Minor withanolides from Physalis philadelphica: structures, quinone reductase induction activities, and liquid chromatography (LC)-MS-MS investigation as artifacts.

As a result of a bioactivity-guided search for novel, plant-derived cancer chemopreventive agents, ixocarpalactone A (5) was isolated previously as a potent quinone reductase inducer from the leaves and stems of Physalis philadelphica. In the present study, this promising lead compound was reisolated in gram quantities for in vivo biological testing. During the course of this work, four additional minor new withanolides were also obtained and characterized, namely, 2,3-dihydro-3beta-methoxyixocarpalactone A (1), 2,3-dihydro-3beta-methoxyixocarpalactone B (2), 2,3-dihydroixocarpalactone B (3), and 4beta,7beta,20R-trihydroxy-1-oxowitha-2,5-dien-22,26-olide (4). However, compounds 1 and 2 were determined using liquid chromatography (LC)-MS-MS to be artifacts generated during the extraction and isolation procedure. Ixocarpalactone A was detected in the fresh fruits (tomatillos) of P. philadelphica by LC-MS-MS analysis at a concentration of 143+/-4.53 ppb.