title: Crystal structures of azathioprine dihydrate and 6-methylmercaptopurine trihydrate.
abstract: The crystal and molecular structures of 6-methylmercaptopurine trihydrate and of azathioprine dihydrate were determined by the use of three-dimensional, X-ray, diffractometer data and were refined by least squares. Both molecules crystallize in the N(9)-H tautomer form, in contrast to the N(7)-H tautomer form found in crystals of 6-mercaptopurine. Unlike 6-mercaptopurine, or other thiopurines that have unsubstituted thio groups, the sulfur atoms of 6-methylmercaptopurine and azathioprine do not act as hydrogen-bond acceptors in the crystal structures. These two derivatives of 6-mercaptopurine assume a conformation in which the substituents on the sulfur atom are directed away from the imidazole moiety of the purine.
mesh_terms: D001379:Azathioprine; D003461:Crystallography; D015122:Mercaptopurine / Q000031:analogs & derivatives*; D008697:Methane; D008961:Models, Structural; D008968:Molecular Conformation; D014961:X-Ray Diffraction
chemical_list: D015122:Mercaptopurine; D001379:Azathioprine; D008697:Methane