First report of two new antioxidative meroterpeno 2H-pyranoids from short-necked yellow-foot clam Paphia malabarica (family: Veneridae) with bioactivity against pro-inflammatory cyclooxygenases and lipoxygenase

Abstract

Two new meroterpeno 2H-pyranoids were isolated from the EtOAc:MeOH extract of yellow-foot clam Paphia malabarica. The structures of these newly reported compounds were elucidated based on spectroscopic interpretations. This is the first report of biogenic 2H-pyrans bearing decadienyl and allyloxy-(isopentanyl)-cyclohexene skeletons from marine biota. The extended C₁₈ sesquiterpenoid with prenylated irregular farnesene framework was characterised as 2-((E)-deca-1,8-dien-10-yl)-11,12-dihydro-13-propyl-2H-pyran (1). The compound 2, 1′-((10E)-10-(10-(pentan-4-yl)-cyclohex-4-enyl)-allyloxy)-tetrahydro-2′,2′-dimethyl-2H-pyran represents the first example of naturally occurring C₂₁ prenylated bisabolene-type meroterpenoid, whereas tetrahydro-2′,2′-dimethyl-2H-pyran remains attached at C-2′ position of rearranged bisabolene framework formed by allyloxy linkage. The antioxidant activities (DPPH/ABTS⁺) of 1 and 2 were comparable (IC₅₀ < 1.0 mg/mL) with α-tocopherol. In addition, these compounds exhibited greater activity against cyclooxygenase-2 than COX-1, and the selectivity indices were significantly lesser (~1.1). No significant differences in anti-5-lipoxygenase activity of 1 and 2 (IC₅₀ 1.02–1.06 mg/mL) than ibuprofen (IC₅₀ 0.93 mg/mL) indicated the potential anti-inflammatory properties of title compounds.

Keywords:

• Paphia malabarica
• meroterpeno 2H-pyranoids
• antioxidative
• anti-inflammatory
• cyclooxygenases
• 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 of Central Marine Fisheries Research Institute for facilitating the research works. One of us, M.J. acknowledges Ministry of Earth Science for the award of a scholarship.