Chemical modification of lactose. VII. Synthesis of 4-O-.BETA.-D-idopyranosyl-D-glucopyranose

The title new reducing disaccharide (12) was synthesized starting from 1, 6-anhydro-β-lactose. Selective benzoylation of 1, 6-anhydro-4', 6'-O-benzylidene-β-lactose with 4 molar equivalents of benzoyl chloride in pyridine afforded the corresponding 2, 3, 3'-tri-O-benzoate (3) in 41% yield. Sulfonylation of 3 gave 2'-O-mesylate (4) or 2'-O-tosylate (6). Treatment of 4 or 6 with 1.1 molar equivalents of sodium methoxide in boiling MeOH yielded 1, 6-anhydro-4-O-(2, 3-anhydro-4, 6-O-benzylidene-β-D-talopyranosyl)-β-D-glucopyranose (7) in 50 or 66% yield. Further crop of 7 was isolated from the filtrate of 7 as the corresponding diacetate. Heating of a mixture of 7 with excess aq. KOH at 100° for 3 hr cleaved the epoxide ring of 7 trans-diaxially and, after acetylation, 2, 3-di-O-acetyl-1, 6-anhydro-4-O-(2, 3-di-O-acetyl-4, 6-O-benzylidene-β-D-idopyranosyl)-β-D-glucopyranose (9) was isolated in 84% yield. Debenzylidenation of 9 followed by acetylation, and subsequent opening of the 1, 6-anhydro-β-ring with titanium tetrachloride in CHCl3, then treatment with mercuric acetate in glacial AcOH, afforded 1, 2, 3-tri-O-acetyl-4-O-(2, 3, 4, 6-tetra-O-acetyl-β-D-idopyranosyl)-β-D-glucopyranose (11) in 43% yield. Deacetylation of 11 afforded the title compound (12) as a hygroscopic, amorphous powder which gave the crystalline tosylhydrazone.