Cucurbitane triterpenoids from Leucopaxillus gentianeus.
In addition to the known bioactive triterpene cucurbitacin B (1), two new cucurbitane triterpenoids, namely, leucopaxillones A (3) and B (4), exhibiting a new oxygenation pattern among cucurbitacins, have been isolated from the mushroom Leucopaxillus gentianeus (syn. L. amarus). Cucurbitacin B (1) imparts a bitter taste to the flesh of the fungus; however, it occurs in the fruiting bodies mainly esterified as tasteless fatty acid esters 2a-c. In vitro growth inhibitory effects of compounds 1-4 on proliferation of four different human tumor cell lines (A549, CAKI-1, HepG2, MCF-7) were evaluated by using a 1-day MTT assay. Only cucurbitacin B was highly active on all lines. Free cucurbitacin B is presumed to be formed in vivo by an enzyme-mediated scission of esters 2a-c, thus constituting a chemical weapon that protects the mushrooms against parasites and predators. Compounds 1-4 are structurally different from the other few cucurbitacins isolated from Basidiomycetes, being, instead, more similar to those occurring in plants. In particular, cucurbitacin B (1) seems to represent an interesting example of secondary metabolite convergence between distant taxa such as fungi and vascular plants, where they likely exert a similar role of protection. The structures of the compounds were established by means of spectroscopic methods and X-ray diffraction on a single crystal. The absolute configuration of leucopaxillone A has been assigned on the basis of CD chirality rules.
Clericuzio
Marco
M
Dipartimento di Chimica Generale ed Organica Applicata, Università di Torino, Via P. Giuria 7, 10125 Torino, Italy. marco.clericuzio@unito.it
Mella
Mariella
M
Vita-Finzi
Paola
P
Zema
Michele
M
Vidari
Giovanni
G
D000363:Agaricales / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004354:Drug Screening Assays, Antitumor; D006801:Humans; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D014315:Triterpenes / Q000737:chemistry* / Q000302:isolation & purification* / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D014315:Triterpenes; C495045:leucopaxillone A; C495046:leucopaxillone B; C041246:cucurbitacin B