Planarity and Constraint of the Carbonyl Groups in 1,2-Diones Are Determinants for Selective Inhibition of Human Carboxylesterase 1

Carboxylesterases (CE) are ubiquitous enzymes responsible for the detoxification of xenobiotics, including
numerous clinically used drugs. Therefore, the selective inhibition of these proteins may prove useful in
modulating drug half-life and bioavailability. Recently, we identified 1,2-diones as potent inhibitors of CEs,
although little selectivity was observed in the inhibition of either human liver CE (hCE1) or human intestinal
CE (hiCE). In this paper, we have further examined the inhibitory properties of ethane-1,2-diones toward
these proteins and determined that, when the carbonyl oxygen atoms are cis-coplanar, the compounds
demonstrate specificity for hCE1. Conversely, when the dione oxygen atoms are not planar (or are trans-coplanar), the compounds are more potent at hiCE inhibition. These properties have been validated in over
40 1,2-diones that demonstrate inhibitory activity toward at least one of these enzymes. Statistical analysis
of the results confirms the correlation (P < 0.001) between the dione dihedral angle and the preferential
inhibition of either hiCE or hCE1. Overall, the results presented here define the parameters necessary for
small molecule inhibition of human CEs.