Conformation and sandwiching of bases by azido groups in the crystal structure of 3′-azido-3′-deoxy-thymidine (AZT), an antiviral agent that inhibits HIV reverse transcriptase
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Abstract
The crystal structure of 3'-azido-3'-deoxy-thymidine (AZT), an antiviral agent that
inhibits HIV reverse transcriptase, has been determined from three-dimensional x-ray
diffractometer data. The crystal structure contains two independent molecules of AZT
forming a hydrogen bonded dimer but exhibiting different conformations. These conformations
are different from those theoretically calculated by molecular mechanics methods.
The azido groups associate with each other and interrupt the base stacking, forming
a sandwich of two stacked bases. The close conformational similarity of AZT to thymidine
explains why AZT is a good substrate for thymidine kinase. The selective inhibition
of reverse transcriptase by AZT is not due to any conformational restrictions imposed
by the azido group but likely due to their stereoelectronic properties.