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  • 1
    Electronic Resource
    Electronic Resource
    Heterocyclische Verbindungen aus Zuckern, XV: Zur Konfiguration chiraler C-2-substituierter 4-Thiazolidincarbonsäuren. Chiralitätstransfer auf C-3 in 3,4-Dihydro-1H-pyrrolo[1,2-c]thiazolen (1994)
    Springer
    Monatshefte für Chemie 125 (1994), S. 189-208 
    Details
    ISSN: 1434-4475
    Keywords: 4-Thiazolidine carboxylic acids ; Chirality ; 3,4-Dihydro-1H-pyrrolo[1,2-c]thiazoles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary 5-Substituted 3,4-dihydro-pyrrolo[1,2-c]thiazole-6,7-dicarboxylic acid esters3 are obtained from 2-substituted-3-acyl-1,3-thiazolidine-4-carboxylic acids,1 in [3+2]-cycloaddition reactions via mesoionic oxazolone (“münchnone”) intermediates. The chirality at C-4 of the starting carboxylic acids1 is eliminated in the products3, and the chirality at C-3 (C-2 in the starting carboxylic acids1) can thus be determined through chiroptical measurements. Several representatives of the ring system3 have been characterised through1H- and CD-spectra and the molecular structure of (3S)-3da has been determined by X-ray crystallography.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00818164
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  • 2
    Electronic Resource
    Electronic Resource
    Chiroptical labeling of folded polypeptide conformations: The thioamide probe (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 1061-1072 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper reports the chiroptical properties of thionated N-acyl amino acid and N-acyl dipeptide N′-methylamide models. It was found that the optical activity of the thioamide chromophore is dominated by the chiral contribution of perturbants attached to Cα at the N-H side of the thioamide group. The appearance of a strong negative ππ* band near 270 nm is indicative of the semiextended conformation of this residue. The φ ∼ -70°, ψ ≥ 120° set of torsion angles is compatible with a type II βt-turn or a γt-turn conformation with the perturbing N-H side residue in the i + 1 position of the turn. (The subscript t or tt denotes that one or both of the H-bonded moieties is thioamide.) Earlier data show that both βt- and γt-turns may be fixed by C=S⃛H-N(CO) intramolecular H bonds. The appearance of one or two weak nπ* bands and a positive ππ* band at about 270 nm is characteristic of type II βt-turns containing the H-bonded thioamide group attached to the glycine residue in position i + 2. The extended conformation (φ ∼ -140°, ψ ∼ 140°) of a residue after the thioamide group gives rise to a negative nπ* and a positive ππ* band of comparable magnitude. Peptid1e sequences with alternating thioamide-amide-thioamide backbone tend to adopt 1t ⇆ 4t H-bonded βtt conformations. CD studies show that type II βtt-turns have unique chiroptical properties: the ππ* region is dominated by an exceedingly strong negative band near 260 nm (|Δε| = 19-24) accompanied by a weaker band at higher wavelength values.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360301107
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  • 3
    Electronic Resource
    Electronic Resource
    Carrier design: Conformational studies of amino acid (X) and oligopeptide (X-DL-Alam) substituted poly(L-lysine) (1993)
    New York : Wiley-Blackwell
    Biopolymers 33 (1993), S. 873-885 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The present study was undertaken to examine the influence of the reversal of the sidechain sequential order on the conformation of branched polypeptides. At the same time, the influence of the optically active amino acid joined directly to the poly (L-Lys) backbone and the DL-Ala oligomer grafted as chain-terminating fragment were separately analyzed. Therefore two sets of polypeptides were synthesized corresponding to the general formula poly [Lys-(Xi,)] (XK) and poly[Lys-(DL-Alam-Xi)] (AXK) when X = Ala, D-Ala, Leu, D-Leu, Phe, D-Phe, Ile, Pro, Glu.,D-Glu, or His. For coupling amino acid X to polylysine, three types of active ester methods were compared: the use of pentafluorophenyl or pentachlorophenyl ester, and the effect of the addition of an equimolar amount of 1-hydroxybenzotriazole. After cleavage of protecting groups, AXK polypeptides were synthesized by grafting short oligo (DL-Ala) chains to XK by using N-carboxy-DL-Ala anhydride. The CD measurements performed in water solutions of various pH values and ionic strengths were used for classification of the polypeptide conformations as either ordered (helical) or unordered. Different from what was observed with the unsubstituted poly (L-Lys), poly[Lys-(Xi)] type polypeptides can adopt ordered structure even under nearly physiological conditions (pH 7.3, 0.2M NaCl). These data suggest that the introduction of amino acid residue with either (ar) alkyl side chain (Ala, Leu, Phe) or negatively charged side chain (Glu) promotes markedly the formation of ordered structure. Comparison of chiroptical properties of poly [Lys- (DL-Alam-Xi)] and of poly [Lys- (Xi)] reveals that side-chain interactions play an important role in the stabilization of ordered solution conformation of AXK type branched polypeptides. The results give rather conclusive evidence that not only hydrophobic interactions, but also ionic attraction, can be involved in the formation and stabilization of helical conformation of branched polypeptides. © 1993 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360330603
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  • 4
    Electronic Resource
    Electronic Resource
    The influence of the side-chain sequence on the structure-activity correlations of immunomodulatory branched polypeptides. Synthesis and conformational analysis of new model polypeptidesA preliminary account of part of this work was presented at the International Conference on Functional Polymers and Biopolymers, Oxford, September 15-19, 1986. (1989)
    New York : Wiley-Blackwell
    Biopolymers 28 (1989), S. 1801-1826 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New branched polypeptides were synthesized for a detailed study of the influence of the side-chain structure on the conformation and biological properties. The first subset of polypeptides were prepared by coupling of tetrapeptides to poly[L-Lys]. These polymers contain either DL-Ala3-X {poly[Lys-(X-DL-Ala3)n]} X-DL-Ala3 {poly[Lys-(DL-Ala3-X)n] (n ≤ 1)} tetrapeptide side chains. Another group of branched polymers comprise a mixture of DL-Alam and of DL-Alam-X oligomeric branches in a random distribution {poly[Lys-(DL-Alam-Xi)](i 〈 1, m ∼ 3)}. In each subset the X = Leu or Phe derivatives were prepared.The N-protected tetrapeptides were synthesized by conventional liquid phase methods and were coupled as active esters. The degree of racemization was found relatively high both for active esters and coupled derivatives, when optically active amino acids were in the C-terminal position of the tetrapeptides. In the case of the poly[Lys-(Leu-DL-Ala3)n] derivative, comparative experiments were carred out using various methodical alterations. The highest stereochemical homogeniety could be achieved when the tetrapeptide active ester was synthesized by the “backing off” method.CD spectra of poly[Lys-(Xi-DL-Alam)] (i 〈 1, m ∼ 3) and of poly[Lys-(X-DL-Ala3)n] were analyzed and compared to those of poly[Lys-(DL-Ala3-Xi)] and of poly[Lys-(DL-Ala3-X)n]. All measurements were performed in water solutions of varying pH values and ionic strengths. The data obtained suggest that branched polypeptides containing a mixture of two different types of oligomeric side chains (DL-Alam and DL-Alam-Xi or Xi-DL-Alam) distributed randomly adopt an almost indentical conformation to those that comprise only the respective tetrapeptide (DL-Ala3-X or X-DL-Ala3) branches. The results also indicate that the tendency to form an ordered structure is determined by the indentity and the position of the chiral amino acid X (Phe or Leu) in the side chain.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360281013
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  • 5
    Electronic Resource
    Electronic Resource
    Carrier design: Synthesis and conformational studies of poly (L-lysine) based branched polypeptides with hydroxyl groups in the side chains (1997)
    New York : Wiley-Blackwell
    Biopolymers 42 (1997), S. 719-730 
    Details
    ISSN: 0006-3525
    Keywords: carrier design ; poly (L-lysine) ; branched polypeptides ; hydroxyl groups ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the present study the development of a new series of branched polypeptides that contain hydroxyl groups in side chains is reported. Serine or threonine were attached by 1-hydroxy-benzotriazole catalyzed active ester method to the N-terminals of oligo (DL-alanine) chains grafted to a polylysine backbone resulted in poly[Lys-(Ser1-DL-Alam)] (SAK) and poly-[Lys-(Thri-DL-Alam)] (TAK). Ser was coupled also directly to the η-amino groups of polylysine followed by polymerization of N-carboxy-DL-alanine anhydride resulting oligo (DL-Ala) chain terminals. In this way a reverse sequence was built up in the side chain corresponding to the poly[Lys-(DL-Alam-Seri)] (ASK). The number of hydroxyl groups in the polymer was increased by the synthesis of a branched polypeptide with oligo (DL-serine) branches instead of oligo (DL-alanine) ones - poly[Lys-(DL-Serm)] (SK). Classification of solution conformations of branched polypeptides was carried out by CD spectroscopy performed in water solution of various pH values and ionic strengths. Incorporation of single Ser residues in poly[Lys-(Xi)]-type polypeptides markedly promotes the formation of ordered structure without resulting precipitation even in high salt concentration. The presence of branches with multiple DL-Ser residues resulted in a slightly decreased ability of the polypeptide backbone to adopt an ordered conformation. Comparison of the CD properties of the SAK-ASK pair demonstrates that these compounds are similar, showing an increased tendency to form an ordered spatial arrangement in solution at elevated pH or ionic strength; however, differences in their CD spectra suggest that SAK has higher capability to form regular conformation under comparable conditions. The replacement of Ser by the Thr residue in poly[Lys-(Xi-DL-Alam)] induced a conformational transition and TAK exhibited a more helical structure. These results might indicate that not only hydrophobic or ionic attraction, but also H-bond interaction, can play a role in the formation and/or stabilization of ordered conformation of branched polypeptides. Findings with the hydroxyl group containing polymers reported in this paper can also explain their prolonged shelf stability and high water solubility. © 1997 John Wiley & Sons, Inc. Biopoly 42: 719-730, 1997
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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