A simple access to lactose-derived building blocks required in glycoconjugate synthesis

Lactose was readily transformed into thexyldimethylsilyl (3,4-O-isopropylidene-beta-D-galactopyranosyl)-(1 --> 4)-beta-D-glucopyranoside (5); this compound served as intermediate for the generation of partially O-protected lactose building blocks required in oligosaccharide and glycoconjugate synthesis. Thus, from 5 via per-O-benzoylation, desilylation, trichloroacetimidate formation, glycosylation of the Lemieux spacer, and acid-catalyzed de-O-isopropylidenation methoxycarbonyloctyl (2,6-di-O-benzoyl-beta-D-galactopyranosyl)-(1 --> 4)-2,3,6-tri-O-benzoyl-beta-D-glucopyranoside (12) was obtained. Regioselective benzoylation of 5 with benzoyl cyanide under various conditions afforded 3-O- (13), 2,3,2'-O- (14), 3,2'-O- (16), and 2,2'-O-unprotected (17) lactoside, respectively. De-O-isopropylidenation of 16 gave thexyldimethylsilyl (6-O-benzoyl-beta-D-galactopyranosyl)-(1 --> 4)-2,6-di-O-benzoyl-beta-D-glucopyranoside (18), an important 2',3',4'-O-unprotected lactose derivative. Fucosylation of 13 and then de-O-isopropylidenation afforded thexyldimethylsilyl (2,6-di-O-benzoyI-beta-D-galactopyranosyl)-(1 --> 4)-[(3,4-di-O-acetyl-2-O-benzoyl-alpha-L-fucopyranosyl)-(1 --> 3)]-2,6-di-O-benzoyl-beta-D-glucopyranoside (21), an important fucosyllactose building block. (C) 1997 Elsevier Science Ltd.