Synthesis of methyl 3-O-α-d-mannopyranosyl-α-d-talopyranoside and methyl 3-O-α-d-talopyranosyl-α-d-talopyranoside

Methyl 2-O-benzyl-3-O-(2,3,4,6-tetra-O-acetyl-α-d-mannopyranosyl)-α-d-mannopyranoside (4) and methyl 2-O-benzyl-3-O-α-d-mannopyranosyl-α-d-mannopyranoside (6) were prepared form a common intermediate, namely, methyl 2-O-benzyl-4,6-O-benzylidene-3-O-(2,3,4,6-tetra-O-acetyl-α-d-mannopyranosyl)-α-d-mannopyranoside. On treatment with tert-butylchlorodiphenylsilane, in N,N-dimethylformamide in the presence of imidazole, 4 and 6 afforded methyl 2-O-benzyl-6-O-tert-butyldiphenylsilyl-3-O-(2,3,4,6-tetra-O-acetyl-α-d-mannopyranosyl)-α-d-mannopyranoside (7), and methyl 2-O-benzyl-6-O-tert-butyldiphenylsilyl-3-O-(6-O-tert-butyldiphenylsilyl-α-d-mannopyranosyl)-α-d-mannopyranoside (8), respectively. Compound 8 was converted into its 2,3-O-isopropylidene derivative (9), and oxidation of 7 and 9 with pyridinium chlorochromate, and reduction of the resulting carbonyl intermediates gave methyl 2-O-benzyl-6-O-tert-butyldiphenylsilyl-3-O-(2,3,4,6-tetra-O-acetyl-α-d-mannopyranosyl)-α-d-talopyranoside and methyl 2-O-benzyl-6-O-tert-butyldiphenylsilyl-3-O-(6-O-tert-butyldiphenylsilyl-2,3-O-isopropylidene-α-d- talopyranosyl)-α-d-talopyranoside, respective. Removal of the protecting groups furnished the title disaccharides.