n.m.r.-spectral stuidies of 2-linked glycosides: 2-O-glycosylation shifts of 2-O-glycosyilated α- and β-L-arabinopyranoides

Article abstract of DOI:10.1016/0008-6215(84)85376-8

Anomalous glycosylation shift values of the signals for C-1 (the anomeric carbon atom) and C-2 (the glycosylated carbon atom) were sometimes observed for 2-O-β-D-glycopyranosyl (or -β-D-xylopyranosyl)-β-D-glucopyranosides, whereas no remarkable displacements of the other sugar-carbon signals were observed in these cases.This can be explained in terms of chanmge of the orientation of the glycosyl linkages, owing to strong, steric interaction between the 2-O-glycosyl group and the 1-O-aglycon (or -sugar) group.Various 2-O-glycosylated α- and β-L-arabinopyranosides were synthesized.In the case of α-L-arabinopyranosides, the processes of 2-O-β-D-glucosylation, -β-D-xylosylation, and -α-L-arabinosylation resulted in unexpected, upfield shifts of the C-3, -4, and -5 signals, together with displacement of the C-1 and -2 resonances.Furthermore, significant alteration of the values of ³J_H1,H2 and ¹J_C1,H1 was also observed for the 2-O-glycosylated α-L arabinopyranoside moiety, indicating an increase in the contribution of the ¹C₄ conformation of the glycosylated α-L-arabinopyranoside in these cases.On the other hand no remarkable variation in the signals of C-3, -4, and -5, or in the ³J_H1,H2 and ¹J_C1,H1 values, was found for 2-O-α-L-rhamnosylation, except for 4-epihederagenin-3-yl 2-O-α-L-rhamnopyranosyl-α-L-arabinopyranoside.In the present study, such unusual 2-O-glycosylation shifts were not encountered for the 2-O-glycosylation of β-L-arabinopyranosides.