Studies On The Synthesis Of Resorcinol Derivatives And Their Antienzymatic Browning Effects

Browning is one of important factors which cause the loss of fruits and vegetables. Application of tyrosinase inhibitors is one of the common methods used to control enzymatic browning. Tyrosinase is the key enzyme in the synthesis of melanin in animals and human beings, and its activity is closely related to the browning of fruits, vegetables, the skin hyperpigmentation. Chalcones are abundant in fruits, vegetables, spices, tea and soy based food stuff and traditional herbal medicine. Their derivatives have attracted much interest in recent years because of their variety of biological activities such as antityrosinase, antimicrobial, anticancer and antioxidants. It is reported that 2,4 dihydroxy substituted resorcinol structure is an activity group for the high tyrosinase inhibition. So in this study, we synthetized series of chalcone and its derivatives and studied their antienzymatic browning effects.First of all, The reaction conditions such as the catalysts, solvents, and the reaction time were optimized to ensure the best reaction condition. 2,4,2’,4’-tetrahydroxychalcone and its two derivatives inluding 1,3,5-tris-(2,4-dihydroxy-phenyl)-pentane-1,5-dione(new compound) and 7,2’,4’-trihydroxyflavonone were synthetized through one-pot green procedure catalyzed by boric acid in polyethylene glycol 400. The synthetic compounds were purified by column chromatography on silica gel and preparative HPLC, identified by HPLC-ESI-MS and NMR spectral. Changing the position, number of the substituent group and the reaction time, fourteen chalcones and its derivative were got including four new compounds which have never been reported. The four new compounds contained two 1,5-dions, a triarylmethane and a 2- ethanone derivative. Tyrosinase inhibitory activity of the fourteen compouds were tested, the results showed that ten compouds showed high inhibition activities almost 3~1800-fold stronger than kojic acid. Three chalcones including 2,4,2’,4’-tetrahydroxychalcone, 2,2’,4-trihydroxychalcone and 2,4,4’-trihydroxychalcone showed the strongest tyrosinase inhibitory activity with IC50=0.027~0.029 μmol/L。In order to improve the application of synthetic compounds in the food system, The antienzymatic browning effects on fruits and vegetables of the synthetic compounds were examed. The results of antienzymatic browning experiments on the fresh-cut lotus root slices showed that 1,3,5-tris-(2,4-dihydroxy- phenyl)-pentane-1,5-dione exhibited best antibrowning effect even better than 4-HR which was a well-known tyrosinase inhibitor. Fresh-cut lotus root slices treated with 0.01% 1,3,5-tris-(2,4-dihydroxy- phenyl)-pentane-1,5-dione + 0.5% Vc could maintain the colour in 12 h in room temperature. The results of the antibrowning test on apple slices showed 0.01% 2,4,2’,4’-tetrahydroxychalcone+0.5% Vc could protect the colour in 12 h. In the apple juice experiment, the 7,2’,4’-trihydroxyflavonone, Vc, 4-HR, 4-HR + Vc, 7,2’,4’-trihydroxyflavonone + Vc were added in the juice respectively, the results showed that 7,2’,4’-trihydroxyflavonone + Vc showed great antibrowning effect and the colour of the juice could remain unchanged in 24 h.It was reported that most of the chalcones equiped with high antioxidants, so the antioxidant capacity of the synthetic compounds were tested. From the results, it can be seen that hydroxychalcone and its derivatives exhibited great antioxidant activities, while methoxy substituted chalcones showed weak antioxidant activities. Further investigated relationship between tyrosinase inhibition and antioxidant activity and the results revealed that DPPH?、ABTS+? showed significantly negative correlation with the tyrosinase inhibition. However, FRAP was independent of the tyrosinase inhibitory effect.