Structure of Alnustic Acid, a New Secodammarane-type Triterpenic Acid from Alnus sieboldiana

Abstract
A novel C31 3,4-secodammarane-type triterpenoid, alnustic acid, was isolated from the male flowers of Alnus sieboldiana Matsum. (Betulaceae). Its structure was elucidated to be (12R,20S)-12,20-dihydroxy-24-methylene-3,4-secodammar-4(28)-en-3-oic acid by a combination of chemical and spectroscopic methods.