Deep eutectic solvents (DESs) are an alternative to traditional organic solvents for enzymatic reactions between compounds with poor solubility. DESs have a number of advantages over organic solvents: nontoxicity, nonflammability, biodegradability, etc. They are considered “green” solvents. In this work, we have demonstrated the possibility of using betaine–glycerol DES as a cosolvent for the effective laccase-catalyzed polymerization of the flavonoids dihydroquercetin (DHQ, taxifolin) and (+)-catechin (CC). We have studied the effects of several betain based DESs on the catalytic activity and stability of laccase from the basidial fungus Trametes hirsuta and performed enzymatic polymerization of the flavonoids in a DES–buffer mixture containing 60 vol.% of betaine-glycerol DES (molar ratio 1:2). The use of the laccase redox mediator TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) enabled an increased yield of DHQ oligomers (oligoDHQ), with a number average molecular weight of 1800 g/mol and a polydispersity index of 1.09. The structure of the synthesized product was studied using different physicochemical methods. NMR spectroscopy showed that oligoDHQ had a linear structure with an average chain length of 6 monomers. A scheme for enzymatic polymerization of DHQ in a DES–buffer mixture was proposed. Biocatalytic polymerization of the flavonoid (+)-catechin (CC) was carried out with T. hirsuta fungal laccase in a DES–buffer mixture. The conditions for the synthesis of catechin oligomers (oligoCCs) soluble in organic solvents have been selected. It has been shown that as a result of polymerization of CC in a DES-buffer mixture, two products are formed with an average molecular weight of 10620 and 2540 g/mol and polydispersity indices of 1.1 and 1.09, respectively. The degree of polymerization of the resulting products was 24 and 6, respectively. The physicochemical properties of the obtained oligomers were studied via UV-visible, FTIR, NMR spectroscopy. The synthesized oligoCCs efficiently inhibited the α-glucosidase activity (IC50 ~ 8 μg/mL) and may be promising substances for the treatment of type-2 diabetes mellitus.

Conflicts of Interest:
The authors declare that they have no conflict of interest in the publication of this article. The authors have no conflicts of interest to report in this work. Abstract was not submitted elsewhere and published here firstly.

Funding:
This study was supported in part by Lomonosov MSU Reg. Theme 121041500039-8.