Syntheses of acetylated trisaccharides, Man.ALPHA.1.RAR.3Man.BETA.1.RAR.4GlcNAc and Man.ALPHA.1.RAR.2Man.BETA.1.RAR.4GlcNAc, relating to mannosidosis.

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The title trisaccharides (22 and 30) were synthesized by stepwise condensation of suitably protected monosaccharide units. 3-O-Allyl-2-O-benzoyl-4, 6-di-O-benzyl-α-D-glucopyranosyl bromide (9) and 2-acetamido-1, 6-anhydro-3-O-benzyl-2-deoxy-β-D-glucopyranose (10) were coupled by a modified Koenigs-Knorr glycosidation to give the protected Glcβ1→4GlcNAc (12) in 63.7% yield. After removal of the benzoyl group of 12, the C-2' hydroxyl group was isomerized to the D-manno configuration by a sequence consisting of oxidation to ulose and stereoselective borohydride reduction to give the protected Manβ1→4GlcNAc (15). Benzylation of 15, followed by deallylation, gave the Manβ1→4GlcNAc derivative (18) having an unprotected hydroxyl group at the C-3' position. α-D-Mannosidation of 18 with acetobromomannose gave the protected Manα1→3Manβ1→4GlcNAc (20) in 47.1% yield. Deprotection of 20, followed by acetylation, yielded 22. 2-O-Acetyl-3, 4, 6-tri-O-benzyl-α-D-glucopyranosyl bromide (23) and 10 were coupled to give the protected Glcβ1→4GlcNAc (24) in 39.2% yield. Compound 30 was obtained from 24 via four steps using procedures analogous to those used to obtain 22 from 12.

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