Synthesis of a thio-linked Lewis A (Lea) epitope

Article abstract of DOI:10.1016/S0008-6215(97)10044-1

The synthesis of heptyl (α-L-fucopyranosyl)-(1 → 4)-S-[(β-D- galactopyranosyl)-(1 → 3)]-1,4-dithio-β-D-glucopyranoside (2), as thio- linked Lewis A analogue was based on thexyldimethylsilyl 3-O-allyl-2-O- benzoyl-6-O-(4-methoxybenzyl)-4-thio-β-D-glucopyranoside (15) which was readily obtained from D-galactose. Reaction of 15 with O-3,4-di-O-acetyl-2- O-(4-methoxybenzyl)-α-L-fucopyranosyl trichloroacetimidate (8) as fucosyl donor afforded the α-(1 → 4)-thio-linked disaccharide. Replacement of the 4-methoxybenzyl groups by acetyl groups and removal of the 3a-O-allyl group afforded as 3a-O-unprotected acceptor thexyldimethylsilyl (2,3,4-tri-O- acetyl-α-L-fucopyranosyl)-(1 → 4)-S-6-O-acetyl-2-O-benzoyl-4-thio-β-D- glucopyranoside (19), which gave with 2,3,4,6-tetra-O-acetyl-α-D- galactopyranosyl trichloroacetimidate as galactosyl donor (20) the trisaccharide. Transformation into a trichloroacetimidate as glycosyl donor, glycosylation of heptylmercaptan, and then removal of the O-acyl protective groups afforded target molecule 2.