Structural analysis of comb-like,amylose derivatives by 13C-N.M.R. spectroscopy

¹³C-N.m.r. spectra have been recorded for previously reported, comb-like derivatives of amylose produced by orthoester and Helferich condensation of D-glucose to amylose. As known from monomeric studies, the Helferich condensation conditions (the presence of mercury salts) favor α-D-glucosylation, and orthoester condensation conditions favor β-D-glycosylation. It was anticipated that, for these polymer condensations, the Helferich and orthoester condensations would also favor α- or β-D-glycosylation, respectively. The ¹³C-n.m.r. spectra of representative products of the Helferich and orthoester condensations confirmed the presence of 4,6-di-O-substituted α-D-glucopyranosyl residues, and also the degree of polymer linearity derived from independent, analytical data. However, these spectra indicate extensive, if not exclusive, β-D-glycosylation for both the helferich and the orthoester conditions. These results were obtained by using the product from an enzymically synthesized, strictly linear amylose in the Helferich condensation reaction.