Comprehensive Analysis of Secondary Metabolites in Usnea longissima (Lichenized Ascomycetes, Parmeliaceae) Using UPLC-ESI-QTOF-MS/MS and Pro-Apoptotic Activity of Barbatic Acid.

Considering the importance of ultra-performance liquid chromatography-electrospray ionization-quadrupole time of flight-tandem mass spectrometry (UPLC-ESI-QTOF-MS/MS) hyphenated techniques for analysis of secondary metabolites from crude extracts, the present study was aimed at identification of secondary metabolites in acetone extract of the lichen Usnea longissima. From our study, 19 compounds were tentatively identified through comparison of exact molecular masses from their MS/MS spectra, mass fragmentation studies and comparison with literature data. In addition, potent cytotoxic activity of U. longissima extract prompted us to isolate four compounds, 18R-hydroxy-dihydroalloprotolichesterinic acid (19), neuropogolic acid (20), barbatic acid (21), and usnic acid (22) from this extract which were adequately identified through mass spectrometry and NMR spectroscopy. All four compounds displayed cytotoxic activity. Barbatic acid (21) manifested doxorubicin equivalent activity against A549 lung cancer cell line with IC50 of 1.78 µM and strong G0/G1 accumulation of cells. Poly ADP-ribose polymerase (PARP) cleavage confirmed that it induced cytotoxic activity via apoptosis. Finally, our work has discerned the depside, barbatic acid (21) from crude extract as a candidate anti-cancer molecule, which induces cell death by stepping up apoptosis.

New cytotoxic spatane diterpenoids from marine alga Stoechospermum marginatum.

Three new spatane diterpenoids (1-3) were isolated from the brown alga Stoechospermum marginatum together with three known compounds (4-6). The structures of these compounds were determined by the detailed NMR spectroscopic and Mass spectrometric analyses. All the isolated compounds were screened for their cytotoxic potentials against a panel of four human cancer cell lines, which include DU145 (Prostate), B16F10 (Melanoma), MDA MB-231 (Breast), and HeLa (Cervical) along with a normal cell line (HEK). The screening results indicated that compounds 1, 4 and 5 displayed significant activities against B16F10 [IC50, 6.21 ± 0.14, 5.88 ± 0.21, 5.31 ± 0.24 µM] and MDA MB-231 [9.25 ± 0.61, 4.59 ± 0.14, 4.19 ± 0.13 µM] cell lines, respectively. In view of their significant activity, these compounds 1, 4 and 5 were further taken up for detailed fluorescence assays, scratch assay and flow cytometry analysis, which revealed that they diminished proliferation and arrested cell cycle in the S phase and G2/M phase, which induced cell death by apoptosis. Overall, based on their considerable results, these compounds could serve as lead molecules in the development of anticancer drug candidates.