Chemoenzymatic synthesis of the Salmonella group E-1 core trisaccharide using a recombinant beta-(1 -> 4)-mannosyltransferase

The chemical synthesis of the bacterial O-antigen from Salmonella serogroup E-1, 3-O-(4-O-beta-D-mannopyranosyl-alpha-L-rhamnopyranosyl)-alpha-D-gaIac tose, presents a particular challenge because it contains a beta-(1 --> 4) mannosidic linkage to L-rhamnose. We report a chemoenzymatic synthesis of t his crucial antigenic material which culminates in the enzymatic formation of the critical beta-mannosyl connection catalyzed by Salmonella GDP-alpha- D-Man:alpha Rha1 --> 3 alpha Gal-PP-Und beta-(1 --> 4)-mannosyltransferase (ManT(beta 4)). In comparison with previous synthetic routes, this method i s advantageous since it utilizes intermediates, available in significant yi eld, which can be readily derivatized from the reducing end to present flex ibility for analog construction, while the enzymatic construction of the Ma n1 --> 4Rha glycosidic bond is both rapid and occurs in high yield. Further more, the reported spectroscopic and enzymatic structural characterization of the trisaccharide product furnishes the first indisputable functional li nk between wbaO and ManT(84) and clearly sets the stage for the future mech anistic study and exploitation of this fascinating glycocatalyst. (C) 1999 Elsevier Science Ltd. All rights reserved.