Phosphorylation of nucleoside derivatives with aryl phosphoramidochloridates

The preparation of three aryl phosphorocyclohexylamidochloridates (7a, 7b and 7c) and an aryl phosphoromorpholidochloridate (8) is described. These aryl phosphoramidochloridates react with 2′,3′-O-methoxymethylene-uridine, -4-N-anisoylcytidine and -6-N-anisoyladenosine (9a, 9b and 9c, respectively), in the presence of the 1-ethylimidazole derivative (11a) to give high yields of the corresponding fully-protected 5′-phosphoramidates (10). Treatment of the latter compounds with aqueous alkali gives the nucleoside 5′-phosphoramidate derivatives (14) which, on mild acidic hydrolysis, give the corresponding unprotected 5′-nucleotides (15) in virtually quantitative yields. Phosphorylation of 2′-O-methoxytetrahydropyranyluridine (12) with 7a and 8, under the same conditions, occurs regiospecifically to give the corresponding 5′-phosphoramidate derivatives (13). The partially-protected dinucleoside phosphate (16b) has been prepared and phosphorylated with 7a to give, after removal of the protecting groups, the dinucleotide (18, pUpU) in high yield.