Cycloartane Triterpenes Isolated from Combretum quadrangulare in a Screening Program for Death-Receptor Expression Enhancing Activity

In our screening program for natural products that increase DR5 (death-receptor 5) expression, nine new cycloartane triterpenes, combretanones A-G (1-7), combretic acid A (8), and combretic acid B (9), were isolated from a MeOH extract of Combretum quadrangulare leaves. The known oleanane triterpenes (10, 11) and six known flavonols (12-17) were also isolated. The structures of 1-9 were elucidated by spectroscopic studies. Compounds 7, 9, 12, 16, and 17 enhanced DRS expression, and 16 showed TRAIL-resistance abrogating activity.