The search for the new selective and efficient inhibitors of carboxylesterases is a fairly topical issue [1–4]. The enzymes of serine esterase subclass including acetylcholinesterase, butyrylcholinesterase, cholesterol esterase, and others on top of carboxylesterase have a similar structure of the active center [5, 6]. Consequently, a single compound can potentially inhibit all the enzymes of this subclass. Therefore, research on serine esterase inhibitors should always take into account the selectivity issue. Using the selective inhibitors of serine esterases should allow preferential modulation of metabolism of esterified xenobiotics including drugs.

The data on inhibitory activity of dimethyl and diethyl phosphorylated flavonoids towards three serine esterases have been published earlier [7, 8]. This work aimed to establish the correlation between the increase of hydrophobicity of the substituents at the phosphate group and the activity as well as selectivity of the final compounds. Chrysin was selected as the starting flavonoid due to high inhibitory activity and selectivity of its diethyl phosphorylated derivative [7].