Synthesis of N-hydroxycinnamoyl amino acid ester analogues and their free radical scavenging and antioxidative activities

Hydroxycinnamic acids have a variety of biological activities, including antioxidant activity. To find more active antioxidants with hydroxycinnamoyl moiety, we synthesized a series of N-hydroxycinnamoyl amino acid esters and evaluated their antioxidative activities by 2,2-diphenyl-1-picryl hydrazyl (DPPH) radical scavenging and human red blood cells (RBCs) haemolysis methods. It was found that N-caffeoyl amides exhibited the highest DPPH-scavenging activities, whereas N-feruloyl amides demonstrated the highest antihaemolysis activities among the three different hydroxycinnamamides (caffeoyl, feruloyl, and p-coumaroyl), and that hydroxycinnamoyl amides were more effective than their corresponding free acid and ester compounds in both DPPH and RBC haemolysis tests.