Cancer Chemopreventive Potential of Claoxylon longifolium Grown in Southern Thailand: A Bioassay-Guided Isolation of Vicenin 1 as the Active Compound and In Silico Studies on Related C-Glycosyl Flavones.

Claoxylon longifolium (Euphorbiaceae) is an indigenous vegetable that has been used in southern Thai traditional medicine and cuisine. A bioassay-guided approach was adopted to investigate the phytochemicals and chemopreventive potential of C. longifolium leaves and stems. Phytochemical investigation of the active MeOH fractions afforded six known compounds, including caffeic acid (1), isovitexin (2), and vicenins 1-3 (3-5) from leaves and hexadecanoic acid methyl ester (6) from stems. Their structures were determined by spectroscopic means. Ten constituents were tentatively identified from the oily fractions of stems by GC-MS. Non-cytotoxic concentrations of compounds 1-6 were identified using the MTT cell viability assay. The ability of compounds 1-6 at non-cytotoxic concentrations to induce Nrf2 activation, correlating to their potential chemopreventive properties, was determined using a luciferase reporter assay in the AREc32 cell line. Only vicenin 1 (3) was considered to be a potent chemopreventive compound, as it increased luciferase activity by 2.3-fold. In silico studies on compounds 2-5 and vitexin (16) revealed the potential of these compounds as cancer chemopreventive and chemotherapeutic agents. This study provides the first report on the chemopreventive properties of C. longifolium. All identified and isolated compounds are reported here for the first time from this species.