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  • 1990-1994  (4,765)
  • 1980-1984  (6,476)
  • Organic Chemistry  (7,936)
  • Physics  (2,658)
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  • 101
    Electronic Resource
    Electronic Resource
    Mitteilungen - Communications (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 883-883 
    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.19940770328
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  • 102
    Electronic Resource
    Electronic Resource
    Masthead (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994) 
    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.19940770401
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  • 103
    Electronic Resource
    Electronic Resource
    Synthesis of Certain 5-Substituted 2′-Deoxytubercidin Derivatives (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 897-903 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the 7-deaza-2′-deoxy-adenine derivatives 7b-3 with chloro, bromo, or methyl substituents at C(5) is described. Glycosylation of the 5-substituted 4-chloropyrrolo[2,3-d]pyrimidines 4b-d with 2-deoxy-3,5-di-O-(4-toluoyl)-α-D-erythro-pentofuranosyl chloride (3) gave the β-D-nucleosides 5b-d, exclusively. They were deblocked (→6b-d) and converted into the tubercidin derivatives 7b-d.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770403
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  • 104
    Electronic Resource
    Electronic Resource
    1-(2′-Deoxy-β-D-xylofuranosyl)cytosine: Base pairing of oligonucleotides with a configurationally altered sugar-phosphate backbone (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 883-896 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solid-phase synthesis of the oligo(2′-deoxynucleotides) 19 and 20 containing 2′-deoxy-β-D-xylocytidine (4) is described. For this purpose, 1-(2-deoxy-β-D-threo-pentofuranosyl)cytosine ( = 1-(2-deoxy-β-D-xylofuranosyl)-cytosine; 4) was protected at its 4-NH2 group with a benzoyl (→ 5) or an isobutyryl (→8) residue, and a dimethoxytrityl group was introduced at 5′-OH (→ 7, 10; Scheme 2). Compounds 7 and 10 were converted into the 3′-phosphonates 11a,b. While 19 could be hybridized with 21 and 22 under formation of duplexes with a two-nucleotide overhang on both termini (19 · 21: Tm 29°; 19 · 22: Tm 22°), the decamer 20 bearing four xCd residues could no longer be hybridized with one of the opposite strands. Moreover, the oligonucleotides d[(xC)8—C] (13), d[(xC)4—C] (14), d[C—(xC)4—C] (15), and d[C—(xC)3—C] (16) were synthesized. While 13 exhibits an almost inverted CD spectrum compared to d(C9) (17), the other oligonucleotides show CD spectra typical for regular right-handed single helices. At pH 5, d[(xC)8—C] forms a stable hemi-protonated duplex which exhibits a Tm of 60° (d[(CH+)9] · d(C9): Tm 36°). The thermodynamic parameters of duplex formation of (13H+ · 13) and (17H+ · 17) were calculated from their melting profiles and were found to be identical in ΔH but differ in ΔS (13H+ · 13: ΔS = -287 cal/K mol; 17H+ · 17: ΔS = -172 cal/K mol).
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770402
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  • 105
    Electronic Resource
    Electronic Resource
    Syntheses of Segmental Heteroleptic Ligands for the Self-Assembly of Heteronuclear Helical Supramolecular Complexes (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 931-942 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The development of a modified Phillips reaction allows the synthesis of complicated heteroleptic ligands based on pyridine and 1H-benzimidazole moieties. The key-step formation of aromatic 1H-benzimidazole rings from N-(2-nitroaryl)arenecarboxamides significantly improves the possibilities of the classical intermolecular Phillips reactions and can be applied to the synthesis of large oligo-multidentate units. Segmental heteroleptic ligands containing two different bidentate coordinating units (see 14) or bidentate and terdentate sites connected by ‘diphenylmethane’ ( = methylenebis(phenylene)) spacers (see 15 and 16) were obtained in fair to good yield by using multistep syntheses following this strategy. Heterotrileptic ligands (bidentate-terdentate-bidentate, see 19 and 20; terdentate-terdentate-terdentate, see 23) requiring the simultaneous formation of four 1H-benzimidazole rings in one step were prepared and demonstrate the extended possibilities of this methodology. Data are presented to show that the milder conditions used for this modified Phillips reaction together with its flexibility are essential for the development of ligands adapted for the self-assembly of heteronuclear helical complexes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770406
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  • 106
    Electronic Resource
    Electronic Resource
    Photochemistry of 6,6-Dimethyl- and 2,2,6,6-Tetramethyl-2H,6H-pyran-3-one (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 904-908 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The title compounds 1a and 1b have been synthesized in two steps from the saturated pyran-3-ones 2a and 2b, respectively. Upon irradiation (254 nm or 350 nm) in dilute solutions (10-3-10-2M), compounds 1 undergo a formal [4 + 2] cycloreversion from the excited triplet state to give (2-methylprop-1-enyl)ketene (11) and either formaldehyde or acetone, ketene 11 being trapped by H2O or MeOH to afford 4-methylpent-3-enoic acid (5) or its methyl ester 4 in 75-85% isolated yield. In this (monomolecular) photoreaction, heterocycles 1 differ from their alicyclic counterparts, i.e., 4,4-dimethylcyclohex-2-enone (10a) and 4,4,6,6-tetramethylcyclohex-2-enone (10b), as no rearrangement to a 4-oxabicyclo[3.1.0]hexan-2-one occurs. On the other hand, the photochemical behavior of pyranone 1a in bimolecular reactions (cyclodimerization, [2 + 2] cycloaddition to 2,3-dimethylbut-2-ene) resembles that of enone 10a.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770404
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  • 107
    Electronic Resource
    Electronic Resource
    Redetermination of the Crystal Structure of the 1,2,4,7-anti-tetramethylbicyclo[2.2.1]heptan-2-yl cationFormerly called ‘1,2,4,7-anti-tetramethyl-2-norbornyl cation’. at 110 K (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 943-956 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure of the 1,2,4,7-anti-tetramethylbicyclo[2.2.1]heptan-2-yl cation (1) was redetermined by X-ray crystal structure analysis of its Sb2F11 salt at 110 K (P21/c, R1 = 5.76%). The most important structural features of 1 are: C(1)—C(2) = 1.409(9), C(1)—C(6) = 1.710(8), and C(2)…C(6) = 2.113(9) Å and C(2)—C(1)—C(6) = 84.7(4)°. These results agree with those obtained earlier by other methods for the rapidly equilibrating, partially s̰-delocalized 1,2-dimethylbicyclo[2.2.1]heptan-2-yl cation (2). The detailed experimental procedure for the preparation of crystalline 1 · Sb2F11 and the crystal selection and mounting are described.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770407
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  • 108
    Electronic Resource
    Electronic Resource
    Herstellung von Analoga von Polyamin-Spinnentoxinen (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 957-971 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Polyamine Analoga of Spider ToxinsWithin the last few years, polyamine toxins derived from various arthropods raised increasing interest due to their interaction with glutamate receptors of insects and invertebrates. Compounds 51 and 52 (Scheme 5) were prepared together with 53-58 to study a new pathway to Ala-, Lys-, and Gln-derived polyamine toxins according to Scheme 6.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770408
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  • 109
    Electronic Resource
    Electronic Resource
    Photocycloaddition of Benzothiazole-2-thiones to Alkenes (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 981-987 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photocycloaddition of benzothiazole-2-thiones to electron-rich and aryl-substituted alkenes are described. Irradiation of N-unsubstituted benzothiazole-2-thione (1) in the presence of alkenes 3 gave 2-(2′-mercaptoalkyl)benzothiazoles 4, and 2-substituted benzothiazoles 5 and 6 (in the case of 3a and 3h, resp.) through the ring cleavage of an intermediate 2-aminothietane (Schemes 1 and 3). The latter was formed by [2+2] cycloaddition of the C=S bond of 1 and the C=C bond of 3. Irradiation of N-methylbenzothiazole-2-thione (2) and 2-methylpropene (3a) gave the spiro-1,3-dithiane 8, 1,2,6-benzodithiazocin-5-one 9, and disulfide 10. The structure of 9 was established by X-ray crystal-structure analysis.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770410
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  • 110
    Electronic Resource
    Electronic Resource
    Nucleotides. Part XLIII.Part XLII: [1] Solid-phase synthesis of oligoribonucleotides using the 2-dansylethoxycarbonyl ( = 2-{[5-(dimethylamino)naphthalen-1-yl]sulfonyl}ethoxycarbonyl; dnseoc) group for 5′-hydroxy protection (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 988-998 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new efficient method for solid-phase synthesis of oligoribonucleotides via the phosphoramidite approach is described. The combination of the base-labile 2-dansylethoxycarbonyl (Dnseoc) group for 5′-OH protection with the acid-labile tetrahydro-4-methoxy-2H-pyran-4-yl (Thmp) group as 2′-OH blocking group is orthogonal regarding cleavage reactions and fulfills the requirements of an automated synthesis in an excellent manner if the phosphoramidite function carries the N,N-diethyl-O-[2-(4-nitrophenyl)ethyl] substitution.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770411
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  • 111
    Electronic Resource
    Electronic Resource
    (6R,9′Z)-Neoxanthin: Synthese, Schmelzverhalten, Spektren und Konformationsberechnungen (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 909-930 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (6R,9′Z)-Neoxanthin: Synthesis, Physical Properties, Spectra, and Calculations of Its Conformation in SolutionThe synthesis of pure and crystalline (9′Z)-neoxanthin (6) is described. MnO2 Oxidation of (9Z)-C15-alcohol 7 at room temperature produces a mixture 8/9 of (9Z)- and (9E)-aldehydes. Predominant formation of the required (9Z)-aldehyde 8 is achieved by performing the oxidation at - 10°. Condensation of 8 with the mono-Li salt of the symmetrical C10-diphosphonate 10 gave the (9Z)-C25-monophosphonate 11. The Wittig-Horner condensation of 10 with the allenic C15-aldehyde 1b, under selected conditions allows the preparation of pure and crystalline (9′Z)-15,15′-didehydroneoxanthin (12) and, after subsequent semireduction, of crystalline (15Z,9′Z)-neoxanthin (13). Thermal isomerisation of a AcOEt solution of 13 at 95° yields preferentially (9′Z)-neoxanthin (6). Our crystalline sample shows the highest ∊-values in the UV/VIS spectra ever recorded. The CD spectra display a pronounced similarity with those of corresponding violaxanthin isomers. In contrast to the (all-E)-isomer 5, (9′Z)-neoxanthin undergoes very little isomerisation when heated to its melting point. For comparison purposes, a crystalline probe of 6 is also isolated from lawn mowings. Extensive 1H-and 13C-NMR investigations at 600 MHz of a (D6)benzene solution using 2D-experiments such as COSY, TOCSY, ROESY, HMBC, and HMQC techniques permit the unambiguous assignment of all signals. Force-field calculations of a model system of 6 indicate the presence of several interconverting conformers of the violaxanthin end group, 66% of which possess a pseudoequatorial and 34% a pseudoaxial OH—C(3′). The torsion angle (ω1) around the C(6′)—C(7′) bond, known to be of prime importance for the shape of the CD spectra, varies with values of 87° for 55% and 263° for 45% of the molecules. Therefore, the molecules clearly display a preference for the ‘syn’-position of the C(7′)=C(8′) bond and the epoxy group. Unexpectedly, the double bonds of C(7′)=C(8′) and C(9′)=C(10′) are not coplanar. The deviation amounts to ± 20°, both in the ‘syn’ - and the ‘anti’-conformation.
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770405
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  • 112
    Electronic Resource
    Electronic Resource
    Phenylenbis(silandiyl-triflate) als neuartige Synthesebausteine für vielfältig strukturierte Organosilizium-Polymere (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 972-980 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Phenylenebis(silandiyl triflates) - New Synthetic Building Blocks for Variously Structured Organosilicon PolymersOrtho-, meta-, and para-substituted phenylenebis(silandiyl triflates) are prepared as new useful building blocks for the synthesis of polymers with a regular alternating arrangement of an organosilicon unit and a π-electron system (phenylene or ethynylene) in the backbone. Such polymers can be used as photoresists, semiconducting materials or precursors of silicon carbide. The phenylenebis(silandiyl-triflates) 5a-c are obtained by protodesilylation of the corresponding (allylsilyl)- or [(diethylamino)silyl]benzenes 3a-c and 4a-c, respectively, with trifluoromethanesulfonic acid. Reactions with dinucleophiles like Li2C2 and Ph2Si(OH)2 lead to variously structured organosilicon polymers (see Eqns. 11 and 12), which are characterized by spectroscopic methods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770409
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  • 113
    Electronic Resource
    Electronic Resource
    Mixed Azines of Naloxone with Dihydromorphinone Derivatives (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 999-1002 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mixed azines 4 and 5 were prepared by reaction of naloxazone (2) with either oxymorphone (6) or 14-O-methyloxymorphone (7) and tested in vitro using opioid receptor binding assays and in vivo using the AcOH-writhing test in mice. Compound 4 was found to be a partial agonist, while compound 5 was a potent opioid agonist with higher potency than morphine.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770412
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  • 114
    Electronic Resource
    Electronic Resource
    The Protonation of [Pt3(m̈-CO)3(PCy3)3] (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1029-1036 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cluster [Pt3(m̈-CO)3(PCy3)3] can be protonated with HBF4 · OEt2 to form the cluster [Pt3(m̈-CO)3(PCy3)3](m̈3-H) +BF4- (2). This unstable compound was isolated and characterised by NMR and IR spectroscopy.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770415
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  • 115
    Electronic Resource
    Electronic Resource
    Synthesis, Base Pairing, and Structural Transitions of Oligodeoxyribonucleotides Containing 8-Aza-2′-deoxyguanosine (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1003-1017 
    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 8-aza-2′-deoxyguanosine (z8Gd; 1) or its N8-regioisomer z8Gd* (2) instead of 2′-deoxyguanosine (Gd) is described. For this purpose, the NH2 group of 1 and 2 was protected with a (dimethylamino)methylidene residue (→5, 6), a 4,4′-dimethoxytrityl group was introduced at 5′-OH (→ 7, 8), and the phosphonates 3a and 4 as well as the phosphoramidite 3b were prepared. These building blocks were used in solid-phase oligonucleotide synthesis. The oligonucleotides were characterized by enzymatic hydrolysis and melting curves (Tm values). The thermodynamic data of the oligomers 12-15 indicate that duplexes were stabilized when 1 was replacing Gd. The aggregation of d(T-G-G-G-G-T) (18) was studied by RP 18 HPLC, gel electrophoresis and CD spectroscopy and compared with that of oligonucleotides containing an increasing number of z8Gd residues instead of Gd. Similarly to [d(C-G)]3 (12a), the hexamer d(C-z8G-C-z8G-C-G) (14) underwent salt-dependent B-Z transition.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770413
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  • 116
    Electronic Resource
    Electronic Resource
    Syntheses of the First Selenium-Containing Bicyclic β -Lactams as Potent Antimicrobial Agents (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1037-1045 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Syntheses of the cis-configurated isodethiaselenapenam 5 (Scheme 1) as well as the isodethiaselenacephems 29 and 31 (Scheme 2) were accomplished, in which the key step involved addition of Se to the corresponding carbanions of 1, 25, and 27 followed by internal alkylation. β-Lactams 29 and 31 were found to possess biological activity against several pathogenic microorganisms in vitro. The electronic activation of the lactam moiety in the isodethiaselenacephem 31 and the corresponding isocephem 33 remarkably enhanced their biological activity. Isodethiaselenacephem 31 was more toxic than isocephem 33 in experimental animals.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770416
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  • 117
    Electronic Resource
    Electronic Resource
    Synthesis of Chlorophyll a Labeled at C(32) from Pheophorbide a Methyl Ester (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1046-1050 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: [32-14C]Chlorophyll a (10b) was synthesized from pheophorbide a methyl ester (5a) in a seven-step partial synthesis. The key intermediate pheophorbide d methyl ester (6) was obtained by ozonolysis of the vinyl group of 5a in 91% yield. Selective reduction of the CHO group of 6 gave the corresponding alcohol 7, and conversion of the latter to the phosphonium bromide 8 yielded after Wittig reaction with [14C]paraformaldehyde, [32-14C]pheophorbide a methyl ester (5b). The final transformation to the title compound was achieved by acid hydrolysis of 5b, esterification with natural phytol to [32-14C]pheophytin a (9b), and eventual insertion of a Mg2+ ion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770417
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  • 118
    Electronic Resource
    Electronic Resource
    Synthesen mit Übergangsmetall-Komplexen. Teil 2.Teil 1: [1] Neue Fluoranthen-Derivate mit (1,6-Methano[10]annulen-2-yl)- und/oder (Naphthalin-1-yl)-SubstituentenHerrn Professor Dr. Tetsuo Nozoe, Tokyo, zum 90. Geburtstag mit den besten Wünschen gewidmet (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1051-1056 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Syntheses with Transition-Metal Complexes. New Fluoranthene Derivatives with 1,6-Methano[10]annulen-2-yl and/or Naphthalen-1-yl SubstituentsIn the course of investigations of molecules bearing ‘parallel triple bonds’, the fluoranthene derivatives 6-10 were synthesized by reaction of the ‘rhodacycle’ 4 with selected alkynes. The spectroscopic data of 6-10 are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770418
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  • 119
    Electronic Resource
    Electronic Resource
    X-Ray Structure Analysis of 15-Apoviolaxanth-15-al (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1018-1028 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The X-ray structure of 15-apoviolaxanth-15-al ( = (1′S,2′R,4′S,2E,4E,6E,8E)-9-(1′,2′-epoxy-4′-hydroxy-2′,6′,6′-trimethylcyclohexyl)-3,7-dimethylnona-2,4,6,8-tetraenal) is reported. The four symmetry-independent molecules in the asymmetric unit are linked into X-shaped spirals by intermolecular H-bonds. Additional H-bonds interconnect the spirals, forming wave-like chains. The geometry of the polyene side chain possesses the same in-plane bending observed for related retinal and carotenoid compounds. The polyene side chain deviates from planarity by twists of up to 10° about each bond; some of the largest twists are about C=C bonds. The epoxycyclohexane ring possesses a distorted ‘C(3)-sofa’ conformation. The torsion angles about the bond connecting the polyene chain to the cyclohexane ring are compared with equivalent torsion angles in molecules containing epoxide rings substituted with a π-system in order to examine possible interactions between the epoxide group and the π-system, either through pseudoconjugation, or through an interaction of the nonbonding orbitals of the epoxy O-atom with the π-orbitals of the polyene chain. The latter is considered to be more likely.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770414
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  • 120
    Electronic Resource
    Electronic Resource
    Synthesis and Biological Activity of Tetrahydropyrido[2′,3′:4,5]imidazo[1,2-c]pyrimidine-6,8-diones (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1057-1064 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Substituted 4-oxoquinoline-3- (1a) and 4-oxo-1,8-naphthyridine-3- (1b) carboxylic acids are clinically useful antibacterial agents exerting their activity by inhibiting the subunit A of DNA gyrase. Recently, pyrimido-[1,6-a]benzimidazoles 2 were found to be a new class of inhibitors of this enzyme. As, in 1, replacement of C(8) by the N-atom was shown beneficial for the biological properties, a synthesis of the corresponding aza analogues of 2 has been carried out. The synthesis, DNA gyrase inhibitory activity, and in vitro antibacterial activity of the target compounds 16-19 are reported.
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    URL: http://dx.doi.org/10.1002/hlca.19940770419
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    Stereoselective Syntheses of Tetrahydroesterastin-β -Lactam Analogues (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1065-1075 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A total synthesis of the optically active tetrahydroesterastin β -lactam analogue 2 using Miller's hydroxamate approach is described (Scheme 2). Significant modification of published procedures has resulted in a short and facile stereospecific preparation of the N-[(benzyloxycarbonyl)methyl]-β -lactam 17 starting from the readily available D-serine. This material served as intermediate for the preparation of a variety of N-[(benzyloxycarbonyl)methyl]tetrahydroesterastin β-lactam analogues (Scheme 5).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770420
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  • 122
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    Reaktion von Phenyldiazomethan mit 1,3-Thiazol-5(4H)-thionen: Basenkatalysierte Ring-Öffnung des Primäradduktes (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1076-1086 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of Phenyldiazomethane with 1,3-Thiazole-5(4H)-thiones: Base-Catalyzed Ring Opening of the Primary AdductReaction of 1,3-thiazole-5(4H)-thiones 1 and phenyldiazomethane (2a) in toluene at room temperature yields the thiiranes trans- and cis-1,4-dithia-6-azaspiro[2.4]hept-5-enes (trans- and cis-4; Scheme 2). With Ph3P in THF at 70°, these thiiranes are transformed stereospecifically into (E)- and (Z)-5-benzylidene-4,5-dihydro-1,3-thiazoles 5, respectively. In the presence of DBU, 1 and 2a react to give 1,3,4-thiadiazole derivatives 6 or 7 via base-catalyzed ring opening of the primary cycloadduct (Scheme 3). In the case of 2-(alkylthio)-substituted 1,3-thiazole-5(4H)-thiones 1c and 1d, this ring opening proceeds by elimination of the corresponding alkylthiolate, yielding isothiocyanate 7. The structures of (Z)-5c and 6b have been established by X-ray crystallography.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770421
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  • 123
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    β -Cyclodextrin-Mediated Regioselective Hydrolysis of 5,10,15,20-tetrakis[2,4-bis(pivaloyloxy)phenyl]-21H,23H -porphine (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1087-1098 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The four peripheral ester moieties of the title compound 5 are regioselectively hydrolyzed under mild conditions in the presence of β -cyclodextrin (10), providing a new entry to tetraphenylporphyrin derivatives with differently substituted Ph groups in the meso-positions. UV, 1H-NMR and mass spectroscopy of the inclusion complex 9 of 2,6-O-dimethyl-β-cyclodextrin (12) and 5 indicate a stoichiometry of 2:1 for 10/5. Moreover, calculations confirm NOE experiments consistent with the fact that the cyclodextrins 10 and 12 approach the Ph groups of the porphyrin with the small opening of the cavity (primary face).
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770422
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  • 124
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    N-(4-Nitrophenyl)oxamic Acid and Related N-Acylanilines Are Non-competitive Inhibitors of vibrio cholerae sialidase but do not inhibit trypanosoma cruzi or trypanosoma brucei trans-sialidases (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1166-1174 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: N-(4-Nitrophenyl)oxamic acid 1, N-(2-fluoro-4-nitrophenyl)oxamic acid 7, N-(4-nitrophenyl)-trifluoroacetamide 3, and N-(2-methoxy-4-nitrophenyl)trifluoroacetamide 9 are non-competitive inhibitors of Vibrio cholerae sialidase with Ki-values ranging from 2.66 to 5.18 · 10-4 M. These compounds, and the N-acetylneuraminic-acid analogues 11-13 do not inhibit the sialidase and trans-sialidase activities from Trypanosoma cruzi; nor does N-(4-nitrophenyl)oxamic acid (1) inhibit the corresponding enzyme activities from T. brucei.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770425
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  • 125
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    Synthesis of Linear Oligomers of (R)-3-Hydroxybutyrate and Solid-State Structural Investigations by electron microscopy and X-ray scatteringDedicated to Prof. Dr. H. Ringsdorf on the occasion of his 65th birthday (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1099-1123 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Repetitive treatment of the biopolymer P(3-HB) (molecular weight 〉 105 Dalton, storage or s-P(3-HB)), with lithium hexamethyl disilazanid (LHMDS) at -70° in THF leads to a mixture of oligomers with increasingly sharp distribution around a 15-, 30-, and 45mer. Discrete fragments are also isolated when P(3-HB) is heated under reflux (89°) in neat Et3N. Linear oligo(3-HB) derivatives (3-7) containing up to 96 3-HB units are synthesized using an exponential segment-coupling strategy. These oligomers are used to calibrate size-exclusion chromatography columns for the analysis of oligo(3-HB) samples from the different sources. The linear oligo-(3-HB) derivatives also served as a model with respect to the physical properties of high molecular weight P(3-HB) and were investigated as such by transmission electron microscopy (TEM) and by small- and wide-angle X-ray scattering (SAXS and WAXS). The thicknesses of the lamellar crystallites (long periods) formed by the 8mer, 16mer, and 32mer, are ca. 26, 52, and 53 Å, respectively, indicating that the 32mer molecules are folded once, very tightly, into a ‘hair-pin’-type conformation. High-molecular-weight P(3-HB), which was crystallized in a similar way, also has a lamellar crystallite thickness of ca. 50-65 Å. Thus, the treatment of P(3-HB) with LHMDS at low temperature causes etching of the amorphous regions, an effect well known in polymer science for studying the regularity of chain folding. The ca. 50-Å packing within the tight folds of P(3-HB) is discussed in view of its possible function in ion transport through cell membranes.
    Additional Material: 10 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770423
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  • 126
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    Peptide Enolates. C-Alkylation of Glycine Residues in linear tri-, tetra-, and pentapeptides via dilithium azadienediolates (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1124-1165 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Boc-protected tripeptides Boc-Val-Gly-Leu-OH (1), Boc-Leu-Sar-Leu-OH (2), Boc-Leu-Gly-MeLeu-OH (3), and Boc-Val-BzlGly-Leu-OMe (64), tetrapeptide Boc-Leu-Gly-Pro-Leu-OH (9), and pentapeptides Boc-Val-Leu-Gly-Abu-Ile-OH (4), Boc-Val-Leu-Sar-MeAbu-Ile-OH (5), Boc-Val-Leu-Gly-MeAbu-Ile-OH (6), Boc-Val-Leu-BzlGly-BzlAbu-Ile-OH (7), and Boc-Val-Leu-Gly-BzlAbu-Ile-OH (8) are prepared by conventional methods (Schemes 4-7) or by direct benzylation of the corresponding precursors (Scheme 8). Polylithiations in THF give up to Li6 derivatives containing glycine, sarcosine or N-benzylglycine Li enolate moieties (A-H). The polylithiated systems with a dilithium azadienediolate unit (C, F-H) are best generated by treatment with t-BuLi. The yields of alkylation of the glycine or sarcosine residues are up to 90%, with diastereoselectivities from nil to 9:1. Normally, the newly formed stereogenic center has (R)-configuration (i.e. a D-amino-acid residue is incorporated in the peptide chain). Electrophiles which can be employed with the highly reactive azadienediolate moiety are: MeI, EtI, i-PrI, allyl and benzyl bromide, ethyl bromoacetate, CO2, and Me2S2 (Schemes 11-13). No epimerizations of the starting materials (racemization of the amino-acid residues) are observed under the strongly basic conditions. Selected conformations of the peptide precursors, generated by shock-freezing or by very slow cooling from room temperature to -75° before lithiation, give rise to different stereoselectivities (Scheme 11). The latter and the yields can also be influenced by tempering the lithiated species before (Scheme 9) or after addition of the electrophiles (Scheme 12). Besides the desired products, starting peptides are recovered in the chromatographic purification and isolation procedures (material balance 80-95%). The results described are yet another demonstration that peptides may be backbone-modified through Li enolates, and that whole series of analogous peptide derivatives with various side chains may thus be produced from a given precursor.
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    URL: http://dx.doi.org/10.1002/hlca.19940770424
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    Mitteilungen - Communications (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1193-1193 
    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.19940770427
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  • 128
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    Masthead (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994) 
    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.19940770501
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  • 129
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    Glycosylidene Carbenes. Part 17. Glycosidation of benzyl β-D- and β-L-ribopyranosides. Further evidence for the effect of stereoelectronic control on the regioselectivity of glycosidation (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1175-1192 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The H-bonds of the enantiomeric ribosides 4 and 5 and their glycosidation by the diazirine 1 are described. HO-C(2) and HO—C(4) of 4 and 5 form a ‘flip-flop’ H-bonding system, with HO—C(3) acting as a H-bond donor to O—C(2) or O—C(4). HO—C(2) and HO—C(4) of monomeric 4 and 5 are thus the most strongly acidic OH groups. Glycosidation of 4 and 5 by 1 depends on the solvent, the temperature, and the concentration. It yields up to 91% of a mixture of anomeric pairs of the 1,2-, 1,3-, and 1,4-linked disaccharides 8-13 and 20-25, respectively, which were characterized as their diacetates 14-19 and 26-31 (Scheme). Glycosidation in CH2Cl2 and in dioxane yielded mostly the 1,3-linked disaccharides 10/11 and 22/23 (α/β ca. 4:1), while glycosidation in THF leads mostly to the 1,2- and 1,4-linked regioisomers (β〉α). There are small, but significant differences in the glycosidation of 4 and 5. These, the regio-, and the stereoselectivities are rationalized as the consequences of the stereoelectronic control of both the H-transfer from HO—C(2) or HO—C(4) to the intermediate carbene and of the formation of the glycosidic C—O bond, and of the coordination of the intermediate oxycarbenium ion with THF.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770426
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  • 130
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    Asymmetric Catalysis by Vitamin B12: The isomerization of achiral cyclopropanes to optically active olefins (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1193-1202 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Achiral spiroactivated cyclopropanes are isomerized to optically active (R)-(cycloalk-2-enyl)-Meldrum's acids ( = (R)-5-(cycloalk-2-enyl)-2,2-dimethyl-1,3-dioxane-4,6-diones) in high yield and ee's up to 86% by catalytic amounts of cob(I)alamin in polar protic solvents.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19940770502
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  • 131
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    Xenicane Diterpenes Revisited: Thermal (E)→(Z) isomerization and conformational motions. A unifying picture (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1203-1221 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Kinetic and equilibrium studies show that typical xenicanes such as dictyolactone (1) and 4-hydroxydictyolactone (3) undergo slow conformation medium-ring flipping between the predominant trans-(1a or 3a; Me(20) trans to H-C(3)) and the minor cis-conformers (1b or 3b; Me(20) cis to H-C(3); see Scheme 1). The formation of the latter is inhibited in heterocyclic-ring-opened congeners such as 18-acetoxy-4-hydroxydictyo-19-al (7). Molecular-mechanics calculations suggest that typical-xenicane cis-conformers are disfavoured by mainly C(4)-C(5) torsional strain. This is confirmed by the observation of two sizably populated cis-and trans-conformers for the unnatural 4-oxoxenicanes 10-12. Unusually facile thermal (E)→(Z) isomerization of xenicanes 1,3,10-12, and 7 is also observed (→ 13-17 and 9, resp.; Scheme 3), reflecting great strain relief in the transition state. Conflicting results in the literature now fit into this scheme which provides a basis for unravelling recognition phenomena with these biologically active systems.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770503
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  • 132
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    A Short Synthesis of (-)-Carbovir (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1236-1240 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (-)-Carbovir ((-)-1) was synthesized via the cyclic carbonate 2 in four steps starting from enantiomerically enriched (-)-(S)-(cyclopent-2-enyl)methanol ((-)-3).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770506
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  • 133
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    N4-Benzoylspermidine from Oncinotis tenuiloba: Analytical differentiation of the three isomeric N-benzoylspermidines (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1229-1235 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: During the examination of extracts from Oncinotis tenuiloba STAPF a new polyamine, N4-benzoylsperimidine (8), was isolated. For unambiguous structure elucidation, it was transformed into the diacetyl derivative 13, and the three possible N-benzoyl-substituted isomers of spermidine 5, 8, and 11 together with their peracetylated derivatives 12-14, respectively, were synthesized and identified.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770505
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  • 134
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    [M(bpy)3] (M = Fe, Ru, Os): New Crystalline Materials from the reductive electrocrystallization of [M(bpy)3](PF6)2 (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1222-1228 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reductive electrocrystallization at a constant current density (11.0-11.5 μA/cm2) of millimolar solutions of [M(bpy)3](PF6)2, where M = Fe, Ru, or Os, and bpy = 2,2′-bipyridine in acetonitrile containing 0.1M Bu4NPF6 results in the formation of dark crystals on the Pt cathode. The crystals grow as long, thin, and shiny needles having a hexagonal cross section of 0.1-0.5 mm in diameter. Combustion microanalyses results are consistent with the composition for [Fe(bpy)3], [Ru(bpy)3], and [Os(bpy)3]. In addition, the chromophores are conserved, as confirmed by recording both the electronic and the 1H-NMR spectra after reoxidation of the electrocrystals in humid air. The spectra are identical to those for authentic samples of [Fe(bpy)3]2+, [Ru(bpy)3]2+, and [Os(bpy)3]2+. A ratio of 2.0 ± 0.1 e-/molecule is observed upon completion of the controlled potential electrolysis of a solution of [M(bpy)3]2+, which results in the precipitation of a dark solid and the almost complete fading of the color of the original solution. Unexpectedly, the crystals do not exhibit an ESR signal. These data indicate the formation of novel materials, crystalline [Fe(bpy)3], [Ru(bpy)3], and [Os(bpy)3].
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770504
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  • 135
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    Synthesis of the Thiazolone Analogue of the Acetylcholinesterase Inhibitor, Huperzine A (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1256-1266 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation of an analogue 3a of the acetylcholinesterase inhibitor, huperzine A (1), is described in which the pyridinone moiety of the natural product is replaced with a thiazolone moiety. The synthesis started from cyclohexane-1,4-dione monoethylene ketal (7) by first annulating the thiazole ring using the Gewald protocol (→ 8; Scheme 1) and then constructing the bicyclo[3.3.1]nonane substructure using our previously described Michael addition/aldol condensation methodology (Scheme 3). The central problem was the protection of the thiazolone carbonyl group; only the 2-unsubstituted thiazole survived the reaction conditions of the first half of the synthesis. Refunctionalization was later effected by lithiation and subsequent chlorination with hexachloroethane (30→31). Compound 3a was ineffective in the acetylcholinesterase inhibition assay in concentrations up to 14 μM.
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    URL: http://dx.doi.org/10.1002/hlca.19940770508
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  • 136
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    Synthesis and Structure-Activity Relationships of Juvenoids Derived from 2-(4-hydroxybenzyl)cycloalkan-1-ones (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1241-1255 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Juvenoids 16-30, 32, 36, 38-41, 44-46, and 49-56 containing carbamate, carbonate, and urea moieties in the molecule were synthesized and subjected to a biological screening (Schemes 2-7, Table 2). Carbamate juvenoids 1-4 were used as reference compounds for a detailed structure-activity study of their analogues. A clear relationship between the nature of the side chain functional group and the biological activity was found. Surprisingly, not only the juvenoids 1-4 but also 38-41, the compounds with a reversed carbamate N,O-substitution pattern, showed very promising biological activity. In contrast, the carbonate and urea derivatives displayed a remarkably low activity. The relationship between the size and substitution at atoms C(2) and C(3) of the saturated ring and the biological activity is very complex and is still not completely understood.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19940770507
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  • 137
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    Synthesis of Enantiomerically Pure D- and L-(Heteroaryl)alanines by asymmetric hydrogenation of (Z)-α-amino-αβ-didehydro esters (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1395-1411 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Homogeneous asymmetric hydrogenation of a wide range of methyl and tert-butyl (Z)-2-(acylamino)-3-(heteroaryl)acrylates (see 1a-f and 2a-d, f, g, resp.) catalyzed by diphosphinerhodium catalysts was studied for the synthesis of enantiomerically pure 3-furyl-, 3-thienyl-, and 3-pyrrolylalanines (see 3a-f, and 4a-d, g; Scheme 1). The precursors, the (Z)-α-amino-α,β-didehydro esters 1a-f and 2a-d, f, g were prepared in high yields using the phosphorylglycine-ester method (Scheme 1). Isomerically pure (Z)-α-amino-α,β-didehydro esters were required to obtain the highest enantiomeric excesses (ee's) in the asymmetric hydrogenation, and the tert-butyl-ester strategy was beneficial in terms of both getting pure (Z)-α-amino-α,β-didehydro esters and obtaining high ee's in the hydrogenation. Finally, in contrast to the methyl-ester series, deprotection of the tert-butyl esters 4a-d, g was easily performed using CF3CO2H without any racemization.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770518
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  • 138
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    Synthetic Attempts towards ‘Aromatic’ NonafulvenesFulvenes, Fulvalenes, Part 67; Part 66: [1]. (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1377-1394 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: According to their spectroscopic behavior, four classes of nonafulvenes may be distinguished, but, so far, only three classes have been identified. Type-A nonafulvenes (including parent 1a) are typically olefinic molecules with strongly alternating bond lengths and a nonplanar nine-membered ring. Type-B nonafulvenes are characterized by four pairs of equivalent ring H-atoms and ring C-atoms. Spectra of both Type-A and Type-B nonafulvenes are not dependent on temperature and solvent polarity. However, spectra of Type-C nonafulvenes (including prototype 1d with R1 = R2 = NMe2) are strongly influenced by temperature and solvent polarity due to an equilibrium 1⇄1± between the nonpolar olefinic 1 and dipolar planarized 1±. So far, Type-D nonafulvenes occurring exclusively in the dipolar form 1± were unknown. Synthetic attempts towards nonafulvenes of Type D are described and problems encountered in nonafulvene syntheses are discussed. Several new cyclononatetraenes and four new nonafulvenes (or nonafulvalenes) 31, 1n, 3, and 5 have been synthesized. Spectroscopic evidence shows that 11,12-bis(diethylamino)nonatriafulvalene 5 is the first Type-D nonafulvene.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770517
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  • 139
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    Synthesis of β -Cyperone via Fungal Hydroxylation of thujone-derived tricyclic cyclopropanes (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1707-1720 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of optically active sesquiterpenes with a eudesmane C-skeleton from the chiral starting material thujone involves transformation of a tricyclic intermediate (1R,2R,4S)-1,7-dimethyl-4-(1-methylethyl)tricyclo[4.4.0.02,4]dec-6-en-8-one (2) into the bicyclic compound β -cyperone (5). Hydroxylation of 2 at C(5) or C(11) permits subsequent opening of the cyclopropane ring and rearrangement to β -cyperone. In this publication, studies involving hydroxylation of 2 by fungal cultures are presented. The resultant products are useful intermediates in efficient synthesis of eudesmane sesquiterpenes. Of five fungi tested, Rhizopus oryzae ATCC 11145 proved most versatile. It hydroxylates at the exocyclic C(11) position in high yield (70%) and, to a lesser extent, at C(5) (5%). Enzymatic activity appears at the end of growth phase and at least 2.2 g of 2 per liter can be metabolized without significant loss of product yield. A second fungus, Cunninghamella echinulata ATCC 9244, proved most useful for hydroxylation of derivatives of 2 for the preparation of derivatives of β -cyperone, although product yields were low (2-20%), some derivatives were nonreactive, and hydroxylation at C(9) occurred. The relationship between precursor structure and enzyme affinity is discussed.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770704
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  • 140
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    A Practical Synthesis of (2S, 3R)-3-Amino-2-methylpentanoic Acid from L-Aspartic Acid (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 2142-2146 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: L-Aspartic acid by successive N-tosylation, anhydride formation, and reduction was converted into (3S)-3-(tosylamino)butano-4-lactone (4). Electrophilic methylation of 4, subsequent iodo-esterification and nucleophilic methylation, followed by saponification and deprotection, gave (2S, 3R)-3-amino-2-methylpentanoic acid (2) with an ee of 〉 99% in seven steps and in an overall yield of 34%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770807
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  • 141
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    Monocarboxylates of 3-Methylidene-β-lactams: Synthesis and unusual oxidative rearrangement into a spiro[azetidine-3,3′-pyrrolidine] derivative (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 2147-2152 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of the 3-silylated β-lactams 1 with glycoxalates gives bis-lactam 3, but the same reaction in the presence of 1 equiv. of Me3SiCl leads to the formation of the disilylated adducts 5. The latter is desilylated by (Bu4N)F yielding the monocarboxylates 7 of 3-methylidene-β-lactams, which, with oxidizing agents, give the spiro compound 8. The structure of 8 is established by spectroscopic data and a crystal-structure analysis.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770808
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  • 142
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    In vivo Investigation of Plant-Cell Metabolism by means of natural-abundance 13C-NMR spectroscopy (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 2153-2161 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Based on the natural abundance of 13C, in vivo 13C-NMR was used for the first time to monitor the metabolism of sucrose and hydroquinone (1) in cell suspensions of the plant Rauwolfia serpentina (L.) BENTH. ex KURZ. Cells converted sucrose extracellularly into α-D- and β -D-glucose as well as into β -D-fructofuranose and β -D-fructopyranose, respectively. The sugar mixture was completely taken up by the cells after 4 days. Hydroquinone fed at that time resulted in optimum conversion into its β -D-glucoside arbutin (2) within 10 h. A further metabolite, the primeveroside (3) of hydroquinone, appeared as a trace compound after 10 h. The formation of this diglycoside can be increased by further addition of sucrose.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770809
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  • 143
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    Multiorganyltin Compounds. Designing a novel phosphate-selective carrier (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 2191-2196 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of distannyl derivatives, 1-9, were studied for their application as phosphate-selective carriers in polymer-based liquid membranes. A drastically different potentiometric behavior was observed depending on the distance between the tin(IV) coordinating centers and the ligands attached to them. Some of the compounds examined, i.e. (PhSnBr2)2CH2(1) and (Me3SiCH2SnCl2CH2)2 (3) showed very high potentiometric selectivity towards phosphate over other lipophilic anions such as perchlorate and thiocyanate. Results indicate that (1) the optimal number of CH2 groups between the Sn-centers are either one or three, (2) the electron-withdrawing power of the organic ligands attached to Sn-centers strongly influences the overall response towards phosphate, and (3) the steric effect of the organic substituents is important in the potentiometric selectivity observed.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770812
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  • 144
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    The Structure of 1H-Perimidin-2(3H)-one and Its Derivatives in the solid state (x-ray crystallography and CP/MAS 13C-NMR), in solution (13C-NMR), and in the gas phase (mass spectrometry) (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 121-139 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The X-ray crystal and molecular structures of 1-methyl- 1H-perimidin-2(3H)-one (5b) and 1,3-dimethyl-1H-perimidin-2(3H)-one (6) were determined. The crystals are built of piles of dimers faced head-to-head in 5b and of alternating independent head-to-tail molecules in 6, both along the b axis. Semiempirical calculations at the AM 1 level revealed that the eclipsed conformation of the Me groups with respect to the C=O group, found in the crystals, is the most stable. The lack of planarity of the whole molecules is a consequence of the packing forces since it is not found in the calculations. A comparative NMR study was carried out in solution (1H and 13C) and in the solid state (CP/MAS 13C) for 1H-perimidin-2(3H)-one (2) and 1H-benzimidazol-2(3H)-one (3) with the conclusion that in both heterocycles the oxo tautomer is the most abundant. The structure in the gas phase was approached by mass spectrometry. In the case of 3, the oxo tautomer loses CO after ionization, while the oxo form of 2 tautomerizes to the hydroxy form which loses, H2O after a [1,3]-H shift. AM 1 calculations were carried out on the ground and ionized states of 2.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770115
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  • 145
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    Metal complexes with macrocyclic ligands. Part XXXVIPart XXXVI:[1].. Thermodynamic and kinetic studies of bivalent and trivalent metal ions with 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 383-398 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: NMR, potentiometric, and UV/VIS measurements were run to study the protonation and the In3+ and Cu2+ stability constants of 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (do3a, L). The protonation of do3a follows the typical scheme with two high and several low log KH values. Between pH 11 and 13, the protonation mainly occurs at the N-atom, which is not substituted by an acetate side chain. The In3+ complex is not appreciably protonated even at low pH values (pH ⋐ 1.7), whereas [CuL] can add up to three protons in acidic solution to give the species [CuLH], [CuLH2], and [CuLH3], the stability of which was determined. The formation rates of the Y3+, Gd3+, Ga3+, and In3+ complexes with do3a were measured using a pH-stat technique, whereas that of Cu2+, being faster, was followed on a stopped-flow spectrophotometer. In all cases, the reaction scheme implies the rapid formation of partially protonated intermediates, which rearrange themselves to the final product in the rate-determining process. ([MLH])in, an intermediate, in which the metal ion probably is coordinated by two amino acetate groups, proved to be the reactive species for Y3+, Gd3+, and Ga3+. The formation of [Cu(do3a)] was interpreted by postulating that either ([CuLH])in or ([CuLH])in, and ([CuLH2])in are the reactive complexes. The rates of dissociation of the Y3+, Gd3+, and Cu2+ complexes with do3a were studied spectrophotometrically. For Y3+ and Gd3+, arsenazo III was used as a scavenger, whereas for Cu2+ the absorption associated with d-d* transition was followed. For [Y(do3a)] and [Gd(do3a)], the rate law follows the kinetic expression kobsd = k0 + k1[H+]. The dissociation of [Cu(do3a)] goes through the proton-independent dissociation of [CuLH3], which is the main species at low pH.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770136
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  • 146
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    Umsetzung von Di(tert-butyl)- und Diphenyldiazomethan mit 1,3-Thiazol-5(4H)-thionen: Isolierung und Kristallstruktur des primären Cycloadduktes (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 435-444 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of Di(tert-butyl)- and Diphenyldiazomethane and 1,3-Thiazole-5(4H)-thiones: Isolation and Crystal Structure of the Primary CycloadductReactions of diazo compounds with C=S bonds proceed via the formation of thiocarbonyl ylides, which, under the reaction conditions, undergo either 1,3-dipolar cycloadditions or electrocyclic ring closer to thiiranes (Scheme 1). With the sterically hindered di(tert-butyl)diazomethane (2c), 1,3-thiazole-5(4H)-thiones 1 react to give spirocyclic 2,5-dihydro-1,3,4-thiadiazoles 3 (Scheme 2). These adducts are stable in solution at -20°, and they could be isolated in crystalline form. The structure of 3c was established by X-ray crystallography. In CDCl3 solution at room temperature, a cycloreversion occurs, and the adducts of type 3 are in an equilibrium with 1 and 2c. In contrast, the reaction of 1 with diphenyldiazomethane (2d) gave spirocyclic thiiranes 4 as the only product in high yield (Scheme 3). The crystal structure of 4b was also determined by X-ray analysis. The desulfurization of compounds 4 to 4,5-dihydro-5-(diphenylmethylidene)-1,3-thiazoles 5 was achieved by treating 4 with triphenylphosphine in boiling THF. The crystal structure of 5f is shown.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770204
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    Preparation of Boc-Amino-Acid or Peptide Aldehydes via Reduction of Corresponding Phenyl Esters (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 150-154 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new alternative method for the preparation of amino-acid and peptide aldehydes based on reduction of corresponding phenyl esters with lithium tri(tert-butoxy)aluminium hydride is described.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19940770117
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  • 148
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    FT-IR Investigation of Rare-Earth and Metal-Ion Solvation. Part 14. Interaction between uranyl perchlorate and dimethyl sulfoxide in anhydrous acetonitrilePart 13: [1]. (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 140-149 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interaction between the uranyl ion and perchlorate in anhydrous acetonitrile has been investigated by FT-IR and Raman spectroscopy. Vibrations assigned to uncoordinated (u), monodentate (m), and bidentate (b) perchlorate anions were identified in 0.075M solutions. Quantitative data indicate that perchlorate is distributed as follows: 37 ± 2% are uncoordinated, 36 ± 7% are monodentate, and 27 ± 7% are bidentate. This is in agreement with the conductivity of the solutions which is at the lower end of the range accepted for 1:1 electrolytes. The splittings v4-v1(m) and v8-v1(b) of 147 and 246 cm-1, respectively, point to a large inner-sphere interaction. An equilibrium occurs between two differently coordinated species. Various amounts of DMSO were added to 0.05M perchlorate solutions (R′ = [DMSO]t/[UO22+]t = 1-10). The v7 (SO) and v22 (CS) vibrations of DMSO were used to determine the average number of coordinated DMSO molecules per uranyl ion, which is close to 4. Some bidentate perchlorate ions are still present in these solutions, but all the MeCN molecules (2.6 on average) are expelled out of the inner coordination sphere. The data can again be interpreted in terms of an equilibrium between differently coordinated species. The average coordination number of the uranyl ion is 4.4, as the perchlorate salt in MeCN solution, and may be somewhat smaller in the presence of DMSO. The possible presence of dimeric species is also discussed.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770116
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    Mitteilungen - Communications (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 597-598 
    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.19940770223
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  • 150
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    Synthese des Pyrrolizidin-Alkaloides (±)-TrachelanthamidinHerrn Professor H. C. Helmut Werner zum 60. Geburtstag gewidmet (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 579-585 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of the Pyrrolizidine Alkaloid (±)-TrachelanthamidineThe important intermediate in the synthesis of the title compound 8 is the diastereoisomer mixture of ethyl 2-[2-(1,3 dioxolan-2-yl)ethyl]-5-oxopyrrolidine-3-carboxylate (3a/3b) which was prepared from nitromethane, acrylaldehyde, and diethyl fumarate (Scheme). Its reduction (NaBH4, t-BuOH, MeOH) gave exclusively the trans-alcohol 4a, which was converted to the protected pyrrolidine derivative 6. The deprotection and reduction of 6 gave the pyrrolizidine alkaloid 8, characterized as its hydrochloride.
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    URL: http://dx.doi.org/10.1002/hlca.19940770221
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    Masthead (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994) 
    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.19940770301
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  • 152
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    3′-Amino-Modified Nucleotides Useful as Potent Chain Terminators for current DNA sequencing methods (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 586-596 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We describe the synthesis of modified nucleoside triphosphates of the four DNA bases containing a 3′-amino group which were prepared from the corresponding 3′-azido derivatives. Introduction of the triphosphate and subsequent reduction of the N3 to the NH2 group led directly to the target molecules 6a-d. Furthermore, 3′-amino-2′,3′-dideoxynucleoside 5′-triphosphates proved to be potent inhibitors of the enzymatic synthesis of DNA catalyzed by the standard sequencing enzymes T7 DNA polymerase, sequenase version 2.0, Thermus aquaticus DNA polymerase, and Thermus thermophilus DNA polymerase. Both radioactive and fluorescent sequencing methods were applied successfully to the 3′-amino-modified terminators. Investigations in view of using these chain terminators according to Sanger's sequencing method for fluorescence labeling were done.
    Additional Material: 4 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19940770222
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  • 153
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    N7-DNA: Synthesis and Base Pairing of Oligonucleotides containing 7-(2-Deoxy-β -D-erythro-pentofuranosyl)adenine (N7Ad) (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 597-607 
    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 7-(2-deoxy-β -D-erythro-pentofuranosyl)adenine (N7Ad; 1) is described. Compound 1 was obtained from the precursor 4-amino-1H -imidazole-5-carbonitrile 2-deoxyribonucleoside 6 and was found to be much more labile than Ad. The N6-benzoyl protecting group (see 8) destabilized the N-glycosylic bond further and was difficult to remove by NH3-catalyzed hydrolysis. Therefore, a (dimethyl-amino)methylidene residue was introduced (→9). Amidine 9 was blocked at OH—C(5′) with the dimethoxytrityl residue ((MeO)2Tr), and phosphonate 4 as well as phosphoramidite 5 were prepared under standard conditions. Phosphonate 4 was employed in solid-phase oligonucleotide synthesis. Homooligonucleotides as well as self-complementary oligonucleotides were prepared. The oligomer d[(N7A)11-A] (11) formed a duplex with d(T12) (13). Antiparallel chain polarity and reverse Watson-Crick base pairing was deduced from duplex formation of the self-complementary d[(N7A)8-T8] (14).
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770302
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    Aldehyde Intermediates in the Synthesis of Tacamine-Type Indole Alkaloids: Preparation of (±)-apotacamine (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 709-715 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of aldehyde intermediates suitable for the preparation of indole alkaloids of the tacamine (1) type is described. The four possible aldehydes 4-7 were prepared from methyl 5-ethylnicotinate (8) in a few simple steps using a base-catalyzed epimerization as the final step (Schemes 1 and 2). The key aldehyde 4, which is an analogue of the important vincamine intermediate 3 (‘Oppolzer's aldehyde’), was finally converted into the indole alkaloid (±)-apotacamine (21).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770314
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  • 155
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    Novel Juvenoids of the 2-(4-hydroxybenzyl)cyclohexan-1-one Series (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 502-508 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of insect juvenile hormone analogs (juvenoids) was synthesized and studied. The basic skeleton of these juvenoids contains three rings and a short aliphatic subunit and bears two or three chiral centers (depending on the appropriate structure; see 6-9). The chiral center located in the 1,2-diphenoxypropane subunit has the configuration (RS), (R) (a series), or (S) (b series). The juvenoids were subjected to a biological screening, the preliminary results of which are briefly described.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770210
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  • 156
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    Oligosaccharides Related to Tumor-Associated Antigens. Part I. Synthesis of the propyl glycoside of the trisaccharide α-L-Fucp-(1 → 2)-β-D-Galp-(1 → 3)-β-D-GalpNAc, component of a tumor antigen recognized by the antibody MBr1 (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 509-514 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the trisaccharide α-L-Fucp-(1 → 2)-β-D-Galp-(1 → 3)-β-D-GalpNAc-1-OPr (2) is described. The N-acetylgalactosamine 6 was obtained from 4 by an intramolecular displacement of a (trifluoromethyl)sulfonyloxy by a pivaloyloxy group with its concomitant migration from position 3 to position 4 (Scheme 1). The galactosyl donor 9 was obtained from 7 via 8 by regioselective opening of the orthoester function with AcOH/pyridine followed by treatment with CCl3CN and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) (Scheme 2). Glycosylation of 6 with 9 in the presence of BF3 · OEt2 gave the disaccharide 10. Selective deprotection of 10 at O—C(2′) followed by glycosylation with 12 and by standard deprotection afforded the title trisaccharide 2 (Scheme 3). Preliminary biological testing showed that 2 is able to inhibit the binding of the monoclonal antibody MBrl to the target tumor cells MCF7 in a dose-dependent manner.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770211
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  • 157
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    Metal Complexes of Pentadentate Macrocyclic Ligands Containing Oxygen and Nitrogen as Donor Atoms (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 515-524 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four macrocyclic ligands have been synthesized: 1-oxa-4,7,10,13-tetraazacyclopentadecane (1), 1,4-dioxa-7,10,13-triazacyclopentadecane (2), 1,4-dioxa-7,11,14-triazacyclohexadecane (3), 1,4-dioxa-7,11,15-triazacycloheptadecane (4), one of them 3, for the first time. The protonation constants of the ligands and the stability constants of the complexes formed by the four ligands with some divalent first-series transition-metal ions, Cd2+ and Pb2+, were determined by potentiometric methods, in aqueous solution, at 25° and I = 0.10M (KNO3). The sequence of protonation of ligand 1 was studied by 1H-NMR spectroscopy. The Irving-Williams' order of stability is obeyed for the complexes of all the ligands, and the metal complexes of 1 present the higher values of stability. A drop in the stability of all the metal complexes studied is observed when the metal complexes of 1 are compared with the corresponding complexes of 2. The effect of the increase of the ring size of the macrocycle can be observed for metal complexes of the series of ligands 2 4, where, in spite of the slight increase of the overall basicity of the ligands (20.28, 22.25, and 24.96 for 2, 3, and 4 respectively), small differences in stability are found for the corresponding complexes of 2 and 3, but a significant drop occurs for all the metal complexes formed with the 17-membered ligand, specially for the larger metal ions like Mn2+ and Pb2+.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770212
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    Construction de complexes tétranucléaires de ruthénium à ossature planaire par condensation de deux unités diruthénium à l'aide de ligands pontants: Synthèse et structure moléculaire de [Ru4(CO)8{μ2-P(Cy)2}4] et de [Ru4(CO)8{μ4-P(Cy)}2{μ2-P(Cy)2}2] (Cy = cyclohexyl) (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 525-532 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Assembly of Tetranuclear Ruthenium Complexes with Planar Metal Core by Condensation of Two Diruthenium Units Using Bridging Ligands: Synthesis and Molecular Structure of [Ru4(CO)8{μ2-P(Cy)2}4] and [Ru4(CO)8{μ4-P(Cy)}2{μ2}2](Cy = Cyclohexyl)The dinuclear complexes [Ru2(CO)6{μ-P(Cy)2}2] (1) or [Ru2(CO)4{μ-(HCO2)}2{P(Cy)2H}2] (2) react in THF solution at 160° to give the tetranuclear complexes [Ru4(CO)8{μ2-P(Cy)2}4] (3) and [Ru4(CO)8{μ4-P(Cy)}2{μ2-P(Cy)2}2] (4), as well as the trinuclear complex [Ru3(CO)7(μ2-H){μ2-P(Cy)2}3] (5). If the reaction is performed at 200°, the bicapped tetranuclear species 4 is obtained in a higher yield, whereas 3 and 5 are formed in trace amounts only. The phenyl derivatives [Ru2(CO)6{μ-P(Ph)2}2] (6) or [Ru2(CO)4{μ-(EtCO2)}2{P(Ph)2H}2] (7) react in a similar manner to give only the complex [Ru4(CO)8{μ4-P(Ph)}2{μ2-P(Ph)2}2] (8), analogous to 4. The molecular structure of 3 consists of a planar framework of four Ru-atoms, each Ru - Ru bond being bridged by a μ2-dicyclohexylphosphino ligand. The complex 4 represents a planar rectangular Ru core, both faces being capped by μ4-cyclohexylphosphinidene ligands and two opposite edges being bridged by μ2-dicyclohexylphosphino ligands.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770213
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  • 159
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    Carbamate Series of Juvenoids: Variation of the O-alkyl substituent (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 561-568 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By changing the O-alkyl substituents of the carbamate moiety of alkyl N-{2-{4-[(2-oxocyclohexyl)methyl]phenoxy}ethyl}carbamates and subsequent transformation of the oxo group in the cyclohexyl substituent, the juvenoids 1-20 were synthesized (Scheme). The methyl (1-4), propyl (9-12), isopropyl (13-16), and prop-2-ynylcarbamates (17-20) were subjected to biological screening on several non-related insect species (Tenebrio molitor, Galleria mellonella, Dysdercus cingulatus, and Pyrrhocoris apterus). Some of the juvenoids showed high biological activity and excellent selectivity with respect to target insect species (Table 2).
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770218
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  • 160
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    Metabolic Products of Microorganisms. Part 269Part 268: [1].. 5-Phenylpentadienoic-acid derivatives from Streptomyces sp. (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 569-574 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two new phenylpentadienamides isolated from the culture filtrate of Streptomyces sp. were assigned the structures 5-(4-aminophenyl)penta-2,4-dienamide (2) and N2-[5-(4-aminophenyl)penta-2,4-dienoyl]-L-glutamine (3). In addition, 5-(4-aminophenyl)penta-2,4-dienoic acid (1) has been isolated, and its spectroscopic characteristics are reported for the first time. Compounds 1-3 exist in both the (2E,4E)- and (2E,4Z)-configurations. Electrospray and tandem MS, and HPLC/MS proved to be particularly suitable for the characterization of these metabolites.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770219
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  • 161
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    α,α-Disubstituted Allyl Sulfones: An approach to the synthesis of vinyl-branched pheromone analogues (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1281-1287 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The two-step alkylation of phenyl prop-2-enyl sulfone (1) with protected ω-bromoalkanols and 1-iodoalkanes (→3; see Scheme 1) followed by a Pd-catalyzed desulfonylation with LiBH4 affords a 96:4 mixture of vinylbranched, protected alcohols and corresponding ethylidene-branched isomers (see Scheme 2; 4 and 5, respectively). By utilizing the large difference in reactivity of mono- and trisubstituted C=C bonds towards singlet oxygen, the ethylidene derivatives are easily removed from the mixture by photo-oxygenation. The vinyl-branched compounds are inert to this reaction and can be conveniently isolated in highly pure form (99.5%) and ca. 45% overall yield.
    Additional Material: 3 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19940770510
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  • 162
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    Nucleosides. Part LVIPart LV: [1].. Aminolysis of carbamates of adenosine and cytidine (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1267-1280 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 2-(4-nitrophenyl)ethoxycarbonyl(npeoc) group, introduced 1984 as protecting group for exocyclic amino functions of nucleic-acid bases, reacts with amines under mild conditions to urea derivatives. Treatment of 2′,5′-di-O-acetyl-N6-[2-(4-nitrophenyl) ethoxycarbonyl]cordycepin (3) with NH3/MeOH overnight at room temperature affords cordycepin (4) and N6-carbamoylcordycepin (5). Preliminary investigations towards the elucidation of the reaction mechanism indicate that the aminolysis proceeds via an addition-elimination or an isocyanate mechanism, depending on the reaction conditions. The phenoxycarbonyl (phoc) group at N6 or N4 was chosen to study the mild conversion of carbamates with aromatic amines into ureas of adenosine and cytidine, respectively.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19940770509
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  • 163
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    Synthesis, Crystal Structure, and Thermal Behaviour of Some New Copper Complexes with tridentate β-iminoketone ligands (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1288-1298 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of Cu(AcO)2 · H2O and tridentate β-iminoketone ligands yielded four new copper complexes: acetato{4-{[2-(dimethylamino)ethyl]amino}pent-3-en-2-onato}copper(II) (1), triacetato{4-{[3-(dimethylamino)-propyl]amino}pent-3-en-2-onato}dicopper(II) (2), {4-{[2-(dimethylamino)ethyl]amino}-1,1,1-trifluoropent-3-en-2-onato}( trifluoroacetato)copper(II) (3), and pentaacetato{4-{[3-(dimethylamino)propyl]amino}-1,1,1-trifluoropent-3-en-2- onato}tricopper(II) (4). All compounds were coloured and air-stable solids. The crystal structures of 1 and the dioxane adduct of 3, μ-(1,4-dioxane)bis{{4-{[2-(dimethylamino)ethyl]amino}-1,1,1-trifluoropent-3- en-2-onato}(trifluoroacetato)copper(II)} (3a), were determined. Complex 1 consists of dimeric units [{Cu(AcO)L}2] in the solid state (L = β-iminoketonato ligand). In 3a, two [Cu(CF3COO)L] are linked via the O-atoms of the coordinated solvent 1,4-dioxane. Compound 1 crystallized in the monoclinic space group P21/n with a formula unit in a cell having the dimensions a = 11.152(6)Å, b = 10.104(3)Å, c = 11.805(7)Å, and β = 99.02(4)Å, and compound 3a crystallized in the triclinic space group P1 with a formula unit in a cell having the dimensions a = 8.709(3)Å, b = 9.439(4)Å, c = 12.395(3)Å, α = 67.57(3)°, β = 77.01(2)°, and β = 84.17(3)°. Mass spectra (MS), thermal analysis (DTA/TG), and evaporation-rate measurements are reported for all compounds. The influence of fluorination on the structure and volatility will be discussed.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770511
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  • 164
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    Umsetzung von Diazoessigsäure-ethylester mit 1,3-Thiazol-5(4H)-thionen (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1299-1312 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of Ethyl Diazoacetate with 1,3-Thiazole-5(4H)-thionesReaction of ethyl diazoacetate (2a) and 1,3-thiazole-5(4H)-thiones 1a,b in Et2O at room temperature leads to a complex mixture of the products 5-9 (Scheme 2). Without solvent, 1a and 2a react to give 10a in addition to 5a-9a. In Et2O in the presence of aniline, reaction of 1a,b with 2a affords the ethyl 1,3,4-thiadiazole-2-carboxylate 10a and 10b, respectively, as major products. The structures of the unexpected products 6a, 7a, and 10a have been established by X-ray crystallography. Ethyl 4H-1,3-thiazine-carboxylate 8b was transformed into ethyl 7H-thieno[2,3-e][1,3]thiazine-carboxylate 11 (Scheme 3) by treatment with aqueous NaOH or during chromatography. The structure of the latter has also been established by X-ray crystallography. In the presence of thiols and alcohols, the reaction of 1a and 2a yields mainly adducts of type 12 (Scheme 4), compounds 5a,7a, and 9a being by-products (Table 1). Reaction mechanisms for the formation of the isolated products are delineated in Schemes 4-7: the primary cycloadduct 3 of the diazo compound and the C=S bond of 1 undergoes a base-catalyzed ring opening of the 1,3-thiazole-ring to give 10. In the absence of a base, elimination of N2 yields the thiocarbonyl ylide A′, which is trapped by nucleophiles to give 12. Trapping of A′, by H2O yields 1,3-thiazole-5(4H)-one 9 and ethyl mercaptoacetate, which is also a trapping agent for A′, yielding the diester 7. The formation of products 6 and 8 can be explained again via trapping of thiocarbonyl ylide A′, either by thiirane C (Scheme 6) or by 2a (Scheme 7). The latter adduct F yields 8 via a Demjanoff-Tiffeneau-type ring expansion of a 1,3-thiazole to give the 1,3-thiazine.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770512
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  • 165
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    Total Synthesis of Racemic and Optically Active Compounds Related to Physostigmine and Ring-C Heteroanalogues from 3-[2′-(dimethylamino)ethyl]2,3-dihydro-5-methoxy-1,3-dimethyl-1H-indo l-2-ol (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1412-1422 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oxindole 11, obtained on 3-[2′-(dimethylamino)ethyl]alkylation of oxindole 12, yielded, on stereoselective reduction with sodium dihydridobis(2-methoxyethoxy)aluminate, aminoalcohol 8 (Scheme 2). The quaternary methiodide 10, obtained from 8 with MeI, gave, in nucleophilic displacements concurring with a Hofmann elimination, (±)-esermethole 6, (±)-5-O-methylphysovenol (14), (±)-5-O-methyl-1-thiaphysovenol (15), and (±)-1-benzyl-1-demethylesermethole (16). Syntheses of (±)-1-benzyl-1-demethylphenserine (18), (±)-1-demethylphenserine (19), and (±)-phenserine (4) from 6 and 16 are described. Optically active 8a and 8b, obtained by chemical resolution, similarly gave the enantiomers 6a and 14a-16a of the (3aS)-series (prepared earlier from physostigmine (1a)) and their (3R)-enantiomers. The anticholinesterase activity of (±)-4, (±)-18, and (±)-19 was compared with that of their optically active enantiomers.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770519
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    A Reinvestigation of the α-Alkylation of 4-Monosubstituted 2-phenyloxazol-5(4H)-ones (‘azlactones’): A general entry into highly functionalized α,α-disubstituted α-amino acidsDedicated to Prof. R.E. Ireland on the occasion of his 65th birthday (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1423-1429 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Novel, more reliable and general reaction conditions for the α-alkylation of 4-monosubstituted 2-phenyloxazol-5(4H)-ones ( = 4-monosubstituted 2-phenyl-azlactones) rac-2 to 4,4-disubstituted 2-phenyloxazol-5(4H)-ones rac-1 were found (Scheme 2). Thus, a whole range of highly functionalized rac-1 were prepared in medium-to-good overall yields (40-90%, see Table). Azlactones rac-1 are ideal precursors for the synthesis of optically pure α,α -disubstituted (R)- and (S)-α-amino acids.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19940770520
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  • 167
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    Glycosylidene Carbenes. Part 18. Insertion of glycosylidene carbenes into the Sn—H bond of tributyl- and triphenylstannane: A synthesis of stannoglycosides (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1430-1440 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Insertion of the glycosylidene carbenes, derived from the gluco- and the manno-diazirines 1 and 2, into the Sn—H bond of R3SnH (R = Bu or Ph) leads to the fully substituted stannoglycosides 3-8 (53-77%). The 1,2-cis-configurated products are formed preferentially (α-D/β -D ranges from 2.5:1 to 5.1:1 with 1, and 1:1.3 to 1:4.2 with 2). Relative to CH2Cl2, THF favors formation of the equatorial Sn-glycosides. The stannylated (benzyloxy)glucals 9 and 10 were isolated as side products. The reaction of 1 with (Bu3Sn)2 yielded 9 (17% in CH2Cl2; 36% in CCl4) together with the azines 11 and the benzyloxyglucal 12. NMR Data of the Sn-glycosides 3-8 show evidence for an anomeric effect, 1J(C(1),H) being larger in the axial and 1J(Sn,C(1)) larger in the equatorial anomers.
    Additional Material: 5 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19940770521
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  • 168
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    Solution Structure of One-Electron Reduced and Oxidized Molecules with Twisted Donor and Acceptor Moieties (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1466-1474 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The solution structures of the radical anion and the radical cation of the donor-acceptor molecules 3,4-di(1,3-dithiol-2-ylidene)-4-phenylbut-1-ene-1,1-dicarbonitrile (1) and 3,4-di(1,3-dithiol-2-ylidene)-4-phenylbut-1-ene-1,1,2-tricarbonitrile (2) are discussed based on cyclovoltammetric and ESR/ENDOR measurements. It is shown that the spin population of the radical anions is limited to the di- and tricyanoethene moiety and the coplanar 1,3-dithiole at C(3), whereas that of the radical cations resides mainly inside the two 1,3-dithiole rings. The energies of the long-wave bands in the electronic-absorption spectra of 1 and 2 correspond to the differences between the oxidation and reduction potentials and thus point to a charge-transfer character of these transitions.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770524
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  • 169
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    Radical Anions of Polyalkylazulenes: An ESR and ENDOR Study (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1458-1465 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Proton-hyperfine data are reported for the radical anions generated from azulene (1) and its alkyl derivatives 2-11 in 1,2-dimethoxyethane both ‘chemically’ with K and electrolytically. The alkyl derivatives are 1,3-dimethyl- (2), 5,7-dimethyl- (3), 1,3,5,7-tetramethyl- (4), 2-methyl- (5), 4,6,8-trimethyl- (6), 2,4,6,8-tetramethyl-(7), 1,3,4,6,8-pentamethyl- (8), 1,3,4,8-tetramethyl-6-propyl- (9), 6-(tert-butyl)-1,3,4,8-tetramethyl- (10), and 1,2,3,4,6,8-hexamethylazulene (11). Alkyl substituents at the odd-numbered centers μ = 1, 3, 5, and 7 partly shift the π-spin population from the seven- to the five-membered ring, whereas those at the even-numbered centers μ = 4, 6, and 8 exert an opposite effect on the π-spin distribution.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770523
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  • 170
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    Synthetic Routes to the Cyclo[n]carbons (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1441-1457 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cyclo[n]carbons (cyclo-Cn) are n-membered monocyclic rings of sp-hybridized C-atoms with unique electronic structures resulting from two perpendicular systems of conjugated π-orbitals, one in-plane and one out-of-plane. Several synthetic approaches to generate cyclo-C18 from stable precursors were investigated. In a six-step sequence from anthracene, tris(anthraceno)hexadehydro[18]annulene 5 was prepared and shown by laser-desorption time-of-flight mass spectrometry to generate C18 in three successive retro-Diels-Alder reactions, together with anthracene as the by-product. The attempted preparation of C18 by flash-vacuum pyrolysis of 5 using solvent-assisted sublimation only afforded anthracene next to polymers. The reaction of 1,6-bis(triisopropylsilyl)hexa-1,3,5-triyne with [Co2(CO)8] followed by exchange of two CO groups for a bridging bis(diphenylphosphino)methane (dppm) ligand gave Co complex 22 which, after removal of the silyl groups, was oxidatively cyclized to afford the very stable trimeric and tetrameric macrocycles 6 and 7, complexes with cyclo-C18 and cyclo-C24, respectively. An X-ray crystal structure established the identity of 6 and showed that the butadiyne units within the C18 core are considerably bent. Attempts to free cyclo-C18 from the coordinating metal atoms in 6 did not succeed, presumably due to the steric shielding of the Co-atoms by the dppm ligands. Low-temperature matrix isolation studies using IR and UV/VIS spectroscopy showed that irradiation of carbon oxide 2 (C24O6) leads to ketene intermediates and, by subsequent loss of six CO molecules, presumably to cyclo-C18.
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    URL: http://dx.doi.org/10.1002/hlca.19940770522
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  • 171
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    Mitteilungen - Communications (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1475-1476 
    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.19940770525
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  • 172
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    Masthead (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994) 
    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.19940770601
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  • 173
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    Crystal Structure and Packing of 1-(4, 6-Diamino-1, 3, 5-triazin-2-yl)guanidinium nitrate (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1475-1479 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The title compound is a condensation product of four guanidinium ions formed during crystallization of guanidinium nitrate. The crystal structure consists of infinite molecular ribbons stacked into layers which are rotated 58.5° with respect to each other and connected by two different networks of hydrogen bonds.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770602
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    Efficient Synthesis of Methyl 2-(tert-Butyl)acrylate and Analogous Esters (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1480-1484 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The title products are prepared via an efficient three-step synthesis which involves hydroalumination of methyl propiolate and Lewis-acid-promoted reaction with acetone in the presence of BF3 followed by two highly selective SN2′ reactions. The key step is the reaction of 2-(chloromethyl)acrylates with R2CuLi/ZnCl2 reagents which takes place with complete allylic rearrangement.
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  • 175
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    Asymmetric Total Synthesis of (11R, 12S, 13S, 9Z, 15Z)-9, 12, 13-Trihydroxyoctadeca-9, 15-dienoic Acid, a self-defensive agent against rice-blast disease (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1500-1504 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Diels-Alder adduct of furan and 1-cyanovinyl (1′R)-camphanate was converted into methyl [(tert-butyl)-dimethylsilyl 5-deoxy-2, 3-O-isopropylidene-β-L-ribo-hexofuranosid] uronate ((+)-4). Reduction with diisobutyl-aluminium hydride gave the corresponding aldehyde which was condensed with the ylide derived from triphenyl-(propyl)phosphonium bromide to give (1R, 2S, 3S, 4S)-1-[(tert-butyl)dimethylsilyloxy]tetrahedro-2, 3-(isopropyl-idenedioxy)-4-[(Z)-pent-2′ -enyl]furan ((+)-7). Removal of the silyl protective group gave a mixture of the corresponding furanose that underwent Wittig reaction with the ylide derived from [8-(methoxycarbonyl)-octyl]triphenylphosphonium bromide to yield methyl (11R, 12S, 13S, 9Z, 15Z)-13-hydroxy-11, 12-(isopropylidene-dioxy)octadeca-9, 15-dienoate ((-)-9). Acidic hydrolysis, then saponification afforded (11R, 12S, 13S, 9Z, 15Z)-11, 12, 13-trihydroxyoctadeca-9, 15-dienoic acid (1).
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  • 176
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    Hoogsteen-Duplex DNA: Synthesis and base pairing of oligonucleotides containing 1-deaza-2′-deoxyadenosine (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1485-1499 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oligodeoxyribonucleotides containing 1-deaza-2′-deoxyadenosine ( = 7-amino-3-(2-deoxy-β-D-erythro-pentofuranosyl)-3H-imidazo[4, 5-b]pyridine; 1b) form Hoogsteen duplexes. Watson-Crick base pairs cannot be built up due to the absence of N(1). For these studies, oligonucleotide building blocks - the phosphonate 3a and the phosphoramidite 3b - were prepared from 1b via 4a and 5, as well as the Fractosil-linked 6b, and used in solid-phase synthesis. The applicability of various N-protecting groups (see 4a-c) was also studied. The Hoogsteen duplex d[(c1A)20] · d(T20) (11 · 13; Tm 15°) is less stable than d(A20) · d(T20) (12 · 13; Tm 60°). The block oligomers d([c1A)10-;T10] (14) and d[T10-(c1A)10] (15) containing purine and pyrimidine bases in the same strand are also able to form duplexes with each other. The chain polarity was found to be parallel.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770604
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  • 177
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    On the Stacking of β -Rings: The solution self-association behavior of two partially N-methylated cyclo(hexaleucines) (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1520-1526 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cyclo(-D-Leu-L-MeLeu-D-Leu-L-MeLeu-D-Leu-L-MeLeu-) (1) and cyclo(-L-Leu-D-Leu-L-MeLeu-D-Leu-L-Leu-D-Leu-) (2) were synthesized and used for a study of the interaction of β -rings in solution. In appropriate solvents, 1 and 2 formed dimers consisting of two β -rings connected through six interannular H-bonds and having the N -Me group(s) on the solvent-exposed face. The study also afforded indications that 2 formed different dimers of this kind, differing in the relative orientation of the two β -rings. These experimental observations provide strong support to the idea that unsubstituted D,L-alternating cyclooligopeptides, such as cyclo(hexaleucine), can self-assemble and give rise to long tubular stacks of β -rings.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770607
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  • 178
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    Strukturen und Molekül-Eigenschaften ladungsgestörter Moleküle. 52. Mitteilung51.Mitteilung: [1]. Teil der Dissertation von A.J. [2]. Vorläufige Mitteilung: [3].. 2, 3-Diphenylchinoxalin-Radikalanionen in Lösung und im Kristall (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1505-1519 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Structures and Molecular Properties of Charge-Pertubed Molecules. 2, 3-Diphenylquinoxaline Radical Anions in Solution and in CrystalsThe Na⊕ and K⊕ radical-ion salts of 2, 3-diphenylquinoxaline seem to be (according to a structural database search) among the first ones of N-heterocyclic radical anions in crystals. The one-electron reduction in aprotic 1, 2-dimethoxyethan (DME) solution at metal mirrors and the crystallization under Ar have been preceded by cyclovoltammetric (CV) and ESR/ENDOR measurement. The first electron insertion at -1.63 V proves to be reversible, whereas the irreversible second step, which is accompanied by an overcrossing of the CV line, can be rationalized by an ‘ECE-DISP’ mechanism via a dianion redox disproportionation. The ENDOR spectrum resolves four 1H couplings and allows to simulate the ESR spectrum including the 14N hyperfine splittings. Both dark-blue single crystals of the radical ion salts \documentclass{article}\pagestyle{empty}\begin{document}$[2,3{\rm - diphenylquinoxaline}^{{.} \ominus} {\rm Met}^ \oplus ({\rm DME})]^.$\end{document} show unexpected similarities for Met⊕ = Na⊕, K⊕ despite the 36-pm difference in their ionic radii. The largest structural changes inflicted by the one-electron reduction of the N-heterocyclic molecule are observed in the vicinity of the N-centers bearing the highest effective nuclear charge. The DME-chelated metal cations coordinate at the N electron pairs and form Met⊕(DME)-bridged polymer chains of the radical anion, which are differently ondulated in the Na⊕ and K⊕ radical anion salts. The take-home lesson suggests that many more N-heterocyclic molecules might be analogously reduced under optimized conditions and isolated as single crystals.
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  • 179
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    An Efficient Total Synthesis of Carbocyclic 2′-Deoxyribonucleosides (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1527-1540 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The present work describes a new and efficient method for the preparation of either racemic or enantiomerically pure carbocyclic 2′-deoxyribonucleosides 1. Key steps are the efficient assembly of the racemic carbocyclic 2′-deoxyribose core (±)-12, its enzymatic resolution, and a new approach to covalently link the purine and pyrimidine bases with the cyclopentane moiety via the cyclic sulfate (+)-19. This total synthesis of enantiomerically pure and racemic carbocyclic 2′-deoxyribonucleosides 1 represents one of the most efficient approaches reported to date. Starting from cyclopentadiene, the four carbocycles corresponding to the naturally occurring 2′-deoxyribonucleosides could be prepared in 12 steps and 9-12% overall yield. For the corresponding racemic compounds, 10 steps were used with overall yields between 22 and 30%.
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    URL: http://dx.doi.org/10.1002/hlca.19940770608
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  • 180
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    Permanganate Oxidation of Quinoxaline and Its Derivatives (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1549-1556 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oxidation reactions of a series of quinoxaline derivatives, using KMnO4 in the presence or absence of NaOH, are described. Neutral oxidation of 2-chloro- and 2, 3-dichloroquinoxalines 2-4 afforded the corresponding chloro- and dichloropyrazinedicarboxylic acids 13 and 14 in good yield. On the other hand, oxidation of quinoxalin-2(1H)-one and 1, 4-dihydroquinoxaline-2, 3-dione derivatives in alkaline medium gave different products, with the quinoxalin-2(1H)-one (5) forming 1, 4-dihydroquinoxaline-2, 3-dione (9), while various substituted quinoxalin-2, 3-dione derivatives (see 9-11) gave a new type of dimeric products. The structural assignments for the new compounds were based on spectroscopic data.
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  • 181
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    Triplet Energy of 2, 2-Dimethylisoindene from Electron-Energy-Loss Spectroscopy and Photoinduced Triplet Energy Transfer (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1541-1548 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The excited electronic states of 2, 2-dimethylisoindene (1) have been studied by electron-energy-loss spectroscopy. Its vertical gas-phase triplet (13B2), and singlet (11B2) excitation energies are 1.61 and 3.19 eV, respectively. The excited states are thus lowered by 0.49 eV and 1.21 eV, respectively, when compared to the corresponding states of (all-E)-octatetraene, which serves as a reference compound. These shifts are partially reproduced by ZINDO calculations. The spectra give no evidence for a 21Ag state below the 11B2 state, but this lack of observation does not exclude its existence. The lowest triplet state T1(1) was further characterized by flash photolysis. T1(1) was observed as a transient intermediate, λ ≤ 350 nm, with a lifetime of 8 m̈s in degassed hexane. The adiabatic excitation energy of T1(1) was bracketed to the range of 1.1 ± 0.1 eV by energy-transfer experiments. Relationships between the energies of the lowest excited singlet and triplet states of 1 and the lowest excited doublet state of its radical cation \documentclass{article}\pagestyle{empty}\begin{document}${1}^{+\kern0pt {.}}$\end{document} - essentially a non-Koopmans' state - are discussed.
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  • 182
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    Synthese von Phosphinico-Analog des PantetheinsHerrn Kollegen Fritz Sauter, Wien, mit den besten Wünschen zum 65. Geburtstag gewidmet (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1570-1576 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Phosphinico Analogues of PantetheineThe synthesis of phosphinico analogues 9a-c of pantetheine is described where the carbonyl group of one of the amide linkage is replaced by a methyl-, ethyl-, or phenylphosphinoyl group.
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  • 183
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    Theoretical Calculations of β-Lactam Antibiotics. Part VI. AM1 calculations of alkaline hydrolysis of clavulanic acid (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1557-1569 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The gas-phase basic hydrolysis of clavulanic acid (a) was studied by using the AM1 semi-empirical method. The results obtained show that the hydroxyethylidene side chain at C(2) is pivotal to the stability of the different reaction products involved. The products with an open oxazolidine ring are more stable than those with a closed ring fused to the β-lactam ring. This behaviour differs from that of penicillins and cephalosporins where the most stable degradation products are those with an intact thiazolidine or dihydrothiazine ring, respectively, fused to the β-lactam ring. The different chemical reactivity of clavulanic acid relative to penicillins and cephalosporins could explain the disparate behaviour of the latter two types of compound towards β-lactamases. Once the acyl-enzyme intermediate of clavulanic acid has been formed, it can evolve with cleavage of the oxazolidine ring to form a difficult to deacylate compound.
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  • 184
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    Radical Arylation Reactions of 4, 6, 8-Trimethylazulene (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1577-1584 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of 1- and 2-aryl-substituted (aryl = Ph, 4-NO2—C6H4, and 4-MeO—C6H4) 4, 6, 8-trimethylazulenes (4 and 3, respectively) in moderate yields by direct arylation of 4, 6, 8-trimethylazulene (8) with the corresponding arylhydrazines 13 in the presence of CuIIions in pyridine (see Scheme 4) as well as with 4-MeO—C6H4Pb(OAc)3 (16) in CF3COOH (see Scheme 5) is described. With 13, also small amounts of 1, 2- and 1, 3-diarylated azulenes (see 14 and 15, respectively, in Scheme 4) are formed. The 4-methoxyphenylation of 8 with 16 yielded also the 1, 1′-biazulene 17 in minor amounts (see Scheme 5). 4, 6, 8-Trimethyl-2-phenylazulene (3a) was also obtained as the sole product in moderate yields by the reaction of sodium phenylclopentadienide (1a) with 2, 4, 6-trimethylpyrylium tetrafluoroborate (2) in THF (Scheme 1). The attempted phenylation of 8 as well as of azulene (9) itself with N-nitroso-N-phenylacetamide (10) led only to the formation of the corresponding 1-(phenylazo)-substituted azulenes 12 and 11, respectively (Scheme 3).
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  • 185
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    Synthesis and Biological Evaluation of 14-Alkoxymorphinans. Part 10Part 9: [1].. 14-O-Methyl derivatives of 5-methylnaltrexone and 5-methylnaloxone (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1585-1589 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In several steps, 5, 14-O-dimethylnaltrexone (3) and 5, 14-O-dimethylnaloxone (4) were prepared starting from 5, 14-O-dimethyloxycodone (5). Compound 3 exhibited opioid agonism in vitro (guinea-pig ileum and mouse vas deferens preparations) and antagonism in vivo (AcOH-writhing test in mice), while compound 4 was found to be an agonist in vitro and in vivo.
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  • 186
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    Synthesis of Benzazepine Analogues of Noscapine (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1590-1594 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of benzazepine analogues of the opium alkaloid noscapine (1) is described. The benzazepines 2 and 3 were prepared starting from nornarceine ethyl ester (4; readily available from 1) in several steps. X-Ray analysis of compound 2 revealed that it is not a diastereosisomer mixture but a racemate of the threo-form and thus has the same configuration as 1.
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  • 187
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    Synthesis of 3-Methoxy- and 3-(β-D-Glucopyranosyloxy)flavylium Ions. Influence of the flavylium substitution pattern on the reactivity of anthocyanins in aqueous solution (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1595-1610 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of 3-glycosyloxylated flavylium ions (anthocyanins), in particular of callistephin (4), a natural anthocyanin, is described. The structural transformations in aqueous solution and molecular complexation with chlorogenic acid (7) and caffeine (8) of the synthesized pigments 3 and 4 are investigated and compared to those of the corresponding 3-methoxyflavylium ions 1 and 2 and to those of oenin (5) and malvin (6), two very common natural anthocyanins. The results are discussed in terms of the role played by the glycosyloxy residues in the chemical properties of anthocyanins. Anthocyanin molecular complexation (copigmentaion) is quantitatively investigated by UV/VIS spectroscopy and 1H-NMR. In particular, the UV/VIS spectroscopic data are interpreted using a general theoretical treatment, which, e.g., allows to demonstrate the formation of molecular complexes between the colourless forms of an anthocyanin and 8.
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  • 188
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    Einkristall-Strukturen eines Donator-Akzeptor-substituierten Cyclopentadiens, seines Kations und seines dimeren Anions: Verschiedenartige Störungen eines Kohlenstoff-FünfringesGewidmet Prof. H. G. Wagner anlässlich seines 65. Geburtstages56. Mitteilung über “Strukturen ladungsgestörter Moleküle und über Wechselwirkungen in Kristallen”; 55. Mitteilung: [1]. (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 2162-2174 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Single-Crystal Structures of a Donor-Acceptor-Substituted Cyclopentadiene, Its Cation and Its Anion Dimer: Different Distortion of a Five-Membered Carbon Ring1,4-Dimethyl-2,3,4,6-tetrahydro-1 H-cyclopentapyrazine-5,7-dicarbonitrile, its molecular cation, and its dimer dianion, generated by hydride abstraction or deprotonation, and crystallized, differ remarkably in their structures: the five-membered ring in the neutral compound is of (Z)-butadiene-type, whereas, in the tetrafluorborate salt, a peripheric NCCCCCN⊕ cyanine distortion occurs and in the sodium derivatives, solvated by either one or two 1,2-dimethoxyethane molecules, a cyclopentadienyl anion is formed. The structural perturbations induced by changing molecular charges are rationalized by extensive MNDO calculations, which on geometry optimization, reproduce the experimental structures and, in addition, provide charge distributions, further confirming the nN/π and π/π interactions already recognizable from the structural parameters.
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  • 189
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    2,3-Dihydrospiro[1H-4- and 5-azabenzimidazole-2,1′ -cyclohexane] ( = Spiro[cyclohexane-1,2′(3′H)-1′H-imidazo[4,5-b]pyridine] and Spiro[cyclohexane-1,2′(3′H)-1′H-imidazo[4, 5-c]pyridine]): Reactions with NucleophilesDedicated to Rolf Huisgen on the occasion of his 75th birthday (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 2175-2190 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The readily available title compounds 4a and 24 react with N-, O-, S-, and C-nucleophiles in presence of MnO2 to give the corresponding mono- or disubstituted 2H-azabenzimidazoles ( = azaisobenzimidazoles), e.g., 11-18 and 26a-h, respectively, or 2,3-dihydro-1H-azabenzimidazoles ( = dihydro-azabenzimidazoles) such as 9 and 10 and 27 and 28, respectively, by a 1, 4- or 1,6-Michael addition (Schemes 2 and 4). The bromo-dihydro-1H-azabenzimidazole 4b lost the Br-atom when treated with piperidine or morpholine yielding the corresponding disubstituted 2H-azabenzimidazole 21 (Scheme 3). Reductive ring opening of the substituted spiro compounds leads to mono- and disubstituted diaminopyridines which are intermediates for fused pyridine ring systems with substituents often not available by conventional routes and of potential pharmaceutical interest (see 32-37). E.g., starting from 4a, a three-step synthesis of the analgesic flupirtine maleate (= ethyl {2-amino-6-[(4-fluorobenzyl)amino]pyridin-3-yl}carbamate maleate = Katadolon®; 39) and of its non-fluorinated derivative D-7195 is described. Its analogue 40 was similarly made from the spiro compound 24.
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  • 190
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    Insertion Reactions of [ReH(CO)5-n(PMe3)n] Complexes (n = 2-4) with aldehydes, CO2, and activated acetylenes (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 2197-2208 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The complexes of the type [ReH(CO)5-n(PMe3)n] (n = 4, 3) were reacted with aldehydes, CO2, and RC≡CCOOMe (R = H, Me) to establish a phosphine-substitutional effect on the reactivity of the Re-H bond. In the series 1-3, benzaldehyde showed conversion with only 3 to afford a (benzyloxy)carbonyltetrakis(trimethylphosphine)rhenium complex 4. Pyridine-2-carbaldehyde allowed reaction with all hydrides 1-3. With 1 and 2, the same dicarbonyl[(pyridin-2-yl)methoxy-O, N]bis(trimethylphosphine)rhenium 5b was formed with the intermediacy of a [(pyridin-2-yl)methoxy-O]-ligated species and extrusion of CO or PMe3, respectively. The analogous conversion of 3 afforded the carbonyl[(pyridin-2-yl)methoxy-O,N]tris(trimethylphosphine)rhenium (1) 7b. While 1 did not react with CO2, 2 and 3 yielded under relatively mild conditions the formato-ligated [Re(HCO2)(CO)(L)(PMe3)3] species (8 (L = CO) and 9 (L = PMe3)). Methyl propiolate and methyl butynoate were transformed, in the presence of 1, to [Re{C(CO2Me)=CHR}(CO)3(PMe3)2] systems (10a (R = H), and 10b(R = Me)), with prevailing α-metallation and trans-insertion stereochemistry. Similarly, HC≡CCO2Me afforded with 2 and 3, the α-metallation products [Re{C(CO2Me)=CH2}(CO)(L)(PMe3)3] 11 (L = CO) and 12(L = PMe3). The methyl butyonate insertion into 2 resulted in formation of a mixture of the (Z)- and (E)-isomers of [Re{C(CO2Me)=CHMe} (CO)2(PMe3)3] (13a,b). In the case of the conversion of 3 with MeC≡CCO2Me, a Re-H cis-addition product [Re{(E)-C(CO2Me)=CHMe}(CO)(PMe3)4] (14) was selectively obtained. Complex 11 was characterized by an X-ray crystal-structure analysis.
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  • 191
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    Chemie von α-Aminonitrilen11. Mitteilung: [1].. 12. Mitteilung. Sondierungen über thermische Umwandlungen von α-Aminonitrilen (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 2209-2250 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chemistry of α-Amino Nitriles11. Mitteilung: [1]. . Exploratory Experiments on Thermal Reactions of α-Amino NitrilesThe paper extends a previously published report [4] on chemical properties of α-amino nitriles and of members of the C3H4N2 ensemble (Scheme 1) as observed in experiments carried out under non-aqueous conditions. The reactions investigated and the observations made are summarized in some detail in the English footnotes (*) referring to Schemes 1-17 and Fig. 1.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770814
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    Conformational Parameters of the Sandalwood-Odor Activity: Conformational calculations on sandalwood odorDedicated to Dr. G. Ohloff on the occasion of his 70th birthdayPart X; for part IX, see [1]. (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 2286-2296 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational parameters responsible for sandalwood odor were investigated by the “active-analog approach”. The pharmacophoric (osmophoric) pattern of sandalwood-odor molecules can be outlined as three points: the OH group (point PI), a lipophilic group (point P2) 2.9-3.0 Å distant from the OH group, and a bulky rigid group (point P3), represented as a dummy atom in the middle of the alicyclic system (norbornane bicycle or cyclopentene ring) or a quaternary C-atom. This concept was tested on a series of representative sandalwood-odor compounds and on some structurally similar, but odorless substances.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770816
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  • 193
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    Cyclopropanization of Methyl Carboxylates with Tebbe-Type Reagents (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 2297-2302 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The methylenation reaction of methyl azulene-2-carboxylates (cf. Schemes 1 and 2) with Tebbe's or Takai's reagent is described. When the prescribed amount of Takai's reagent is applied in a four-fold excess, the corresponding cyclopropyl methyl ethers are formed instead of the enol ethers (cf. Schemes 2 and 3). Similarly, methyl benzoate and methyl 2-naphthoate yield, after treatment with Takai's reagent and hydrolysis, the corresponding cyclopropanols 18 and 19, respectively (Scheme 3). The cyclopropyl methyl ether 4 or cyclopropanol 5 rearrange, on acid catalysis, into the l-(azulen-2-yl)propan-l-one 20 (Scheme 4). whose reduction with Et3SiH in CF3COOH yields the 2-propylazulene 21.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770817
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  • 194
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    Chemie von α-Aminonitrilen1. Mitteilung: [1], 12. Mitteilung: [2].. 13. Mitteilung. Über die Bildung von 2-Oxoethyl-phosphaten (“Glycoladehyd-phosphaten”) aus rac-Oxirancarbonitril und anorganischem Phosphat und über (formale) Konstitutionelle Zusammenhänge zwischen 2-Oxoethyl-phosphaten und Oligo (hexo- und pentopyranosyl)nucleotid-Rückgraten (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 2251-2285 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chemistry of α-Aminonitriles. Formation of 2-Oxoethyl Phosphates (“Glycolaldehyde Phosphates”) from rac-Oxiranecarbonitrile and on (Formal) Constitutional Relationships between 2-Oxoethyl Phosphates and Oligo(hexo- and pentopyranosyl)nucleotide BackbonesOxiranecarbonitrile in basic acqueous solution at room temperature reacts regioselectively with inorganic phosphate to give the cyanohydrin of 2-oxoethyl phosphate (“glycolaldehyde phosphate”), a source of (the hydrate of) the free aldehyde, preferably in the presence of formaldehyde. In aqueous phosphate solution buffered to nearly neutral pH, oxiranecarbonitrile produces the phosphodiester of glycoladehyde as its bis-cyanohydrin in good yield. In contrast to mono- and dialkylation, trialkylation of phosphate with oxiranecarbonitrile is difficult, and the triester derivative is highly sensitive to hydrolysis. Glycolaldehyde phosphate per se is of prebiotic interest, since it had been shown [5] to aldomerize in basic aqueous solution regioselectively to rac-hexose 2, 4, 6-triphosphates and - in the presence of formaldehyde - mainly to rac-pentose 2, 4-diphosphates with, under appropriate conditions, rac-pentose 2, 4-diphosphates as the major reaction product. However, the question as to whether oxiranecarbonitrile itself has the potential of having been a prebiological natural constituent remains unanswered.Backbone structures of hexopyranosyl-oligonucleotides with phosphodiester linkages specifically between the positions 6′ → 4′, 6′ → 2′, or 4′ → 2′ of the sugar residues can formally be derived via the (hypothetical) aldomerization pathway, a combinatorial intermolecular aldomerization of glycoladehyde phosphate and bis(glycolaldehyde)-phosphodiester in a 1: 1 ratio. The constitutional relationships revealed by this synthetic analysis has played a decisive role as a selection criterion in the pursuit of our experimental studies toward a chemical etiology of the natural nucleic acids' structure. The Discussion in this paper delineates how the analysis contributed to the conception of the structure of p-RNA.The English Footnotes to Schemes 1-11 provide an extension of this summary.
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    URL: http://dx.doi.org/10.1002/hlca.19940770815
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  • 195
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    Chemische Reaktionen mit Fischer-Carben-Komplexen des 1,6-Methano[10]annulensHerrn Kollegen Günther Wilke, Mülheim (Ruhr), zum 70. Geburtstag gewidmet (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 2303-2322 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of Fischer Carbene Complexes of 1,6-Methano[10]annuleneThe new Fischer carbene complexes 7, 8, and 10 of 1,6-methano[10]annulene as well as the bis(carbene) complex 15, were readily available in moderate yields by using the classical Fischer method (Schemes 1 and 2). The complexes 5 and 7 reacted easily with several alkynes under benzo-annulation conditions (Dötz reaction). Depending on the workup conditions, the new benzoquinones 16 and 17 (Scheme 5), hydroquinones 19 and 20 (Scheme 6), and protected hydroquinones 23-25 (Schemes 6 and 7) were synthesized. Surprisingly, in one run we were able to isolate the air-stable [Cr(η6-arene)(CO)3] complex 26 (Scheme 7). The X-ray structure and NMR data of 26 established a remarkable perturbation of the 10π perimeter of the 1,6-methano[10]annulene part in the hydroquinones 19-26, but no evidence of a σ-homoaromatic “bis(trinorcaradiene)” system. The first double Dötz reaction of 15 with hex-3-yne resulted in the formation of the “anti”-dibenzo-annulated 1,6-methano[10]annulene 32 (Scheme 8), which does not exist furthermore as a π-homoaromatic system, but as its σ-homoaromatic valence isomer.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770818
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  • 196
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    Diazoaldehyde Chemistry. Part 1. Transdiazotization of Acylacetaldehydes in Neutral-to-Acidic Medium. A Direct Approach to the Synthesis of α-Diazo-β-oxoaldehydesAbstracted from the Ph. D. Thesis by Ö.S., Istanbul, 1994. (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 2323-2334 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: First ever non-deformylating transdiazotization of acylacetaldehydes was achieved: the reactions of 2-azido-l-ethylpyridinium tetrafluoroborate (4) with acylacetaldehydes 3 proceeded partially without deformylation to yield 16 new α-diazo-β-oxoaldehydes 1 along with diazomethyl ketones 2, especially in the presence of NaOAc (Scheme 1, Tables 1 and 2). The product distribution was substituent-dependent and could be correlated quantitatively. This new diazotization reaction appears as an alternative, direct, and more general method for the synthesis of these diazooxoaldehydes. α-Oxocycloalkanecarbaldehydes 5 gave only traces (if any) of α-diazocycloalkanones 7, and rearrangement products 6 were isolated (Scheme 2). Mechanisms of the reactions are discussed (Schemes 4 and 5).
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19940770819
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    Instructions to Authors (1994) (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1-18 
    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.19940770102
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  • 198
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    NMR of Terminal Oxygen. Part 14Part 13: [1].. Kinetically stabilized simple enols containing methylated uracil groups: Application of a 17O-NMR test of H-bonding (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 317-322 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the crystalline N,N′-dimethylated uracil derivatives 2a, b, the kinetically stabilized enol group forms an H-bond with O—C(4), as demonstrated by increased shielding of specifically labelled 2a and 2b in the 17O-NMR spectra (Δδ(17O)(C(4) - O) = -30 ppm); absence of dilution and solvent effects show that the H-bridge is intra-molecular, forming an eight-membered chelate ring. The (apparent) shielding effect Δδ(17O) in 2a, b is larger than that in salicylamide. The strong H-bond explains why the enols 2, in spite of the absence of steric hindrance, are kinetically stabilized.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19940770131
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  • 199
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    Synthesis and NMR Spectroscopic Investigation of a Macrocyclic Diphosphine Ligand and its nickel(II) and palladium(II) complexes (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 409-418 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation of a macrocyclic diphosphine ligand 5 incorporating a binaphthyl unit and its NiII and PdII complexes, 6 and 7, is described. A complete assignment of 1H,- 13C-, and 31P-NMR data on the basis of 2D NMR spectroscopy (1H, 1H-, 13C, 1H-, 31P, 1H-, 31P, 13C-COSY) was possible for 5, and also - in part - for 6 and 7.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770138
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  • 200
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    Synthesis of oligoribonucleotides containing isoguanosine (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 399-408 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oligoribonucleotides containing isoguanosine ( = 1,2-dihydro-2-oxoadenosine; isoG; 1) were prepared. The building block 2 was synthesized using the (dimethylamino)methylidene residue as NH2 protecting group. The monomethoxytrityl as well as dimethoxytrityl group were introduced at OH-C(5′) (→5 and 6). Silylation of 5 with triisopropylsilyl chloride formed the 2′-O-blocked derivative 7 almost exclusively. Reaction with PCl3/1,2,4-1H-triazole furnished the phosphonate 2 which was used in solid-phase synthesis of the oligoribonucleotides 10 and 11. RNAse T1 hydrolyzed U-A-G-U-U-isoG-U-U-A-G (10) at the 3′-site of G but not of isoG. The self-complementary oligomer (A-U-isoG-U)3 (11) formed a duplex which was less stable than that of (A-U)6.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19940770137
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