A convenient synthetic route to the disaccharide repeating-unit of peptidoglycan

Abstract

Glycosylation of the readily accessible benzyl 2-acetamido-6- O-benzyl-2-deoxy-3- O-[( R)-1-(methoxycarbonyl)ethyl]-α- d-glucopyranoside wity 3,4,6-tri- O-acetyl-2-deoxy-2-phthalimido-β- d-glucopyranosyl chloride ( 2), using the silver triflate method in the absence of a base, afforded 65–70% of the fully protected [β- d-GlcNPhth-(1→4)-MurNAc] methyl ester derivative 4, the structure of which was ascertained on the basis of 500-MHz 1H-n.m.r. data. 2,2′-Dideoxy-2,2′-diphthalimido-β,β-trehalose hexa-acetate was a by-product. Removal of the Phth group from 4, followed by acetylation, yielded 90% of the acetylated 1,6-di- O-benzyl derivative 5, which, on saponification and catalytic hydrogenation, afforded 2-acetamido-4- O-(2-acetamido-2-deoxy-β- d-glucopyranosyl)-3- O-[( R)-1-carboxy-ethyl]-2-deoxy- d-glucopyranose. Similarly, 5 was converted into the acetylated methyl ester derivative, which, on selective removal of the methyl ester group, gave benzyl 2-acetamido-4- O-(2-acetamido-3,4,6-tri- O-acetyl-2-deoxy-β- d-glucopyranosyl)-6- O-benzyl-3- O-[( R-1-carboxyethyl]-2-deoxy-α- d-glucopyranoside. An alternative route for the preparation of 2 is described.