This study reports pharmacological and physiological effects of cis-and trans-(3-aminocyclopentanyl)butylphosphinic acid . These compounds are conformationally restricted analogs of the orally active GABA B/C receptor antagonist (3-aminopropyl)-n-butylphosphinic acid (CGP36742 or SGS742). cis- [IC 50 (1) ϭ 5.06 M and IC 50 (2) ϭ 11.08 M; n ϭ 4] and trans-3-ACPMPA [IC 50 (1) ϭ 72.58 M and IC 50 (2) ϭ 189.7 M; n ϭ 4] seem competitive at GABA C receptors expressed in Xenopus laevis oocytes, having no effect as agonists (1 mM) but exerting weak antagonist (1 mM) effects on human GABA A and GABA B receptors. cis-3-ACPBPA was more potent and selective than the trans-compound, being more than 100 times more potent at GABA C than GABA A or GABA B receptors. cis-3-ACPBPA was further evaluated on dissociated rat retinal bipolar cells and dose-dependently inhibited the native GABA C receptor (IC 50 ϭ 47 Ϯ 4.5 M; n ϭ 6). When applied to the eye as intravitreal injections, cis-and trans-3-ACPBPA prevented experimental myopia development and inhibited the associated vitreous chamber elongation, in a dose-dependent manner in the chick model. Doses only 10 times greater than required to inhibit recombinant GABA C receptors caused the antimyopia effects. Using intraperitoneal administration, cis-(30 mg/ kg) and trans-3-ACPBPA (100 mg/kg) enhanced learning and memory in male Wistar rats; compared with vehicle there was a significant reduction in time for rats to find the platform in the Morris water maze task (p Ͻ 0.05; n ϭ 10). As the physiological effects of cis-and trans-3-ACPBPA are similar to those reported for CGP36742, the memory and refractive effects of CGP36742 may be due in part to its GABA C activity.GABA is an abundant neurotransmitter that mediates inhibition throughout the retina and central nervous system. Three main classes of GABA receptors exist and are termed GABA A , GABA B , and GABA C receptors (Bormann, 2000;Chebib and Johnston, 2000). The GABA A and GABA C are ionotropic receptors, belonging to the Cys-loop family of ligand-gated ion channels, which includes nicotinic acetylcholine, strychnine-sensitive glycine, serotonin type 3, and some invertebrate anionic glutamate receptors (Bormann, 2000;Chebib and Johnston, 2000). Both GABA A and GABA C receptors are chloride channels that mediate fast synaptic inhibition when activated by GABA. In contrast, GABA B receptors are members of the metabotropic receptor family; these receptors couple via G proteins (G i/o ) to interact with neuronal inwardly rectifying potassium and voltage-gated calcium channels, mediating slow synaptic inhibition by increasing ABBREVIATIONS: TPMPA, (1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid; 3-APMPA, (3-aminopropyl)-methylphosphinic acid; cis-and trans-3-ACPMPA, cis-and trans-(3-aminocyclopentanyl)methylphosphinic acid; cis-and trans-3-ACPBPA, cis-and trans-(3-aminocyclopentanyl)butylphosphinic acid; CGP36742 or SGS742, (3-aminopropyl)-n-butylphosphinic acid; GIRK, G protein-coupled inwardly rectifying potassium ...

Gamma-aminobutyric acid (GABA) analogues based on 4-amino-cyclopent-1-enyl phosphinic acid ( 34- 42) and 3-aminocyclobutane phosphinic acids ( 51, 52, 56, 57) were investigated in order to obtain selective homomeric rho 1 GABA C receptor antagonists. The effect of the stereochemistry and phosphinic acid substituent of these compounds on potency and selectivity within the GABA receptor subtypes was investigated. Compounds of high potency at GABA C rho 1 receptors ( 36, K B = 0.78 microM) and selectivity greater than 100 times ( 41, K B = 4.97 microM) were obtained. The data obtained was analyzed along with the known set of GABA C rho 1 receptor-ligands, leading to the development of a pharmacophore model for this receptor, which can be used for in silico screening.

The inhibitory neurotransmitter, GABA, is a low-molecular-weight molecule that can achieve many low-energy conformations, which are recognized by GABA receptors and transporters. In this article, we assess the structure-activity relationship profiles of GABA analogs at the ionotropic ρ GABA(C) receptor. Such studies have significantly contributed to the design and development of potent and selective agonists and antagonists for this subclass of GABA receptors. With these tools in hand, the role of ρ GABA(C) receptors is slowly being realized. Of particular interest is the development of selective phosphinic acid analogs of GABA and their potential use in sleep disorders, inhibiting the development of myopia, and in improving learning and memory.

The ρ 1 GABA C receptor is a ligand-gated chloride ion channel that shows promise as a therapeutic target for myopia, sleep disorders, memory and learning facilitation, and anxietyrelated disorders. As such, there is a need for molecular probes to understand the role GABA C receptors play in physiological and pathological processes. To date, no labeled (either radioactive or fluorescent) GABA C selective ligand has been developed that can act as a marker for GABA C receptor visualization and localization studies. Herein, we report a series of fluorescent ligands containing different-sized linkers and fluorophores based around (S)-4-ACPBPA [(4-aminocyclopenten-1-yl)-butylphosphinic acid], a selective GABA C antagonist. One of these conjugates, (S)-4-ACPBPA-C5-BODIPY (13), displayed moderate potency (IC 50 = 58.61 μM) and selectivity (>100 times) for ρ 1 over α 1 β 2 γ 2L GABA A receptors. These conjugates are novel lead agents for the development of more potent and selective fluorescent probes for studying the localization and function of GABA C receptors in living cells. KEYWORDS: Human ρ 1 GABA C receptors, CNS-related disorders, GABA C antagonists, fluorescent and biotinylated probes, homology modeling and docking

Ischemic stroke remains a leading cause of disability worldwide, with limited treatment options available. This study investigates GABAC receptors as novel pharmacological targets for stroke recovery. The expression of r1 and r2 mRNA in mice were determined in peri-infarct tissue following photothrombotic motor cortex stroke. (R)-4-amino-cyclopent-1-enyl butylphosphinic acid (R)-4-ACPBPA and (S)-4-ACPBPA were assessed using 2-elecotrode voltage electrophysiology in Xenopus laevis oocytes. Stroke mice were treated for 4 weeks with either vehicle, the α5-selective negative allosteric modulator, L655,708, or the r1/2 antagonists, (R)-4-ACPBPA and (S)-4-ACPBPA respectively from 3 days post-stroke. Infarct size and expression levels of GAT3 and reactive astrogliosis were determined using histochemistry and immunohistochemistry respectively, and motor function was assessed using both the grid-walking and cylinder tasks. After stroke, significant increases in r1 and r2 mRNAs were observed on day 3, with r2 showing a further increase on day 7. (R)- and (S)-4-ACPBPA are both potent antagonists at r2 and only weak inhibitors of α5β2γ2 receptors. Treatment with either L655,708, (S)-4-ACPBPA (r1/2 antagonist; 5 mM only), or (R)-4-ACPBPA (r2 antagonist; 2.5 and 5 mM) from 3 days after stroke resulted in a significant improvement in motor recovery on the grid-walking task, with L655,708 and (R)-4-ACPBPA also showing an improvement in the cylinder task. Infarct size was unaffected, and only (R)-4-ACPBPA significantly increased peri-infarct GAT3 expression and decreased the level of reactive astrogliosis. Importantly, inhibiting GABAC receptors affords significant improvement in motor function after stroke. Targeting the r-subunit could provide a novel delayed treatment option for stroke recovery.