A new phenyl alkyl ester and a new combretin triterpene derivative from Combretum fragrans F. Hoffm (Combretaceae) and antiproliferative activity

This work concerns the isolation and structure elucidation of compounds obtained from the extract of leaves and stem bark of Combretum fragrans F. Hoffm. Both extracts and some isolated compounds were tested for antiproliferative activity on glioblastoma (U87MG and C6 cells) and prostate (PC-3 cells) cancer cell lines using XTT (2,3-bis[2-methoxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxyanilide inner salt) assay. The dichloromethane/methanol (1:1) extract of the leaves led to the isolation of two new compounds such as fragransinate (1) and combretin C (2), alongside five known compounds such as combretin A (3), belamcanidin (4), cirsilineol (5), velutin (6), and a mixture of β-sitosterol-3-O-β-d-glucopyranoside (10a) and stigmasterol-3-O-β-d-glucopyranoside (10b), whereas the methanol extract of the stem bark led to the isolation of three known compounds betulinic acid (7), bellericagenin B (8), and a mixture of β-sitosterol (9a) and stigmasterol (9b). The structure of compounds was elucidated by nuclear magnetic resonance and mass spectrometry data. The methanol extract of the stem bark showed a powerful antiproliferative activity on all tested cells, as well as the extract of leaves which also showed important cytotoxicity effect. Compound (3) showed good antiproliferative activity particularly on U87MG and PC-3 cells, whereas compound (5) exhibits moderated activity. Compounds (2) and (8) were not active on all tested cells.