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‐triazolo[4,5‐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.