Abstract: Phytochemical investigation on the stems of Trigonostemon howii resulted in the isolation of four degraded diterpenoids.A new compound,trigohowilone A (1), was defined as the enantiomer of trigoxyphin P based on the analyses of its spectroscopic data including NMR,MS,and the specific rotation data.The structures of known compounds were identified as trigoxyphin Q (2),trigohowilol H (revised trivial name) (3),and 9-O-demethyltrigonostemone (4). All compounds were obtained from the plant for the first time.

Key words: Euphorbiaceae, Trigonostemon howii, degraded diterpenoids, trigohowilone A, (-)-trigoxyphin P