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  • Articles: DFG German National Licenses  (2)
  • 1990-1994  (2)
  • 1975-1979
  • Polymer and Materials Science  (2)
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  • Articles: DFG German National Licenses  (2)
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  • 1
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The molecular and crystal structures of three compounds, representing the repeating units of the β-bend ribbon (an approximate 310-helix, with an intramolecular hydrogen-bonding donor every two residues), have been determined by x-ray diffraction. They are Boc-Aib-Hib-NHBzl, Z-Aib-Hib-NHBzl, and Z-L-Hyp-Aib-NHMe (Aib, α-aminoisobutyric acid; Bzl, benzyl; Boc, t-butyloxycarbonyl; Hyp, hydroxyproline Hib, α-hydroxyisobutyric acid; Z, benzyloxycarbonyl). The two former compounds are folded in a β-bend conformation: type III (III′) for Boc-Aib-Hib-NHBzl, while type II (II′) for the Z analogue. Conversely, the structure of Z-L-Hyp-Aib-NHMe, although not far from a type II β-bend, is partially open.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The molecular structures of four protected isovaline- (Iva-) containing peptides to the pentamer level have been determined by x-ray diffraction. The peptides are t-Boc-Ala-(S)-Iva-Ala-OMe (t-Boc : tert-butyloxycarbonyl; OMe : methoxy) and its (R)-Iva diastereomer, and t-Boc-[Ala-(R)-Iva]2-Ala-OH and its (S)-Iva diastereomeric methyl ester analogue. The two tripeptides are folded in an open type II β-bend conformation. The fully developed right-handed 310-helix formed by the (R)-Iva pentapeptide, which includes an unusual intramolecular (acid) O—H⃛O=C(peptide) H bond, is partially unfolded (near the C-terminus) in the (S) -Iva pentapeptide. 1H-nmr and Fourier transform ir absorption studies suggest that in CDCl3 solution (a) the two tripeptides maintain a type II β-bend conformation of comparable stability and (b) both diastereomeric pentapeptide sequences adopt a fully developed 310-helix. A comparison with the preferred conformation of other extensively investigated Cα,α-disubstituted glycines is made and the implications for the use of the Iva residue in designing conformationally constrained analogues of bioactive peptides are briefly discussed.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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