Solution- and solid-phase synthesis of N-protected glycopeptide esters of the benzyl type as substrates for subtilisin-catalyzed glycopeptide couplings

This paper describes the solution-and solid-phase synthesis of glycopeptides containing a GlcNAc moiety at different positions and investigates them as substrates for subtilisin-catalyzed glycopeptide condensation, with an aim to develop enzymatic synthesis of complex glycopeptides and glycoproteins. A systematic study was performed to determine the sites at which the protease subtilisin will accept a glycosylated residue in enzymatic peptide ligations. It was found that Fmoc-glycopeptide esters with unprotected side chains can be prepared by solid-phase methodology using the Rink amide resin. Both removal of the side chain protecting groups as well as release from the resin was accomplished by treatment with acid to provide glycopeptide esters of the benzyl type which were used directly as substrates. One such 12 residue peptide ester was used in a subtilisin-catalyzed glycopeptide condensation in a kinetically controlled mode to demonstrate the utility of this approach.