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.