Malbrancheamide, a new calmodulin inhibitor from the fungus Malbranchea aurantiaca

Malbrancheamide (1) is a novel indole alkaloid whose structure was unequivocally established by NMR, MS and X-ray studies. It caused moderate inhibition of radicle growth of Amaranthus hypochondriacus (IC50=0.37 μM) and inhibited the activation of the calmodulin (CaM)-dependent enzyme PDE1 (IC50=3.65±0.74 μM). The inhibition mechanism was competitive with respect to CaM according to a kinetic analysis (Ki=47.4±5.63 μM).