Antioxidant constituents from the stems and fruits of Momordica charantia.

A new cucurbitane-type triterpene glycoside taiwacin A (1), a new 23,24,25,26,27-pentanorcucurbitane, taiwacin B (2) and a known cucurbitane-type triterpene glycoside (3), and a known steroid glycoside (4), were isolated from the stems and fruits of Momordica charantia, respectively. The structure of new compound was elucidated by spectroscopic methods. These four compounds, 1, 2, 3 and 4 revealed ABTS radical cation scavenging activity with an IC(50) values of 119.1±4.3, 204.5±1.2, 159.7±11.0 and 98.1±2.4μM, respectively. Compounds 1 and 3 displayed an inhibitory effect on xanthine oxidase (XO) activity with IC(50) values of 24.1±3.4 and 158.3±35.6μM, respectively. Compounds 2-4 significantly displayed O(2)(-) scavenging activity with an IC(50) values of 12.5±2.2, 16.5±0.1 and 27.3±1.4μM, respectively and the relative oxygen radical absorbance capacity (ORAC) values of 2 and 3, using ORAC-pyrogallol red (PGR) assay, were determined to be 0.88±0.02 and 0.55±0.09, respectively. These findings showed that 1-4 may be used as antioxidants.