New Cytotoxic Laurene‐, Cuparene‐, and Laurokamurene‐Type Sesquiterpenes from the Red Alga Laurencia obtusa

Three new sesquiterpene alcohols, laur‐2‐ene‐3,12‐diol (1), cuparene‐3,12‐diol (2), and 8,11‐dihydro‐1‐methoxylaurokamuren‐12‐ol (3), along with one known diterpene, kahukuen‐10‐ol (4) have been isolated from the organic extract of the red alga Laurencia obtusa. The chemical structures were elucidated on the basis of spectroscopic analysis. The cytotoxicity of the isolated compounds were evaluated against three cancer cell lines, i.e., KB, HepG2, and MCF‐7. Compound 4 exhibited a wide range of cytotoxic activity against KB, HepG2, and MCF‐7 cell lines with IC50 of 0.100, 0.057, and 0.054 μm, respectively. In addition, 1 showed moderate activities towards KB and MCF‐7 cell lines with IC50 values of 0.171 and 0.184 μM, respectively and 2 exhibited a moderate activity against KB cell line at a concentration of 0.213 μg/ml. On the other hand, compound 3 exhibited no cytotoxic activity against any of the three cell lines.