Antibacterial and antioxidant aryl-enclosed macrocyclic polyketide from intertidal macroalgae associated heterotrophic bacterium Shewanella algae

Abstract

Previously unreported aryl-enclosed 12-membered macrocyclic polyketide characterised as 2′-[(8-ethyl-8-methyl-2,5-dioxo-1-oxacyclododecanyl)methoxy]-methyl benzoate, was identified from the organic extract of Shewanella algae, a heterotrophic gamma proteobacterium, isolated from an intertidal marine macroalgae Hypnea valentiae. The titled macrocyclic polyketide displayed potential antibacterial activity (minimum inhibitory concentration 3.75 µg/mL) compared to that exhibited by chloramphenicol (6.25 µg/mL). Potent antioxidant activity of the studied compound was characterised by its greater scavenging effects on 2,2-diphenyl-1-picrylhydrazyl radical and 2,2′-azino-bis-3-ethylbenzothiozoline-6-sulfonic acid (IC50 0.59 and 0.53 mg/mL, respectively) compared with standard, α-tocopherol (IC50 > 0.65 mg/mL). In silico molecular docking studies of the polyketide with the penicillin binding protein active sites encoded in methicillin resistant Staphylococcus aureus core genome displayed lesser binding energy of −10.31 kcal/mol, which could be correlated with its in vitro antibacterial activities. Structure-activity correlation studies demonstrated the direct relationship of electronic and optimum hydrophobic properties of the macrocyclic polyketide with its bioactivities. Therefore, the presently studied aryl-enclosed macrocyclic compound could be utilised as potent antioxidant and antibacterial pharmacophore in the medicinal formulations.