Novel hydroxypyridinone derivatives containing an oxime ether moiety: Synthesis, inhibition on mushroom tyrosinase and application in anti-browning of fresh-cut apples

A range of hydroxypyridinone derivatives were synthesized starting from kojic acid. Among them, 10 and 11 were found to possess the strongest inhibitory effect on monophenolase activity of mushroom tyrosinase, having IC 50 values of 2.04 and 1.60   μM, respectively. The IC 50 values of 10 and 11 for the inhibition of diphenolase activity of mushroom tyrosinase were determined as 13.89 and 7.99   μM, respectively. Investigation of the inhibitory mechanism of these two compounds indicated that the inhibition was reversible and of a competitive-uncompetitive mixed type. The K I and K IS values of 10 were determined to be 24.84 and 32.54   μM, respectively, and the corresponding values for 11 being 18.07 and 21.34   μM, respectively. The effect of 11 on the browning process of fresh-cut apples was evaluated by measuring the color change and browning index. The results indicated that 11 had a significant effect on controlling the browning of fresh-cut apple slices.