The possibility of cleavage of the alpha-bond between mannose (or galactose) and serine (or threonine) in the presence of alpha-mannosidase and alpha-galactosidase has been studied. Using model compounds simulating the O-glycosyl bond in glycoproteins, several glycopeptides have been synthesized: N-tertbutyloxycarbonyl-O-alpha-mannopyranosyl-seryl-glycine methylamide (alpha-Man-Ser-Gly), tertbutyl-oxycarbonyl-O-alpha-mannopyranosyl-threonyl- glycine methylamide (alpha-Man-Thr-Gly), N-tertbutyloxy-carbonyl-O-alpha-galactopyranosyl-seryl-glycine methylamide (alpha-Gal-Ser-Gly) as well as N-tertbutyloxy-carbonyl-O-beta-mannopyranosyl-seryl-glycine methylamide (beta-Man-Ser-Gly). The cleavage has been shown to occur in glucoamylase after proteolytic degradation.