Endo-beta-N-acetylglucosaminidase-catalyzed polymerization of beta-Glcp-(1-->4)-GlcpNAc oxazoline: a revisit to enzymatic transglycosylation.

An alternative synthesis of beta-Glcp-(1-->4)-GlcpNAc oxazoline is described, and its enzymatic reaction with the endo-beta-N-acetylglucosaminidase from Arthrobacter protophormiae (Endo-A) was re-investigated. Under normal transglycosylation conditions with a catalytic amount of enzyme, Endo-A showed only marginal activity for transglycosylation with the disaccharide oxazoline, consistent with our previous observations. However, when used in a relatively large quantity, Endo-A could promote the transglycosylation of the disaccharide oxazoline to a GlcpNAc-Asn acceptor. In addition to the initial transglycosylation product, a series of large oligosaccharides were also formed due to the tandem transglycosylation to the terminal glucose residues in the intermediate products. In the absence of an external acceptor, Endo-A could polymerize the disaccharide oxazoline to form oligo- and polysaccharides having the -4-beta-(Glcp-(1-->4)-beta -GlcpNAc)-1-repeating units. This is the first example of an endo-beta-N-acetylglucosaminidase-promoted polymerization of activated oligosaccharide substrates. This enzymatic polymerization may find useful applications for the synthesis of novel artificial polysaccharides.