Ribose conformations of 8-azapurine nucleosides in solution.

The ribose conformations of 8-azaadenosine, 8-azaguanosine, and 8-azainosine have been studied using proton magnetic resonance in ND3 solutions, in D2O solutions, and in pyridine solutions. The temperature was varied between -60 and +40 degrees C in ND3 and between +10 and +60 degrees C in D20 solutions. The analysis is based on the two state S in equilibrium N model of the ribose moiety proposed by Altona and Sundaralingam. In D2O, the 8-aza substitution destabilizes the gg rotamer and simultaneously diminishes the population of the S state of the ribose. It is deduced that the anti population of the base is greater in the 8-azapurine(beta)ribosides than in the common purine(beta)-ribosides.