Conformational Investigations on Glycosylated Asparagine-Oligopeptides of Increasing Chain Length

Stepwise solution syntheses of the homo-oligomers Boc-(Asn)(n)-NHCH3 (n= 1-5: I1-5), Boc([GlcNAc(Ac)3(beta)]Asn)(n)-NHCH3 (n=1-8: II1-8). and Boc-[(GlcNAcbeta)Asn](n)-NHCH3 (n=1-8: III1-8) are described. Members of the series III were obtained by deacetylation of the corresponding members of the series II. The conformational preferences of the N-protected homo-peptides of the three series were investigated by spectroscopic techniques. H-1-NMR measurements were carried out in various solvents: the CD spectra were recorded in water. aqueous SDS and TFE. The poor solubility of the oligomers of the three series prevented FT-IR measurements in solution. NMR and IR measurements indicate the existence of unordered structures containing some gamma-turns in the carbohydrate-free oligomers and the presence of beta-turns in the glycosylated oligopeptides. whether acetylated or not. The CD spectra do not indicate the presence of organized structures. The sugar moieties apparently do not have a structure-inducing effect on the asparagine homo-oligomer main chain.