Agonists of the γ-aminobutyric acid type B (GABAB) receptor derived from β-hydroxy and β-amino difluoromethyl ketones

Synthesis of α,α-Difluoro-β-amino Ketones from N-Boc-α-Amidosulfones and Pentafluoro-gem-diols

To circumvent the synthesis and isolation of imines, a method was devised to construct α,α-difluoro-β-amino ketones from N-Boc-α-amidosulfones. The reactive nucleophiles, difluoroenolates, are generated in situ from the pentafluoro-gem-diols using cesium fluoride in pyridine. NMR studies confirm the role of the α-amidosulfones in this process. Incubation of the α,α-difluoro-β-amino ketones in rat serum demonstrates the relative stability of this structure as well as its value as a chemical probe or lead.

GABAB Receptor Chemistry and Pharmacology: Agonists, Antagonists, and Allosteric Modulators

The GABA_B receptors are metabotropic G protein-coupled receptors (GPCRs) that mediate the actions of the primary inhibitory neurotransmitter, γ-aminobutyric acid (GABA). In the CNS, GABA plays an important role in behavior, learning and memory, cognition, and stress. GABA is also located throughout the gastrointestinal (GI) tract and is involved in the autonomic control of the intestine and esophageal reflex. Consequently, dysregulated GABA_B receptor signaling is associated with neurological, mental health, and gastrointestinal disorders; hence, these receptors have been identified as key therapeutic targets and are the focus of multiple drug discovery efforts for indications such as muscle spasticity disorders, schizophrenia, pain, addiction, and gastroesophageal reflex disease (GERD). Numerous agonists, antagonists, and allosteric modulators of the GABA_B receptor have been described; however, Lioresal^® (Baclofen; β-(4-chlorophenyl)-γ-aminobutyric acid) is the only FDA-approved drug that selectively targets GABA_B receptors in clinical use; undesirable side effects, such as sedation, muscle weakness, fatigue, cognitive deficits, seizures, tolerance and potential for abuse, limit their therapeutic use. Here, we review GABA_B receptor chemistry and pharmacology, presenting orthosteric agonists, antagonists, and positive and negative allosteric modulators, and highlight the therapeutic potential of targeting GABA_B receptor modulation for the treatment of various CNS and peripheral disorders.

Pseudo-Dipeptide Bearing α,α-Difluoromethyl Ketone Moiety as Electrophilic Warhead with Activity against Coronaviruses

The synthesis of α-fluorinated methyl ketones has always been challenging. New methods based on the homologation chemistry via nucleophilic halocarbenoid transfer, carried out recently in our labs, allowed us to design and synthesize a target-directed dipeptidyl α,α-difluoromethyl ketone (DFMK) 8 as a potential antiviral agent with activity against human coronaviruses. The ability of the newly synthesized compound to inhibit viral replication was evaluated by a viral cytopathic effect (CPE)-based assay performed on MCR5 cells infected with one of the four human coronaviruses associated with respiratory distress, i.e., hCoV-229E, showing antiproliferative activity in the micromolar range (EC₅₀ = 12.9 ± 1.22 µM), with a very low cytotoxicity profile (CC₅₀ = 170 ± 3.79 µM, 307 ± 11.63 µM, and 174 ± 7.6 µM for A549, human embryonic lung fibroblasts (HELFs), and MRC5 cells, respectively). Docking and molecular dynamics simulations studies indicated that 8 efficaciously binds to the intended target hCoV-229E main protease (M^pro). Moreover, due to the high similarity between hCoV-229E M^pro and SARS-CoV-2 M^pro, we also performed the in silico analysis towards the second target, which showed results comparable to those obtained for hCoV-229E M^pro and promising in terms of energy of binding and docking pose.

The GABAB Receptor-Structure, Ligand Binding and Drug Development

The γ-aminobutyric acid (GABA) type B receptor (GABA_B-R) belongs to class C of the G-protein coupled receptors (GPCRs). Together with the GABA_A receptor, the receptor mediates the neurotransmission of GABA, the main inhibitory neurotransmitter in the central nervous system (CNS). In recent decades, the receptor has been extensively studied with the intention being to understand pathophysiological roles, structural mechanisms and develop drugs. The dysfunction of the receptor is linked to a broad variety of disorders, including anxiety, depression, alcohol addiction, memory and cancer. Despite extensive efforts, few compounds are known to target the receptor, and only the agonist baclofen is approved for clinical use. The receptor is a mandatory heterodimer of the GABA_B1 and GABA_B2 subunits, and each subunit is composed of an extracellular Venus Flytrap domain (VFT) and a transmembrane domain of seven α-helices (7TM domain). In this review, we briefly present the existing knowledge about the receptor structure, activation and compounds targeting the receptor, emphasizing the role of the receptor in previous and future drug design and discovery efforts.

Classics in Chemical Neuroscience: Baclofen

Baclofen, β-(4-chlorophenyl)-γ-aminobutyric acid, holds a unique position in neuroscience, remaining the only U.S. Food and Drug Administration (FDA) approved GABA_B agonist. While intended to be a more brain penetrant, i.e, ability to cross the blood-brain barrier (BBB), version of GABA (γ-aminobutyric acid) for the potential treatment of epilepsy, baclofen's highly efficacious muscle relaxant properties led to its approval, as a racemate, for the treatment of spasticity. Interestingly, baclofen received FDA approval before its receptor, GABA_B, was discovered and its exact mechanism of action was known. In recent times, baclofen has a myriad of off-label uses, with the treatment for alcohol abuse and drug addiction garnering a great deal of attention. This Review aims to capture the >60 year legacy of baclofen by walking through the history, pharmacology, synthesis, drug metabolism, routes of administration, and societal impact of this Classic in chemical neuroscience.

Chemistry of detrifluoroacetylativelyin situgenerated fluoro-enolates

This review article provides a summary of the detrifluoroacetylativein situgeneration of fluorine-containing enolates and their related reactions.