Replacement of Canonical DNA Nucleobases by Benzotriazole and 1,2,3‐Triazolo[4,5‐d]pyrimidine: Synthesis,Fluorescence, and Ambiguous Base Pairing

The syntheses and the fluorescence properties of 7H‐3,6‐dihydro‐1,2,3‐triazolo4,5‐d]pyrimidin‐7‐one 2′‐deoxy‐β‐D ‐ribonucleosides (=2′‐deoxy‐8‐azainosine) 3 (N³), 15 (N²), and 16 (N¹) as well as of 1,2,3‐benzotriazole 2′‐O‐methyl‐β‐ or ‐α‐D ‐ribofuranosides 6 (N¹) and 24 (N¹) are described. Also the fluorescence properties of 1,2,3‐benzotriazole 2′‐deoxy‐β‐D ‐ribofuranosides 4 (N¹) and 5 (N²) are evaluated. From the nucleosides 3 – 6 , the phosphoramidites 19, 26a, 26b , and 28 are prepared and employed in solid‐phase oligonucleotide synthesis. In 12‐mer DNA duplexes, compound 3 shows similar ambiguous base‐pairing properties as 2′‐deoxyinosine ( 1 ), while the nucleosides 4 – 6 show strong pairing with each other and discriminate very little the four canonical DNA constituents.