ИСТИНА

Dihydroquercetin (taxifolin, DHQ) belongs to natural flavonoids and has a wide range of pharmacological effects, in particular antioxidant, angioprotective, hepatoprotective, antitumor and others. Furthermore, DHQ also shows regulatory properties and can control DNA reparation, apoptosis, and mitochondrial biogenesis, as well as it can regulate the activity of certain enzymes. It is known that many flavonoids including DHQ decompose rather quickly in vivo while their relatively high molecular weight derivatives have a longer lifespan. These data show promise for the synthesis of novel DHQ derivatives. In this work a new method for dihydroquercitin oxidative polymerization has been proposed. Multicopper oxidases, namely, bilirubin oxidase (BOD) from Myrothecium verrucaria and laccase (LC) from the basidial fungus Trametes hirsuta were used as catalysts. The conditions selected enabled good yields of DHQ oligomers, which were then analyzed using UV-vis, FTIR, 1Н and 13С NMR spectroscopy. DHQ oligomers synthesized using both enzymes demonstrated higher thermostability as compared with the monomer. Depending on the enzyme used, the products of DHQ polymerization differed in physico-chemical properties, and as shown by NMR studies, had different structures. To estimate antioxidant properties the DHQ oligomers were tested for their DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging activity. The significant increase of antioxidant activity (more than 2.5 times) was observed for BOD synthesized DHQ oligomers in comparison with antioxidant activity of DHQ monomer. In order to improve the efficiency of DHQ polymerization process a fungal laccase (LC) was immobilized in hydrophobic ionic liquid (IL). It was found that the enzyme included into IL can be reused. The physicochemical characteristics of DHQ oligomers synthesized using LC/IL did not differ from the characteristics of the oligomers obtained with native laccase. Comparative study of the antioxidant activity of monomer and DHQ oligomers was conducted on dog kidney cell culture (MDCK 1). 2'7'-dihlorofluorestsein diacetate (DHFD) was applied to detect free radicals. It was found that the DHQ oligomers obtained by enzymatic synthesis with immobilized into IL laccases also possess stronger antioxidant properties as compared with the monomer.