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.
📜 SIMILAR VOLUMES
A highly efficient and stereoselective technique for additions to syn-β-alkyl-β-hydroxy-α-methyl ketones is now available. The methodology is based on the conversion of the starting material into a trichlorotitanium alkoxide derivative, which is able to assume a stable cyclic arrangement exhibiting