Ebelactone A is a β-lactone enzyme inhibitor that was first isolated from a cultured strain of soil actinomycetes. It can inhibit esterases, lipases, and N-formylmethionine aminopeptidases (IC50s = 0.056, 0.003, and 0.08 μg/ml, respectively) found on cell surfaces, which has been shown to stimulate host defense in immune cells. Ebelactone A is also reported to inhibit cutinases produced by fungal pathogens, thus demonstrating a plant-protective function.