Novel Tirucallane‐Type Triterpenoids from Aphanamixis grandifolia

Phytochemical investigation on the stem bark of Aphanamixis grandifolia afforded five novel tirucallane‐type triterpenoids, (13 α ,14 β ,17 α ,23 Z )‐25‐methoxy‐21,23‐epoxylanosta‐7,20(22),23‐triene‐3,21‐dione ( 1 ), (13 α ,14 β ,17 α ,23 Z )‐21,23‐epoxylanosta‐7,20(22),23,25‐tetraene‐3,21‐dione ( 2 ), (3 R ,5 R , 9 R ,10 R ,13 S ,14 S ,17 S )‐17‐{(2 R ,3 S ,5 R )‐5‐[(2 S )‐3,3‐dimethyloxiran‐2‐yl]‐2,3,4,5‐tetrahydro‐2,5‐dimethoxyfuran‐3‐yl}‐4,4,10,13,14‐pentamethyl‐2,3,4,5,6,9,10,11,12,13,14,15,16,17‐tetradecahydro‐1 H ‐cyclopenta[ a ]phenanthren‐3‐ol ( 3 ), (5 R ,9 R ,10 R ,13 S ,14 S ,17 S )‐17‐{(2 R ,3 S ,5 R )‐5‐[(2 S )‐3,3‐dimethyloxiran‐2‐yl]‐2,5‐dimethoxytetrahydrofuran‐3‐yl}‐1,2,4,5,6,9,10,11,12,13,14,15,16,17‐tetradecahydro‐4,4,10,13,14‐pentamethyl‐3 H ‐cyclopenta[ a ]phenanthren‐3‐one ( 4 ), and (3 α ,13 α ,14 β ,17 α ,20 S ,23 R )‐23‐ethoxy‐3‐hydroxy‐21,23‐epoxylanost‐7‐en‐24‐one ( 5 ). The 1 H‐ and 13 C‐NMR spectra of all compounds were fully assigned using a combination of 2D‐NMR experiments, including HSQC, HMBC, and ROESY sequences. The structure of 1 with the absolute configuration was determined by ECD calculation. Compounds 3 and 4 showed moderate activities against human MCF‐7 and HeLa cancer cells.