A novel cadinane sesquiterpene with a propan-2-ylidene, named (1R,4R,6S,10R)-1-hydroxy-7(11)-cadinen-5,8-dione (1), and a new sesquiterpene, named (2R,6R,7S,9S)-1(10),4-cadinadiene-2,9-diol (2), were isolated from the ethanol extract of the rhizome of Acorus calamus L. Their structures were elucidated on the basis of spectroscopic data including NMR spectroscopy and X-ray crystallography. The absolute configurations of compounds 1 and 2 were confirmed by comparison of their experimental optical rotations with those obtained from theoretical calculations at the B3LYP/6-311+G (d) level of theory.
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