SYNTHESIS OF 4-DEOXY AND 4-DEOXY-4-HALOGENO DERIVATIVES OF L-FUCOSE AS POTENTIAL ENZYME-INHIBITORS

Methyl 2,3-di-O-benzoyl-6-deoxy-alpha-L-galactopyranoside (2) was converted into the 4-deoxy-4-iodo-alpha-L-gluco derivative 4 by triflate-mediated inversion. Catalytic reduction of 4 gave methyl 2,3-di-O-benzoyl-4,6-dideoxy-alpha-L-xylo-hexopyranoside (6) and subsequent O-debenzoylation gave methyl 4,6-dideoxy-alpha-L-xylo-hexopyranoside (7). Selective benzoylation of L-fucose gave 1,2,3-tri-O-benzoyl-alpha-L-fucopyrnose (14). An analogous sequence of reactions, based on the inversion of configuration at C-4, yielded 4,6-dideoxy-4-iodo-L-glucopyranose (17) and 4,6-dideoxy-L-xylo-hexopyranose (19). Reaction of the 4-trifluoromethanesulfonate (15) of 14 with sodium fluoride in N,N-dimethylformamide gave 1,2,3-tri-O-benzoyl-6-deoxy-4-O-formyl-alpha-L-glucopyranose (12) and 1,2,3-tri-O-benzoyl-4,6,-dideoxy-alpha-L-threo-hex-4-enopyranose (13). Treatment of 14 with diethylaminosulfur trifluoride and then O-debenzoylation gave 4,6-dideoxy-4-fluoro-L-glucopyranose (11). Reaction of 15 with sodium iodide in N,N-dimethylformamide gave 1,2,3-tri-O-benzoyl-4,6-dideoxy-4-iodo-alpha-L-glucopyranose (16). The alpha-glycosyl bromide (20) derived from 16 reacted stereoselectively with dibenzyl phosphate to give the beta-(21) or alpha-glycosyl dibenzyl phosphate (22).