Antimicrobial and Radical Scavenging Activities of N-Hydroxycinnamoyl L-Cysteine and - L-Proline Ethyl Esters

Hydroxycinnamic acids are widely distributed in the plant kingdom secondary metabolites, found also as simple derivatives including amides, esters, and glycosides. These acids and their derivatives are known to possess antibacterial, antiviral, anti-inflammatory, antioxidative, antiproliferative, immunostimulatory and neuroprotective properties. The aim of the present work was the synthesis of new hydroxycinnamoyl amides of the (L)-cysteine and (L)-proline and evaluation of their radical scavenging and antimicrobial activity. The structures of the synthesized analogues were characterized by UV, H-1 NMR, C-13 NMR, ESI-MS. The compounds were screened for their antibacterial (against Staphylococcus aureus 209, Streptococcus pyogenes 10535, Bacillus subtilis 1A95, Listeria monocytogenes C12) and antifungal (against Candida albicans 62) activities. All amides demonstrated the most potent activity against Streptococcus pyogenes, even higher in comparison with the free hydroxycinnamic acids. The ability of hydroxycinnamoyl amides to interact with 1, 1-diphenyl-2-picryl-hydrazyl (DPPH) stable free radical in vitro was also evaluated. The results obtained showed that the radical scavenging activity of the sinapoyl-and caffeoyl amides of L-cysteine is superior to the standards ferulic acid, eugenol and isoeugenol.