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

Abstract

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-$1_{{\text{IC}}_{50}}$/anti-cycloxygense-$2_{{\text{IC}}_{50}}$ ~ 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).

Keywords:

• Red seaweed
• Gracilaria opuntia
• highly oxygenated 2H-chromen
• antioxidative
• anti-inflammatory
• cyclooxygenase, lipoxygenase

Acknowledgements

The authors thank the Director, Central Marine Fisheries Research Institute, for his guidance and support. Thanks are due to the Head, Marine Biotechnology Division, Central Marine Fisheries Research Institute for facilitating the research activity. One of us, F.M. acknowledges Department of Science and Technology, for the award of fellowship.