Crystal structure of ammonium 3′-azido-3′-deoxythymidine-5′-aminocarbonylphosphonate hemihydrate: an anti-HIV agent

The asymmetric unit of the title compound, NH4+·C11H14N6O7P−·0.5H2O, contains one 3′-azido-3′-deoxythymidine-5′aminocarbonylphosphonate (ACP–AZT) anion, half of an NH4+ cation lying on a twofold rotation axis and in another position, occupied with equal probabilities of 0.5, an NH4+ cation and a water molecule. The amide group of the ACP–AZT anion is disordered (occupancy ratio 0.5:0.5), with one part forming an N—H...O (involving C=O...H4N+) hydrogen bond and the other an O—H...N (involving C—NH2...OH2) hydrogen bond with the components of the split NH4+/H2O position. The pseudorotation parameters of ACP–AZT set it apart from previously studied AZT and thymidine. In the crystal, the various components are linked by N—H...O, O—H...O, N—H...N, C—H...O and C—H...N hydrogen bonds, forming a three-dimensional framework