Characteristic odoriferous compounds of brown algae: Syntheses of possible oxidation products of (6Z, 9Z, 12Z, 15Z)-1,6,9,12,15-heneicosapentaene and (6Z, 9Z, 12Z, 15Z, 18Z)-1,6,9,12,15,18-heneicosahexaene

Chemical Defense against Herbivory in the Brown Marine Macroalga Padina gymnospora Could Be Attributed to a New Hydrocarbon Compound

Brown marine macroalga Padina gymnospora (Phaeophyceae, Ochrophyta) produces both secondary metabolites (phlorotannins) and precipitate calcium carbonate (CaCO₃-aragonite) on its surface as potential defensive strategies against herbivory. Here, we have evaluated the effect of natural concentrations of organic extracts (dichloromethane-DI; ethyl acetate-EA and methanol-ME, and three isolated fractions) and mineralized tissues of P. gymnospora as chemical and physical resistance, respectively, against the sea urchin Lytechinus variegatus through experimental laboratory feeding bioassays. Fatty acids (FA), glycolipids (GLY), phlorotannins (PH) and hydrocarbons (HC) were also characterized and/or quantified in extracts and fractions from P. gymnospora using nuclear magnetic resonance (NMR) and gas chromatography (GC) coupled to mass spectrometry (CG/MS) or GC coupled to flame ionization detector (FID) and chemical analysis. Our results showed that chemicals from the EA extract of P. gymnospora were significantly important in reducing consumption by L. variegatus, but the CaCO₃ did not act as a physical protection against consumption by this sea urchin. An enriched fraction containing 76% of the new hydrocarbon 5Z,8Z,11Z,14Z-heneicosatetraene exhibited a significant defensive property, while other chemicals found in minor amounts, such as GLY, PH, saturated and monounsaturated FAs and CaCO₃ did not interfere with the susceptibility of P. gymnospora to L. variegatus consumption. We suggest that the unsaturation of the 5Z,8Z,11Z,14Z-heneicosatetraene from P. gymnospora is probably an important structural characteristic responsible for the defensive property verified against the sea urchin.

Characteristic Aroma Components from Dried "Wakame" Undaria pinnatifida

An essential oil from dried "wakame" (Undaria pinnatifida), prepared by a simultaneous distillation extraction method, was analyzed by GC-MS, indicating the presence of one major component of volatiles. The volatile component was identified as (6Z,9Z,12Z,15Z,18Z)-1,6,9,12,15,18-henicosahexaene by comparison with the GC-MS and NMR spectra of synthetic. The henicosahexaene showed a subtly marine aroma. (6Z,9Z,12Z,15Z)-1,6,9,12,15-Henicosapentaene was also detected as a minor polyene in the essential oils. It was suggested that these polyenes contribute to the characteristic aroma of the dried wakame.

Lipoxygenase inhibitors derived from marine macroalgae

The solvent extracts from the algae Sargassum thunbergii (Sargassaceae) and Odonthalia corymbifera (Rhodomelaceae) were subjected to soybean lipoxygenase inhibitory screening. Two hydrophobic inhibitors were obtained from the extracts of S. thunbergii through inhibitory assay-guided fractionation. The inhibitors were identified as known exo-methylenic alkapolyenes (6Z,9Z,12Z,15Z)-1,6,9,12,15-henicosapentaene (1) and (6Z,9Z,12Z,15Z,18Z)-1,6,9,12,15,18-henicosahexaene (2). The alkapolyenes 1 and 2 showed higher inhibitory activity than the known inhibitor nordihydroguaiaretic acid (NDGA). Pheophytin a (3) was obtained from the extract of O. corymbifera. The inhibitor 3 also showed higher inhibitory activity than NDGA. This is the first report on lipoxygenase inhibition of exo-methylenic alkapolyenes and a chlorophyll a-related substance.