SYNTHESIS OF A THIO-LINKED LEWIS-A (LE(A)) EPITOPE

The synthesis of heptyl (alpha-L-fucopyranosyl)-(1 --> 4)-S-[(beta-D-g alactopyranosyl)-(1 --> 3)]1,4-dithio-beta-D-glucopyranoside (2), as t hio-linked Lewis A analogue was based on thexyldimethylsilyl -O-(4-met hoxybenzyl)-4-thio-beta-D-glucopyranoside (15) which was readily obtai ned from D-galactose, Reaction of 15 with acetyl-2-O-(4-methoxybenzyl) -alpha-L-fucopyranosyl trichloroacetimidate (8) as fucosyl donor affor ded the alpha-(1 --> 4)-thio-linked disaccharide. Replacement of the 4 -methoxybenzyl groups by acetyl groups and removal of the 3a-O-allyl g roup afforded as 3a-O-unprotected acceptor thexyldimethylsilyl (2,3,4- tri-O-acetyl-alpha-L-fucopyranosyl)-(1 --> O-acetyl-2-0-benzoyl-4-thio -beta-D-glucopyranoside (19), which gave with 2,3,4,6-tetra-O-acetyl-a lpha-D-galactopyranosyl trichloroacetimidate as galactosyl donor (20) the trisaccharide. Transformation into a trichloroacetimidate as glyco syl donor, glycosylation of heptylmercaptan, and then removal of the O -acyl protective groups afforded target molecule 2. (C) 1998 Elsevier Science Ltd. All rights reserved.