Two new cassane-type diterpenes from Calliandra californica with antituberculosis and cytotoxic activities

From the root of Calliandra californica two new cassane-type diterpenes were isolated and characterized, escobarine A (1) and B (2), which showed promising activities against two Mycobacterium tuberculosis strains. The microplate alamar blue assay was used to determine the minimum inhibitory concentrations (MIC) of 1 and 2 against M. tuberculosis H37Rv and the resistant CIBIN/UMF15 : 099 strains. The MIC of 1 against the resistant M. tuberculosis strain showed a value 8 times lower than that of rifampin. The structures of the bioactive constituents were established by extensive NMR data analyses (including 1D and 2D NMR). The relative configuration of 2 was confirmed by X-ray analysis and the absolute configurations of 1 and 2 were determined by the circular dichroism method. Additionally, 1 and 2 displayed remarkable cytotoxic activity when evaluated against five human tumor cell lines.