N-Hydroxyformamide LpxC inhibitors, their in vivo efficacy in a mouse Escherichia coli infection model, and their safety in a rat hemodynamic assay.

UDP-3-O-(R-3-hydroxyacyl)-N-acetylglucosamine deacetylase (LpxC), the zinc metalloenzyme catalyzing the first committed step of lipid A biosynthesis in Gram-negative bacteria, has been a target for antibacterial drug discovery for many years. All inhibitor chemotypes reaching an advanced preclinical stage and clinical phase 1 have contained terminal hydroxamic acid, and none have been successfully advanced due, in part, to safety concerns, including hemodynamic effects. We hypothesized that the safety of LpxC inhibitors could be improved by replacing the terminal hydroxamic acid with a different zinc-binding group. After choosing an N-hydroxyformamide zinc-binding group, we investigated the structure-activity relationship of each part of the inhibitor scaffold with respect to Pseudomonas aeruginosa and Escherichia coli LpxC binding affinity, in vitro antibacterial potency and pharmacological properties. We identified a novel, potency-enhancing hydrophobic binding interaction for an LpxC inhibitor. We demonstrated in vivo efficacy of one compound in a neutropenic mouse E. coli infection model. Another compound was tested in a rat hemodynamic assay and was found to have a hypotensive effect. This result demonstrated that replacing the terminal hydroxamic acid with a different zinc-binding group was insufficient to avoid this previously recognized safety issue with LpxC inhibitors.

Ocular Distribution and Pharmacodynamics of SF0166, a Topically Administered αvß3 Integrin Antagonist, for the Treatment of Retinal Diseases.

SF0166, a small-molecule αvß3 antagonist, has physiochemical properties that allow distribution to the posterior segment of the eye after topical administration in an ophthalmic solution. The pharmacodynamics and ocular distribution of SF0166 were evaluated in several cell lines, chick chorioallantoic membrane assays, and models of ocular neovascularization in mice and pigmented rabbits. SF0166 inhibited cellular adhesion to vitronectin across human, rat, rabbit, and dog cell lines with IC50 values of 7.6 pM to 76 nM. SF0166 inhibited integrin-ligand interactions at IC50 values of 0.6-13 nM for human αvß3, αvß6, and αvß8 SF0166 significantly decreased neovascularization in the oxygen-induced retinopathy mouse model. SF0166 distributed to the choroid and retina after topical ocular administration in amounts that substantially exceeded the cellular IC50 for adhesion to vitronectin; drug concentrations were maintained for >12 hours. In the laser-induced choroidal neovascularization model, topical ocular administration of SF0166 decreased lesion area compared with vehicle and was comparable to a bevacizumab injection. In the vascular endothelial growth factor-induced early neovascularization and vascular leakage model, topical ocular application of SF0166 resulted in a dose-dependent reduction in vascular leakage; the highest ocular doses tested showed comparable activity to a bevacizumab injection.

Catalysis for fluorination and trifluoromethylation.

Recent advances in catalysis have made the incorporation of fluorine into complex organic molecules easier than ever before, but selective, general and practical fluorination reactions remain sought after. Fluorination of molecules often imparts desirable properties, such as metabolic and thermal stability, and fluorinated molecules are therefore frequently used as pharmaceuticals or materials. But the formation of carbon-fluorine bonds in complex molecules is a significant challenge. Here we discuss reactions to make organofluorides that have emerged within the past few years and which exemplify how to overcome some of the intricate challenges associated with fluorination.

Potent KCNQ2/3-specific channel activator suppresses in vivo epileptic activity and prevents the development of tinnitus.

Voltage-gated Kv7 (KCNQ) channels are voltage-dependent potassium channels that are activated at resting membrane potentials and therefore provide a powerful brake on neuronal excitability. Genetic or experience-dependent reduction of KCNQ2/3 channel activity is linked with disorders that are characterized by neuronal hyperexcitability, such as epilepsy and tinnitus. Retigabine, a small molecule that activates KCNQ2-5 channels by shifting their voltage-dependent opening to more negative voltages, is an US Food and Drug Administration (FDA) approved anti-epileptic drug. However, recently identified side effects have limited its clinical use. As a result, the development of improved KCNQ2/3 channel activators is crucial for the treatment of hyperexcitability-related disorders. By incorporating a fluorine substituent in the 3-position of the tri-aminophenyl ring of retigabine, we synthesized a small-molecule activator (SF0034) with novel properties. Heterologous expression of KCNQ2/3 channels in HEK293T cells showed that SF0034 was five times more potent than retigabine at shifting the voltage dependence of KCNQ2/3 channels to more negative voltages. Moreover, unlike retigabine, SF0034 did not shift the voltage dependence of either KCNQ4 or KCNQ5 homomeric channels. Conditional deletion of Kcnq2 from cerebral cortical pyramidal neurons showed that SF0034 requires the expression of KCNQ2/3 channels for reducing the excitability of CA1 hippocampal neurons. Behavioral studies demonstrated that SF0034 was a more potent and less toxic anticonvulsant than retigabine in rodents. Furthermore, SF0034 prevented the development of tinnitus in mice. We propose that SF0034 provides, not only a powerful tool for investigating ion channel properties, but, most importantly, it provides a clinical candidate for treating epilepsy and preventing tinnitus.

Discovery of Potent Allosteric DRP1 Inhibitors by Disrupting Protein-Protein Interaction with MiD49.

Mitochondrial dysfunction has been attributed to many disease indications, including metabolic, cardiovascular, neoplastic, and neurodegenerative diseases. Dynamin related protein 1 (DRP1) is crucial in regulating mitochondrial fission and maintaining mitochondrial homeostasis. MiD49 is a dynamic peripheral protein receptor on the surface of the mitochondrial membrane that recruits DRP1 protein to induce mitochondrial binary fission. By targeting the protein-protein interaction of DRP1/MiD49, we have discovered a novel and potent allosteric DRP1 inhibitor that inhibits mitochondria fragmentation in vitro. X-ray cocrystal structure revealed that it locked the closed DRP1 conformation by induced dimerization.

Silver-catalyzed late-stage fluorination.

Carbon-fluorine bond formation by transition metal catalysis is difficult, and only a few methods for the synthesis of aryl fluorides have been developed. All reported transition-metal-catalyzed fluorination reactions for the synthesis of functionalized arenes are based on palladium. Here we present silver catalysis for carbon-fluorine bond formation. Our report is the first example of the use of the transition metal silver to form carbon-heteroatom bonds by cross-coupling catalysis. The functional group tolerance and substrate scope presented here have not been demonstrated for any other fluorination reaction to date.

Mechanism of C-F reductive elimination from palladium(IV) fluorides.

The first systematic mechanism study of C-F reductive elimination from a transition metal complex is described. C-F bond formation from three different Pd(IV) fluoride complexes was mechanistically evaluated. The experimental data suggest that reductive elimination occurs from cationic Pd(IV) fluoride complexes via a dissociative mechanism. The ancillary pyridyl-sulfonamide ligand plays a crucial role for C-F reductive elimination, likely due to a kappa(3) coordination mode, in which an oxygen atom of the sulfonyl group coordinates to Pd. The pyridyl-sulfonamide can support Pd(IV) and has the appropriate geometry and electronic structure to induce reductive elimination.

Silver-mediated fluorination of functionalized aryl stannanes.

We report a regiospecific silver-mediated fluorination of aryl stannanes. The presented reaction can afford complex fluoroarenes from readily available phenols in three steps. The operational simplicity and the broad substrate scope of the fluorination should render this reaction a useful tool for the synthesis of milligram to gram quantities of functionalized aryl fluorides. Silver-mediated oxidative transformations of aryl nucleophiles that proceed via bimetallic redox processes are a new avenue to develop carbon-heteroatom bond formations.

Carbon-fluorine reductive elimination from a high-valent palladium fluoride.

We have observed two high-valent arylpalladiumfluoride complexes that afford carbon-fluorine bond formation upon thermolysis.

Carbon-fluorine bond formation.

A selection of carbon-fluorine bond-forming reactions that have been developed in the recent past are presented. An overview of the most common fluorination reagents is followed by descriptions of fluorination reactions that are organized by reactivity. The distinction between nucleophilic and electrophilic fluorinations is highlighted, as well as between aliphatic and aromatic fluorinations. Each section is divided into more specific reaction classes and examples for the synthesis of pharmaceuticals, [18F]radiolabeling and mechanistic investigations are provided.

A fluoride-derived electrophilic late-stage fluorination reagent for PET imaging.

The unnatural isotope fluorine-18 ((18)F) is used as a positron emitter in molecular imaging. Currently, many potentially useful (18)F-labeled probe molecules are inaccessible for imaging because no fluorination chemistry is available to make them. The 110-minute half-life of (18)F requires rapid syntheses for which [(18)F]fluoride is the preferred source of fluorine because of its practical access and suitable isotope enrichment. However, conventional [(18)F]fluoride chemistry has been limited to nucleophilic fluorination reactions. We report the development of a palladium-based electrophilic fluorination reagent derived from fluoride and its application to the synthesis of aromatic (18)F-labeled molecules via late-stage fluorination. Late-stage fluorination enables the synthesis of conventionally unavailable positron emission tomography (PET) tracers for anticipated applications in pharmaceutical development as well as preclinical and clinical PET imaging.

C-F Bond Formation for the Synthesis of Aryl Fluorides.

A selection of carbon-fluorine bond-forming reactions is presented with particular focus on transition metal-mediated fluorination. A brief summary of conventional fluorination reactions is followed by a discussion of fluorination reactions mediated by palladium and silver. Investigations into the mechanism as well as the conceptual difficulty associated with transition metal-mediated carbon-fluorine bond formation are presented.

Fluorination of boronic acids mediated by silver(I) triflate.

A regiospecific Ag-mediated fluorination reaction of aryl- and alkenylboronic acids and esters is reported. The fluorination reaction uses commercially available reagents, does not require the addition of exogenous ligands, and can be performed on a multigram scale. This report discloses the first practical reaction sequence from arylboronic acid to aryl fluorides.