VIBRATIONAL SPECTROSCOPY OF C-7 H-BONDED STRUCTURES - STUDIES ON PEPTIDE AND GLYCOPEPTIDE MODELS

This paper reports FTIR spectroscopic studies on cyclic peptides and N -glycosylated bridged cyclic peptides {cyclo[Gly-Pro-Xxx(GlcNAc)-Gly-d elta-Ava], Xxx = Asn, Gln} with possible H-bonded beta- (C-10) and/or gamma-turn (C-7) structures, as well as on model compounds which are c apable of forming C-7 intramolecular hydrogen bonds (IHBs), such as Ac -Gly-NHMe and etyl-2-acetamido-2-deoxy-beta-D-glucopyranosylamin (GlcN Ac-NHAc). In certain cases, the assignment of the characteristic amide I frequencies to the acceptor amide carbonyls was assisted by C-13 is otope labelling or by additional structural information inferred from NMR measurements. The influence of solvent (trifluoroethanol and dimet hyl sulphoxide) on the stability of C-10 and C-7 IHBs is also discusse d. (C) 1997 Elsevier Science B.V.