Salicornolides A-C from Gracilaria salicornia attenuate pro-inflammatory 5-lipoxygense: Prospective natural anti-inflammatory leads

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Three macrolides bearing the carbon framework of oxabicyclo[21.3.1]heptacosa-ene-diones (A and B) and oxabicyclo[19.3.1]pentacosa-ene-dione (C) were isolated and characterised from the organic extract of the intertidal red seaweed Gracilaria salicornia (family Gracilariaceae), which were named as salicornolides A-C. These natural macrolides were conformationally pre-organised ring structure providing diverse functionalities, and their potential bioactive properties led to the development of pharmacophores with anti-inflammatory properties. The 21-membered pyran-enclosed salicornolide B displayed greater cyclooxygenase-2 (IC50 COX-2 1.13 mM) inhibitory activity than those exhibited by the 21-membered aryl salicornolide A and 19-membered salicornolide C (IC50 COX-2–1.2 mM). The attenuating potential of the studied compounds against pro-inflammatory enzyme, 5-lipoxygenase (IC50 LOX < 1.5 mM) was significantly greater than that displayed by the non-steroidal anti-inflammatory ibuprofen (IC50 4.5 mM), whereas the selectivity indices exhibited by salicornolides against cyclooxygenase-2 was significantly higher (1.18–1.41, P < 0.05) when compared to that of ibuprofen (SI 0.43) attributing the greater selectivity profile of the former towards inducible pro-inflammatory mediators than the latter. The minimal binding energy of salicornolide B (−9.64 kcal mol−1), a greater number of hydrogen-bonds and lesser inhibitory constant (Ki 85.15 nM) might be responsible for effective binding towards 5-lipoxygenase, and that could attribute its greater anti-inflammation potential than those displayed by other compounds. The putative biosynthetic cascade initiated by malonate-acyl carrier protein unambiguously confirmed the structural attributions of the titled macrocyclic lactones. The undescribed salicornolides A-C from seaweed Gracilaria salicornia attenuating pro-inflammatory 5-lipoxygense might be considered as prospective natural anti-inflammatory leads for pharmaceutical applications.