In a previous papeti in this series, we described the synthesis of L-fucosyldisaccharides having sulfate groups at C-3 or C-4. Such r_-fucosyl-oligosaccharides occur naturally as a part of the structure of fucoidan, a sulfated L-fucose polysaccharide, know to possess anticoagulant acticity 3,4 This polymer and other sulfated poly-.
saccharides are also known to be inhibitors of various envelope viruses including the human immunodeficiency viruses j-' Thus in a continuing effort to synthesize well-. defined sulfated oligosaccharides that occuias a part of fucoidan, we describe herein the synthesis of two sulfated disaccharides of L-fucose. A common intermediate, namely, methyl 3,4-di-0-benzyl-2-O-(2-O-benzyl-3,4-O-isopropylidene-a-L-fucopyranosyl)-a-L-fucopyranoside (8) was utilized for the synthesis of both disaccharides. Methyl 2-0-benzyl-3,4-O-isopropylidene-l-thio-/3-L-fucopyranoside (3), which was obtained by the isopropylidenation of methyl I-thio+Lfucopyranoside followed by benzylation with sodium hydride-benzyl bromide, was the key glycosyl donor. Dejter-Juszynski and Flowers' synthesyzed methyl 3,4-di-O-benzyl-a-L-fucopyranoside (6) in low yield from methyl a-L-fucopyranoside, whereas our synthesis involved the benzylation of known methyl 2-O-allyl-a-L-fucopyranoside' with subsequent removal of the ally1 group. Glycosylation of 6 with methyl 2-O-benzyl-3,4-0isopropylidene-I-thio-p-fucopyranoside (3) in dichloroethane-N,N-dimethylformamide, in the presence of cupric bromide-tetrabutylammonium bromide", gave methyl 3,4-di-O-benzyl-2-O-(2-0-benzyl-3,4-isopropylidene-Q-L-fucopyranosyl) -a-L-fucopyranoside (7) and methyl 3,4-di-O-benzyl-2-0-(2-0-benzyl-3,4-O-isopropylidene-a-~fucopyranosyl)-a-L-fucopyranoside (8) in 27 and 4 1% yield, respectively, after column chromatographic purification. The 'H-n.m.r. spectra of 7 and 8 were in accord with the structures assigned. Cleavage of the isopropylidene group of 8 with acetic acid gave, in