Conformations of the Nucleoside Analogs Formycin, 2-Azaadenosine, and Nebularine in Solution

Abstract

The ribose conformations of formycin, 2-azaadenosine, nebularine, 8-bromoinosine, and 8-bromo- xanthosine have been studied using proton magnetic resonance in ND3 solutions, in D2O solutions, and in pyridine solutions. The temperature was varied between - 60 °C and +40 °C in ND3 and between +10 °C and +60 °C in D2O solutions. In solution, 2-azaadenosine and nebularine have a conformational behaviour similar to that of the common purine (β) ribosides. This is in agreement with the conformations observed in the solid state. The conformations of formycin and formycin B have strong analogies with those of the 8-bromopurineribosides and differ significantly from those of the 8-azapurineribosides since they adopt preferentially the syn-S-g+ conformation. This con­formation is very probably stabilized by an intramolecular hydrogen bond between O (5′) and N (3).

Pyrazolo[3,4-d][1,2,3]triazine DNA: Synthesis and Base Pairing of 7-Deaza-2,8-diaza-2‘-deoxyadenosine

“…The 2-azapurines, such as 2-azaadenine and 2-azahypoxanthine, have also long been known to inhibit the growth of both microbial and mammalian cells. − Although the physical properties of these nucleosides have been studied, very few were incorporated in oligonucleotides . Recently, 2-aza-2‘-deoxyadenosine ( 3 ) was synthesized by our laboratory, and its behavior within oligonucleotide duplexes was studied. , In continuation of the work on 2-azapurine nucleosides and oligonucleotides and as the result of the unusual base pairing properties of 3 , the related 7-deaza-2,8-diazapurine (7 H -pyrazolo[3,4- d ][1,2,3]triazine) system is now investigated (purine numbering is used throughout the general part).…”