Synthesis and antimicrobial evaluation of gallate esters

Parabens are esters of p-hydroxybenzoates that are commonly found in everyday consumer products as well as pharmaceuticals. They are often used in commercial products to prevent bacterial growth as well as to provide extended shelf life, but have been shown to activate estrogen receptors in vivo, a contributing factor in human breast cancer proliferation. Our lab has previously generated a multitude of paraben derivatives that do not mimic estrogen. Many of these derivatives have other safety concerns, but gallate esters appear to have the least hazardous properties. The oestrogenic and antimicrobial properties of the gallate ester family are not currently understood; therefore, our lab set out to synthesize the non-commercially available gallate esters through Fischer esterification. Both synthesized and commercial gallate esters (methyl through dodecyl esters) were subsequently screened by serial dilution for the minimum inhibitory concentration (MIC) against Staphylococcus epidermidis and Serratia marcescens as representatives of Gram-positive and Gram-negative bacteria respectively. Our results indicate that increasing alkyl chain length improves the MIC against Gram-positive bacteria, with dodecyl gallate being the most effective antimicrobial agent at 32 µg/mL. These observed MIC values were improved relative to commercially available amoxicillin and erythromycin (no inhibition observed). Both compounds of interest and known antimicrobial agents were ineffective against Gram-negative bacterial growth. Additionally, the results of this study can be used to further evaluate the effectiveness of paraben ester derivatives in prevention of cancer cell development as well as antimicrobial agents.