Biogenic guaianolide-type sesquiterpene lactones with antioxidative and anti-inflammatory properties from natural mangrove hybrid <i>Rhizophora annamalayana</i>

<p>Previously undescribed guaianolide-type sesquiterpene lactones were isolated from the chloroform fraction of the natural hybrid mangrove <i>Rhizophora annamalayana</i>, and were characterised as (<i>Z</i>)-3α,4,5,6-tetrahydro-5α-isobutyl-2β-(methoxymethyl)-7-methyl-3<i>H</i>-cyclohepta[b]carbolactone (<b>1</b>) and (7<i>Z</i>)-isopentyl 3α,4,5,6,7,8-hexahydro-2β-((<i>E</i>)-11-methylbut-10-enyl)-1-oxo-2<i>H</i>-cyclohepta[b]furan-6-carboxylate (<b>2</b>). Compound <b>2</b> displayed greater antioxidative activities {1, 1-diphenyl-2-picrylhydrazyl (DPPH) and 2, 2′-azino-bis-3 ethylbenzothiozoline-6-sulphonic acid diammonium salt (ABTS), IC₅₀ 0.65 and 0.62 mg/mL, respectively)} compared to <b>1</b> (IC₅₀ 0.83 and 1.14 mg/mL, respectively) (<i>p</i> < 0.05). Compound <b>2</b> recorded no significant difference in DPPH^. scavenging activities (IC₅₀ 0.65 mg/mL) compared to α-tocopherol (IC₅₀ 0.63 mg/mL). Pro-inflammatory 5-lipoxygenase inhibitory activity of <b>2</b> was found to be comparable (IC₅₀ 0.98 mg/mL) to that displayed by synthetic anti-inflammatory drug ibuprofen (IC₅₀ 0.93 mg/mL). Compound <b>2</b> showed significantly greater selectivity index (anti-cyclooxygenase-1/anti-cyclooxygenase-2 = 2.15) than non-steroidal anti-inflammatory ibuprofen (<0.5) (<i>p</i> < 0.05), and therefore, might be used as selective cyclooxygenase-2 inhibitor. The hitherto undescribed guaianolide lactones might be used as potential anti-inflammatory and antioxidative pharmacophore leads.