A new sesquiterpene, named neo-acorane A (1), and two known ones, acoric acid (2) and calamusin D (3), were isolated from a 95% ethanol extract of the rhizome parts of Acorus calamus L. Their structures were elucidated by spectroscopic methods, and the absolute configurations were determined by single-crystal X-ray diffraction analysis. Compounds 1 and 2 are nonisoprenoid sesquiterpenoids, likely biosynthesized from an acorane-type sesquiterpene by oxidative fission of the six-or five-membered ring. Moreover, compounds 1 (10 mu M), 2 (5 mu M and 10 mu M) and 3 (10 ...
