Potent calcineurin (protein phosphatase 2B) inhibitor that requires FK 506-binding protein 12 (FKBP12) for activity (IC50 = 3 nM). Inhibits secretion of IL-1, IL-2 (IC50 = 1 nM), IL-3, IL-4, IL-6 (IC50 = 35 nM), GM-CSF, TNFα (IC50 = 10 nM), IFNγ and Myc from activated T-cells in vitro. Exhibits potent immunosuppressive, neuroprotective and anticonvulsant activity in vivo. Analog (ascomycin, Cat. No. 4210) also available.