Antibiotic class with potent in vivo activity targeting lipopolysaccharide synthesis in Gram-negative bacteria.

Here, we describe the identification of an antibiotic class acting via LpxH, a clinically unexploited target in lipopolysaccharide synthesis. The lipopolysaccharide synthesis pathway is essential in most Gram-negative bacteria and there is no analogous pathway in humans. Based on a series of phenotypic screens, we identified a hit targeting this pathway that had activity on efflux-defective strains of Escherichia coli. We recognized common structural elements between this hit and a previously published inhibitor, also with activity against efflux-deficient bacteria. With the help of X-ray structures, this information was used to design inhibitors with activity on efflux-proficient, wild-type strains. Optimization of properties such as solubility, metabolic stability and serum protein binding resulted in compounds having potent in vivo efficacy against bloodstream infections caused by the critical Gram-negative pathogens E. coli and Klebsiella pneumoniae. Other favorable properties of the series include a lack of pre-existing resistance in clinical isolates, and no loss of activity against strains expressing extended-spectrum-ß-lactamase, metallo-ß-lactamase, or carbapenemase-resistance genes. Further development of this class of antibiotics could make an important contribution to the ongoing struggle against antibiotic resistance.

Chiral 4-MeO-Pyridine (MOPY) Catalyst for Enantioselective Cyclopropanation: Attenuation of Lewis Basicity Leads to Improved Catalytic Efficiency.

The design of pyridine-derived organocatalysts aims at the increase of their Lewis basicity, however such an approach is not always efficient. For example, strongly Lewis basic DMAP is completely inefficient as catalyst in the cyclopropanation reaction. Herein we disclose an alternative approach that relies on attenuation of DMAP Lewis basicity. Specifically, the replacement of 4-dimethylamino substituent in DMAP for 4-MeO group delivered a highly efficient catalyst for cyclopropanation of electron-deficient olefins with α-bromoketones. Kinetic studies provide compelling evidence that the superior catalytic efficiency of 4-MeO pyridine (MOPY) is to be attributed to the favorable balance between Lewis basicity and leaving group ability. The use of chiral, enantiomerically pure MOPY catalyst has helped to achieve high enantioselectivities (up to 91 : 9 er) in the previously unreported pyridine-catalyzed cyclopropanation reaction.

Electrochemistry and Reactivity of Chelation-stabilized Hypervalent Bromine(III) Compounds.

Hypervalent bromine(III) reagents possess a higher electrophilicity and a stronger oxidizing power compared to their iodine(III) counterparts. Despite the superior reactivity, bromine(III) reagents have a reputation of hard-to-control and difficult-to-synthesize compounds. This is partly due to their low stability, and partly because their synthesis typically relies on the use of the toxic and highly reactive BrF3 as a precursor. Recently, we proposed chelation-stabilized hypervalent bromine(III) compounds as a possible solution to both problems. First, they can be conveniently prepared by electro-oxidation of the corresponding bromoarenes. Second, the chelation endows bromine(III) species with increased stability while retaining sufficient reactivity, comparable to that of iodine(III) counterparts. Finally, their intrinsic reactivity can be unlocked in the presence of acids. Herein, an in-depth mechanistic study of both the electrochemical generation and the reactivity of the bromine(III) compounds is disclosed, with implications for known applications and future developments in the field.

N-Terminal Modification of Gly-His-Tagged Proteins with Azidogluconolactone.

Site-specific protein modifications are vital for biopharmaceutical drug development. Gluconoylation is a non-enzymatic, post-translational modification of N-terminal HisTags. We report high-yield, site-selective in vitro α-aminoacylation of peptides, glycoproteins, antibodies, and virus-like particles (VLPs) with azidogluconolactone at pH 7.5 in 1 h. Conjugates slowly hydrolyse, but diol-masking with borate esters inhibits reversibility. In an example, we multimerise azidogluconoylated SARS-CoV-2 receptor-binding domain (RBD) onto VLPs via click-chemistry, to give a COVID-19 vaccine. Compared to yeast antigen, HEK-derived RBD was immunologically superior, likely due to observed differences in glycosylation. We show the benefits of ordered over randomly oriented multimeric antigen display, by demonstrating single-shot seroconversion and best virus-neutralizing antibodies. Azidogluconoylation is simple, fast and robust chemistry, and should accelerate research and development.

Acylative Dynamic Kinetic Resolution of Secondary Alcohols: Tandem Catalysis by HyperBTM and Bäckvall's Ruthenium Complex.

Non-enzymatic dynamic kinetic resolution (DKR) of secondary alcohols by enantioselective acylation using an isothiourea-derived HyperBTM catalyst and racemization of slowly reacting alcohol by Bäckvall's ruthenium complex is reported. The DKR approach features high enantioselectivities (up to 99:1), employs easy-to-handle crystalline 4-nitrophenyl isobutyrate as the acylating reagent, and proceeds at room temperature and under an ambient atmosphere. The stereoinduction model featuring cation-π system interactions between the acylated HyperBTM catalyst and π electrons of an alcohol aryl subunit has been elaborated by DFT calculations.

Electrochemical Generation of Hypervalent Bromine(III) Compounds.

In sharp contrast to hypervalent iodine(III) compounds, the isoelectronic bromine(III) counterparts have been little studied to date. This knowledge gap is mainly attributed to the difficult-to-control reactivity of λ3 -bromanes as well as to their challenging preparation from the highly toxic and corrosive BrF3 precursor. In this context, we present a straightforward and scalable approach to chelation-stabilized λ3 -bromanes by anodic oxidation of parent aryl bromides possessing two coordinating hexafluoro-2-hydroxypropanyl substituents. A series of para-substituted λ3 -bromanes with remarkably high redox potentials spanning a range from 1.86 V to 2.60 V vs. Ag/AgNO3 was synthesized by the electrochemical method. We demonstrate that the intrinsic reactivity of the bench-stable bromine(III) species can be unlocked by addition of a Lewis or a Brønsted acid. The synthetic utility of the λ3 -bromane activation is exemplified by oxidative C-C, C-N, and C-O bond forming reactions.

Structure-activity relationship studies on the inhibition of the bacterial translation of novel Odilorhabdins analogues.

A structure-activity relationship (SAR) study of NOSO-95179, a nonapeptide from the Odilorhabdin class of antibacterials, was performed by systematic variations of amino acids in positions 2 and 5 of the peptide. A series of non-proteinogenic amino acids was synthesized in high enantiomeric purity from Williams' chiral diphenyloxazinone by highly diastereoselective alkylation or by aldol-type reaction. NOSO-95179 analogues for SAR studies were prepared using solid-phase peptide synthesis. Inhibition of bacterial translation by each of the synthesized Odilorhabdin analogues was measured using an in vitro test. For the most efficient analogues, antibacterial efficacy was measured against two wild-type Enterobacteriaceae (Escherichia coli and Klebsiella pneumoniae) and against an efflux defective E. coli strain (ΔtolC) to evaluate the impact of efflux on the antibacterial activity.

Intramolecular Base-Free Catalytic Wittig Reaction: Synthesis of Benzoxepinones.

A straightforward two-step synthesis of benzoxepinones was developed via base-free phosphane-catalyzed Wittig reaction. 3-Methyl-1-phenyl-2-phospholene 1-oxide was used as a precatalyst and trimethoxysilane as a reducing agent. Additionally benzoic acid is employed as a catalyst to facilitate the reduction of the phosphane oxide. Mechanistic investigation revealed the formation of a coumarin as a side product, which was identified by 2D NMR experiments. First results of metabolic activity tests on the prepared benzoxepinones are reported.

Preparative-Scale Synthesis of Vedejs Chiral DMAP Catalysts.

A scalable synthesis of chiral Vedejs-type DMAP catalysts is reported. The key step of the synthesis is amination of the enantiomerically pure 4-chloropyridine derivative using well-defined ZnCl2(amine)2 complexes. A series of Zn(II)-amine complexes have been synthesized to explore the scope of the ZnCl2-mediated amination of 4-halopyridines. Mechanistic studies support a Zn(II)-facilitated nucleophilic aromatic substitution as a plausible mechanism for the chlorine-to-amine exchange.

Azole-based non-peptidomimetic plasmepsin inhibitors.

The spread of drug-resistant malaria parasites urges the search for new antimalarial drugs. Malarial aspartic proteases - plasmepsins (Plms) - are differentially expressed in multiple stages of the Plasmodium parasite's lifecycle and are considered as attractive drug targets. We report the development of novel azole-based non-peptidomimetic plasmepsin inhibitors that have been designed by bioisosteric substitution of the amide moiety in the Actelion amino-piperazine inhibitors. The best triazole-based inhibitors show submicromolar potency toward Plm II, which is comparable to that of the parent Actelion compounds. The new inhibitors can be used as a starting point for the development of a resistance-free antimalarial drug targeting the non-digestive Plm IX or X, which are essential for the malaria parasite life cycle.

Synthesis of Benzoxazoles Using Electrochemically Generated Hypervalent Iodine.

The indirect ("ex-cell") electrochemical synthesis of benzoxazoles from imines using a redox mediator based on the iodine(I)/iodine(III) redox couple is reported. Tethering the redox-active iodophenyl subunit to a tetra-alkylammonium moiety allowed for anodic oxidation to be performed without supporting electrolyte. The mediator salt can be easily recovered and reused. Our "ex-cell" approach toward the electrosynthesis of benzoxazoles is compatible with a range of redox-sensitive functional groups. An unprecedented concerted reductive elimination mechanism for benzoxazole formation is proposed on the basis of control experiments and DFT calculations.

Development of a Chiral DMAP Catalyst for the Dynamic Kinetic Resolution of Azole Hemiaminals.

A new catalyst for the dynamic kinetic resolution of azole hemiaminals has been developed using late-stage structural modifications of the tert-leucinol-derived chiral subunit of DMAP species.

Para-Selective Cu-Catalyzed C-H Aryloxylation of Electron-Rich Arenes and Heteroarenes.

Cu-catalyzed reaction of phenols with electron-rich arene or heteroarene ligands of unsymmetrical diaryl-λ(3)-iodanes is a key step in the developed one-pot two-step method for intermolecular para-selective C-H aryloxylation of heteroarenes and arenes.

Stereoselective synthesis of the diazonamide a macrocyclic core.

Stereoselective synthesis of the right-hand heteroaromatic macrocycle of diazonamide A features C16-C18 bond formation in the Suzuki-Miyaura cross-coupling and atropodiastereoselective Dieckmann-type macrocyclization as key steps. The Suzuki-Miyaura cross-coupling gave the best yields when it was catalyzed by a palladium-dioxygen complex.

Copper-catalyzed intermolecular C-H amination of (hetero)arenes via transient unsymmetrical λ³-iodanes.

A one-pot two-step method for intermolecular C-H amination of electron-rich heteroarenes and arenes has been developed. The approach is based on a room-temperature copper-catalyzed regioselective reaction of the in situ formed unsymmetrical (hetero)aryl-λ(3)-iodanes with a wide range of primary and secondary aliphatic amines and anilines.

Diastereoselective hydroxymethylation of cyclic N-tert-butanesulfinylketimines using methoxymethanol as formaldehyde source.

Hydroxymethylation of cyclic tert-butanesulfinylketimine-derived lithium enamides with methoxymethanol proceeds with excellent diastereoselectivity (99:1 dr). Methoxymethanol is a stable and easy-to-handle source of anhydrous monomeric formaldehyde in the reaction with lithium enamides. Cyclic α-hydroxymethyl ketimines undergo highly diastereoselective reduction to syn- or anti-1,3-amino alcohols.

Development of Potent Microtubule Targeting Agent by Structural Simplification of Natural Diazonamide.

The marine metabolite diazonamide A exerts low nanomolar cytotoxicity against a range of tumor cell lines; however, its highly complex molecular architecture undermines the therapeutic potential of the natural product. We demonstrate that truncation of heteroaromatic macrocycle in natural diazonamide A, combined with the replacement of the challenging-to-synthesize tetracyclic hemiaminal subunit by oxindole moiety leads to considerably less complex analogues with improved drug-like properties and nanomolar antiproliferative potency. The structurally simplified macrocycles are accessible in 12 steps from readily available indolin-2-one and tert-leucine with excellent diastereoselectivity (99:1 dr) in the key macrocyclization step. The most potent macrocycle acts as a tubulin assembly inhibitor and exerts similar effects on A2058 cell cycle progression and induction of apoptosis as does marketed microtubule-targeting agent vinorelbine.

The novel adrenergic agonist ATR-127 targets skeletal muscle and brown adipose tissue to tackle diabesity and steatohepatitis.

OBJECTIVE: Simultaneous activation of ß2- and ß3-adrenoceptors (ARs) improves whole-body metabolism via beneficial effects in skeletal muscle and brown adipose tissue (BAT). Nevertheless, high-efficacy agonists simultaneously targeting these receptors whilst limiting activation of ß1-ARs - and thus inducing cardiovascular complications - are currently non-existent. Therefore, we here developed and evaluated the therapeutic potential of a novel ß2-and ß3-AR, named ATR-127, for the treatment of obesity and its associated metabolic perturbations in preclinical models. METHODS: In the developmental phase, we assessed the impact of ATR-127's on cAMP accumulation in relation to the non-selective ß-AR agonist isoprenaline across various rodent ß-AR subtypes, including neonatal rat cardiomyocytes. Following these experiments, L6 muscle cells were stimulated with ATR-127 to assess the impact on GLUT4-mediated glucose uptake and intramyocellular cAMP accumulation. Additionally, in vitro, and in vivo assessments are conducted to measure ATR-127's effects on BAT glucose uptake and thermogenesis. Finally, diet-induced obese mice were treated with 5 mg/kg ATR-127 for 21 days to investigate the effects on glucose homeostasis, body weight, fat mass, skeletal muscle glucose uptake, BAT thermogenesis and hepatic steatosis. RESULTS: Exposure of L6 muscle cells to ATR-127 robustly enhanced GLUT4-mediated glucose uptake despite low intramyocellular cAMP accumulation. Similarly, ATR-127 markedly increased BAT glucose uptake and thermogenesis both in vitro and in vivo. Prolonged treatment of diet-induced obese mice with ATR-127 dramatically improved glucose homeostasis, an effect accompanied by decreases in body weight and fat mass. These effects were paralleled by an enhanced skeletal muscle glucose uptake, BAT thermogenesis, and improvements in hepatic steatosis. CONCLUSIONS: Our results demonstrate that ATR-127 is a highly effective, novel ß2- and ß3-ARs agonist holding great therapeutic promise for the treatment of obesity and its comorbidities, whilst potentially limiting cardiovascular complications. As such, the therapeutic effects of ATR-127 should be investigated in more detail in clinical studies.

Electrochemical Synthesis of Dimeric λ3-Bromane: Platform for Hypervalent Bromine(III) Compounds.

A straightforward and scalable approach to a previously unreported class of cyclic hypervalent Br(III) species capitalizes on the anodic oxidation of aryl bromide to dimeric benzbromoxole that serves as a versatile platform to access a range of structurally diverse Br(III) congeners such as acetoxy-, alkoxy-, and ethynyl-λ3-bromanes as well as diaryl-λ3-bromanes. The synthetic utility of dimeric λ3-bromane is exemplified by photoinduced Minisci-type heteroarylation reactions and benzylic oxidation.

The emission efficiency of cationic solid state luminophores is directly proportional to the intermolecular charge transfer intensity.

Cationic luminophores have recently emerged as a class of efficient emitters in both the solid state and solutions. However, the underlying processes that secure the emission in these luminophores are poorly understood. Here, we employ charge transfer integral (CTI) analysis in combination with X-ray single crystal data to uncover the emission mechanism in a series of pyridinium luminophores. We demonstrate that the solid state photoluminescence quantum yield (Φ) of cationic luminophores is directly proportional to the charge transfer (CT) intensity within a network of molecules in the crystal lattice. Electrostatic intermolecular interactions between π+-systems in the crystal lattice provide a disproportionately high contribution to the CT intensity and therefore are instrumental in achieving high Φ. In addition, the strength of electrostatic interactions can be increased by a through-space (TS) electron-donation strategy. Hence, electrostatic interactions can be utilized as a tool to achieve radiative CT, which is useful in the development of efficient luminophores, sensors and nonlinear optical materials.