engleski

Interactions of chiral quinuclidin-3-yl benzoates with butyrylcholinesterase: kinetic study and docking simulations

We have synthesized both enantiomers of quinuclidin-3-yl benzoate (RQBz and SQBz) in order to examine the stereoselectivity of the hydrolysis of these esters catalyzed by horse serum butyrylcholinesterase (BChE). The hydrolysis of benzoylcholine (BzCh) was also studied in order to determine the influence of the alcohol part of the esters upon the kinetics. The kcat for the substrates decreased in order: BzCh>RQBz (4-fold slower)>>SQBz (76-fold slower reaction). KM values determined for quinuclidinium substrates revealed that the binding affinity of RQBz (0.28 mM) is approximately 2-fold lower than that of SQBz (0.13 mM) toward BChE. From the ratio of the enantiomeric kcat/KM values, an enantiomeric excess of 78 % was calculated indicating that the resolution of racemic quinuclidin-3-yl benzoate can be achieved by the hydrolysis with BChE. The orientations of all studied benzoate esters and butyrylcholine (BuCh) in the active site of human BChE have been proposed by flexible ligand docking with AutoDock 3.0. Analyses of the obtained Michaelis complexes revealed that there are numerous similar close contacts in the active site. The main difference in binding of quinuclidinium and choline esters was found in the ammonium electrostatic region which includes cation-p interaction of the ammonium moiety of substrates with the indole ring of Trp84. The important cation-p interaction with Trp84 was lowest in the case of (S)-enantiomer of QBz and that might be the main explanation for the slowest rate of hydrolysis of that compound.

(R) and (S) quinuclidin-3-yl benzoates; butyrylcholinesterase; kinetics of hydrolysis; benzoylcholine; butyrylcholine; docking study

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