Identification of cytotoxic sesquiterpenes from Laurus nobilis L.
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A new sesquiterpene, lauroxepine and six known sesquiterpene lactones, were obtained through bioactivity-directed isolation from a methanol extract of the fruits of Laurus nobilis. The hexane-soluble part of the methanol extract yielded lauroxepine, costunolide and gazaniolide, while the dichloromethane- soluble part of the methanol extract afforded costunolide and four other sesquiterpene lactones including santamarine, reynosin, 11,13-dehydrosantonin and spirafolide. The new sesquiterpene lauroxepine and spirafolide have a rare molecular structure carrying an oxepine ring. Structures of the compounds were determined through 1D and 2D NMR and mass (EI-MS) techniques. The extracts were investigated for both ovarian cytotoxic activity and DNA damaging properties against three yeasts. Among the three tested extracts prepared from flowers, leaves and fruits of L. nobilis, the most cytotoxic active extract against ovarian cancer cell line was found to be the fruit extract with 98% inhibition. Among all tested extracts, only the fruit extract showed marginal inhibition (63.2%) against one DNA repair-deficient yeast strain (pRAD52 Gat). Six known sesquiterpene lactones were found to be highly cytotoxic against the A2780 ovarian cancer cell line, however, lauroxepine was not found to be active in A2780.