Originally identified as an antitumor antibiotic from Streptomyces pulveraceous. Displays potent inhibition of protein phosphatase types 2A (PP2A) and 4 (PP4) with IC50 values of 1.5 nM and 3 nM respectively. Also exhibits weaker inhibition of topoisomerase II (IC50 = 40 μM) and protein phosphatase type 1 (PP1) (IC50 = 131 μM) with no apparent inhibition of protein phosphatase type 2B (PP2B). Active in vivo.