Branched-chain fluoro nitro D- and L-sugars from glucose

sMixed crystals of methyl 3-deoxy-3-C-methyl-3-nitro-alpha-D- and beta-L-glucopyranosides (1:1), easily available from D-glucose by means of the Baer reaction, were completely characterised by X-ray diffraction analysis. These diastereomeric components, separation of which could be achieved through their 4,6-O-benzylidene derivatives, were selectively fluorinated at position 6 by treatment with DAST and stereoselectively transformed into phenyl 3-deoxy-3-C-methyl-3-nitro-1-thio-beta-D-glucopyranoside and phenyl 3-deoxy-3-C-methyl-3-nitro-1-thio-beta-L-glucopyranoside, respectively. Fluorination with DAST of each pure enantiomer afforded, depending on the conditions, the corresponding enantiomeric phenyl 3,6-dideoxy-6-fluoro-3-C-methyl-3-nitro-1-thio-beta-D- and beta-L-glucopyranosides or the respective rearranged 2,3,6-trideoxy-6-fluoro-3-C-methyl-3-nitro-2-alpha-D- and alpha-L-mannopyranosyl fluorides. This route constitutes a simple method for obtaining fair-to-good yields of 6-fluorinated branched-chain D- and L-sugar derivatives, potentially useful as glycosyl donors, starting from D-glucose. (C) 1999 Elsevier Science Ltd. All rights reserved.