Cucurbitane triterpenes from the fruiting bodies and cultivated mycelia of Leucopaxillus gentianeus

A reinvestigation of the fruiting bodies of the mushroom Leucopaxillus gentianeus, allowed the isolation of two minor cucurbitane triterpenes, namely, cucurbitacin D (5) and the new metabolite 16-deoxycucurbitacin B (6). The latter compound lacks an oxygenated substituent at C-16, an unprecedented structural feature among congeners of cucurbitacin B. The cucurbitanes present in the fruiting bodies were compared with those extracted from mycelia grown on the modified Melin-Norkans (MMN) culture medium. Cucurbitacins B (1) and D (5), as well as leucopaxillones A (3) and B (4), were isolated from both sources; in contrast, 16-deoxycucurbitacin B (6) and a mixture of fatty acid esters of cucurbitacin B (2) were absent in the mycelia. A new triterpene, 18-deoxyleucopaxillone A (7), was isolated from the mycelia, but was not detected in the fruiting bodies. The antiproliferative activity of the isolated triterpenes was determined against the NCI-H460 human tumor cell line, in comparison with the antitumor compound topotecan, a well-known topoisomerase I inhibitor.