Patent ID: 7439344

Claim:
A process for the selective O-acylation of a nucleoside I to afford a O-acyl nucleoside II under basic reaction conditions wherein: A is A1, A2 or A3 R 1 is hydrogen, azide, C 1-6 alkyl or C 1-3 acyl; R a1 and R a2 are independently hydrogen or hydroxyl; R b1 and R b2 are hydrogen or —O 2 CR 2 ; and, R 2 is C 1-10 alkyl or phenyl; which process comprises the steps of: (i) dissolving I and DMAP in an heterogeneous aqueous solvent mixture and adding aqueous base to adjust the pH from 7 to 13; (ii) optionally adding sufficient saturated aqueous NaCl to produce a biphasic reaction mixture; (iii) adding an acylating agent and additional base sufficient to maintain the pH from 7 to 13; (iv) monitoring the reaction and discontinuing addition of said acylating agent and said base when the conversion reaches a satisfactory level; (v) optionally contacting the O-acyl nucleoside with a pharmaceutically acceptable acid to permit isolation of an acid additional salt of the O-acyl nucleoside.