Synthesis and some biochemical properties of a novel 5,6,7,8-tetrahydropyrimido[4,5-c]pyridazine nucleoside

A novel nucleoside analogue is described based on the pyridazine ring system. The nucleoside was successfully incorporated into DNA via both its phosphoramidite and 5′-triphosphate derivatives. Enzymatically, the analogue behaves essentially as thymidine: it is a good substrate for the DNA polymerases Taq and exonuclease-free Klenow fragment, leading to full-length products when present in either the primer or template strands. In hybridisation studies, the nucleoside displays ambiguous base-pairing properties, including universal base properties.