Highly oxygenated antioxidative 2H-chromen derivative from the red seaweed Gracilaria opuntia with pro-inflammatory cyclooxygenase and lipoxygenase inhibitory properties

Phytochemical investigation of the thalli of ethyl acetate-methanol extract of the red seaweed Gracilaria opuntia led to isolation of a substituted 2H-chromen derivative of unusual structure possessing highly oxygenated carbon skeleton, characterised as 2-acetoxy-2-(5- acetoxy-4-methyl-2-oxotetrahydro-2H-pyran-4-yl)ethyl 4-(3-methoxy- 2-(methoxymethyl)-7-methyl-3,4,4a,7,8,8a-hexahydro-2H-chromen-4- yloxy)-5-methylheptanoate, which have not been reported in nature. The chemical structure was resolved by detailed spectroscopic analysis. The anti-inflammatory activity of the newly reported metabolite was determined by pro-inflammatory cyclooxygenase and 5-lipoxygenase inhibitory assays. The anti-inflammatory selectivity index of the title compound recorded greater value (SI: anti-cycloxygense-1IC50 /anti-cycloxygense-2IC50 ~ 1.26) than synthetic NSAIDs (aspirin and ibuprofen, SI: 0.02 and 0.44, respectively), and consequently, appeared to be safer. The antioxidative activity of the title compound was significantly greater as determined by 2, 2-diphenyl-1-picrylhydrazyl and 2, 2′-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) radical scavenging activities (IC50 0.26–0.32 mg/mL) compared to α-tocopherol (IC50 > 0.6 mg/mL), and was comparable to the synthetic antioxidants butylated hydroxytoluene and butylated hydroxyanisole (IC50 ~ 0.25–0.34 mg/mL)