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  • 1
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 182 (1981), S. 941-947 
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Monodispersed N-and C-protected linear homo-oligomers of S-methyl-L-cysteine (n = 2 - 7) are studied by measurements of circular dichroism in the vacuum-ultraviolet region. In the solid state higher members of the series take up a β-conformation. The results are compared with earlier circular dichroism and infrared absorption measurements on the same series, and also with the related norvaline and methionine series.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 2
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A newly designed host-guest approach is introduced as a experimental tool to explore the relationship between the sequence of peptides and their secondary structure. From the CD spectra of the host-guest peptides studied, a tentative scale for the α-helix potential in 2,2,2-trifluorethanol of guest amino acids is delineated. The conformational preferences are also examined in β-structure supporting media (solid state, CH2Cl2, CH3OH, H2O) using ir-absorption and CD techniques. Scales for the β-forming tendency of guest amino acid residues in the different media are delineated. It is shown that the preferred conformation of the host-guest peptides is a function of the medium, the chain length, and the protecting groups. Given the fact that conformational effects are important in peptide synthesis, the tentative scales may serve as a guideline to predict secondary structures of side-chain-protected or -deprotected peptides in a given solvent, complementing the well-known empirical conformational prediction parameters.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 3
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Conformational energy computations on a derivative and a homo-dipeptide of Cα,α-diethylglycine were performed. In both cases the N- and C-terminal groups are blocked as acetamido and methylamido moieties, respectively. It was found that the Cα,α-diethylglycine residues are conformationally restricted and that the minimum energy conformation corresponds to the fully extended C5 structure when the N—Cα—C′ bond angle is smaller than 108° (as experimentally observed). The results of the theoretical analysis are in agreement with the crystal-state structural propensity of the complete series of N-trifluoroacetylated homo-peptides of this Cα,α-dialkylated residue from monomer to pentamer, determined by x-ray diffraction and also described in this work. Interestingly, for the first time, a crystallographically planar peptide backbone was observed (in the protected tripeptide). A comparison with peptides of Cα,α-dimethylglycine, Cα-methyl, Cα-ethylglycine, and Cα,α-di-n-propylglycine indicates that the fully extended conformation becomes more stable than the helical structures when both amino acid side-chain Cβ atoms are substituted.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 4
    ISSN: 0006-3525
    Schlagwort(e): conformational analysis, of peptides ; disubstituted glycines, peptides rich in ; Fourier transform in absorption, of peptides ; 310-helical conformation, in peptides ; Cα-methylated α-amino acids, peptides rich in ; nmr, of peptides ; peptide conformation ; x-ray diffraction, of peptides ; β-turn conformation, of peptides ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The preferred conformations of Cα-methyl phenylglycine, Cα-methyl phenylalanine, and Cα-methyl homophenylalanine residues, as determined in model peptides (including homopeptides) by Fourier transform ir absorption, 1H-nmr, CD, and x-ray diffraction techniques, are compared with the aim of investigating the effect of phenyl ring position in the Cα-methylated amino acid side chain. This study shows that (a) β-turn and 310-helical structures are preferentially adopted by peptides rich in these Cα-methylated, aromatic α-amino acids and (b) turn and helix handedness is critically biased by the position of side-chain branching. © 1997 John Wiley & Sons, Inc. Biopoly 40: 523-527, 1996
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 5
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: An ir-absorption and Raman-scattering study, in the solid state, has been carried out on monodispersed, N- and C-protected homooligopeptides (number of residues, n, from 2 to 7) of L-valine, L-isoleucine, and L-phenylalanine. The amide I, II, III, V, and vNH regions have been examined. Some deuterated (ND) samples have been examined to complete the assignments. L-Phenylalanine dipeptide displays spectral characteristics compatible with the parallel β-structure; L-isoleucine and L-valine dipeptides are probably in a distorted structure. A mixture of parallel and antiparallel extended chains cannot be excluded for the peptides with n = 3. In the amide I region the spectra of peptides with n ≥ 4 show the existence of the β-conformation. The problem of chain orientation within the pleated-sheet structure is discussed on the basis of a recent theoretical treatment of vibrational interactions of the amide I mode.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 6
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The crystal-state molecular structures of five linear Ac3c homo-oligopeptides to the tetramer were determined by x-ray diffraction. The oligomers are H-(Ac3c)2-OMe, Fmoc-(Ac3c)2-OMe MeOH, Ac-(Ac3c)2-OMe, pBrBz-(Ac3c)3-OMe · H2O, and t-Boc-(Ac3c)4-OMe · 2H2O. The results indicate the propensity of the tri- and tetrapeptides to fold into type I β-bends and distorted 310-helices, respectively, in partial contrast to Aib, Ac5c, and Ac6c homo-peptides of comparable main-chain length, where regular type III β-bends and 310-helical structures were found. When the influence of the constraints produced by the intramolecular H bonds of the C10-type is absent, other less common structural features may be observed. The average geometry of the cyclopropyl group of the Ac3c residue is found to be asymmetric and the N—Cα—C′ bond angle significantly expanded from the regular tetrahedral value.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 28 (1989), S. 247-257 
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The use of backbone conformational constraints has acquired increasing importance in the design and synthesis of structurally restricted agonists and antagonists of bioactive peptides. Here I discuss the preferred conformations of four among the most popular types of such peptide surrogates: (a) Peptides from Cα,α-dialkylated residues, (b) tetrazolyl peptides, (c) (γ- and δ-) lactam-containing peptides, and (d) thiated peptides. Emphasis is given to conformational energy computations and x-ray diffraction analyses of selected model compounds and analogues of small bioactive peptides such as the formylmethionyl tripeptide chemoattractant and MIF.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 8
    ISSN: 0006-3525
    Schlagwort(e): conformational analysis, of peptides ; disubstituted glycines, peptides rich in ; Fourier transform ir absorption, of peptides ; 310-helical conformation, in peptides ; Cα-methylated α-amino acids, peptides rich in ; nmr, of peptides ; peptide conformation ; x-ray diffraction, of peptides ; β-turn conformation, in peptides ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The conformational preferences of the alicyclic Cα,α-disubstituted glycines Acnc (1-amino-1-cycloalkane-carboxylic acid; n = 4, 7, 9, 12) were assessed in selected model compounds, including homopeptides and Ala (or Aib, α-aminoisobutyric acid)/Acnc peptides containing a small total number of residues, by Fourier transform ir absorption, 1H-nmr, and x-ray diffraction analyses. The results obtained indicate that β-turn and 310-helical structures are preferentially adopted by short peptides rich in these cycloaliphatic α-amino acids. © 1997 John Wiley & Sons, Inc. Biopoly 40: 519-522, 1996
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 9
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The conformational preferences of the N-trifluoroacetylated homo-peptides of Cα,α-diethylglycine from monomer to pentamer in chloroform solution were determined by using ir absorption and 1H-nmr. Intramolecular hydrogen bonding was found to be the dominant factor for all NH groups. The likely absence of a conformational transition upon increasing main-chain length, and the remarkable stability to dilution, heating, and addition of perturbing agents, are additional relevant findings of this study. These results are in agreement with those of the fully extended, C5-conformation-forming homo-peptides from the higher homolog Cα,α-di-n-propylglycine, but contrast dramatically to those of the homo-peptides from the lower homolog Cα,α-dimethylglycine, which have been shown to adopt the 310-helical structure.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 10
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The preferred conformation of the Cα,α-diphenylglycine residue was determined in simple derivatives and dipeptides. The dipeptides were synthesized by the 5(4H)-oxazolone (from the N-para-bromobenzoylated amino acid) method. This activated intermediate and a reaction by-product, para-bromobenzoylbenzhydrylamine, were characterized inter alia by x-ray diffraction. Conformational energy calculations on the Cα,α-diphenylglycine mono-peptide, Ac-Døg-NHMe, indicate that this Cα,α-symmetrically disubstituted residue is conformationally restricted and that its minimum energy conformation falls in the fully extended (C5) region. The results of the theoretical analysis are in agreement with the solution and crystal-state structural tendency of mClAc-Døg-OH, Z-Døg-OtBu, pBrBz-Døg-Gly-OMe and its tert-butyl ester analogue, determined by ir absorption, lH-nmr, and x-ray diffraction, and also described in this work. The implications for the use of the Døg residue in designing conformationally constrained analogues of bioactive peptides are briefly discussed.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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