A ring-cleaved sesquiterpene, named seco-laurokamurone, four laurane-type sesquiterpenes, laurepoxyene, 3β-hydroperoxyaplysin, 3α-hydroperoxy-3-epiaplysin, and 8,10-dibromoisoaplysin, one laurokamurane-type sesquiterpene, laurokamurene D, and one bisabolane-type sesquiterpene, (5S)-5-acetoxy-β-bisabolene, have been isolated from a re-collection of the red alga Laurencia okamurai Yamada, together with six other known sesquiterpenes. Their structures, including relative configuration, were elucidated by detailed analysis of spectroscopic data, and by comparison with data for related known compounds. In addition, on the basis of chemical conversions, degradation results, and biogenetic considerations, the absolute configurations of several of these compounds were also tentatively proposed. seco-Laurokamurone possesses an unprecedented carbon skeleton, formed from an oxidative cleavage of the laurokamurane skeleton, and laurokamurene D represents the fourth example of a laurokamurane-type sesquiterpene from a natural source. The in vitro antifungal activity of many of these compounds was evaluated against four fungi (Cryptococcus neoformans, Candida glabrata, Trichophyton rubrum, and Aspergillus fumigatus), as well as assessing cytotoxicity against HL-60 and A-549 human cancer cell lines. The compounds studied displayed moderate activities, relative to controls.
Keywords: Antifungal activity; Bisabolane sesquiterpene; Cytotoxicity; Laurane sesquiterpene; Laurencia; Laurencia okamurai; Laurokamurane sesquiterpene; Rhodomelaceae; seco-Laurokamurane sesquiterpene.
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