NUCLEIC-ACID RELATED-COMPOUNDS .88. EFFICIENT CONVERSIONS OF RIBONUCLEOSIDES INTO THEIR 2',3'-ANHYDRO, 2'(AND 3')-DEOXY, 2',3'-DIDEHYDRO-2',3'-DIDEOXY, AND 2',3'-DIDEOXYNUCLEOSIDE ANALOGS

Treatment of purine, pyrimidine, and modified purine (antibiotic) ribonucleosides with 2-acetoxy-2-methylpropanoyl (alpha-acetoxyisobutyryl) bromide in acetonitrile gave mixtures of 2',3'-bromohydrin acetates with different O5' substituents. Significant amounts of 5'-unprotected (hydroxyl) bromo acetates were obtained in some cases, and formation of 2',3'-O-isopropylidene derivatives as minor byproducts was detected for the first time. Acid-catalyzed nucleophilic displacement of chloride by bromide occurred with 2-amino-6-chloropurine riboside, but no substitution of fluoride by bromide was detected with 6-amino-2-fluoropurine riboside. Treatment of the trans bromo acetate mixtures obtained from purine-type nucleosides with Dowex 1 x 2 (OH-) in methanol gave the 2',3'-anhydro (ribo epoxide) compounds. Radical-mediated hydrogenolytic debromination and deprotection gave 2'- and 3'-deoxynucleosides. Treatment of the bromo acetate mixtures with zinc-copper couple or acetic acid-activated zinc effected reductive elimination, and deprotection gave 2',3'-didehydro-2',3'-dideoxy compounds which were hydrogenated to give 2',3'-dideoxynucleosides. A number of these analogues have potent inhibitory activity against AIDS and hepatitis B viruses. New C-13 NMR data for several types of unsaturated-sugar nucleosides are tabulated. These procedures are directly applicable for the preparation of L-didehydro-dideoxy and L-dideoxy nucleoside analogues.