Thirteen Novel Cycloartane-Type Triterpenes from <i>Combretum quadrangulare</i>

Thirteen novel cycloartane-type triterpenes were isolated from <i>Combretum quadrangulare</i>, a Vietnamese medicinal plant. The structures of the novel triterpenes were determined by spectroscopic methods as well as by chemical transformations. Among those compounds, quadrangularic acids F (<b>1</b>), G (<b>2</b>), and H (<b>4</b>) and 24-epiquadrangularic acid G (<b>3</b>) are the first examples of cycloartane-type triterpenes bearing carboxylic acid groups at both C-4 and C-20. Furthermore, norquadrangularic acid A (<b>13</b>) is the first example of a trinorcycloartane-type triterpene isolated from the genus <i>Combretum</i>.