Shearinines D–K, new indole triterpenoids from an endophytic Penicillium sp. (strain HKI0459) with blocking activity on large-conductance calcium-activated potassium channels

A chemical examination of the endophytic fungus Penicillium sp. isolated from the mangrove plant Aegiceras corniculatum resulted in the isolation and characterization of eight new indole triterpenes named shearinines D–K (1–8), along with shearinine A (9), paspalitrem A (10), and paspaline (11). Their stereostructures were determined by extensive spectroscopic data analyses and quantum chemical circular dichroism calculations. The biosynthetic relationship of all 11 alkaloids is suggested. Shearinines D (1), E (2), and (with reduced potency) G (4) exhibit significant in vitro blocking activity on large-conductance calcium-activated potassium channels.