Evaluation of N-alkyl isatins and indoles as acetylcholinesterase and butyrylcholinesterase inhibitors

Abstract

Two series of N-alkyl isatins and N-alkyl indoles varying in size of the alkyl group were synthesised and evaluated for inhibition of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Among the N-alkyl isatins 4a-j, the addition of the N-alkyl group improved inhibition potency towards AChE and BChE compared to isatin. Selectivity towards inhibition of BChE was observed, and the increase in size of the N-alkyl group positively correlated to improved inhibition potency. The most potent inhibitor for BChE was 4i (IC₅₀ = 3.77 µM, 22-fold selectivity for BChE over AChE). N-alkyl indoles 5a-j showed similar inhibition of AChE, the most potent being 5g (IC₅₀ = 35.0 µM), but 5a-j lost activity towards BChE. This suggests an important role of the 3-oxo group on isatin for BChE inhibition, and molecular docking of 4i with human BChE indicates a key hydrogen bond between this group and Ser198 and His438 of the BChE catalytic triad.

Graphical Abstract

Keywords:

• Isatin
• indole
• acetylcholinesterase
• butyrylcholinesterase

Acknowledgements

The authors thank Dr. Tatiana Laremore and Zilia Koshkina for help with HRMS sample preparation, data collection, and analysis.

Author contributions

TJE is responsible for conception and design of this study. All synthesised compounds were prepared by KNA. All enzyme inhibition assays were conducted by IAO. TJE performed molecular modelling and BBB preditions. MDP and TJE performed NMR analysis and wrote the initial draft of the manuscript. All authors assisted in the revision and final approval of the manuscript, and all authors agree to be accountable for all aspects of the work.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data that support the findings of this study are available from the corresponding author, TJE, upon reasonable request.

Additional information

Funding

This work was supported through Penn State Behrend Undergraduate Student Summer Research Fellowships for 2022 (KNA) and 2023 (IAO and MDP). The Bruker Avance 400 NMR Spectrometer used in this work was made possible by gifts from the Thomas Lord Charitable Trust and The Orris C. Hirtzel and Beatrice Dewey Hirtzel Memorial Foundation. Mass spectrometric analyses were performed at the Penn State Proteomics and Mass Spectrometry Core Facility, University Park, PA.