Purity >98% by NMR. Rapamycin is a clinically useful immunosuppressant. Inhibits the response to interleukin-2 blocking activation of T- and B-cells. Rapamycin forms a complex with cytosolic FK-binding protein 12 (FKB12) that binds to mTOR Complex1(mTORC1) inhibiting the mammalian target of rapamycin (mTOR). Rapamycin also binds to mTORC2 leading to decreased glucose tolerance and insensitivity to insulin. Induces autophagy.