Metaproterenol and isoproterenol are bronchodilators that provide a structural basis for many other bronchodilators currently in use. One of these structurally related bronchodilators is terbutaline; it is administered as a prodrug, bambuterol, and is metabolized (bioconverted) into terbutaline by butyrylcholinesterase (BChE). The metabolism rate can be affected by BChE gene polymorphism in the human population and BChE stereoselectivity. The aim of our study was to investigate inhibition of human BChE and acetylcholinesterase (AChE) with metaproterenol, isoproterenol, and newly synthesized racemic bisdimethylcarbamate derivatives of metaproterenol (metacarb) and isoproterenol (isocarb) and their (R)-enantiomers to see if their bioconversion is affected by BChE inhibition in the same way as that for bambuterol. Metacarb and isocarb proved to be selective BChE inhibitors, as they progressively inhibited AChE 960 to 80 times more slowly than BChE(UU). All studied cholinesterases displayed poor affinity for metaproterenol and isoproterenol, yet BChE(UU) had an affinity about five times higher than that of AChE.

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We investigated the influence of bronchodilating β2-agonists on the activity of human acetylcholinesterase (AChE) and usual, atypical and fluoride-resistant butyrylcholinesterase (BChE). We determined the inhibition potency of racemate and enantiomers of fenoterol as a resorcinol derivative, isoetharine and epinephrine as catechol derivatives and salbutamol and salmeterol as saligenin derivatives. All of the tested compounds reversibly inhibited cholinesterases with K constants ranging from 9.4 μM to 6.4 mM and had the highest inhibition potency towards usual BChE, but generally none of the cholinesterases displayed any stereoselectivity. Kinetic and docking results revealed that the inhibition potency of the studied compounds could be related to the size of the hydroxyaminoethyl chain on the benzene ring. The additional π-π interaction of salmeterol's benzene ring and Trp286 and hydrogen bond with His447 probably enhanced inhibition by salmeterol which was singled out as the most potent inhibitor of all the cholinesterases.

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