Roseic Acid and Roseolactones A and B, Furan-Cucurbitane Triterpenes fromRussula auroraandR. minutula(Basidiomycota)

Three new seco-cucurbitane triterpenes, viz. roseic acid (1) and roseolactones A (2) and B (3), all bearing a furan moiety condensed to the B-ring, were isolated from Russula aurora and R. minutula. Their structures were elucidated using 1D and 2D NMR spectroscopy, and ESI HRMS. Compounds 2 and 3 were found to be epimers at C-23. A detailed ab initio theoretical investigation was carried out to assess their rela- tive stereochemistries. The conformations and NMR spectra of the two isomers were calculated, and the results were compared to the experimental data. The new compounds show a bright pink reaction with sulfo-vanillin at room tem- perature, and they are therefore responsible for the systemat- ically significant reaction performed by mycologists on R. aurora and R. minutula fruiting bodies. A mixture of com- pounds 2 and 3 was found to be weakly active against HepG2, WISH, and CAKI-1 human tumour cells.