Conformational investigations on glycosylated threonine-oligopeptides of increasing chain length

Stepwise solution syntheses are described of the homo-oligomers Z-(Thr)(n)-NHCH3 (n=1-4, I1-4), Z- ([Gal(Ac)(4) beta]Thr](n)-NHCH3 (n=1-5, II1-5] and Z[(Gal beta)Thr]n-NHCH3 (n=1-5, III1-5). Members of the III1-5 series were obtained by de-acetylation of the corresponding oligomers of the II1-5 series. The conformational preferences of the terminally protected homo-peptides of the three series were investigated by FT-IR absorption spectroscopy both in the solid state and in CDCl3 solution, at various concentrations. Proton NMR measurements in CDCl3 and in DMSO-d(6) were also carried out and the effect of temperature variation on the chemical shifts of amide protons was determined in DMSO-d(6) (range 298-335 K) and in CDCl3 (range 298- 320 K). CD spectra were recorded in water and in TFE. Solubility problems prevented measurements in CDCl3 solution for Z(Thr)(4)-NHCH3 and for the entire III1-5 series. The existence of unordered structures in the carbohydrate-free oligomers and of more or less extended, organized structures in the glycosylated derivatives is indicated by the NMR and IR measurements. The sugar moieties apparently show a structure-inducing effect on the peptide chain. (C) 1998 European Peptide Society and John Wiley Br Sons, Ltd.