N, N, N-triethyl Ammonium L-Phenylalanine Esters as Potential Antimicrobial Agents

Quaternary ammonium compounds are an important class of molecules with wide variety of applications, mainly in the antimicrobial field. Quaternary ammonium compounds have the ability to bind with the anionic moiety of phospholipids of the bacterial membrane, disrupting the cell membrane of the microorganisms.  However, classical quaternary ammonium salts can have adverse effects on the environment. Therefore the use of amino acid analogues are preferred as raw materials for their synthesis. In this study, quaternary ammonium salts, namely N, N, N-triethyl ammonium  L-Phenylalanine esters were synthesised by tethering the amino end with ethyl groups. The ease of quaternisation with increasing ester chain length of the amino acid was studied. The yields of the quaternary ammonium compounds were found to decrease with increasing alkyl chain of the phenylalanine esters (35% - 6%). The antibacterial activity of the quaternary ammonium compounds were compared to that of the unquaternised phenylalanine ester using the Kirby-Bauer disk diffusion method against  gram positive (B.cereus ATTC 11778, S.aureus ATCC 29213) and gram negative bacteria (S. typhimurium ATCC 14028, P.aeroginosa ATTC 27853). The quaternised ammonium esters were found to be better potential antibacterial agents as compared to the unquaternised esters.