In the course of screening of natural products for Ca2+-blocking activity in the rat thoracic aorta, the extract of Boenninghausenia albiflora var. japonica was found to have such activity. The extract was further fractionated by column chromatography to identify the active constituents. The active principle was identified as a coumarin derivative, chalepensin. In addition, the inhibitory effects of coumarin related compounds, such as coumarin, umbelliferone, 7-isopentenyloxycoumarin, aurapten, esculin, esculetin, esculetin 6, 7-dimethyl ether, decursin, psoralen, bergapten, xanthotoxin and imperatorin were examined. Decursin and imperatorin showed inhibitory effects similarly to that of chalepensin and two orders of magnitude less active than verapamil.
