Novel Derivatives of Salicylanilide: Synthesis, Characterization, PPO Inhibitory Activity and Cytotoxicity

Abstract Two series of novel salicylanilide analogues (4a-4g) and (4h-4t) were designed, synthesized, and characterized, especially the structure of compound 4q was further confirmed by single X-ray diffraction. The inhibitory activity on polyphenoloxidase (PPO) from the cephalothorax of Chinese white shrimp (Fenneropenaeus chinensis) was evaluated. The result indicated that all the synthesized derivatives (except 4g and 4t) exhibited moderate PPO inhibitory properties having IC50 values in the range of 0.21 ± 0.19 to 4.32 ± 0.53 mM, whereas reference inhibitor salicylic acid and 3a have IC50 values 3.93 ± 0.43 mM and 12.83 ± 0.51 mM, respectively. Specifically, 4-nitro-benzoic acid 3-(2-hydroxy-benzoylamino)- propyl ester (4q) exhibited the most potent PPO inhibitory activity with an IC50 value of 0.21 ± 0.19 mM. The kinetic studies of the compound (4q) demonstrated that the inhibitory effects of the compound on the PPO were belonging to competitive inhibitors. Meanwhile, the structure-activity relationship was discussed. Therefore, compound 4q could act as a PPO inhibitor with anti-browning and antimicrobial properties to be applied in the food industry.