A potent inhibitor of certain serine/threonine protein phosphatases, targeting the multiple isoforms of PP1 (IC50 = 10-50 nM), both isoforms of PP2A (IC50 = 0.5 nM) and PP3 (IC50 = 4 nM); a very weak inhibitor of PP2B (IC50 > 2 μM); does not inhibit PP2C or other phosphatases