COMBINED CHEMICAL AND ENZYMATIC SYNTHESIS OF A C-GLYCOPEPTIDE AND ITS INHIBITORY ACTIVITY TOWARD GLYCOAMIDASES

A novel chemoenzymatic approach to synthesizing high-mannose-type N-glycopeptide and its C-linked glycopeptide analog is described. The synthesis consists of two steps:  a chemical synthesis of GlcNAc-containing peptides and an enzymatic glycosyl transfer of Man9GlcNAc to the terminal GlcNAc in the peptides in an aqueous medium containing organic solvents. The essential enzyme used is an endo-β-N-acetyl-glucosaminidase from Arthrobacter protophormiae (Endo-A). This approach should be generally applicable to the synthesis of both natural and designed high-mannose-type glycopeptides. It has been found that, while the natural high-mannose-type N-glycopeptide 2 can be rapidly hydrolyzed by glycoamidases [commonly called N-glycanase or, systematically, peptide-N4-(N-acetyl-β-d-glucosaminylasparagine amidase], the synthetic C-glycopeptide 1 with an insertion of a methylene group at the crucial asparagine−GlcNAc linkage is resistant to the enzyme-catalyzed hydrolysis and shows apparent inhibitory activity toward...