A novel method for the incorporation of glycoprotein-derived oligosaccharides into neoglycopeptides

We describe a new method for the transfer of carbohydrate moieties to polypeptides in which complex carbohydrate, in the form of glycosyl amino acid, is removed from an available glycoprotein, derivatized, and reacted with a polypeptide via an iodoacetylated alpha-amino group. A family of oligomannose chains, N-linked to the side chain of Asn, was obtained from ovalbumin by pronase digestion and purified as previously described. A reactive sulfhydryl group was specifically placed on these molecules by reaction of 2-iminothiolane with the Asn alpha-amino group. Separately, the alpha-amino group of the peptide GGYR was specifically iodoacetylated by reaction with iodoacetic anhydride at pH 6. Reaction of the thiol-containing carbohydrate with iodoacetylated peptide at pH 8 gave in high yield the corresponding oligomannosyl-peptides, whose structures were confirmed by mass spectrometry. A peptide inhibitor of HIV protease was also oligomannosylated by this procedure. The principle advantage of this method is the efficiency of the reaction even when performed with stoichiometric amounts of the two molecules at low concentration. It should be feasible to extend this chemistry to larger polypeptides.