Sesquiterpene lactones and inositol esters from Arnica angustifolia.

From flowerheads of Arnica angustifolia ssp. attenuata nine helenanolides, two 1,5- trans-guaianolides, and a mixture of inositol-tetraesters were isolated. Five of the helenanolides are described for the first time. One of them, 4- O-tigloylarnicalpin, is the first 7(12),6-trans-lactonized pseudoguaianolide isolated from a natural source. The occurrence of inositol esters within the genus Arnica has not been reported before.