A new epicatechin gallate and calpain inhibitory activity from Orostachys japonicus

Calpains are calcium-dependent proteases that cleave a variety of intracellular substrates. The overactivation of μ-calpain is associated with a wide range of disease conditions. To search for calpain inhibitors from natural products, the phytochemical constituents of the ethyl acetate fraction of the whole plant of Orostachys japonicus (Crassulaceae) were studied. The various chromatographic separation of this fraction led to the isolation of a new tannin, (−)-epicatechin 5-gallate (1) along with 9 known compounds. Their structures were elucidated by spectroscopic and chemical analyses. Among them, (−)-epicatechin 5-gallate (1) and kaempferol (9) exhibited moderate inhibitory activity against μ-calpain with IC50 values of 18.0 ± 2.9 and 15.4 ± 2.0 µg/ml, respectively.