Phytochemical investigation of the methanolic extract of Plumena acutifolia (Apocynaceae) leaves has led to the isolation and identification by spectroscopic means of a new monoterpene alkaloid, (R)-4′-{(S)-1- hydroxyethyl)-5,6-dihydro-5′H-spiro[cyclopenta[c]pyridine-7,2′ -furan}-5′-one, for which the name plumerianine was adopted, the iridoid 15-demethylplumeride, and three known triterpenes, i.e., lupeol, uvaol and ursolic acid.