Synthesis of 2 '-deoxyisoguanosine 5 '-triphosphate and 2 '-deoxy-5-methylisocytidine 5 '-triphosphate

The syntheses of the 5'-triphosphates of 2'-deoxyisoguanosine (= p(3)isoG(d )) and 2'-deoxy-5-methylisocytidine (= p(3)me(5)isoC(d)), two new bases for the genetic alphabet, are described. The triphosphates were synthesized fr om the corresponding nucleosides using a transient-protection procedure. Th e introduction of a methyl group at the 5-position of 2'-deoxyisocytidine r emarkably improved the stability of the triphosphate. Characterization of t he triphosphates included enzymatic incorporation opposite the complementar y base in a template oligonucleotide.