Conformational investigations on glycosylated asparagine-oligopeptides of increasing chain length

Stepwise solution syntheses of the homo-oligomers Boc-(Asn)<INF>n</INF>-NHCH<INF>3</INF> (n = 1–5; I<INF>1–5</INF>), Boc-{[GlcNAc(Ac)<INF>3</INF>β]Asn}<INF>n</INF>-NHCH<INF>3</INF> (n = 1–8; II<INF>1–8</INF>), and Boc-[(GlcNAcβ)Asn]<INF>n</INF>-NHCH<INF>3</INF> (n = 1–8; III<INF>1–8</INF>) 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. ¹H-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 γ-turns in the carbohydrate-free oligomers and the presence of β-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. Copyright © 2002 European Peptide Society and John Wiley & Sons, Ltd.