The reductive denitration of carbohydrate α-nitroepoxides by sodium borohydride

Abstract

Action of sodium borohydride upon sugar derivatives that contain an α-nitrooxirane grouping leads to reductive denitration producing high yiel ds of α-hydroxy-β-deoxy derivatives. Thus, 5,6-anhydro-1,2-O-isopropylidene-6-nitro-α-D-glucofuranose (2) gave 5-deoxy-1,2-O-isopropylidene-α-D-xylo-hexofuranose (3). The methyl 2,3-anhydro-4,6-O-benzylidene-3-nitrohexopyranosides having the β-D-talo (4), β-D-allo (5), and β-D-manno (6) configurations readily afforded methyl 4,6-O-benzylidene-2-deoxy- β-D -lyxo-hexopyranoside (10; from 4) and its β-D-arabino isomer (11; from 5 and 6). The corresponding nitroepoxy glycoside of α-D-talo configuration (7) reacted more slowly and gave a mixture of 3-epimeric 2-deoxyglycosides, the analogous α-D-lyxo (13) and α-D-xylo (14) compounds. The α-D-manno (8) and β-D-gulo (9) nitroepoxides proved unreactive under the same conditions. Stereochemical factors considered to be important in these denitrations are discussed.