Selective butyrylcholinesterase inhibition by isatin dimers and 3-indolyl-3-hydroxy-2-oxindole dimers

Polymethylene-linked isatin dimers 1a-g and 3-indolyl-3-hydroxy-2-oxindole dimers 2a-g were synthesized and are reported here as selective butyrylcholinesterase (BChE) inhibitors. The best compound from each series, 1f and 2d, showed IC₅₀ values of 3.20 µM and 4.49 µM, respectively. Both compounds showed > 11-fold selectivity towards BChE, and mixed-type inhibition by Lineweaver-Burk analysis. These two inhibitors shared π-π stacking interactions with Trp82 and H-bonding to Gly116 and Ser198, the catalytic Ser of the enzyme triad, within the BChE active site as predicted by molecular docking. Compound 1d was also shown to be good inhibitor with an IC₅₀ of 7.56 µM, and it shares the same pentamethylene linker as 2d. Inhibitors 1d, 1f, and 2d were predicted to have moderate, low, and moderate blood-brain barrier (BBB) permeability, respectively, making them, overall, promising lead compounds for further exploration of selective BChE inhibitors.