240: Synthesis and biochemical evaluation of isatin derivatives and analogs as acetylcholinesterase and butyrylcholinesterase inhibitors

Abstract: Low level of acetylcholine in the brain is a well-known pathological hallmark of Alzheimer’s disease (AD). Due to this, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) are drug targets for AD. Isatin is a naturally occurring heterocycle that demonstrates a diverse range of biological properties, including acetylcholinesterase (AChE) inhibition. In addition, isatin is readily available, inexpensive, and amenable to synthetic modification, including N-alkylation, 3-oxo addition, and aromatic substitution. The long-term goal of my lab is to explore the inhibitory potential of isatin derivatives and analogs against these enzymes, primarily by targeting the dual-binding sites present in both AChE and BChE. To date, we have synthesized series of methylene-linked bis-isatins, bis-3-indolyl-3-hydroxy-2-oxindoles, and isatin-4,4-dimethyl-5-methylene-4,5-dihydrothiazole-2-thiols (IT2Ts). Bis-isatins and bis-3-indolyl-3-hydroxy-2-oxindoles showed selective inhibition of BChE over AChE. Pentamethylene-linked bis-isatin and bis-3-indolyl-2-hydroxy-2-oxindole showed a BChE IC50 of 7.56 µM and 4.49 µM, respectively. Docking images showed that the molecules adopted an interesting U-shaped orientation in the BChE active site. Subsequent studies explored the structure-activity relationship around the aromatic rings of these selective compounds. 7-Chloro-bis-isatin showed a BChE IC50 1.74 µM and an AChE IC50 of 1.33 µM, indicating that the chloro substituent resulted in loss of selectivity. Docking images obtained for the 7-chloro-bis-isatin with TcAChE and hBChE showed hydrogen bonding and π-π stacking interactions at the active sites of AChE and BChE. Several new series of derivatives resulting from 3-oxo substitution have also shown comparable inhibition, indicating modification at this position is well-tolerated. However, isatin analogs, such as benzoxazolone and benzimidazolinone, have shown mixed results. The propylene-linked inhibitor of the IT2T series outperformed rivastigmine and was comparable to galantamine, both clinically used AChE inhibitors, with a low micromolar AChE IC50, and additional results indicated this series showed significant selectivity for BChE over AChE. The full results of these studies will be presented, along with ongoing studies investigating neurotoxicity and the ability of selected compounds to function as radical scavengers and chelate metals ions, all of which would also be relevant for AD.