Synthesis, base pairing, and fluorescence properties of oligonucleotides containing 1H-pyrazolo[3,4-d]pyrimidin-6-amine (8-aza-7-deazaporin-2-amine) as an analogue of purin-2-amine

The synthesis of the N-9- and N-R-(beta-D-2'-deoxyribonucleosides) 2 and 10 . respectively, of 8-aza-7-deazapurin-2-amine (= 1 H-pyrazolo[3.4-d] rimicl in-6-amine) is described. The fluorescence properties and the stability of the N-glycosylic bond of 2 were determined and compared with those: of the 2'-deoxyribonucleosides 1 and 3 of purin-2-amine and 7-deazapurin-2-amine r espectively. From the nucleoside 2. the phosphormidite 14 was prepared. and oligonucleotides were synthesized. Duplexes containing compound 1 or 2 are slightly less stable than those containing 2'-deoxyadenosine while their C D spectra are rather different. The fluorescence of the nucleosides is stro ngly quenched(> 95%) in single-stranded as well as in duplex DNA. The resid ual fluorescence was used to determine the melting profiles. which save T-m values similar lu those determined from the UV melting curves.