Methods of Protection/Deprotection of Hydroxy Groups in the Synthesis of Polyhydroxy Flavonols

The article represents a review of methods for obtaining polyhydroxy flavonols without protection of hydroxy groups, as well as syntheses using methylation, alkylation and benzylation of the initial reagents and, accordingly, demethylation, dealkylation and debenzylation of the final flavonols. It is shown that the most convenient for the synthesis of natural polyhydroxy flavonols and their analogues is the debenzylation reaction using a Pd/C catalyst in tetrahydrofuran, which allows to obtain flavonols containing both hydroxy and methoxy groups. Syntheses using benzylation/debenzylation reactions are easily scaled up, which allows to obtain of large quantities of polyhydroxy flavonols, in addition, the latter do not contain impurities of hydrogen halides, which makes it possible to use the obtained flavonols in the pharmaceutical and food industries. The syntheses of hydroxy flavonols with a pyrogallol-like structure of the side phenyl ring were carried out, and the natural flavonol fisetin, a promising medicinal product and component of food additives, was obtained through benzylation/debenzylation reactions. effect of ensitrelvir are found in the 1-methyl-1H-1,2,4-triazole and 6-chloro-2-methyl-2H-indazole fragments.