Study on the synthesis and biological activity of kojic acid–piperazine derivatives

Abstract

Tyrosinase inhibitors have potential applications in pharmaceutical and cosmetic products, and also in the food industry. This study aimed to discover novel tyrosinase inhibitors with high inhibitory activity and low toxicity. A series of kojic acid–piperazine derivatives were designed and synthesized, and their biological activities, including anti-tyrosinase, antioxidant, and anti-browning effects, were investigated. Several compounds exhibited significant tyrosinase inhibitory activity. Among them, compound 3o showed the strongest activity, with an IC₅₀ value of 0.21 µM, which was significantly lower than that of the positive control, kojic acid. The mechanism of tyrosinase inhibition was further investigated using compound 3o. Kinetic studies indicated that it acts as a competitive inhibitor (K_i = 0.209 µM, K_is = 0.93 µM). Fluorescence quenching experiments confirmed a dynamic quenching mode. Furthermore, molecular docking and FT-IR studies revealed that compound 3o binds to the CO and N–H bonds of tyrosinase. Specifically, its kojic acid fragment interacts with the copper ion active site and adjacent amino acid residues, while the piperazine ring fragment forms π–π interactions with other residues. Additionally, compound 3o demonstrated notable anti-browning and antioxidant activities, exhibited low cytotoxicity. In conclusion, these findings highlight compound 3o as a highly promising candidate, providing a valuable molecular framework for developing novel, efficient, and safe tyrosinase inhibitors with potent antioxidant and anti-browning capabilities.