Antioxidant and anti-inflammatory oxygenated meroterpenoids from the thalli of red seaweed Kappaphycus alvarezii

Three antioxidant and anti-inflammatory oxygenated meroterpenoids, 1-(3-methoxypropyl)-2-propylcyclohexane (C-13) (1), 3-(methoxymethyl)heptyl 3-(cyclohex-3-enyl) propanoate (C-18) (2), and 2-ethyl-6-(4-methoxy-2-((2-oxotetrahydro-2H-pyran-4-yl)methyl)butoxy)-6-oxohexyl 5-ethyloct-4-enoate (C-29) (3) were purified from the methanol:ethyl acetate fraction of red seaweed Kappaphycus alvarezii (family Solieriaceae) collected from the Gulf-of-Mannar on the southeast coast of peninsular India. The highly oxygenated C-29 meroterpenoid 3 displayed potential antioxidative activities (IC50 < 0.35 mg/mL) as evaluated by 2, 2'-azino-bis (3-ethylbenzothiazoline)-6-sulphonic acid and 1, 1-diphenyl-2-picryl-hydrazil free radical scavenging assays. The compound 3 displayed potential in vitro inhibitory activities towards pro-inflammatory 5-lipoxidase (IC50 1.04 mg/mL), which indicated its potential anti-inflammatory properties against inducible inflammatory mediators causing an inflammatory response. Structure-activity relationship analyses displayed the functional roles of lipophilic-hydrophobic characteristics and electronic parameter to determine its potential anti-inflammatory activity in terms of inhibiting inducible inflammatory cyclooxygenase and lipoxidase.