A novel disaccharide substrate having 1,2-oxazoline moiety for detection of transglycosylating activity of endoglycosidases

A disaccharide substrate of Manβ1-4GlcNAc-oxazoline 2 was designed and synthesized as a novel probe for detection of the transglycosylating activity of endoglycosidases. A regio- and stereoselective transglycosylation reaction of 2 to GlcNAcβ1-O-pNP or Dns-Asn(GlcNAc)-OH catalyzed by endo-β-N-acetylglucosaminidase from Mucor hiemalis (Endo-M) and endo-β-N-acetylglucosaminidase from Arthrobacter protophormiae (Endo-A) has been demonstrated for the first time, resulting in the core trisaccharide derivative Manβ1-4GlcNAcβ1-4GlcNAcβ1-O-pNP 8 (or -(Dns)Asn-OH). Interestingly, the transglycosylation proceeds irreversibly; the resulting trisaccharide 8 was not hydrolyzed by Endo-M and Endo-A. Based on these results, a new mechanism including an oxazolinium ion intermediate has been proposed for the endoglycosidase-catalyzed hydrolysis or transglycosylation.