“… 19 Perhaps this is due to the partial blocking of metabolically sensitive centres by halogen atoms, which is widely used in drug design 20–22 Previously, we synthesised series of fluorinated and chlorinated analogs of t -AUCB derivative 1b and diureas 2 , 13 , 14 namely compounds 9 , 10 , 11a–i , 12a–g and 12i. 23 , 24 Given the remarkable microsomal stability and inhibitory efficiency of compounds 3а , b we proposed to carry out the primary bioscreening of the series 9 , 10 , 11a–i , 12a–g and 12i . In this communication, we present results of biotesting, which showed an unexpectedly sharp increase in inhibitory activity of some compounds to picomolar concentration range.…”