Molecular basis of activity of 8-azapurines in transcription processes.

ABSTRACT

The quantum mechanical perturbation method has been utilized to study the biological activity of 8-azapurine (8-azaguanosine, 8-azaadenosine and 8-aza-2,6-diaminopurine) nucleoside antibiotics. The in-plane (hydrogen bonding) and stacking energy of 8-azapurine bases have been evaluated with nucleic acid bases and base pairs in all possible orientations. The energy values and the sites of association of analogous bases, obtained by optimization of energy values as well as the sites of association of nucleic acid bases during the transcription process have been compared. The model developed earlier for the incorporation of nucleoside analogues has been used to find out the inhibitory effects of the drug on nucleic acid and protein synthesis. It has been observed that the activity of 8-azapurines are of the following order 8-azaguanine > 8-aza-2,6-diaminopurine > 8-azaadenine and these analogues show preference for binding near a guanine or cytosine in the chain. The results are in agreement with the experimental observations.