5-(5-Formylthiophen-2-yl)cytosine and -7-deazaadenosine 2'-deoxyribonucleosides and their triphosphates were converted to the 2,4-dinitrophenyl- or nitrobenzofurazanyl hydrazones. The hydrazone-modified dNTPs were enzymatically incorporated to DNA by polymerase catalyzed primer extension.
This direct incorporation of hydrazone-linked dNTPs was compared to previously reported incorporation of aldehyde-modified dNTPs followed by post-synthetic hydrazone-formation on DNA. Electrochemical study the nitroarylhydrazone-linked nucleosides and DNA was performed confirming the potential of the hydrazones, nitroaryls and benzofurazane groups for redox labelling of DNA.