Biological evaluations of novel vitamin C esters as mushroom tyrosinase inhibitors and antioxidants

The inhibitory effects of vitamin C esters I and 2 on the diphenolase activity of mushroom tyrosinase have been studied. The results showed that compounds I and 2 inhibited tyrosinase with IC50 values of 0.58 and 0.16 mM, respectively. The dose-response curves demonstrated that compounds I and 2 not only lengthened the lag time, but also decreased the steady-state rate. The kinetic analyses showed that the inhibition by compound 2 was reversible and its mechanism was mixed type, which was different from compound 1 (irreversible inhibitor). Furthermore, the antioxidant activities of these compounds against hydroxyl radical scavenging, superoxide anion radical scavenging, and DPPH radical scavenging were also investigated. Compounds I and 2 exhibited potential antioxidant activities. In particular, compound 2 was found to be the most effective antioxidant, more potent than the well-known antioxidants vitamin C and TBHQ. (C) 2009 Published by Elsevier Ltd.