Stereoselective synthesis of the isosteric phosphono analogues of N-acetyl-alpha-D-glucosamine 1-phosphate and N-acetyl-alpha-D-mannosamine 1-phosphate

The isosteric phosphono analogues of N-acetyl-alpha-D-glucosamine I-phosphate and N-acetyl-alpha-D-mannosamine l-phosphate (1 and 2) are stereoselectively synthesized starting from 2,3,5-tri-O-benzyl-D-arabinose (3b). Reaction of 3b with divinylzinc stereoselectively affords the glucoenitol 4c, the mercuriocyclization and subsequent iododemercuriation of which stereoselectively afford the alpha-C-glucopyranosyl iodide 6b with a free hydroxyl group at C-2. Temporary protection of the hydroxyl group and treatment with triethyl phosphite converts 6b into the corresponding phosphonate 7b. The free hydroxyl group of 7b is then converted into an acetamido group by oximation, acetylation of the oxime, reduction, and subsequent acetylation. The reduction of the oxime with diborane stereoselectively affords the gluco isomer, whereas catalytic hydrogenation gives the manno isomer. Acetylation and deprotection afford the desired products 1 and 2.