AZIDO-(AMINO-)FURANOSYL NUCLEOSIDES AND THEIR PHOSPHORAMIDATES

The ring-opening of 2,2'-anhydro-1-[5-azido- 5 and 5-benzamido- 3 5-deoxy-3-O-methylsulfonyl-beta-D-arabinofuranosyl] uracil by the ion exchanger Dowex 50 (H+) afforded the corresponding 1-[5-azido-8 and 5-benzamido- 12 5-deoxy-3-O-methylsulfonyl-beta-D-arabinofuranosyl]uracil. Hydrogenolysis of the azido nucleosides over Pd-black in the presence of benzoic acid anhydride led to the corresponding benzamido nucleosides in high yields. The 5'-azido-2',3'-oxirane 10 on reaction with ethanolic ammonia generated 1-(3-amino-5-azido-3,5-dideoxy-beta-D-arabinofuranosyl)uracil 15 and 1-(2-amino-5-azido-2,5-dideoxy-beta-D-xylofuranosyl)uracil 16 in a ratio 2:1. The 5'-O-mesyl-2',3'-oxirane 25, on being treated with NaN3 in DMF at 100-degrees-C, afforded 2',5'-anhydro-1-(3-azido-3-deoxy-beta-D-arabinofuranosyl) uracil 26 (54.5%), 3',5'-diazido-beta-D-arabinofuranosyl 27 (20.6%) and 2',5'-diazido-beta-D-xylofuranosyl 28 (5.4%). The hydrogenolysis of 5 over Pd-black proceeded into 2,5'-imino-1-(3-O-methylsulfonyl-beta-D-arabinofuranosyl)uracil 32 which, as the 5'-benzamido derivative 36, was transformed into 3. The 5'-azido compound 5 and 10 on reaction with triphenyl phosphite in aqueous dioxane gave the respective 5'-diphenylphosphoramidate 38 and 39. Similarly, the 3'-azido compound 22 was converted into 3'-diphenylphosphoramidate 40.