Low-basicity 5-HT7 receptor agonists synthesized using the van Leusen multicomponent protocol

A series of 5-aryl-1-alkylimidazole derivatives was synthesized using the van Leusen multicomponent reaction. The chemotype is the first example of low-basicity scaffolds exhibiting high affinity for 5-HT7 receptor together with agonist function. The chosen lead compounds 3-(1-ethyl-1H-imidazol-5-yl)-5- iodo-1H-indole (AGH-107, 1o, Ki 5-HT7=6nM, EC50=19nM, 176-fold selectivity over 5-HT1AR) and 1e (5-methoxy analogue, Ki 5-HT7=30nM, EC50=60nM) exhibited high selectivity over related CNS targets, high metabolic stability and low toxicity in HEK-293 and HepG2 cell cultures. A rapid absorption to the blood, high blood-brain barrier permeation and a very high peak concentration in the brain (Cmax=2723 ng/g) were found for 1o after i.p. (5mg/kg) administration in mice. The compound was found active in novel object recognition test in mice, at 0.5, 1 and 5mg/kg. Docking to 5-HT7R homology models indicated a plausible binding mode which explain the unusually high selectivity over the related CNS targets. Halogen bond formation between the most potent derivatives and the receptor is consistent with both the docking results and SAR. 5-Chlorine, bromine and iodine substitution resulted in a 13, 27 and 89-fold increase in binding affinities, respectively, and in enhanced 5-HT1AR selectivity

Benchmarking and Developing Novel Methods for G Protein-coupled Receptor Ligand Discovery

G protein-coupled receptors (GPCR) are integral membrane proteins mediating responses from extracellular effectors that regulate a diverse set of physiological functions. Consequently, GPCR are the targets of ~34% of current FDA-approved drugs.3 Although it is clear that GPCR are therapeutically significant, discovery of novel drugs for these receptors is often impeded by a lack of known ligands and/or experimentally determined structures for potential drug targets. However, computational techniques have provided paths to overcome these obstacles. As such, this work discusses the development and application of novel computational methods and workflows for GPCR ligand discovery. Chapter 1 provides an overview of current obstacles faced in GPCR ligand discovery and defines ligand- and structure-based computational methods of overcoming these obstacles. Furthermore, chapter 1 outlines methods of hit list generation and refinement and provides a GPCR ligand discovery workflow incorporating computational techniques. In chapter 2, a workflow for modeling GPCR structure incorporating template selection via local sequence similarity and refinement of the structurally variable extracellular loop 2 (ECL2) region is benchmarked. Overall, findings in chapter 2 support the use of local template homology modeling in combination with de novo ECL2 modeling in the presence of a ligand from the template crystal structure to generate GPCR models intended to study ligand binding interactions. Chapter 3 details a method of generating structure-based pharmacophore models via the random selection of functional group fragments placed with Multiple Copy Simultaneous Search (MCSS) that is benchmarked in the context of 8 GPCR targets. When pharmacophore model performance was assessed with enrichment factor (EF) and goodness-of-hit (GH) scoring metrics, pharmacophore models possessing the theoretical maximum EF value were produced in both resolved structures (8 of 8 cases) and homology models (7 of 8 cases). Lastly, chapter 4 details a method of structure-based pharmacophore model generation using MCSS that is applicable to targets with no known ligands. Additionally, a method of pharmacophore model selection via machine learning is discussed. Overall, the work in chapter 4 led to the development of pharmacophore models exhibiting high EF values that were able to be accurately selected with machine learning classifiers

Synthesis and Evaluation of C-10 Nitrogenated Aporphine Alkaloids at Serotonin and Dopamine Receptors

Aporphine alkaloids, belonging to the isoquinoline class of compounds, have been investigated as a potential source of ligands for Central Nervous System (CNS) receptors. Previous research indicates that the aporphine scaffold may be manipulated to synthesize selective ligands for serotonin and dopamine receptors. Novel aporphine alkaloids containing C10 nitrogen substitutions were synthesized, and their affinities were evaluated at serotonin (5-HT1A, 5-HT1B, 5-HT2A, 5-HT7A) receptors and dopamine (D1, D2, D3, D4, and D5) receptors. Two series of racemic aporphine compounds with C10 nitrogenous functionalities were synthesized and analyzed at the aforementioned receptors. The first series of aporphine alkaloids contain C10 nitro, amine, amide, and methanesulfonamide motifs. Compounds in this C10 monosubstituted series displayed higher affinity at 5-HT1AR and 5-HT7AR and lacked affinity at 5-HT1BR and 5-HT2AR. This series contained compounds with an N6-methyl group and compounds with and N6-propyl group. The N6-methyl substituted C10 nitrogen functionalized aporphine analogs had higher binding affinities at 5-HT7AR versus 5-HT1AR. In contrast the N6-propyl sub-set of compounds exhibited a reversal of this selectivity. Compound 103a was the most potent compound and behaved as an antagonist at 5-HT7AR (Ki = 4.5 ± 0.6 nM, IC50 = 1.25 μM), with 10-fold selectivity over 5-HT1AR (Ki = 49 ± 6.3 nM). These monosubstituted analogs lacked significant binding among all dopamine receptor subtypes. C10 analogs with a benzofused aminothiazole moiety showed higher affinity and selectivity for serotonin receptors as compared to the C10 monosubstituted compounds. These compounds displayed high binding affinities for 5-HT1AR and 5-HT7AR; analogs containing an N6-methyl substitution favor binding at 5-HT7AR. Among the benzofused aminothiazole analogs compound 108a had the best binding affinity at 5-HT7AR (Ki = 6.5±0.8 nM) and functions as an antagonist (IC50 = 0.26 μM). These benzofused aminothiazole analogs also lacked affinity for dopamine receptors. Unlike analogs in the C10 monosubstituted subset, compounds with the benzofused aminothiazole moiety with an N6-methyl substitution displayed moderate affinity for 5-HT1BR. The second series of compounds contained a C1,2,10-trisusbtitution pattern on the aporphine core. The 1,2,10-trisusbtituted series of compounds as a group displayed weak binding affinity at 5-HT1AR and considerably higher binding affinity at 5-HT1BR. These compounds provided moderate affinity at 5-HT2AR and 5-HT7AR. At dopamine receptors, most of the trisubstituted series of compounds failed to show affinity towards D5 receptors suggesting a lack of tolerability at D5R receptors for C10 N substituted aporphines with moderate to low affinity at D1R, thus attaining D1R versus D5R selectivity. Compound 128e was the most potent D1R ligand (Ki = 58 nM) and lacked binding affinity at all other dopamine receptor subtypes. Compounds 103a, 108a, and 128e have been identified as three new lead compounds with promising pharmacodynamic properties for further tool and pharmaceutical optimization

Behavioral Pharmacology of Alcohol and Legal Psychostimulants

Substance abuse, including alcohol and psychostimulant abuse, is a widespread and dangerous public health issue. In the United States, 8-10% of people 12 years of age or older (accounting for 20-22 million persons) are addicted to alcohol or other drugs, and the results of substance abuse are costly at both the individual and society level. Despite the large financial burden of substance abuse to society, efficacious psychosocial and pharmacologic treatment options are lacking. For example, in the pharmacologic treatment of alcohol use disorders (AUD), only three drugs have been approved by the Food and Drug Administration, and each have their own limitations that restrict efficacy and recovery outcomes. Here, the behavioral pharmacology of alcohol and psychostimulants is investigated using a variety of in vitro and in vivo techniques to better develop treatment options for AUD and to further our basic understanding of adolescent psychostimulant use. Overall, these studies provide significant progress towards the development of novel, functionally selective delta-opioid therapeutics for alcohol use disorder and also help elucidate the potential aversive behavioral outcomes of adolescent psychostimulant use