Mechanistic insight into the free radical scavenging and xanthine oxidase (XO) inhibitor potent of monoacetylphloroglucinols (MAPGs)

Abstract

Three novel antioxidant candidates based on phenolic polyketide, monoacetylphloroglucinol (MAPG), a natural antibiotic compound produced by plant growth-promoting rhizobacteria (PGPR), Pseudomonas fluorescens F113 have been proposed. Initially, a green and highly efficient route to the synthesis of MAPG and its two analogues from phloroglucinol (PG) has been developed. Afterward, their rational mechanism of antioxidant activity has been investigated based on thermodynamic descriptors involved in the double (/) radical trapping processes. These calculations have been performed using the systematic density functional theory (DFT) method at the B3LYP/Def2-SVP level of theory in the gas phase and aqueous solution. Our findings reveal that the double formal hydrogen atom transfer (df-HAT) mechanism is preferred in the gas phase, while the double sequential proton loss electron transfer (dSPLET) mechanism is preferred in aqueous solution for all MAPGs. The 6–OH group represents the most favorable site for trapping radical species for all MAPGs, which is supported by the pKa values obtained from DFT calculations. The role of acyl substituents on the PG ring has been comprehensively discussed. The presence of acyl substituents has a strong influence on the thermodynamic parameters of the phenolic O–H bond in PG. These results are supported by frontier molecular orbitals (FMOs) analysis, where the addition of acyl substituents increases the chemical reactivity of MAPGs significantly. Based on molecular docking and molecular dynamic simulations (MDs), MAPGs are also predicted to be promising candidates for xanthine oxidase (XO) inhibition. Highlights The antioxidant activity of the three synthesized monoacetylphloroglucinols (MAPGs) has been investigated using the density functional theory (DFT) method. Acyl substituents increase the chemical reactivity and antioxidant activity of MAPGs. Double formal hydrogen atom transfer (df-HAT) is the preferred mechanism in the gas phase. Double sequential proton loss electron transfer (dSPLET) seems to be more favored in aqueous solution. MAPGs are expected to be promising xanthine oxidase (XO) inhibitors.