Structure of 1-(S)-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine; an antiviral agent

4-Amino-1-(S)-[2-[(dihydroxyphosphoryl)-methoxy]-3-hydroxypropyl]- 2(1H)-pyrimidinone, C8H14N3O6P, Mr = 279.19, orthorhombic, P2(1)2(1)2(1), a = 6.926 (1), b = 9.084 (2), c = 18.602 (3) A, V = 1170.4 (4) A3, Z = 4, Dx = 1.58 (1) Mg m-3, lambda(Cu K alpha) = 1.54178 A, mu = 2.4 mm-1, F(000) = 584, T = 168 K, final R = 0.024 for 1393 unique observed reflections. The molecule has been found to exist in a folded zwitterionic form where the negatively charged phosphonyl group and the positively charged cytosine ring are in proximity. The crystal packing involves significant intermolecular hydrogen-bond contacts.