Conformations of 3-Deazaadenosine, 3-Deaza-8-azaadenosine, and Benzimidazole-1-β-ᴅ-riboside in Solution: HRNMR-, Proton-Relaxation-Time-, and Nuclear-Overhauser- Effect Studies

The solution conformations of 3-deazaadenosine, 3-deaza-8-azaadenosine, and benzimidazole-1-β- ᴅ-riboside have been determined by nuclear magnetic resonance methods in aqueous and ammonia solutions. The two-state S ⇄ N model of Altona and Sundaralingam is used to analyse the ribose moiety. In order to characterize the orientation of the base relative to the ribose, longitudinal proton relaxation time and nuclear Overhauser enhancement measurements have been carried out. It is shown that 3-deazaadenosine and benzimidazole-1-β-ᴅ-riboside exist preferentially in the S- syn-g+/t (70%) and the N-anti-g+/t (30%) conformation families. In the case of 3-deaza-8-aza- adenosine, some destabilization of the g+ rotamer occurs. In this case, the pulsed methods seem to indicate a preference of the base for the anti range.