Cytotoxic activity of compounds from the lichen: Cladonia convoluta.

The depsidone 9'-( O-methyl)protocetraric acid was isolated from the lichen Cladonia convoluta (Lam.) Anders along with the known (-)-usnic acid and fumarprotocetraric acid. The complete structure of 9'-( O-methyl)protocetraric acid was elucidated using HSQC and HMBC spectral data. (-)-Usnic acid was the only compound to display a moderate cytotoxic activity on various cancer cell lines (IC (50) = 6, 12.1, 15.8, 17.8, 8.2 and 6.8 microg/mL on L1210, 3LL, DU145, MCF7, K-562 and U251, respectively). This compound was also shown to induce apoptosis of murine leukaemia L1210 cells in a dose- and time-dependent manner.