Crystal structure of 6-[(1-methyl-4-nitroimidazol-5-yl)thio] purine

6-[(l-methyl-4-nitroimidazol-5-yl)thio] purine, is an immunosuppressant derivative of the antitumour drug, 6-mercaptopurine. Crystals are monoclinic with a = 4.488(2), b = 31.886(4), c = 8.067(2)A and β= 105.99(2)° in the space group P2₁/c. The crystal structure was solved by direct methods using diffractometer data and refined by least squares to an R- index of 0.065 for 502 observed reflections. The molecule crystallizes in the N(9)-H tautomer form, in contrast to the N(7)-H tautomer form found in crystals of 6-mercaptopurine and assume a conformation in which the substituents on the sulphur atom are directed away from imidazole moiety of the purine