Design, Synthesis and Biological Evaluation of 7-Chloro-9H-pyrimido[4,5-b]indole-based Glycogen Synthase Kinase-3β Inhibitors

Frontiers in Medicinal Chemistry 2022 Goes Virtual

The Frontiers in Medicinal Chemistry (FiMC) meeting, which represents the largest international medicinal chemistry conference in Germany, took place from March 14^th to 16^th 2022 in a fully virtual format. Organized by the Division of Medicinal Chemistry of the German Chemical Society (GDCh) together with the Division of Pharmaceutical & Medicinal Chemistry of the German Pharmaceutical Society (DPhG) and a "local" organization committee from the University of Freiburg headed by Manfred Jung, the meeting brought together 271 participants from around 20 countries. The program included 33 lectures by leading scientists from industry and academia as well as early career investigators. 67 posters were presented in two poster sessions and with over 20.000 poster abstract downloads. The general organization and the time-shift function were very much appreciated as demonstrated by almost 600 on-demand contents retrieved. The online format fitted perfectly to bring together medicinal chemists from academia and industry across the globe.

(S)-3-(3-((7-Ethynyl-9H-pyrimido[4,5-b]indol-4-yl)amino)piperidin-1-yl)propanenitrile

The title compound (S)-3-(3-((7-ethynyl-9H-pyrimido[4,5-b]indol-4-yl)amino)piperidin-1-yl)propanenitrile (2) was synthesized in five steps, starting from 4-chloro-7-iodo-9H-pyrimido[4,5-b]indole (3), and was characterized by 1H-NMR, 13C-NMR, MS and HPLC. Moreover, its structure was confirmed by single crystal X-ray diffraction. Pyrimido[4,5-b]indole 2 demonstrated an IC50 value of 2.24 µM in a NanoBRETTM TE intracellular glycogen synthase kinase-3β assay.

Development of inhibitors targeting glycogen synthase kinase-3β for human diseases: Strategies to improve selectivity

Glycogen synthase kinase-3β (GSK-3β) is a conserved serine/threonine kinase that participates in the transmission of multiple signaling pathways and plays an important role in the occurrence and development of human diseases, such as metabolic diseases, neurological diseases and cancer, making it to be a potential and promising drug target. To date, copious GSK-3β inhibitors have been synthesized, but only few have entered clinical trials. Most of them exerts poor selectivity, concomitant off-target effects and side effects. This review summarizes the structural characteristics, biological functions and relationship with diseases of GSK-3β, as well as the selectivity profile and therapeutic potential of different categories of GSK-3β inhibitors. Strategies for increasing selectivity and reducing adverse effects are proposed for the future design of GSK-3β inhibitors.

Addressing a Trapped High-Energy Water: Design and Synthesis of Highly Potent Pyrimidoindole-Based Glycogen Synthase Kinase-3β Inhibitors

In small molecule binding, water is not a passive bystander but rather takes an active role in the binding site, which may be decisive for the potency of the inhibitor. Here, by addressing a high-energy water, we improved the IC₅₀ value of our co-crystallized glycogen synthase kinase-3β (GSK-3β) inhibitor by nearly two orders of magnitude. Surprisingly, our results demonstrate that this high-energy water was not displaced by our potent inhibitor (S)-3-(3-((7-ethynyl-9H-pyrimido[4,5-b]indol-4-yl)(methyl)amino)piperidin-1-yl)propanenitrile ((S)-15, IC₅₀ value of 6 nM). Instead, only a subtle shift in the location of this water molecule resulted in a dramatic decrease in the energy of this high-energy hydration site, as shown by the WaterMap analysis combined with microsecond timescale molecular dynamics simulations. (S)-15 demonstrated both a favorable kinome selectivity profile and target engagement in a cellular environment and reduced GSK-3 autophosphorylation in neuronal SH-SY5Y cells. Overall, our findings highlight that even a slight adjustment in the location of a high-energy water can be decisive for ligand binding.

Glycogen Synthase Kinase 3 (GSK3): Its Role and Inhibitors

Glycogen Synthase Kinase 3 (GSK3) is one of the Serine/Threonine protein kinases, which has gained a lot of attention for its role in a variety of pathways. It has two isoforms, GSK3α and GSK3β. However, GSK3β is highly expressed in different areas of the brain and has been implicated in Alzheimer's disease as it is involved in tau phosphorylation. Due to its high specificity concerning substrate recognition, GSK3 has been considered as an important target. In the last decade, several GSK3 inhibitors have been reported and two molecules are in clinical trials. This review collates the information published in the last decade about the role of GSK3 in Alzheimer's disease and progress in the development of its inhibitors. Using this collated information, medicinal chemists can strategize and design novel GSK3 inhibitors that could be useful in the treatment of Alzheimer's disease.

Recent Developments in New Therapeutic Agents against Alzheimer and Parkinson Diseases: In-Silico Approaches

Neurodegenerative diseases (ND), including Alzheimer's (AD) and Parkinson's Disease (PD), are becoming increasingly more common and are recognized as a social problem in modern societies. These disorders are characterized by a progressive neurodegeneration and are considered one of the main causes of disability and mortality worldwide. Currently, there is no existing cure for AD nor PD and the clinically used drugs aim only at symptomatic relief, and are not capable of stopping neurodegeneration. Over the last years, several drug candidates reached clinical trials phases, but they were suspended, mainly because of the unsatisfactory pharmacological benefits. Recently, the number of compounds developed using in silico approaches has been increasing at a promising rate, mainly evaluating the affinity for several macromolecular targets and applying filters to exclude compounds with potentially unfavorable pharmacokinetics. Thus, in this review, an overview of the current therapeutics in use for these two ND, the main targets in drug development, and the primary studies published in the last five years that used in silico approaches to design novel drug candidates for AD and PD treatment will be presented. In addition, future perspectives for the treatment of these ND will also be briefly discussed.

Discovery and Evaluation of Enantiopure 9H-pyrimido[4,5-b]indoles as Nanomolar GSK-3β Inhibitors with Improved Metabolic Stability

Glycogen synthase kinase-3β (GSK-3β) is a potential target in the field of Alzheimer's disease drug discovery. We recently reported a new class of 9H-pyrimido[4,5-b]indole-based GSK-3β inhibitors, of which 3-(3-((7-chloro-9H-pyrimido[4,5-b]indol-4-yl)(methyl)amino)piperidin-1-yl)propanenitrile (1) demonstrated promising inhibitory potency. However, this compound underwent rapid degradation by human liver microsomes. Starting from 1, we prepared a series of amide-based derivatives and studied their structure-activity relationships against GSK-3β supported by 1 µs molecular dynamics simulations. The biological potency of this series was substantially enhanced by identifying the eutomer configuration at the stereocenter. Moreover, the introduction of an amide bond proved to be an effective strategy to eliminate the metabolic hotspot. The most potent compounds, (R)-3-(3-((7-chloro-9H-pyrimido[4,5-b]indol-4-yl)(methyl)amino)piperidin-1-yl)-3-oxopropanenitrile ((R)-2) and (R)-1-(3-((7-bromo-9Hpyrimido[4,5-b]indol-4-yl)(methyl)amino)piperidin-1-yl)propan-1-one ((R)-28), exhibited IC₅₀ values of 480 nM and 360 nM, respectively, and displayed improved metabolic stability. Their favorable biological profile is complemented by minimal cytotoxicity and neuroprotective properties.