Synthesis of methyl 2-O-α--mannopyranosyl-α-d-talopyranoside and methyl 2-O-α-d-talopyranosyl-α-d-talopyranoside

Treatment of methyl 3-O-benzyl-2-O-(2,3,4,6-tetra-O-acetyl-α-d-mannopyranosyl)-α-d-mannopyranoside (1) with tert-butyldiphenylsilyl chloride in N,N-dimethylformamide afforded methyl 3-O-benzyl-6-O-tert-butyldiphenylsilyl-2-O-(2,3,4,6-tetra-O-acetyl-α-d-mannopyranosyl)-α-d- mannopyranoside (2). Oxidation of 2 with pyridinium chlorochromate, followed by reduction of the carbonyl group, and subsequent O-deacetylation afforded methyl 3-O-benzyl-6-O-tert-butyldiphenylsilyl-2-O-α-d-mannopyranosyl-α-d-talopyranoside (5). Cleavage of the tert-butyldiphenylsilyl group of 5 with tetrabutyllamonium fluoride in oxolane, followed by hydrogenolysis, gave methyl 2-O-α-d-mannopyranosyl-α-d-talopyranoside (7). O-Deacetylation of 1 gave methyl 3-O-benzyl-2-O-α-d-mannopyranosyl-α-d-mannopyranoside (8). Treatement of 8 with tert-butyldiphenylsilyl chloride afforded a 6,6′-disilyl derivative, which was converted into a 2′,3′-O-isopropylidene derivative, and then further oxidized with pyridinium chlorochromate. The resulting diketone was reduced and removal of the protecting groups gave methyl 2-O-α-d-talopyranosyl-α-d-talopyranoside (15). The structures of both 7 and 15 were established by ¹³C-n.m.r. spectroscopy.