Syntheses of 5-Formyl- and 5-Carboxyl-dC Containing DNA Oligos as Potential Oxidation Products of 5-Hydroxymethylcytosine in DNA

To investigate the potential oxidation products of 5-hydroxymethylcytosine (5-hmC)-containing DNA, we present here efficient syntheses of 5-formyl- and 5-methoxycarbonyl-2'-deoxycytidine phosphoramidites. The 5-formyl group in III was easy to introduce and was compatible with phosphoramidite and DNA syntheses. An additional treatment of ODN1 with NaBH4 produced the corresponding ODN2 quantitatively. Phosphoramidite V was also incorporated into DNA, and the methyl ester could be hydrolyzed under mild basic conditions to afford ODN3.