About

Johan’s masters research focused on the application of quantum merchanical modelling methodologies to better understand the reaction mechanisms behind nucleophilic displacements of alpha-halogenated ketones which had proved challenging in the synthetic lab. Thereafter, he undertook his doctoral studies with a focus on the development of improved molecular docking models for the identification of novel anticholinergic species for the treatment of the symptoms associated with Alzheimer’s disease. Research highlights included development of a model for highthrough put virtual screening of anti-cholinergic agents which displayed imporved enrichment and was used to drive the screening of a commercial compound library composed of 20’000 compounds leading to the identification of several active scaffolds. Finally as a post-doctoral research fellow Johan developed dashboards for controlling and integrating different flow reactors and analytical equipment which he utilised to perform closed-loop optimisations of reactions under flow conditions.

Thesis

Combining in silico and in vitro approaches to discover novel inhibitors of acetylcholinesterase

Dissertation

Nucleophilic reactions of α-haloketones: A computational study.

Publications

3. Discovery of Novel Acetylcholinesterase Inhibitors by Virtual Screening, In Vitro Screening, and Molecular Dynamics Simulations

C. Johan van der Westhuizen, Andre’ Stander, Jenny-Lee Panayides and Darren L. Riley, 2022https://doi.org/10.1021/acs.jcim.1c01443

Alzheimer’s disease is the most common neurodegenerative disease and currently poses a significant socioeconomic problem. This study describes the uses of computer-aided drug discovery techniques to identify novel inhibitors of acetylcholinesterase, a target for Alzheimer’s disease. High-throughput virtual screening was employed to predict potential inhibitors of acetylcholinesterase. Validation of enrichment was performed with the DUD-E data set, showing that an ensemble of binding pocket conformations is critical when a diverse set of ligands are being screened. A total of 720 compounds were submitted for in vitro screening, which led to 25 hits being identified with IC50 values of less than 50 μM. The majority of these hits belonged to two scaffolds: 1-ethyl-3-methoxy-3-methylpyrrolidine and 1H-pyrrolo[3,2-c]pyridin-6-amine both of which are noted to be promising compounds for further optimization. As various possible binding poses were suggested from molecular docking, molecular dynamics simulations were employed to validate the poses. In the case of the most active compounds identified, a critical, stable water bridge formed deep within the binding pocket was identified potentially explaining in part the lack of activity for subsets of compounds that are not able to form this water bridge.

2. Binding pose analysis of hydroxyethylamine based β-secretase inhibitors and application thereof to the design and synthesis of novel indeno[1,2-b]indole based inhibitors 

C. Johan van der Westhuizen, Divan G. van Greunen, Werner Cordier, Margo Nell, Vanessa Steenkamp, André Stander, Jenny-Lee Panayides and Darren L. Riley, Arkivoc2020, v, 84-107

β-Secretase (BACE1) is recognised as a target for the treatment of Alzheimer’s disease, and transition-state isosteres such as hydroxyethylamines have shown promise when incorporated into BACE1 inhibitors. A computational investigation of previously reported carbazole-based hydroxylethylamines with contradictory binding poses was undertaken using molecular dynamic simulations to rationalise the ligands preferred binding preference. Visual inspection of the confirmed binding pocket showed unoccupied space surrounding the carbazole moiety which was probed through the synthesis of seventeen ligands wherein the carbazole ring system was replaced with an indeno[1,2-b]indole ring system. The most active compound, rac-1-[benzyl(methyl)amino]-3-(indeno[1,2-b]indol-5(10H)-yl)propan-2-ol, indicated an inhibition of 91% at 10 μM against β-secretase with a cytotoxicity IC50 value of 10.51 ± 1.11 μM against the SH-SY5Y cell line.

1. Novel N-benzylpiperidine carboxamide derivatives as potential cholinesterase inhibitors for the treatment of Alzheimer’s disease

D.G. van Greunen, C.J. van der Westhuizen, W. Cordier, M. Nell, A. Stander, C. van der Westhuyzen, V. Steenkamp, J.-L. Panayides, D.L. Riley. European Journal of Medicinal Chemistry 2019179, 680-693.

A series of fifteen acetylcholinesterase inhibitors were designed and synthesised based upon the previously identified lead compound 5,6-dimethoxy-1-oxo-2,3-dihydro-1H-inden-2-yl 1-benzylpiperidine-4-carboxylate (5) which showed good inhibitory activity (IC50 0.03 ± 0.07 μM) against acetylcholinesterase. A series of compounds were prepared wherein the ester linker in the original lead compound was exchanged for a more metabolically stable amide linker and the indanone moiety was exchanged for a range of aryl and aromatic heterocycles. The two most active analogues 1-benzyl-N-(5,6-dimethoxy-8H-indeno[1,2-d]thiazol-2-yl)piperidine-4-carboxamide (28) and 1-benzyl-N-(1-methyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl) piperidine-4-carboxamide (20) afforded in vitro IC50 values of 0.41 ± 1.25 and 5.94 ± 1.08 μM, respectively. In silico screening predicts that 20 will be a blood brain-barrier permeant, and molecular dynamic simulations are indicative of a close correlation between the binding of 20 and the Food and Drug Administration-approved cholinesterase inhibitor donepezil (1).

Conferences

  1. CHPC Annual Conference, Pretoria, South Africa, December 2017: Exploring chemical space using in silico studies to identify novel inhibitors of acetylcholinesterase, a target for Alzheimer’s disease, C.J. van der Westhuizen*, J.-L. Panayides, D.L. Riley, B.A. Stander
  2. SAAWK Conference, Pretoria, South Africa, November 2017: Amidasie van die trisikliese 5,6-dimetoksie-8H-ideno[1,2-d]tiazol-2-amien raamwerk met N-bensiel ringe as potensiele inhibeerders van asetiel cholienesterase in Alzheimer se siekte, A.M. Reinhardt*, D.G. van Greunen, C.J. van der Westhuizen, J-L. Panayides, D.L. Riley
  3. 2016 Frank Warren Conference, Rhodes, South Africa, December 2016: Nucleophilic substitution and epoxidation reaction of α-halocarbonyl compounds, C.J. van der Westhuizen*, I. Cukrowski, D.L. Riley
  4. 40th SACI National Convention, Pretoria, South Africa, 2015: Studying nucleophilic substitution and carbonyl addition reactions for α-halocarbonyl compounds, C. Johan van der Westhuizen,* Ignacy Cukrowski, Darren Riley