Chemical constituents of Eugenia ancorifera Amshoff (Myrtaceae): Semisynthetic derivatives and their chemotaxonomic significance

Eugenia ancorifera Amshoff (Myrtaceae) is an endemic African species whose chemical constituents have not been investigated previously. Chemical investigation of the leaves, twigs and stem bark led to the isolation of sixteen compounds, including eight pentacyclic triterpenoids ( 1 – 8 ), three phytosterols ( 9 , 11 ), three steroidal glycosides ( 10 , 12 ), one flavonol glycoside ( 13 ), one xanthone ( 14 ), one sugar ( 15 ) and one glycerol derivative ( 16 ). Their structures were elucidated by MS and NMR spectroscopic data and by comparison of these data with those previously reported in the literature. Among them, pentacyclic triterpenoids of the ursane, oleanane and lupane series were the predominant constituents of the species. In addition, rotundic acid ( 2 ) was used as a scaffold for the preparation of two undescribed semisynthetic derivatives ( 2a and 2b ) through nucleophilic substitution with 5-(bromomethyl)-3-phenylisoxazole. This first phytochemical study of E. ancorifera revealed a chemical profile dominated by ursane-, oleanane-, and lupane-type pentacyclic triterpenoids, which represent characteristic chemophenetic markers of the genus Eugenia . In particular, α-amyrin ( 1 ), rotundic acid ( 2 ), oleanolic acid ( 3 ), lupeol ( 4 ), betulin ( 5 ), betulinic acid ( 7 ), and pyracrenic acid ( 8 ) were identified among the major triterpenoid constituents.