Purity >95%. Rapamycin is an immunosuppressant that is used primarily to prevent the rejection of organ and bone marrow transplant. It was first described as a potent inhibitor of IL-2 activation of lymphocytes (IC50 = 5 pM). It is now known that rapamycin specifically interacts with the cytosolic FK-binding protein 12 (FKBP12) to form a complex which inhibits the mammalian target of rapamycin (mTOR) pathway by directly binding to mTOR Complex 1 (mTORC1). Rapamycin and other inhibitors of mTORC1 signaling show potential in treating cancer, adipogenesis, diabetes, tuberous sclerosis, and cardiovascular disease.