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Stereoselective synthesis of l-vancosamine methyl β-glycoside by addition of an organocerium reagent to O-benzyloxime ethers

✍ Scribed by Ralph Greven; Peter Jütten; Hans-Dieter Scharf


Publisher
Elsevier Science
Year
1995
Tongue
English
Weight
656 KB
Volume
275
Category
Article
ISSN
0008-6215

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✦ Synopsis


The methyl fl-glycopyranoside of L-vancosamine (1, 3-amino-2,3,6-trideoxy-3-C-methyl-Llyxo-hexose), a constituent of vancomycin and related glycopeptide antibiotics, was synthesized stereoselectively from methyl 2,6-dideoxy-fl-L-lyxo-hexopyranoside (2) in eight steps. Compound 2 was subjected in sequence to regioselective 3-O-p-methoxybenzylation, 4-O-tert-butyldimethylsilylation, oxidative 3-O-deprotection, and pyridinium dichromate oxidation to give methyl 4-O-tert-butyldimethylsilyl-2,6-dideoxy-fl-L-threo-hexopyranosid-3-ulose (8). O-Benzyloximation of 8 and removal of the tert-butyldimethylsilyl protective group furnished methyl 2,6-dideoxy-fl-L-threo-hexopyranosid-3-ulose O-benzyloxime (12). Addition of a methylcerium reagent to 12 provided the branched-chain hydroxyamino sugar methyl 3-benzyloxyamino-2,3,6-trideoxy-3-Cmethyl-fl-L-lyxo-hexopyranoside (14) which was easily converted into the title compound by hydrogenolysis. On the other hand, reaction of the 4-benzyl ether 11 with the organocerium reagent gave only traces of the 3-epi-analogue of 14, methyl 4-O-benzyl-3-benzyloxyamino-2,3,6-trideoxy-3-C-methyl-fl-L-xylo-hexopyranoside.


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