7-(5-Methyl-sulfanyl-ß-d-erythrofuran-osyl)-7H-pyrrolo-[2,3-d]pyrimidin-4-amine monohydrate (MT-tubercidin·H(2)O).

The title compound, C(12)H(16)N(4)O(3)S·H(2)O, which has potential as a possible anti-malarial drug, was studied when small deviations in melting points, for two differently aged preparations, were observed. The unexpected existence of a water mol-ecule of crystallization is considered to be the cause of this variation. The 7H-pyrrolo-[2,3-d]pyrimidine unit is very slightly puckered with a total puckering amplitude of 0.035 (2) Å; its mean plane makes an angle of 88.40 (12)° with the mean plane through the ribofuranosyl unit. In the crystal, the mol-ecules are bound by strong O-H⋯N and N-H⋯O hydrogen bonds, utilizing all available protons and linking mainly through the water of crystallization.