Synthesis, Antioxidant and Antimicrobial Evaluation of Simple Aromatic Esters of Ferulic Acid

Aromatic ester derivatives of ferulic acid where the phenolic hydroxyl is free (6a-d) or acetylated (5a-d) were evaluated for their antioxidant and antimicrobial properties. The superoxide radical scavenging capacity of compounds 5d and 6d-e (IC50 of 0.19, 0.27 and 0.20 mM, respectively) was found to be twice as active as a-tocopherol (IC50 = 0.51 mM). DPPH radical scavenging capacity was moderate and only found in compounds bearing free phenolic hydroxyl groups (6a-e). With regard to antimicrobial properties, compounds 6b and 6c displayed significant activity against Enterococcus faecalis (MICs = 16 mu g/mL) and vancomycin-resistant E. faecalis (MIC for 6b, 32 and for 6c, 16 mu g/mL). Compound 6c also demonstrated prominent activity against planktonic Staphylococcus aureus with a MIC value of <8 mu g/mL and it inhibited bacterial biofilm formation by S. aureus with a MBEC value of <8 mu g/mL, which was 64 and 128 times more potent than ofloxacin and vancomycin, respectively.