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Novel thymidine analogue triphosphates, which have an sp3-hybridized carbon at the C5 alpha-position with amino-linker arms, a methyl ester, or a carboxyl group at the C5 sidearm, were good substrates for primer-extension reactions by DNA polymerase from Pyrococcus kodakaraensis (KOD Dash DNA polymerase), yielding exclusively full-length products. The resulting modified DNA was further allowed to react with a functional molecule such as fluorescein isothiocyanate. By contrast, only truncated products were formed from the thymidine analogue substrate bearing the amino-linker arm or the negatively charged carboxyl group using Taq, Tth DNA polymerase, or DNA polymerase I from E. coli (Klenow fragment). The results indicate either that the thymidine analogue was not accepted by the enzymes, or that the polymerases could not extend the products, once the analogue had been incorporated, depending on the type of the analogue. A conventional thymidine analogue bearing an aminopropenyl group at the C5-position was accepted by all enzymes, among which KOD Dash DNA polymerase showed the highest activity for the polymerization with this analogue. Templates bearing the thymidine analogues in place of one thymidine residue were read by KOD Dash, Taq, Tth DNA polymerases, and the Klenow fragment giving the full-length product. KOD Dash DNA polymerase could expand structural diversities of substrates that can be used to prepare modified DNAs.

The modified ODN's bearing C5-substituted 2'-deoxyuridine derivative were synthesized by a post-synthetic modification with an unsymmetrical triamine. The effect of the C5-substituent on the duplex formation with complementary DNA or RNA differed with the position of an imino group in the linker-arms.

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