Pentacyclic triterpenoids from the mangrove plant Rhizophora stylosa

Seven pentacyclic triterpenoids including 3-O-(E)-coumaroyl-15-hydroxy--amyrin (1), 15-hydroxy--amyrin (2), 3-taraxerol (3), 3-taraxerol formate (4), 3-taraxerol acetate (5), 3-O-(E)-coumaroyl-taraxerol (6), and 3-O-(Z)-coumaroyl-taraxerol (7) were isolated and identified from the stems and twigs of the mangrove plant Rhizophora stylosa. The structures of the isolated compounds were determined by extensive analysis of their spectroscopic data. Among these metabolites, compound 1 is a new oleanane-type triterpenoid coumaroyl ester, while compound 4 is a new natural product obtained here as an isolated substance for the first time. The full spectroscopic detail of compound 4 is also reported here for the first time.