Facile methods for the synthesis of 5-formylcytidine

5′-O-Protected 5-methylcytidine 3 was oxidized with Na2S2O8 to give a mixture of the corresponding 5-(hydroxymethyl)- and 5-formylcytidine derivatives, 4 and 5. The hydroxymethyl group of 4 was further oxidized to a formyl group by treatment with ceric(IV) ammonium nitrate (CAN). Alternatively, 2′,3′,5′-O-protected 5-(hydroxymethyl)cytidine 10 was directly oxidized with CAN to give the desired 5-formylcytidine derivative 11. After removal of the protecting groups in each intermediate, 5-formylcytidine (6) was obtained in good yield.