Synthesis and evaluation of the antioxidant, anti-tyrosinase and anti-browning activities of N-caffeoyl amino acid methyl esters

In order to develop novel anti-browning agents with both antioxidant and anti-tyrosinase properties, a series of N-caffeoyl amino acid methyl esters were designed and synthesized. Most of the synthesized compounds exhibited superior scavenging activities against DPPH radicals and ABTS cation radicals compared with caffeic acid and L-ascorbic acid. The kinetics analysis of radical scavenging for both DPPH and ABTS radicals by Ncaffeoyl phenylalanine methyl ester (3a) suggested that the scavenging processes may follow second-order reaction kinetics. Additionally, among the compounds prepared, N-caffeoyl cysteine methyl ester (3o) exhibited stronger inhibitory effect on tyrosinase than kojic acid and the inhibition type was mixed. Molecular docking studies further elucidated that compound 3o binds to tyrosinase with histidine residues in the active pocket. Antibrowning experiments confirmed that the browning rates of apple slices and apple juice treated with compound 3o were significantly reduced, showing a stronger anti-browning effect than kojic acid. In conclusion, compound 3o has potential applications as an anti-browning agent.