Thirteen novel cycloartane-type triterpenes from Combretum quadrangulare

Thirteen novel cycloartane-type triterpenes were isolated from Combretum qu adrangulare, a Vietnamese medicinal plant. The structures of the novel trit erpenes were determined by spectroscopic methods as well as by chemical tra nsformations. Among those compounds, quadrangularic acids F (1), G (2), and H (4) and 24-epiquadrangularic acid G (3) are the first examples of cycloa rtane-type triterpenes bearing carboxylic acid groups at both C-4 and C-20. Furthermore, norquadrangularic acid A (13) is the first example of a trino rcycloartane-type triterpene isolated from the genus Combretum.