New C31 Secodammarane-type Triterpenoids, Alnuseric Acid and Alniselide, in the Male Flowers of Alnus serrulatoides

Abstract
Two novel C31 3,4-secodammarane-type triterpenoids, alnuseric acid and alnuselide, were isolated from the male flowers of Alnus serrulatoides Call. (Betulaceae); their structures were elucidated to be (20S,24R)-20,24-epoxy-24-methyl-3,4-secodammar-4(28)-en-3-oic acid and (11R,2OS,24R)-20,24-epoxy-24-methyl-3,4-secodammar-4(28)-en-3,11α-olactone, respectively, by a combination of chemical and spectroscopic methods.