A SIMPLE ACCESS TO LACTOSE-DERIVED BUILDING-BLOCKS REQUIRED IN GLYCOCONJUGATE SYNTHESIS

Lactose was readily transformed into thexyldimethylsilyl (3,4-O-isopro pylidene-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 g lycoconjugate synthesis. Thus, from 5 via per-O-benzoylation, desilyla tion, trichloroacetimidate formation, glycosylation of the Lemieux spa cer, and acid-catalyzed de-O-isopropylidenation methoxycarbonyloctyl ( 2,6-di-O-benzoyl-beta-D-galactopyranosyl)-(1 --> 4)-2,3,6-tri-O-benzoy l-beta-D-glucopyranoside (12) was obtained. Regioselective benzoylatio n 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 d erivative. Fucosylation of 13 and then de-O-isopropylidenation afforde d thexyldimethylsilyl (2,6-di-O-benzoyI-beta-D-galactopyranosyl)-(1 -- > -di-O-acetyl-2-O-benzoyl-alpha-L-fucopyranosyl)-(1 --> 3)]-2,6-di-O- benzoyl-beta-D-glucopyranoside (21), an important fucosyllactose build ing block. (C) 1997 Elsevier Science Ltd.