A natural resorcylic lactone derived from fungi that selectively inhibits purified TAK1 (IC50 = 8.1 nM when co-expressed with the TAK1-binding protein, TAB1); irreversibly blocks IL-1-induced activation of TAK1, NF-κB, and JNK/p38 (IC50s = 65-83 nM) and sensitizes cells to TRAIL- and TNF-α-induced apoptosis in vitro.