α-Mannosidase-catalyzed synthesis of a (1 → 2)-α-d-rhamnodisaccharide derivative

Enzymatic transglycosylation using p-nitrophenyl α-d-rhamnopyranoside as the glycosyl donor and 6 equiv of ethyl 1-thio-α-d-rhamnopyranoside as the glycosyl acceptor yielded a d-rhamnooligosaccharide derivative. The reaction was catalyzed by jack bean α-mannosidase in a 1:1 (v/v) mixture of 0.1 M sodium citrate buffer (pH 4.5)–MeCN at 25 °C. The enzyme exhibited high catalytic activity for the reaction, to afford in 32.1% isolated yield (based on donor substrate) ethyl α-d-rhamnopyranosyl-(1 → 2)-1-thio-α-d-rhamnopyranoside, which is a derivative of the common oligosaccharide unit of the antigenic lipopolysaccharides from Pseudomonas.