Site-Selective Chemoenzymatic Glycosylation of an HIV-1 Polypeptide Antigen with Two Distinct N-Glycans via an Orthogonal Protecting Group Strategy.

A convergent chemoenzymatic approach for sequential installation of different N-glycans in a polypeptide is described. The method includes introduction of distinguishably protected GlcNAc-Asn building blocks during automated solid phase peptide synthesis (SPPS), followed by orthogonal deprotection of the GlcNAc primers and site-selective sequential extension of the sugar chains through glycosynthase-catalyzed transglycosylation reactions. It was observed that the protecting groups on one neighboring GlcNAc moiety have an impact on the substrate activity of another GlcNAc acceptor toward some endoglycosynthases in transglycosylation. The usefulness of this synthetic strategy was exemplified by an efficient synthesis of the glycopeptide neutralizing epitope of broadly HIV-neutralizing antibody PG9. The method should be generally applicable for the synthesis of complex glycopeptides carrying multiple different N-glycans.