N.m.r. study on conformation of Ac‐Thr(α‐GalNAc)‐Ala‐Ala‐OMe as a model for mucin type glycoprotein

Abstract

This study report on the results of high resolution ¹H n.m.r. investigations on Ac-Thr(α-GalNAc)-Ala-Ala-OMe 1 as a mucin type model glycopeptide of antifreeze glycoprotein (AFGP) in both dimethyl sulfoxide (DMSO) and H₂O. The temperature dependence of amide proton chemical shifts strongly suggested the presence of the intramolecular hydrogen bond between the amide proton of GalNAc and the carbonyl oxygen of the Thr residues. Due to this bond, the orientation of the sugar residue of 1 appears to be fairly restricted relative to its peptide backbone. Despite the lack of the clear evidence for such intramolecular hydrogen bond in H₂O, ¹H coupling constant data suggested the structural similarity of 1 in DMSO and H₂O, indicating the presence of the intramolecular hydrogen bond even in H₂O, which may play an important role in determining the orientation of the sugar moiety with respect to the peptide backbone in glycoprotein.