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  • 1
    Electronic Resource
    Electronic Resource
    Stereoselective alkylation of glycine units in dipeptide derivatives. "Chirality transfer" via a pivalaldehyde N,N-acetal center (1989)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 111 (1989), S. 2622-2632 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00189a042
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  • 2
    Electronic Resource
    Electronic Resource
    Elektrochemische Decarboxylierung von L.-Threonin- und Oligopeptid-Derivaten unter Bildung von N-Acyl-N, O-acetalen: Herstellung von Oligopeptiden mit Carboxamid-oder Phosphonat-C-TerminusTeilweise in einer Kurzmitteilung erwähnt (1989)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989), S. 401-425 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Electrochemical Decarboxylation of L-Threonine and Oligopeptide Derivatives with Formation of N-Acyl-N, O-acetals: Preparation of Oligopeptides with Amide or Phophonate C-TerminusDerivatives of α-amino acids with two stereogenic centers (cf. L-threonine) and of di-, tri-, and tetrapeptides are electrolyzed in MeOH or AcOH, with formation of N-acyl-N, O-acetals (1b-15b, 20b), in an anodic oxidative substitution of the COOH by an OR group. The amine ends of the oligopeptides may be benzyloxycarbonyl(Z)- or (tert-butoxy)carbonyl(Boc)-protected. With unprotected dipeptides, an electrolytic decarboxylative cyclization to imidazolidinones (18c, 19c) may also occur (in H2O/NH4OAc). The electrolyses are carried out in simple flasks with cooling jackets (‘undivided cell’), using constant current conditions and anodes of Pt or glassy C. The electrolyte is generated in situ by adding 10-20 mol-% of a tertiary amine. Mild acidic hydrolysis of electrolysis products thus obtained may lead to amino-acid amides or peptide amides (10c, 11c, 12c, 17c) with one amino acid less than the starting material. The N, O-acetals from L-threonine and the oligopeptides also react with organometallic nucleophiles such as Grignard compounds (→21-26, 29), with formation of products in which the original COOH group has been replaced by alkyl or allyl (sometimes even with moderate stereoselectivity). By treatment of the peptide-derived (open-chain) N, O-acetals with trialkyl or triaryl phosphites/TiCl4 the RO group is replaced by a phosphodiester group in a (non-diastereoselective) Michaelis-Arbuzov-type reaction (1d, 1e, 2d-9d, 5e). Thus, the two-step sequence of electrolysis and phosphonation converts an oligopeptide derivative to an analogue with a phosphonic-acid end group. The diastereoisomeric N-protected dimethyl and diethyl dipeptidephosphonates (also prepared from the corresponding diaryl esters by Ti(OR)4-mediated transesterification) could be separated by preparative HPLC (SiO2, Lichrosorb Si 60, 10 μm); the dextrorotatory isomers of 1d-3d were assigned L, D-, the laevoratory ones L, L-configuration by hydrolysis to and identification of the known amino and aminophosphonic acids. The results described demonstrate a new simple route leading, from a given oligopeptide, to pure peptide analogues of known configuration.
    Notes: No abstract.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19890720302
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  • 3
    Electronic Resource
    Electronic Resource
    Solubilization of Peptides in Non-polar Organic Solvents by the Addition of Inorganic Salts: Facts and ImplicationsDedicated to Prof. Gerhard Schröder on the occasion of his 60th birthday (1989)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989), S. 857-867 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The solubility of open-chain peptide derivatives (12 examples) in non-polar, ether-type organic solvents may be greatly increased by addition of salts (LiCl, LiBr, LiI, LiBF4, LiClO4, NaI, MgBr2 CaBr2, ZnCl2) or of titanates (Ti(OEt)4, Ti(OCHMe2)4). Examples are reported (Tables 2-6) in which this solubilizing effect leads to peptide concentrations more than one-hundred-fold those in the absence of salt (cf, Boc—Ala—Gly—Gly—Gly—OH in THF from 2g·1-1 to ≥ 300 g·1-1 with 6 equiv. of LiCl), 1H-NMR Spectra of one of these solutions are reported (Fig. 1). There are no indications for epimerizations of stereogenic centres on the peptide backbone. Possible applications of these solutions in peptide chemistry are discussed.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19890720502
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  • 4
    Electronic Resource
    Electronic Resource
    On the Macrolactonization of β-Hydroxy Acids. Crystal structures of the pentolide and the hexolide from (R)-3-hydroxybutanoic acid. Molecular modeling studies of the tetrolideDedicated to Prof. Dr. Wilhelm Simon on the occasion of his 60th birthday (1989)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989), S. 1704-1717 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The temperature and concentration dependence of the previously reported formation of oligolides from (R)- or (S)-3-hydroxybutanoic acid under Yamaguchi's macrolactonization conditions (2,4,6-trichlorobenzoyl chloride/base) was studied. While the content of hexolide 2 in the product mixture is almost invariably ca. 35%, the amounts of pentolide 1 and of the larger rings strongly depend upon the temperature employed (Fig.1). Cyclic oligomers (5,6) are also obtained from 3-hydroxypentanoic acid. Enantiomerically pure β-butyrolactone can be used for the preparation of pento-, hexo-, and heptolide under Shanzer's macrolactonization conditions (tetra-oxadistannacyclodecane ‘template’). The X-ray crystal structures of the pentolide 1 and of two modifications (space groups C 2 and P 21) of the hexolide 2 were determined (Figs. 2-6 and Tables 1 and 5). No close contacts between substituent atoms and atoms in the rings or between ring atoms are observed in these structures. The hexolide C 2 modification is ‘just a large ring’, while the crystals of the P 21 modification contain folded rings the backbones of which resemble the seam of a tennis ball. A comparison of the torsion angles in the folded hexolide ring of the P 21 modification with those in the helical poly-(R)-3-hydroxybutanoate (PHB) suggests (Table 2) that the same interactions might be responsible for folding in the first and helix formation in the second case. Molecular modeling with force-field energy minimization of the tetrolide from four homochiral β-hydroxybutanoic acid units was undertaken, in order to find possible reasons for the fact that we failed to detect the tetrolide in the reaction mixtures. The calculated conformational energies (per monomer) for some of the tetrolide models (Figs. 7-9 and Tables 3 and 4) are not significantly higher than for the pentolide and hexolide crystal structures. We conclude that thermodynamic instability is an unlikely reason for the lack of tetrolide isolation. This result and failure to observe equilibration of pentolide 1 to a mixture of oligomers under the reaction conditions suggest that product distribution is governed by kinetic control.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19890720807
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  • 5
    Electronic Resource
    Electronic Resource
    Röntgenstrukturanalyse von 2,4,6-Tri(tert-butyl)phenyl-lithium · N,N,N′,N′-Tetramethylpropan-1,2-diamin: Eine monomere Organolithium-Verbindung (1989)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989), S. 624-630 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: X-Ray Crystal-Structure Analysis of 2,4,6-Tri(tert-butyl)phenyllithium · N,N,N′,N′-Tetramethylpropane-1,2-diamine: a Monomeric Organolithium CompoundTri(tert-butyl)phenyllithium is an important reagent for the preparation of derivatives of main-group elements with low coordination state as well as a highly hindered base for the generation of amine-free Li-enolates. Its monomeric nature in solution was previously deduced from NMR measurements. While Et2O, THF, and N,N,N′,N′-tetramethylethylene-1,2-diamine (tmen) led to crystalline samples which were not suitable for structure analysis, the N,N,N′,N′-tetramethylpropane-1,2-diamine (tmpn) gave good single crystals of the title compound from Et2O/hexane (disorder along the two-fold crystallographic axis running through Li—C(1) and C(4) of the Ph ring. The structure (Fig. 1, Table 1) has some remarkable features: (i) it is one of the very few monomeric organolithium compounds so far, (η1-Li on aromatic ring); (ii) it has the rare trigonal-planar coordination of the Li-atom; iii) there are close contacts between the Li-atom arid one of the Me groups in each ortho-position (Fig. 3). The internal angle on the Ph-ring ipso-C-atom is 114°. This angle as well as those of the other known phenyllithium (Table 2), -magnesium, and -aluminum structures are included in a plot of ipso-angles against Pauling electronegativities (Fig. 2).
    Notes: No abstract.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19890720321
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  • 6
    Electronic Resource
    Electronic Resource
    Mono- and Dialkylation of Derivatives of (1R, 2S)-2-Hydroxycyclopentanecarboxylic Acid and -cyclohexanecarboxylic acid via bicyclic dioxanones: Selective generation of three contiguous stereogenic centers on a cyclohexane ringPartially published in preliminary from [1] or mentioned in a previous paper [2]Dedicated to Dr. Günther Ohloff on the occasion of his 65th birthday (1989)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989), S. 690-714 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ethyl (1R, 2S)-2-hydroxycyclopentanecarboxylate and -cyclohexanecarboxylate (1a and 2a, respectively) obtained in 40 and 70% yield by reduction of 3-oxocyclopentanecarboxylate and cyclohexanecarboxylate, respectively (Scheme 2), with non-fermenting yeast, are converted to bicyclic dioxanone derivatives 3 and 4 with formaldehyde, isobutyraldehyde, and pivalaldehyde (Scheme 3). The Li-enolates of these dioxanones are alkylated (→5a-5i, 5j, 6a-6g), hydroxyalkylated (→51, m, 6d, e), acylated (→5k, 6c) and phenylselenenylated (→7-9) with usually high yields and excellent diastereoselectivities (Scheme 3, Tables and 2). All the major isomers formed under kinetic control are shown to have cis-fused bicyclic structures. Oxidation of the seleno compounds 7-9 leads to α, β-unsaturated carbonyl derivatives 10-13 (Scheme 3) of which the products 12a-c with the C=C bond in the carbocyclic ring (exocyclic on the dioxanone ring) are most readily isolated (70-80% from the saturated precursors). Michael addition of Cu(I)-containing reagents to 12a-c and subsequent alkylations afford dioxanones 14a-i and 16a-d with trans-fused cyclohoxane ring (Scheme 4). All enolate alkylations are carried out in the presence of the cyclic urea DMPU as a cosolvent. The configuration of the products is established by NMR measurements and chemical correlation. Some of the products are converted to single isomers of monocyclic hydroxycyclopentane (17-19) and cyclohexane derivatives (20-23; Scheme 5). Possible uses of the described reactions for EPC synthesis are outlined. The observed steric course of the reactions is discussed and compared with that of analogous transformations of monocyclic and acyclic derivatives.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19890720410
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  • 7
    Electronic Resource
    Electronic Resource
    Cycloadditionen an die Doppelbindung von (R)-2-tert-Butyl-Δ4-1,3-oxazolin-3-carbonsäure-methylestern (1989)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 122 (1989), S. 2377-2389 
    Details
    ISSN: 0009-2940
    Keywords: EPC syntheses ; Δ4-1,3-Oxazoline, derivatives ; Simmons-Smith reaction ; Sakurai reaction ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Cycloadditions to the Double Bond of Methyl (R)-2-tert-Butyl-Δs4-1,3-oxazoline-3-carboxylates1The title compounds (with or without an additional substituent, such as methyl or vinyl, in the 5-position) are allowed to react with peracids (→ dihydroxy derivatives 3), with cyclopropanation reagents (such as ICH2ZnEt, N2CHCOOEt, HCBr3, or HCCl3/NaOH → products 5-9), with tetracyanoethylene and OsO4 (see four- and five-membered rings in 19, 20), with dienophiles (maleic anhydride, see 23). The double bond of the oxazolines reacts in a highly diastereoselective manner, with the attack preferred from the face of the five-membered ring remote from the tert-butyl group. Some of the products obtained undergo or are subjected to further reactions (4, 12-18, 23, 29-33). Stereochemical and synthetic aspects of the reactions are discussed.
    Notes: Die Titelverbindungen (mit und ohne zusätzliche Substituenten wie z. B. Methyl oder Vinyl in der 5-Stellung) werden mit Persäuren (→ Dihydroxyderivate 3), mit Cyclopropanierungsreagentien (wie z.B. ICH2ZnEt, N2CHCOOEt, HCBr3 oder HCCl3/NaOH → Produkte 5-9), mit Tetracyanethylen und OsO4 (→ Produkte 19-20) und mit Dienophilen (Maleinsäureanhydrid, siehe 23) umgesetzt. Die Doppelbindung der Oxazoline reagiert hoch diastereoselektiv, wobei der bevorzugte Angriff von der der tert-Butylgruppe abgewandten Seite erfolgt. Einige der erhaltenen Produkte werden weiter umgesetzt (siehe 4, 12-18, 23, 29-33). Stereochemische und synthetische Aspekte der Reaktionen werden diskutiert.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19891221226
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  • 8
    Electronic Resource
    Electronic Resource
    Notiz über mikrobiologische Umsetzungen mit Halobacterium halobium: Reduktion von 3-Oxobutansäure-ethylester und Hydrolyse von 3-Hydroxybutansäure-ethylester. Cooperative Effekte von Reduktase und Hydrolase (1989)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989), S. 793-799 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Note on Biotransformations with Halobacterium halobium: Reduction of Ethyl 3-Oxobutanoate and Hydrolysis of Ethyl 3-Hydroxybutanoate. Cooperative Effects of Reductase and HydrolaseThe archaebacterium Halobacterium halobium, growing in saturated NaCl solution, is tested for its ability to achieve biotransformations. We found that this microorganism does accept only a small variety of compounds as substrates. Ethyl acetoacetate (1) is reduced to ethyl (S)-3-hydroxybutanoate (2) of optical purity of 40-76%, but in low chemical yields. The reduction is accompanied by hydrolysis of the hydroxy-ester to 3-hydroxybutanoic acid (3). Hydrolysis of rac-ester 2 by Halobacterium halobium gives (R)-2 of optical purity of up to 88%, depending upon reaction time, together with the almost racemic hydroxy-acid 3, both in low chemical yields. Hopes that the ‘extremist’ Halobacterium halobium would be able to effect unique conversions were not fulfilled.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19890720420
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  • 9
    Electronic Resource
    Electronic Resource
    Substitutionen und Additionen an (R)-2-tert-Butyl-Δ4-1,3-oxazolin-3-carbonsäure-methylester (1989)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 122 (1989), S. 2365-2375 
    Details
    ISSN: 0009-2940
    Keywords: EPC syntheses ; Stereogenic centers, self-regeneration of ; Δ4-1,3-Oxazoline, derivatives ; Electrochemistry, oxidative decarboxylation (Hofer-Moest) ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Substitution and Addition reactions of Methyl (R)-2-tert-Butyl-Δ4-1,3-oxazoline-3-carboxylatesEnantiomerically pure Δ4-1,3-oxazolines (1-5) bearing a tert-butyl group in the position 2 are prepared on a 100-g scale from serine or threonine using an electrochemical key step. They contain highly reactive double bonds, amenable to stereoselective electrophilic (1-3) or nucleophilic attack (4, 5). Thus, Vilsmeier and Friedel-Crafts-type reactions (→21, 22) and Michael additions (→11, 13) occur at C-5. Furthermore, substituents may be introduced in position 4 (next to the carbamate group) by lithiation and reaction with electrophiles (products 4, 10). Finally, dienolate 16 (from 5) reacts with aldehydes at the exocyclic position (→18). Hydrogenations of the tri- or tetrasubstituted double bonds in the oxazolines thus obtained are highly stereoselective (→14, 19, 24, 26). In most cases, the 2-tert-butyl substituent directs reactions to the opposite face of the five-membered ring. The overall transformations achieved are discussed with regard to the bonds of serine and threonine.
    Notes: Enantiomerenreine Δ4-1,3-Oxazoline (1-5) mit einer tert-Butyl-Gruppe in 2-Stellung werden über einen elektrochemischen Schlüsselschritt im 100-g-Maßstab aus Serin oder Threonin hergestellt; sie enthalten gegenüber Elektrophilen (1-3) oder Nucleophilen (4, 5) hochreaktive Doppelbindungen, so daß Formylierungen, Acylierungen (→21, 22) oder konjugierte Additionen (→11, 13) an C-5 durchgeführt werden können. Eine Art ortho-Metallierung (neben der Carbamoyl-Gruppe) an C-4 erlaubt es, auch in dieser Position Substituenten einzuführen (→4, 10). Schließlich reagiert das Dienolat aus 5 mit Aldehyden in der exocyclischen Position (→18). In so hergestellten Oxazolinen kann die tri- oder tetrasubstituierte Doppelbindung stereoselektiv hydriert werden (→14, 19, 24, 26). In den meisten Fällen dirigiert die tert-Butyl-Gruppe in 2-Stellung des Heterocyclus den Angriff von Reaktionspartnern auf die andere Seite des Fünfringes. Eine retrosynthetische Analyse zeigt auf, welche Bindungen der ursprünglich eingesetzten Aminosäuren Serin und Threonin durch die hier beschriebenen Reaktionen letztlich betroffen sind.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19891221225
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  • 10
    Electronic Resource
    Electronic Resource
    Synthesis of Nonproteinogenic (R)- or (S)-Amino Acids Analogues of Phenylalanine, Isotopically Labelled and Cyclic Amino Acids from tert-Butyl 2-(tert-Butyl)-3-methyl-4-oxo-1-imidazolidinecarboxylate (Boc-BMI) (1989)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1989 (1989), S. 1215-1232 
    Details
    ISSN: 0170-2041
    Keywords: Glycine enolate derivatives, chiral ; Lithium enolates, reactivity of ; α-Deuterio amino acids ; Diamino dicarboxylic acids ; α-Amino acids, 4-to 7-membered heterocyclic ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Herstellung nichtproteinogener (R)- oder (S)-α-Aminosäuren. - Phenylalanin-analoge, isotopenmarkierte, sowie carbo- und heterocyclische Aminosäuren aus 2-(tert-Butyl)-3-methyl-4-oxo-1-imidazolidincarbonsäure-tert-butylester (Boc-BMI)Das in beiden enantiomeren Formen im kg-Maßstab kommerziell zugängliche Glycin-Derivat Boc-BMI dient als Ausgangsmaterial (Schema 1) für die Herstellung von a) offenkettigen Aminosäuren wie α-Deuterioaminosäuren (4, 5), β-Arylalaninen (2), Derivaten von Asparaginsäure (6, 7a, 8), oder von ω-Halogenalkylaminosäuren (7b, c, 12, 13, 16, 17, 19, 22), b) von α-Aminocycloalkancarbonsäuren (9, 11) und c) von heterocyclischen α-Aminosäuren (14, 15, 18, 20) mit Azetidin-, Pyrrolidin-, Piperidin- und Perhydroazepin-Ring. Inversion durch Deprotonierung / Protonierung erlaubt es, auch ausgehend von einem Boc-BMI-Enantiomeren beide Enantiomere einer gewünschten Aminosäure gezielt herzustellen (Schema 5). Die Effekte von sekundären Aminen, von Lithium-Salzen und des cyclischen Harnstoffs DMPU auf die Reaktivität von Lithium-Enolaten werden diskutiert und zum Teil ausgenutzt.
    Notes: The enantiomerically pure glycine derivatives (R)- and (S)-Boc-BMI, commercially available on a kg scale, are used as starting materials (Scheme 1) for the preparation of (i) open-chain amino acids such as α-deuterio amino acids (4, 5), β-arylalanines (2), aspartic acid derivatives (6, 7a, 8), or ω-halo amino acids (7b, c, 12, 13, 16, 17, 19, 22), (ii) of α-aminocycloalkanecarboxylic acids (9, 11), and (iii) of heterocyclic α-amino acids (14, 15, 18, 20) containing azetidine, pyrrolidine, piperidine or perhydroazepine rings. Inversion by deprotonation / protonation or deuteration allows to prepare either enantiomer of an amino acid from the same Boc-BMI enantiomer (Scheme 5). Effects of additives such as the cyclic urea DMPU, lithium salts, or secondary amines upon the reactivity of lithium enolates are discussed and, in part, exploited.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.198919890293
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