New synthesis of a protected ketonucleoside by a non-cryogenic oxidation with TFAA/DMSO

An improved synthesis of the ketonucleoside 2'-Oxo-3',5'-O-[1,1,3,3-tetrakis(1-methylethyl)-1,3-disiloxanediyl]-cytidine (6), an intermediate in the synthesis of the potent anti-tumor agent 1 (MDL 101;131 or FMdC), is reported which incorporates a trifluoroacetic acid/dimethylsulfoxide oxidation process, This oxidation procedure eliminates the cryogenic reaction conditions and the necessity of protection at the N-4 amine used in the previously published route. Simplified isolation procedures for 3 and 4 eliminate two chromatographic purification steps. Overall yields are comparable to those reported previously.