azathioprine

6-(1-Methyl-4-nitro-5-imidazolyl)thiopurine; a derivative of 6-mercaptopurine, used as a cytotoxic and immunosuppressive agent in organ transplantation and in the treatment of autoimmune diseases such as hemolytic anemias, systemic lupus erythematosus, rheumatoid arthritis and leukemias.