Isolation, Characterization and Antiproliferative Activity of New Metabolites from the South African Endemic Red Algal Species Laurencia alfredensis.

The marine red algae of the genus have been widely studied for their structurally diverse and biologically active secondary metabolites. We report here the natural product investigation of the organic extract of a newly identified South African endemic species, . A sequence of column chromatography, preparative TLC and normal phase HPLC resulted in the isolation of eleven compounds comprising three labdane-type diterpenes (-), four polyether triterpenes (-), three cholestane-type ecdysteroids (-) and a glycolipid (). Compounds -, - and have not previously been reported, while compound is reported here for the first time from a natural source and the known compound isolated for the first time from the genus . The structural elucidation and the relative configuration assignments of the compounds were accomplished by extensive use of 1D- and 2D-NMR, HR-ESI-MS, UV and IR spectroscopic techniques, while the absolute configuration of compound was determined by single-crystal X-ray diffraction analysis. All compounds were evaluated against the MDA-MB-231 breast and HeLa cervical cancer cell lines. Compound exhibited low micromolar antiproliferative activity (IC = 9.3 µM) against the triple negative breast carcinoma and compound was similarly active (IC = 8.8 µM) against the cervical cancer cell line.