Cytotoxic prenylated xanthone derivatives from the twigs of <i>Garcinia cowa</i>

A new prenylated xanthone, kaennacowanol D (<b>1</b>), was isolated from the twigs of <i>Garcinia cowa</i> together with 22 known analogs. The structure of the new metabolite was elucidated by extensive spectroscopic analysis, particularly using HRMS and NMR. Kaennacowanol D is the first example of a natural xanthone containing a levulinyl group incorporated at the terminal prenyl unit <i>via</i> ester bond. Cytotoxic evaluation of the isolated compounds on human cancer cells showed that jacareubin (<b>13</b>), 2-prenylisojacareubin (<b>17</b>), nigrolineaxanthone E (<b>23</b>) were significantly active against KB and Hela S3 cell lines with IC₅₀ values ranging from 1.78 to 9.52 µM, while <b>17</b> and <b>23</b> also suppressed the growth of MCF-7, Hep G2, and HT-29 cells with IC₅₀ values lower than 10 µM.