5-(5-Formylthienyl)-, 5-(4-formylphenyl)- and 5-(2-fluoro-5-formylphenyl)cytosine 2′-deoxyribonucleoside mono- (dCRMP) and triphosphates (dCRTP) were prepared by aqueous Suzuki–Miyaura cross-coupling of 5-iodocytosine nucleotides with the corresponding formylarylboronic acids. The dCRTPs were excellent substrates for DNA polymerases and were incorporated into DNA by primer extension or PCR. Reductive aminations of the model dCRMPs with lysine or lysine-containing tripeptide were studied and optimized. In aqueous phosphate buffer (pH 6.7) the yields of the reductive aminations with tripeptide III were up to 25 %. Bioconjugation of an aldehyde-containing DNA with a lysine-containing tripeptide was achieved through reductive amination in yields of up to 90 % in aqueous phosphate buffer.