28 with the lithiated derivative of 1,3-dithiane 30 by the Corey-Seebach ‘Umpolung’ led to (3S,4E)-32 which is a derivative of the C(7)-to-C(14) segment of 1, suitable for further transformations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790219
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  • 54
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    Channel-Forming Activity of 3-Hydroxybutanoic-Acid Oligomers in Planar Lipid BilayersDedicated to Prof. Dr. Edgar Heilbronner on the occasion of his 75th birthday (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 507-517 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Monodisperse and polydisperse oligomers and polymers of 3-hydroxybutanoic acid (3-HB) containing 8, 16, ca. 28, 32, ca. 60, 64, 96, and ca. 3000 monomer units were incorporated into palmitoyl-oleoyl-phosphatidyl choline (POPC) planar bilayers. At concentrations of 0.1-5% of oligo(3-HB), the resulting phospholipid bilayers showed typical single-channel behavior for Rb+ and Ba2+ ions, using the patch clamp technique. Thus, channel-forming activity of a pure polyester has been demonstrated for the first time (Figs. 1, 3, and 6). Single-channel activity depends upon the following structural parameters of the 3-HB derivatives: unprotected OH and COOH groups on the chain ends; chain length ≥ 16 monomer units; no high-molecular-weight as in P(3-HB). The results are discussed in view of the Ca2+-specific channel formed with the P(3-HP)/Ca · PPi complex from genetically competent Escherichia coli and in view of the ubiquitous occurrence of low-molecular-weight P(3-HB) in prokaryotic and eukaryotic organisms. A simple model for the channel-causing structure is proposed, based on the proven tendency of oligo- and poly(3-HB) to form ca. 50-Å thick lamellar crystallites.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19960790218
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    Mitteilungen (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 568-570 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790224
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  • 56
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    Synthese der p-CumaroylspermidineProf. Edgar Heilbronner zum 75. Geburtstag gewidmet (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 548-559 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Synthesis of p-CumaroylspermidinesThe synthesis of three mono[(E)-3-(4-hydroxyphenyl)prop-2-enoyl]spermidines, 10, 20, and 28, three bis[(E)-3-(4-hydroxyphenyl)prop-2-enoyl]spermidines, 6, 16, and 25, and one tris[(E)-3-(4-hydroxyphenyl)prop-2-enoyl]-spermidine is described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790222
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  • 57
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    Further C-Alkylations of Cyclotetrapeptides via Lithium and Phosphazenium (P4) Enolates: Discovery of a New Conformation (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 588-608 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four cyclotetrapeptides containing one (1, 2) or two (3, 4) chiral amino acids have been C-alkylated or C-hydroxyalkylated through Li+ or phosphazenium (P4 · H+) enolates. The reactions are completely diastereoselective (by NMR or HPLC analysis) with respect to the newly formed backbone stereogenic centres (Tables 2 and 3). The reactivity of the polylithiated species responsible for these alkylations is such that only highly reactive electrophiles (MeI, BnBr, primary allylic halides, aldehydes, CO2) can be employed. It is shown that the position, and thus the chirality sense, of the newly formed stereogenic centre in a given cyclotetrapeptide backbone is controlled by the positioning of N-methyl groups in the starting material (cf. cyclo(-MeLeu-Gly-D-Ala-Sar-) (3) and cyclo(-Leu-Sar-MeDAla-Gly-) (4) in Scheme 1). With Schwesinger's phosphazene P4-base, all NH groups are first benzylated and C-benzylation then takes place at a sarcosine, rather than an N-benzylglycine residue (Table 3). In contrast to open-chain N-benzyl peptides, the N-benzylated cyclotetrapeptides could not be debenzylated under dissolving-metal conditions (Na/NH3). Conformational analysis (NMR spectroscopy and X-ray diffraction) shows that the prevailing species have cis/trans/cis/trans(ctct) peptide bonds (zigzag conformation of Ci backbone symmetry, Figs. 2-4). However, a hitherto unknown conformation of cyclotetrapeptides has been found in CDCl3 solutions of the hydroxyalkylated products 18-21 (obtained with EtCHO and PhCHO as electrophiles; Fig.4). The new conformation has four trans peptide bonds and is believed to result mainly from intramolecular H-bond formation, involving the newly generated alkyl- or arylserine residue. This assumption has also been supported by modelling (TRIPOS force field, SYBYL, see Fig.5 and Table 6). The structure may be considered as a β-turn mimic.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19960790303
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    1,1,2,2-Tetraethynylethanes: Synthons for Tetraethynylethenes and Modules for Acetylenic Molecular ScaffoldingDedicated to Nikolai S. Zefirov on the occasion of his 60th birthday (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 634-645 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of functionalized 1,1,2,2-tetraethynylethanes (= 3,4-diethynylhexa-1,5-diynes) as synthons for tetraethynylethenes (3,4-diethynylhex-3-ene-1,5-diynes) and as building blocks for three-dimensional acetylenic molecular scaffolding targeting the synthesis of the molecular carbon belts 3 and 4 is reported (Scheme 1). Reaction of diethyl oxalate and (trialkylsilyl)ethynyl Grignard reagents afforded the silyl-protected 3,4-diethynylhexa-1,5-diyne-3,4- diols 7 and 8 which were transformed in high yields into the cyclic carbonate 9 and the cyclic orthoesters 10-13, respectively (Scheme 2). The solid-state structures of 9 and 10 were elucidated by X-ray crystallography. The alkyne protecting groups in 9, 10, and 12 were smoothly removed to give the free tetraynes 14-16 as relatively stable oils in nearly quantitative yields (Scheme 3). Orthoesters 15 and 16 underwent Pd-catalyzed cross-coupling with iodobenzene to give the tetraphenyl derivatives 17 and 18 (Scheme 4). Thermal acid-catalyzed elimination of the orthoester moieties in 12 and 13 produced the silyl-protected tetraethynylethenes 19 and 20 and concluded a novel, simple three-step synthesis of these fully two-dimensionally conjugated π-chromophores (Scheme 5).
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19960790306
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  • 59
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    Synthesis of Carbocyclic C-Nucleosides Containing Nonnatural Pyrimidine Bases (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 702-709 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of new carbocyclic C-nucleosides with a cis-4′-(hydroxymethyl)cyclopent-2′-enyl sugar moiety and unnatural pyrimidine bases (2-6) were synthesized in racemic form in two steps starting from the easily accessible cyclic carbonate 1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790312
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  • 60
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    First Fullerene[60]-Containing Thermotropic Liquid Crystal. Preliminary Communication (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 736-741 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and liquid-crystalline and thermal properties of a fullerene[60] functionalized by a framework containing two cholesterol derivatives through a methanofullerene structure are reported. The targeted fullerene derivative showed high thermal stability.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19960790316
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  • 61
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    Nucleic-Acid Analogs with Restricted Conformational Flexibility in the Sugar-Phosphate Backbone (‘Bicyclo-DNA’). Part 6Part 5: [1].. Probing the influence of torsion angle γ on DNA-duplex stability: Syntheis and properties of oligodeoxynucleotides containing [(3′S,5′S)-2′-deoxy-3′,5′-ethano-β-D-ribofuranosyl]adenine and -thymine (‘5′-epi-bicyclodeoxynucleosides’)Prelimimanry communication: [2]. (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1129-1146 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the thymine- and adenine-containing 5′-epi-bicyclodeoxynucleosides 7 and 8 as well as of the corresponding building blocks 13 and 14 for oligonucleotide syntheis according to the phosphoramidite methodology is described. A conformational analysis of 7 and 8 by 1H-NMR spectroscopy, refined by molecular modeling, shows the preferred conformation of the furanose unit in these nucleosides to be of the 1′-exo/2′-endo type. The 5′-OH group on the carbocyclic ring prefers to be axially oriented, thus placing torsion angle γ in the unusual -syn-clinal (-sc) range. These epi-bicyclodeoxynucleosides were successfully incorporated into DNA decamers. From UV/melting curves of such decamers with DNA and RNA complements, a duplex destabilization of -2 to -9° per residue was observed. An oligonucleotide built completely from 5′-epi-bicyclothymidine shows no detectable affinity to its DNA or RNA complement anymore. CD Spectra of duplexes containing 5′-epi-bicyclodeoxynucleotide units are very similar to the natural reference systems, indicating no major structural changes. A molecular-dynamics simulation of a heptamer duplex containing one 5′-epibicyclothymidine residue in the center reveals a conformational change of its carbocyclic unit placing torsion angle γ in the (for the free mononucleoside unfavorable) -anti-clinal (-ac) conformation in the duplex. The role of torsion angle γ on DNA duplex stability is discussed.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19960790421
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    The Enantioselective Synthesis of β-Amino Acids, their α-hydroxy derivatives, and the N-terminal components of bestatin and microginin (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1203-1216 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: L-Aspartic acid by tosylation, anhydride formation, and reduction with NaBH4 was converted into (3S)-3-(tosylamino)butan-4-olide (8; Scheme 1). Tretment of 8 with ethanolic trimethylsilyl iodide gave the N-protected deoxy-iodo-β-homoserine ethyl ester 9. The latter, on successive nucleophilic displacement with lithium dialkyl-cuprates ( → 10a-e), alkaline hydrolysis ( → 11a-e), and reductive removal of the tosyl group, produced the corresponding 4-substituted (3R)-3-aminobutanoic acids 12a-e (ee 〉 99%). Electrophilic hydroxylation of 8 ( → 19; Scheme 3), subsequent iodo-esterification ( → 21; Scheme 4), and nucleophilic alkylation and phenylation afforded, after saponification and deprotection, a series of 4-substituted (2S, 3R)-3-amino-2-hydroxybutanoic acids 24 including the N-terminal acids 24e ( =3) and 24f ( =4) of bestatin and microginin (de 〉 95%), respectively.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19960790426
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    A New Textual Analysis of the Prelog Erlkönig Legend: An Interdisciplinary Approach to Scientific History and Literary Criticism (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1241-1248 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790502
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  • 64
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    Total Synthesis of (+)-(8S,13R)-CyclocelabenzineDedicated to Professor Vladimir Prelog on the occasion of his 90th birthday (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1295-1304 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An asymmetric synthesis of the spermidine alkaloid (+)-cyclocelabenzine (1a) and its (-)-(13S)-epimer 1b is described using optically active (+)-(3S)-3-amino-3-phenylpropionic acid as the chiral building block. The isoquinolin-1-one fragment 15 was synthesized by a modified Bischler-Napieralski reaction. The relative configuration of the (-)-isomer was determined by an X-ray crystal-structure analysis, which enabled us to determine the absolute configuration of natural (+)-1a as (8S,13R).
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19960790506
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    A Reinvestigation of the Oxidative Rearrangement of Yohimbane-Type Alkaloids. Part BPart A: [1].. Formation of Oxindol (= 1,3-Dihydro-2H-indol-2-one) Derivatives (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1361-1378 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The methanolysis of the epimeric 7-chloro-7H-yohimbine derivatives 2 and 3 was reinvestigated. In case of the 7α-epimer 2, the reaction was uneventful and conformed with earlier observations, i.e., under sufficiently mild conditions, only the imino ether 4 (= imino ether A) was produced. Under the same conditions, the less reactive β-isomer 3 furnished a mixture of both imino ethers 4 and 5, accompanied by the elimination product 11, and by equal amounts of yohimbine (1) and 3,4,5,6-tetradehydroyohimbine (12), which are believed to arise through a disproportionation process of the putative intermediate 5,6-didehydroyhimbine (23). The nature of this divergent reactivity and of the ready equilibration of 4 and 5 was investigated by means of extensive force-field and semi-empirical calculations (AM1 and PM3) of various conformers of the compounds 2-5 and of some possible reaction intermediates.
    Additional Material: 7 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19960790510
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  • 66
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    2-Alkynylcyclopent-2-enols from 2-Alkynylcyclohex-2-enones via 1-Alkynyl-7-oxabicyclo[4.1.0]heptan-2-ones (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1428-1434 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2-Alkynylcyclohex-2-enones 1a-c and 2a-c react with H2O2/NaOH in MeOH to afford 1-alkynyl-7-oxabicyclo[4.1.0]heptan-2-ones 3a-c and 4a-c, respectively. The 3-unsubstituted bicyclic epoxy ketones 3a, 3b, and 4a, 4b react further with H2O2/NaOH, undergoing ring contraction and (formal) decarbonylation to give 2-alkynylcy-clopent-2-enols 5a, 5b, and 6a, 6b, respectively. Epoxy ketones 3 are also obtained under neutral conditions on irradiation (λ = 350 nm) of cyclohexenones 1 in air-saturated benzene solution. Similarly, under neutral conditions oxo-cycloalkenecarbonitriles 8 react (thermally) with H2O2 in MeCN to give the oxabicyclic carbonitriles 9.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790515
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    Xylose-DNA Containing the Four Natural Bases (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1451-1461 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oligonucleotides containing (2′-deoxy-β-D-xylofuranosyl)guanine have been prepared. For this purpose 2-aminoadenosine (5) was synthesized and converted to 2′-deoxy-β-D-xyloguanosine (1). The related 2′-deoxy-β-D-xyloisoguanosine (3) and 2′-deoxy-β-D-xyloxanthosine (4) were also synthesized. Compound 1 was converted to the phosphonate and phosphoramidite building blocks 10 and 11, respectively. The oligodeoxynucleotide (5′-3′)d(xG-xT-xA-xG-xA-xA-xT-xT-xC-xT-xA-xC-T) (18) formed a duplex with the same Tm as the parent (5′-3′)-(G-T-A-G-A-A-T-T-C-T-A-C) (19), but with an inverted CD spectrum.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19960790518
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    Masthead (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996) 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790601
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    Biosynthesis of Dodecano-4-lactone in Ripening Fruits: Crucial Role of an Epoxide-Hydrolase in Enantioselective Generation of Aroma Components of the Nectarine (Prunus persica var. nucipersica) and the Strawberry (Fragaria ananassa) (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1488-1496 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Early steps in the biosynthesis of dedecano-4-lactone in ripening nectarines (Prunus persica var. nucipersica) and strawberries (Fragaria ananassa) were studied using cis-9,10-([18O]epoxy)heptadecanoic acid (5), instead of the natural C18-precursor epoxystearic acid 1. In nectarines, an epoxide hydrolase catalyzed, in a highly regio- and enantioselective reaction, the attack of H2O at C(9) of epoxy acid 5 yielding preferentially (9R,10R)-dihydroxyheptadecanoic acid 6a as an early intermediate and, after further metabolization, undecano-4-lactone 7a. In strawberries, the same transformation exhibited only a moderate regio- and enantioselectivity. Besides the previously established function of phytogenic epoxide hydrolases involved in generating oxygenated fatty-acid derivatives, which are used in cutin monomer production and plant defence, a new rǒle for these enzymes now emerges in the enantioselective production of aroma components of ripening fruits. The cis-9,10-([18O]epoxy)heptadecanoic acid (≥ 98% 18O; 5) was obtained in good overall yield (68%) from isopropyl (9Z)-heptadec-9-enoate using 18O2 gas in a free-radical chain reaction in the presence of 2-methylbutanal.
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    URL: http://dx.doi.org/10.1002/hlca.19960790521
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    Synthese von Trifluoromethyl-substituierten Schwefel-Heterocyclen unter Verwendung von 3,3,3-Trifluorobrenztraubensäure-DerivatenVorgetragen von H. H. am ‘Symposium on Fluoroorganic Chemistry’, Warschau, 17. Mai 1996. (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1537-1548 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Trifluoromethyl-Substituted Sulfur Heterocycles Using 3,3,3-Trifluoropyruvic-Acid DerivativesThe reaction of methyl 3,3,3-trifluoropyruvate (1) with 2,5-dihydro-1,3,4-thiadiazoles 4a, b in benzene at 45° yielded the corresponding methyl 5-(trifluoromethyl)-1,3-oxathiolane-5-carboxylates 5a, b (Scheme 1) via a regioselective 1,3-dipolar cycloaddition of an intermediate ‘thiocarbonyl ylide’ of type 3. With methyl pyruvate, 4a reacted similarly to give 6 in good yield. Methyl 2-diazo-3,3,3-trifluoropropanoate (2) and thiobenzophenone (7a) in toluene underwent a reaction at 50°; the only product detected in the reaction mixture was thiirane 8a (Scheme 2). With the less reactive thiocarbonyl compounds 9H-xanthene-9-thione (7b) and 9H-thioxanthene-9-thione (7c) as well as with 1,3-thiazole-5(4H)-thione 12, diazo compound 2 reacted only in the presence of catalytic amounts of Rh2(OAc)4. In the cases of 7a and 7b, thiiranes 8b and 8c, respectively, were the sole products (Scheme 3). The crystal struture of 8c has been established by X-ray crystallography (Fig.). In the reaction with 12, desulfurization of the primarily formed thiirane 14 gave the methyl 3,3,3-trifluoro-2-(4,5-dihydro-1,3-thiazol-5-ylidene)propanoates (E)-and (Z)-15 (Scheme 4). A mechanism of the Rh-catalyzed reaction via a carbene addition to the thiocarbonyl S-atom is proposed in Scheme 5.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19960790604
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    Duplex Stability of 7-Deazapurine DNA: Oligonucleotides containing 7-bromo- or 7-iodo-7-deazaguanine (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1549-1558 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oligonucleotide building blocks, the phosphonates 1a, b and the phosphoramidites 2a, b derived from 7-iodo- and 7-bromo-7-deaza-2′-deoxyguanosines 3a, b were prepared. They were employed in solid-phase oligonucleotide synthesis of the alternating octamers d(Br7c7G-C)4 (8) and d(I7c7G-C)4 (9) as well as the homo-oligonucleotides d[(Br7c7G)5-G] (11) and d[(I7c7G)5-G] (12). The melting profiles and CD spectra of oligonucleotide duplexes were measured. The Tm values as well as the thermodynamic data were determined and correlated to the major-groove modification of this DNA. The self-complementary octamers 8 and 9 form more stable duplexes compared to the parent oligomer d(G-C)4. The heteroduplex of d[(I7c7G)5-G] (12) with d(C6) is slightly destabilized (ΔTm = -12°) over that of d[(c7G)5-G] with d(C6). However, the complex of 12 with poly(C) is more stable than that of d[(c7G5-G)] with poly(C).
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19960790605
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    The Crystal and Molecular Structure of [Co(tmen)3](C7H7SO3)3·2 H2O and [Co(tmen)3](CH3SO3)2·EtOH·1/2 H2O (tmen = 2,3-dimethylbutane-2,3-diamine) (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1607-1610 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The molecular structure of the two complex ions [Co(tmen)3]3+ and [Co(tmen)3]2+ (tmen = 2,3-dimethylbutane-2,3-diamine) have been determined at 100 K. They show a strong trigonal distortion of the octahedral CoN6 core. The twist angle is 26.2(2.8)° for CoII and 43.9(9)° for CoIII. Average Co—N distances are 2.193(13) Å (CoII) and 1.997(2) Å (CoIII), 0.02 Å longer than for the main body of CoIII amines.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790610
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    Hydrolytical Cleavage of TAR-RNA, the trans-Activation Responsive Region of HIV-1, by a Bis(guanidinium) Catalyst Attached to Arginine (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1967-1979 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Guanidinium compounds imitating the bis(arginine) structural motif of staphylococcal nuclease (e.g. 3) are known to be powerful catalysts for phosphoryl transfer reactions in dipolar aprotic solvents. Compound 3 also accelerates the hydrolysis of RNA (H2O, pH 7). However, due to diminished substrate affinity in H2O, the rate effects are less pronounced in aqueous than in aprotic solution. To test if a synthetic ribonuclease may be derived from the bis(guanidinium) moiety of 3 by the addition of RNA-binding substructures, the TAR sequence of HIV-1 was chosen as a target. The arginine residue of compound 4 serves as an extremely simplified mimic of tat, a protein responsible for boosting the viral transcription by complex formation with TAR. Here, we present the synthesis of 4 and its ability to bind and to cleave efficiently the truncated TAR sequence 1. In addition, the synthesis of an acridine arginine conjugate, 19, is reported in preliminary form. Compound 19 associates with 1 and completely blocks the cleavage induced by 4.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19960790719
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  • 74
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    Lipid Masking and Reactivation of Angiotensin Analogues (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 2023-2034 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Studies on post-angioplastic restenosis have shown the implication of angiotensin II (Ang) as a myoproliferative mediator. The antiproliferative efficacy of non-peptide Ang antagonists on the rat carotid model is of 50%, whereas a continuously infused peptide antagonist at low doses totally blocks neointimal growth. To explore the feasibility of depot forms of Ang that may be introduced during angioplasty and thus prevent restenois, lipid-masked Ang analogues of the following general structure were prepared: [Xxx°, Yyy1]Ang with Xxx = decanoyl or palmitoyl and Yyy = Ser, Cys, Asp, β-lactoyl, 3-mercaptopropanoyl or succinyl. All fatty acylated peptides [Xxx°, Yyy1]Ang were practically inactive, and O- or S-esterified Ser and Cys peptides underwent intramolecular transcylation giving inactive Nx-acylated peptides. O-Acylated [β-mercaptopropanoyl1]Ang were easily hydrolyzed into their biologically active[Yyy1]Ang forms, either by mild saponification or by lipase activity.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19960790723
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  • 75
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    From Inactive Nortopsentin D, a Novel Bis(indole) Alkaloid Isolated from the Axinellid Sponge Dragmacidon sp. from Deep Waters South of New Caledonia, to a Strongly Cytotoxic Derivative (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 2075-2082 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nortopsentin D (5), a bis(indole) alkaloid unique for bearing a 2-amino-methylimidazole appendage at the central 1H-imidazol-5(4H)-one nucleus, was isolated in abundance, besides the putative biogenetic precursor 6 of its appendage, from the deep-water axinellid sponge Dragmacidon sp. Structural elucidation of 5 by NMR and MS methods heavily relied on its N-methyl derivatives 8-11. Unusually for topsentin-type structures, natural 5 and semisynthetic methyl derivatives 8 and 10 proved inactive on KB tumoural cells, while introduction of the last three methyl groups, amazingly led to highly cytotoxic 11.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19960790804
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  • 76
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    Model Studies for the Coenzyme-B12-Catalyzed Methylmalonyl→Succinyl Rearrangement. The Importance of Hydrophobic Peripheral Associations (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 2100-2113 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interaction between a vitamin B12 derivative containing a peripheral C18 alkyl chain (see 1a) and a (methyl)thiomalonate substrate bearing alkyl chains of various length at the thioester group (see 5) was investigated. A catalytic cycle was established for the methylmalonyl→succinyl rearrangement by using electrochemistry and photolysis (see Scheme 3). Increased yields of the succinate relative to the reduction product were obtained (2:3 ratio), when the reaction was run in MeOH/H2O, and when both the substrate and the catalyst had an octadecyl substituent capable of hydrophobic interactions.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19960790807
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  • 77
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    Electrospray-Ionization Mass Spectrometry. Part III.Part II:[1] Acid-Catalyzed Isomerization of N,N′-Bis[(E)-3-(4-hydroxyphenyl)prop-2-enoyl]spermidines by the Zip ReactionPresented by L.B. at the ‘29. Diskussionstagung der Arbeitsgemeinschaft Massenspektrometrie der Deutschen Physikalischen Gesellschaft’, on May 28-31, 1996, University of Bremen, Germany. (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 2152-2163 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electrospray tandem mass spectra (ESI-MS/MS) of the three N,N′-bis[(E)-3-(4-hydroxyphenyl)prop-2-enoyl]spermidines 1-3 displayed the same fragment-ion signals. These isomers could not be differentiated by ESI-MS/MS, since their fragmentation patterns are similar. (E,E)-N-(3-[15N]Aminopropyl)-3,3′-bis(4- hydroxyphenyl)-N,N′-(butane-1,4-diyl)bis[prop-2-enamide] ([15N(1)])-(1) was synthesized in order to get further information about the fragmentation mechanisms. The comparison of the ESI-MS/MS of 1 and [15N(1)]-1 revealed a transamidation, the Zip reaction, under mass-spectral conditions of the [1 + H]+ ions. Because of this reaction, the three isomers 1-3 could not be distinguished.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19960790810
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  • 78
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    Total Synthesis of Cyclothialidine (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 2219-2234 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A total synthesis of cyclothialidine (1), a new DNA gyrase inhibitor isolated from Streptomyces filipinensis, is described. The synthetic concept was tested by preparing the lactone 13 (Scheme 2) which contains the characteristic bicyclic core entity of 1. Key features of the synthesis of 1 are: preparation of 3,5-dihydroxy-2,6-dimethylbenzoic acid (23) from 3,5-dihydroxybenzoic acid (19) by two consecutive Mannich aminomethylation/hydrogenation sequences; benzylic N-bromosuccinimide bromination of an ester derivative 25 thereof and its subsequent coupling with Boc-Ser-Cys-OMe (11); cyclization of the ω-hydroxy acid 29 29 to the 12-membered lactone 30 using preferably Mitsunobu conditions; completion of the peptidic side chains of 1 using Boc strategy (Scheme 4). Optically pure cis-N-(tert-butoxycarbonyl)-3-hydroxy-L-proline ((-)-14) was obtained by resolution of the racemate via an efficient reaction sequence containing a lipase-catalyzed enantiospecific acetate hydrolysis (Scheme 3). The structure of natural 1 was confirmed by comparison with the synthetic material. The synthetic route described provides also easy access to analogues of 1, e.g., via the intermediate 30.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19960790816
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  • 79
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    Donor/Acceptor-Substituted Tetraethynylethenes: Systematic Assembly of Molecules for Use as Advanced Materials (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 2249-2281 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A comprehensive series of tetraethynylethenes (= 3,4-diethynylhex-3-ene-1,5-diynes, TEEs) bearing electrondonating (p-methoxyphenyl or p-aminophenyl) and/or electron-accepting (p-nitrophenyl) groups was prepared via [Pd]-catalyzed Sonogashira cross-coupling reactions. The electronic and photonic properties of these molecules were investigated with a special emphasis on the effects caused by degree and pattern of donor/acceptor substitution around the central TEE core. This analysis showed that intramolecular donor-acceptor interactions, as evidenced by a long-wavelength charge-transfer band, are considerably more effective in TEEs 44 and 46, with trans and cis, linearly-conjugated electronic pathways between donor and acceptor, than in 11, with a geminal, cross-conjugated electronic pathway. UV/VIS Spectroscopy revealed a steady bathochromic shift of the longest-wavelength absorption band (λmax) as the number of donor-acceptor conjugation paths increased upon changing from bis-arylated (11, 44, and 46) to tetrakis-arylated (14, 31, and 35) TEEs. The position of the longest-wavelength absorption was also found to be strongly dependent on the nature of the N-substituents in the R2NC6H4-donor groups. Electronic emission spectroscopic investigations demonstrated a considerable solvent dependency of the fluorescence of donor-acceptor-substituted TEEs such as 11 or 44, in agreement with the presence of highly polarized excited states in these molecules. Correspondingly, fluorescence spectra of TEEs bearing only donor or acceptor substituents showed little solvent dependency. The large majority of the donor/acceptor-substituted TEEs are thermally and environmentally stable molecules. They can be stored for months as solids in the air at room temperature, and many decompose only upon heating to temperatures above 200°. X-Ray analysis showed the conjugated C-atom scaffolds of 44, 46, and 67 to be essentially planar, whereas the aryl substituents in 28 and 30 are rotated out of the plane of the TEE core by varying degrees.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19960790818
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    Mitteilungen (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 913-913 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790330
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  • 81
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    β-Peptides: Synthesis by Arndt-Eistert homologation with concomitant peptide coupling. Structure determination by NMR and CD spectroscopy and by X-ray crystallography. Helical secondary structure of a β-hexapeptide in solution and its stability towards pepsin (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 913-941 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The β-hexapeptide (H-β-HVal-β-HAla-β-HLeu)2-OH (2) was prepared from the component L-β-amino acids by conventional peptide synthesis, including fragment coupling. A cyclo-β-tri- and a cyclo-β-hexapeptide were also prepared. The β-amino acids were obtained from α-amino acids by Arndt-Eistert homologation. All reactions leading to the β-peptides occur smoothly and in high yields. The β-peptides were characterized by their CD and NMR spectra (COSY, ROESY, TOCSY, and NOE-restricted modelling), and by an X-ray crystal-structure analysis. β-Sheet-type structures (in the solid state) and a compact, left-handed or (M) 31 helix of 5-Å pitch (in solution) were discovered. Comparison with the analogous secondary structures of α-peptides shows fundamental differences, the most surprising one at this point being the greater stability of β-peptide helices. There are structural relationships of β-peptides with oligomers of β-hydroxyalkanoic acids, and dissimilarities between the two classes of compounds are a demonstration of the power of H-bonding. The β-hexapeptide 2 is stable to cleavage by pepsin at pH 2 in H2O for at least 60 h at 37°, while the corresponding α-peptide H-(Val-Ala-Leu)2-OH is cleaved instantaneously under these conditions. The implication of the described results are discussed.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19960790402
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    Novel Cholic-Acid-Type Sterones of Deltocyathus magnificus, a deep-water scleractinian coral from the Loyalty Islands, SW Pacific (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 982-988 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cholic-acid-type 3-keto steroids 1-8, all isolated from Deltocyathus magnificus (2-8 after CH2N2 treatment), are the first secondary metabolites obtained from a deep-water scleractinian. Steroids 1-3, 5, and 7 are new, their main structural oddities being loss of C(24) (see 5) or hydroxylation in the side chain (see 3 and 7). Steroids 4, 6, and 8, from the same coral, were previously known from other marine organisms.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19960790406
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  • 83
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    Acid-Catalysed Backbone Rearrangement of cholesta-6,8(14)-dienes (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 989-998 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rearrangement of 5α- and 5β-cholesta-6,8(14)-dienes (13a and 13b, resp.) in the presence of anhydrous toluene-4-sulfonic acid in acetic acid leads to 5α- and 5β-12(13 → 14)-abeo-cholesta-8,13(17)-dienes (15a and 15b, resp.) via 5α- and 5β-cholesta-8,14-dienes (14a and 14b, resp.), respectively. Epimerization at C(20) of the spirosteradienes 15a and 15b occurs with increasing reaction time. Molecular-mechanics calculation of the relative stabilities of these compounds and of congeners thereof is in agreement with the observed reaction pathway.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19960790407
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  • 84
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    Asymmetric Synthesis of the Alkaloids mayfoline and N(1)-acetyl-N(1)-deoxymayfoline (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1085-1094 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The total syntheses of the spermidine alkaloids (-)-mayfoline (11) and (+)-N(1)-acetyl-N(1)-deoxymayfoline (12) are described. These macrocyclic lactams belong to the most interesting conjugates of the polyamine derivatives very commonly found in nature. The enantioselective syntheses were achieved through resolution of the methyl 3-amino-3-phenylpropanoate (2) by recrystallization of its (+)-L-tartrate salt. Construction of the 13-membered ring ensued through condensation, reductive ring expansion (internal bond cleavage), and finally a transamidation reaction involving a second ring expansion.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19960790417
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  • 85
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    Electrochemical Behaviour and Antioxidant Activity of Some Natural Polyphenols (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1147-1158 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A number of natural polyphenols (chlorogenic acid (9), cordigol (11), cordigone (12), danthrone (1), 1,5-dihydroxy-3-methoxyxanthone (2), eriosematin (7), flemichin D (8), frutinone A (6), mangiferin (4), quercetin (5), 1,3,6,7-tetrahydroxyxanthone (3) and verbascoside (10)) were investigated for their redox properties using cyclic voltammetry. The antioxidant properties of these compounds were also examined in two models, namely lipid peroxidation in rat synaptosomes and AAPH-mediated oxidation of serum albumin. Compounds with a catechol group (9, 4, 5, 3 and 10) were oxidized below 0.4 V and inhibited lipid peroxidation with IC50 values between 2 and 8 μM. Compounds having one or more isolated phenolic groups and showing an oxidation potential between 0.45 and 0.8 V (11, 12 and 8) inhibited lipid peroxidation with IC50 between 7 and 9 μM, except 2 (0.45 V), danthrone (0.96 V) and eriosematin which showed no or modest antioxidant activity. Some of the investigated compounds also protected albumin from oxidation, but no structure-activity relationship was apparent, suggesting that other factors beside redox potential influence this activity.
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    URL: http://dx.doi.org/10.1002/hlca.19960790422
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    Glycosylidene Carbenes. Part 23. Regioselective glycosidation of deoxy- and fluorodeoxy-myo-inositol derivativesDedicated to Edgar Heilbronner on the occasion of his 75th birthday (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1169-1191 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: To demonstrate the relevance of the kinetic acidity of individual OH groups for the regioselectivity of glycosylation by glycosylidene carbenes, we compared the glycosylation by 1 of the known triol 2 with the glycosylation of the diol D-3 and the fluorodiol L-4. Deoxygenation with Bu3SnH of the phenoxythiocarbonyl derivative of 5 (Scheme 1) or the carbonothioate 6 gave the racemic alcohol (±)-7. The enantiomers were separated via the allophanates 9a and 9b, and desilylated to the deoxydiols D- and L-3, respectively. The assignment of their absolute configuration is based upon the CD spectra of the bis(4-bromobenzoates) D- and L-10. The (+)-(R)-1-phenylethylcarbamates 13a and 13b (Scheme 2) were prepared from the fluoroinositol (±)-11 via (±)-4 and the silyl ether (±)-12 and separated by chromatography. The absolute configuration of 13a was established by X-ray analysis. Decarbamoylation of 13a ( → L-12) and desilylation afforded the fluorodiol L-4. The H-bonds of D-3 and L-4 in chlorinated solvents and in dioxane were studied by IR and 1H-NMR spectroscopy (Fig. 2). In both diols, HO—C(2) forms an intramolecular, bifurcated H-bond. There is an intramolecular H-bond between HO—C(6) and F in solutions of L-4 in CH2Cl2, but not in 1,4-dioxane; the solubility of L-4 in CH2Cl2 is too low to permit a meaningful glycosidation in this solvent. Glycosidation of D-3 in dioxane by the carbene derived from 1 (Scheme 3) followed by acetylation gave predominantly the pseudodisaccharides 18/19 (38%), derived from glycosidation of the axial OH group besides the pseudodisaccharides 16/17 (13%) and the epoxides 20/21 (7%), derived from protonation of the carbene by the equatorial OH group. Similarly, the reaction of L-4 with 1 (Scheme 4) led to the pseudodisaccharides 28/29 (46%) and 26/27 (14%), derived from deprotonation of the axial and equatorial OH groups, respectively. Formation of the epoxides involved deprotonation of the intramolecularly H-bonded tautomer, followed by intramolecular alkylation, elimination, and substitution (Scheme 4). The regio- and diastereoselectivities of the glycosidation correlate with the H-bonds in the starting diols.
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    URL: http://dx.doi.org/10.1002/hlca.19960790424
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    A Novel Asymmetric Benzoin Reaction Catalyzed by a Chiral Triazolium Salt. Preliminary communication (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1217-1221 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using the chiral triazolium salt 1 as catalyst, a novel asymmetric variant of the benzoin reaction is reported. For the first time, the scope of the method is extended to a broader range of aromatic aldehydes 2, affording the acyloins 3a-h in yields of 22-72% and enantiomeric excesses up to 86%.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19960790427
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    Erratum (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1239-1239 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790429
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  • 89
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    Variation and SelectionDedicated to Professor Vladimir Prelog on the occasion of his 90th birthday (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1260-1278 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ninety years ago, chemical methods were used in solving biological problems. In our days, methods of evolutionary biology are going to be used in solving problems of synthetic chemistry.
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    URL: http://dx.doi.org/10.1002/hlca.19960790504
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  • 90
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    Oligosaccharide Analogues of Polysaccharides. Part 8. Orthogonally Protected Cellobiose-Derived Dialkynes. A Convenient Method for the Regioselective Bromo- and Protodegermylation of Trimethylgermyl- and Trimethylsilyl-protected DialkynesDedicated to Vlado Prelog on the occasion of his 90th birthday (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1279-1294 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cellobiose-derived dialkynes 14 and 15 were prepared by glycosidation of the acceptor 9 with the thioglycosides 12(82%) and 13(85%), respectively. The acceptor 9 was prepared from the known alcohol 2 via the lactone 7 in five steps (48% overall), and the donors 12 and 13 were prepared from the alkynylated anhydroglucose derivative 10 (60% overall). Acetolytic debenzylation of 14 and 15 (→16 and 17, resp.) followed by deacylation of 16 yielded 60% of the cellobiose-derived dialkyne 18. Deacylation of 14 (→19), methoxymethylation (→20) and trimethylgermylation led to the orthogonally protected dialkyne 21 (69% overall). Protodesilylation of 21 with K2CO3/MeOH gave 22 (90%), while the Me3Ge group was selectively removed with CuBr (19 mol-%) in THF/MeOH to give 20 (95%). Treatment of 21 with aqueous HCl solution led to 19 (80%). Bromodegermylation of 21 (NBS/AgOOCCF3) led to a mixture of 23 (85%) and 24 (11%). Similar conditions using CuBr instead of AgOOCCF3 gave exclusively the bromoalkyne 23 (93%). The temperature dependence of the δ values of the OH resonances of 18 in (D6)DMSO evidence a strong intramolecular H-bond between C(5′)—O…HO—C(5).
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19960790505
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  • 91
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    Analogs of Cinchona Alkaloids Incorporating a 9,9′-Spirobifluorene MoietyDedicated to Professor Vladimir Prelog on the occasion of his 90th birthday (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1338-1360 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Cinchona alkaloid analogs (+)- and (-)-5 with a quinuclidine-2-methanol residue attached to C(2) of a 9,9′-spirobifluorene moiety were prepared as a racemic mixture by reacting lithiated 2-bromo-9,9′-spirobifluorene 7 with (2-ethoxycarbonyl)quinuclidine (±)-6 to give ketone (±)-8, followed by diastereoselective reduction with diisobutylaluminum hydride (DIBAL-H). The absolute configuration at C(9) and C(8), i.e., at the methanol bridge and the adjacent quinuclidine C-atom, in the two enantiomers of 5 is identical to the configuration at the corresponding centers in (-)-quinine (1) and (+)-quinidine (2), respectively. For the optical resolution of (±)-5, a chiral stationary phase for HPLC was prepared by covalently bonding quinine via a thiol spacer to a silica-gel surface. The enantiomer separation was accomplished at an α value of 1.61 with (±)-5 being eluted last, in agreement with 1H-NMR studies in CDCl3 which showed that (+)-5 underwent a more stable host-guest association with quinine than (-)-5. 1H{1H} Nuclear Overhauser effect (NOE) difference spectroscopical analysis of the host-guest associations with quinine in CDCl3, combined with computer-model examinations, allowed the assignment of the absolute configurations as (+)-(8R,9S)-5 and (-)-(8S,9R)-5. A detailed conformational analysis displayed excellent agreement between the results of computational methods (Monte Carlo multiple minimum simulations, analyses of the total energy as a function of the flexible dihedral angles in the molecule) and 1H{1H}-NOE difference spectroscopical data. It was found that (-)-5 and (+)-5 differ significantly in their conformational preference from their natural counterparts quinine (1) and quinidine (2). Whereas the natural alkaloids prefer the ‘open’ conformation, with the quinuclidine N-atom pointing away from the quinoline ring, analog (±)-5 adopts preferentially (by ca. 4 kcal mol-1) a ‘closed’ conformation, in which the quinuclidine N-atom points into the cleft of the 9,9′-spirobifluorene moiety. Since the basic quinuclidine N-atom in the ‘closed’ conformation is sterically shielded from forming strong H-bonds, the new Cinchona alkaloid analogs form less stable host-guest associations via H-bonding than quinine or quinidine.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790509
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  • 92
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    A New Approach to the Synthesis of Long-Chain Polypropionates Based on the Diels-Alder Monoadditions of 2,2′-Ethylidenebis[3,5-dimethylfuran]Part of the Ph.D. thesis of J.A., University of Lausanne, 1995. (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1393-1414 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Acidic condensation of 2,4-dimethylfuran with acetaldehyde provided 2,2′-ethylidenebis[3,5-dimethylfuran] (7) which added 1 equiv. of methyl bromopropynoate to give a major adduct 8. Regio- and stereoselective hydroboration of the latter 7-oxanorbornadiene derivative followed by alcohol protection and methanolysis of its β-bromoacrylate moiety gave (1RS,2RS,4RS,5SR,6SR,1′RS)-methyl 4-[1′-(3″,5″-dimethylfuran-2″-yl)ethyl]-3,3-dimethoxy-6-exo-[(2-methoxy)ethoxy]-1,5-endo-dimethyl-7-oxabicyclo[2.2.1]heptane-2-endo-carboxylate (24) (Schemes 2 and 3). Reduction of 24 with LiAlH4, followed by H2O and MeOH elimination gave the 3-methyl-idene-7-oxanorbornan-2-one derivative 26 which underwent 7-oxa ring opening through a SN2′ type of reaction with Me2CuLi (Scheme 4). Stereoselective hydrogenation and ketone reduction provided (1RS, 2SR,3RS,4RS,5RS,6RS,1′SR)-1- [1″-(3 ″,5″-dimethylfuran-2″-yl)]-c-3-ethyl-c-5-[(2-methoxyethoxy)m e-c-ethyl-c-c-5-(2-methoxyethoxy)methoxy]-t-4,t-6-dimethyl-cyclohexane-r-1,c-2-diol (32), the oxidative cleavage of which with Pb(OAc)4 generated a 6-oxo-aldehyde 33 (Schemes 4 and 5). Chemoselective protection of 33 and chemo- and stereoselective reductions generated (2RS,3RS,4SR,5SR,6SR,7RS)-7-(3′,5″-dimethylfuran-2′-yl)-2-ethyl-6-hydroxy-4-[(2-methoxyethoxy)methoxy]-3,5-dimethyloct-1-yl pivaloate (36) and its 4-hydroxy 6-epimer 40 (12 and 13 steps, resp., from adduct 8; Scheme 5). Oxidation of the furan ring of 36 led to a (2RS,3SR,4RS,5SR,6RS,7RS)-7-ethyl-3,5,8-trihydroxy-2,4,6-trimethyl-octanoic acid derivative 44, a polypropionate fragment with six contiguous stereogenic centres (Scheme 6).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790513
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  • 93
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    Isomerisierung von (all-E)-Cycloviolaxanthin Herstellung und Charakterisierung von (9Z)-und (13Z)-Cycloviolaxanthin (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1444-1450 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Isomerization of (all-E)-Cycloviolaxanthin. Preparation and Characterization of (9Z)- and (13Z)-CycloviolaxanthinFrom (all-E)-cycloviolaxanthin (ex Capsicum annuum), (9Z)- and (13Z)-cycloviolaxanthin were prepared in a highly pure state. The configuration of both isomers was determined by means of UV/VIS, NMR, and CD spectroscopy.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790517
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  • 94
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    Electronic Resource
    Mitteilungen (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1518-1518 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790523
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  • 95
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    Intramolecular Vinyl Radical Cyclization Reactions of cyclohexadienes derived from sequential additions to (arene)(tricarbonyl)chromium complexes. Preliminary communicationDedicated to the memory of our late colleague Wolfgang Oppolzer (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1533-1536 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cyclohexa-1,3-dienes 7-10 with a 1,5,6-substitution pattern were prepared in a one-pot reaction sequence by sequential addition of MeLi and propargyl bromides to the tricarbonylchromium complex 1a. These products were subjected to radical cyclization procedures. Vinyl radical generation by Bu3Sn addition to the propargyl group in 7-10 was followed by regio- and diastereoselective intramolecular ring closure. Two different 5-exo-trig cyclizations are possible via different vinyl radical intermediates and cyclization to one or the other of the termini of the cyclohexadiene moiety. Internal alkynes reacted to yield exclusively the cis-fused hexahydroindene products 12-14, whereas the terminal alkyne yielded bicyclo[3.2.1]octenes 11 as sole products.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790603
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  • 96
    Electronic Resource
    Electronic Resource
    The First Asymmetric Intramolecular Stetter Reaction. Preliminary Communication (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1899-1902 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The first asymmetric intramolecular Stetter reaction is reported, using the chiral triazolium salt 1 as catalyst. Starting from the easily accessible 4-(2-formylphenoxy)but-2-enoates 2, this protocol opens up an enantioselective pathway to the benzo-annulated pyran-4-ones (chroman-4-ones) 3a-h with good yields and enantiomeric excesses of up to 74%.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790712
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  • 97
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    Reactions of 3-(Prop-2-enylidene)azetidin-2-ones with 4,5-Dihydro-3H-1,2,4-triazole-3,5-dionesDedicated to Prof. Gunther Seitz. Marburg. on the occasion of his 60th birthday (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1925-1929 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 3-(2-propenylidene)-β-lactams 1a-c react as semicyclic dienes with the dihydrotriazole-diones 2 in a stereoselective fashion leading to the cycloadducts 3. The 3′,3′-disubstituted derivative 4 gives no [4 + 2]-cycloaddition products but forms the adducts 5 and 6. Sterochemistry and reaction pathways are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790715
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  • 98
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    Mechanistic Details of the Fe+-Mediated C—C and C—H Bond Activations in Propane: A Theoretical Investigation (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1939-1956 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Quantum-chemical calculations employing a density-functional theory/Hartree-Fock hybrid method (B3LYP) have been used to explore the mechanistic details of the C—C and C—H bond-activation processes in propane mediated by a bare Fe+ ion. While the theoretically predicted results are in complete accord with all available experimental data, they give rise to a different mechanistic picture than envisaged previously. In contrast to earlier speculation, the activation barriers for the initial insertion steps of Fe+ into a C—H or C—C bond are found to be significantly below the Fe+ + C3H8 channel. The rate-determining steps for both, the C—C and the C—H bond activation branches of the [FeC3H8]+ potential-energy surface rather occur late on the respective reaction coordinates and are connected with saddle points of concerted rearrangement processes. The C—C bond activation, which leads to the exothermic reductive elimination of methane, occurs via the C—C inserted species and not as a side channel originating from a C—H inserted ion, as assumed hitherto. For the C—H bond-activation processes, which finally results in the exothermic expulsion of molecular hydrogen, two energetically similar reaction channels for an [1,2]-elimination exist. The results clearly show, that an [1,3]-H2-elimination mechanism cannot compete with the [1,2]-elimination paths, in line with the experimental findings. Overall, a lower energy demand for the reductive elimination of methane compared to the loss of H2 is obtained, straightforwardly explaining the preference of the former process observed experimentally.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790717
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  • 99
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    Electronic Resource
    Masthead (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996) 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790801
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  • 100
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    Electronic Resource
    Synthesis of 1,2,5-Thiadiazepine Derivatives by Ring Enlargement of 1,2-Thiazetidin-3-one 1,1-Dioxides with 3-Amino-2H-azirines (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 2067-2074 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: At 0° in MeCN, 2,2-disubstituted 3-amino-2H-azirines 1 and 4,4-disubstituted 1,2-thiazetidin-3-one 1,1-dioxides 7 react smoothly to give 1,2,5-thiadiazepin-6-one 1,1-dioxides of type 8 (Scheme 2). The reaction mechanism of this regiospecific ring enlargement to seven-membered heterocycles follows previously described pathways. The structures of 7a and 8b were established by X-ray crystallography (see Figs. 1 and 2).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790803
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