Crotofolane‐ and Casbane‐Type Diterpenes from Croton argyrophyllus

Phytochemical analysis of Croton argyrophyllus led to the isolation of five new diterpenes named (5β,6β)‐5,6 : 13,16‐diepoxycrotofola‐4(9),10(18),13,15‐tetraen‐1‐one ( 1 ), (5β,6β)‐5,6 : 13,16‐diepoxy‐2‐epicrotofola‐4(9),10(18),13,15‐tetraen‐1‐one ( 2 ), (5β,6β)‐5,6 : 13,16‐diepoxy‐16‐hydroxy‐2‐epicrotofola‐4(9),10(18),13,15‐tetraen‐1‐one ( 3 ), (5β,6β)‐5,6 : 13,16‐diepoxy‐16‐hydroxy‐2‐epicrotofola‐4(9), 10(18),13,15‐tetraen‐1‐one ( 4 ) and (2E,5β,6E,12E)‐5‐hydroxycasba‐2,6,12‐trien‐4‐one ( 5 ), in addition to the known diterpenes crotonepetin and depressin, and acetylaleuritolic acid and spinasterol. The structures of the isolated compounds were established by a combination of spectroscopic methods, including HR‐ESI‐MS, 2D‐NMR, and X‐ray crystallography.