Biogenic antioxidative and anti-inflammatory aryl polyketides from the venerid bivalve clam Paphia malabarica

Chemical investigation of ethyl acetate-methanol extract of the venerid bivalve clam Paphia malabarica led to isolation of three unprecedented aryl polyketide derivatives, characterized as (E)-12-(17-ethyl-tetrahydro-16-hydroxy-15-(methyl pentanoate)-14-oxo-2H-pyran-13-yl)-9-methyl-but-11-enyl benzoate (1), isobutyl-13-(6-(benzoyloxy)-10-methylpentyl)-tetrahydro-13-methyl-2H-pyran-17-carboxylate (2) and (13-(methoxycarbonyl)-11-((E)-18-ethylhexa-16,19-dienyl)-12-propyl-cyclohex-10-enyl)-methyl-3-hydroxy benzoate (3). The structures of the polyketides were assigned by extensive spectroscopic experiments. Compound 1 displayed comparatively greater 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical quenching potential (50% inhibitory concentration, IC50 ∼0.59 mg/mL) than commercially available α-tocopherol (IC50 0.63 mg/mL). Potential pro-inflammatory 5-lipoxygenase (5-LOX) inhibition potential (IC50 0.76-0.92 mg/mL) of the polyketides in consonant with significantly greater anti-inflammatory selectivity indices (anti-cyclooxygense-1IC50/anti-cyclooxygense-2IC50 > 1) than non-steroidal anti-inflammatory agent ibuprofen (0.44) described the safety profile of the title compounds. Putative biosynthetic route by means of polyketide synthatase biocatalyzed pathways unambiguously established the structural assignments of the previously undescribed polyketide analogues. The potential of hitherto undescribed polyketides from P. malabarica as natural antioxidative and anti-inflammatory functional food ingredients was demonstrated in the present study.