Rapamycin (Rapa, or Sirolimus) is a new form of macrolide immunosuppressive agent. It is a white solid crystal. Its melting point is 183-185ºC and it is lipophilic. It is soluble in methanol, ethanol, acetone, chloroform, and other organic solvents, very slightly soluble in water, and almost insoluble in ether. It was first discovered in 1975 on the Chilean Easter Island as a secondary metabolite secreted by soil Streptomyces, and its chemical structure is that of a three-polyene macrolide compound. Rapamycin is a new form of immunosuppressive agent with good curative effects, low toxicity, and no nephrotoxicity. It can be used to maintain the immunity of transplant organs (especially in kidney transplants) to alleviate immunological rejections after organ transplant surgeries. The latest research has shown that Rapamycin can also be used to treat Alzheimer's. When used on afflicted lab rats, it had a memory-restoring effect. Rapamycin oral tablets can be taken with grapefruit juice to treat melanoma (a type of benign tumor common among Western populations), dramatically increase other chemotherapy drugs' anticancer effects, and extend patient survival. Rapamycin is a mammalian target of rapamycin (mTOR) targeting inhibitor, which can treat tumors that are related to this pathway including kidney cancer, lymphoma, lung cancer, liver cancer, breast cancer, neuroendocrine carcinoma, gastric cancer, etc. Its curative effects are especially strong for the rare diseases LAM (lymphangiomyomatosis) and TSC (tuberous sclerosis).