Oligonucleotides containing 7-deaza-7-(hex-1-ynyl)-2'-deoxyadenosine (1) and 7-deaza-7-iodo-2'-deoxyadenosine (2) are described. The corresponding phosphoramidites (3 a,b) were synthesized and employed in solid-phase oligonucleotide synthesis. The modified 7-deazaadenine residues show selective base-pairing with dT. According to the T m values and the thermodynamic data of duplex formation, the 7-iodo and the 7-(hex-1-ynyl) residues of a 7-deazaadenine moiety increase the duplex stability with retention of the particular DNA structure. This is different from 8-substituted adenine, which destabilizes the nucleic acid duplex significantly. The nucleoside 1 fluoresces strongly.

No abstract

7‐Alkynylated 7‐deazaadenine (pyrrolo[2,3‐d]pyrimidin‐4‐amine) 2′‐deoxyribonucleosides show strong fluorescence which is induced by the 7‐alkynyl side chain (Table 3). A large Stokes shift with an emission around 400 nm is observed when the compound is irradiated at 280 nm. The solvent dependence indicates the formation of a charged transition state. The fluorescence appears when the triple bond is in conjugation with the heterocyclic base. Electron‐donating substituents at the triple bond increase the fluorescence, while electron‐withdrawing residues reduce it. In comparison, the 7‐alkynylated 8‐aza‐7‐deazaadenine (pyrazolo[3,4‐d]pyrimidin‐4‐amine) 2′‐deoxyribonucleosides are rather weakly fluorescent (Table 4). Quantum yields and fluorescence decay times are measured. The synthesis of the 7‐alkynylated 7‐deaza‐2′‐deoxyadenosines and 8‐aza‐7‐deaza‐2′‐deoxyadenosines was performed with 7‐deaza‐2′‐deoxy‐7‐iodoadenosine (6) or 8‐aza‐7‐deaza‐2′‐deoxy‐7‐iodoadenosine (22) as starting materials and employing the Pd0‐catalyzed cross‐coupling reaction with the corresponding alkynes (Schemes 1, 4, and 5). Catalytic hydrogenation of the side chain of the unsaturated nucleosides 5 and 17 afforded the 7‐alkyl derivatives 18 and 19, respectively, which do not show significant fluorescence (Scheme 2).

No abstract

No abstract