Elucidation of an anaerobic pathway for metabolism of l-carnitine-derived γ-butyrobetaine to trimethylamine in human gut bacteria.

Trimethylamine (TMA) is an important gut microbial metabolite strongly associated with human disease. There are prominent gaps in our understanding of how TMA is produced from the essential dietary nutrient l-carnitine, particularly in the anoxic environment of the human gut where oxygen-dependent l-carnitine-metabolizing enzymes are likely inactive. Here, we elucidate the chemical and genetic basis for anaerobic TMA generation from the l-carnitine-derived metabolite γ-butyrobetaine (γbb) by the human gut bacterium Emergencia timonensis We identify a set of genes up-regulated by γbb and demonstrate that the enzymes encoded by the induced γbb utilization (bbu) gene cluster convert γbb to TMA. The key TMA-generating step is catalyzed by a previously unknown type of TMA-lyase enzyme that utilizes a putative flavin cofactor to catalyze a redox-neutral transformation. We identify additional cultured and uncultured host-associated bacteria that possess the bbu gene cluster, providing insights into the distribution of anaerobic γbb metabolism. Lastly, we present genetic, transcriptional, and metabolomic evidence that confirms the relevance of this metabolic pathway in the human gut microbiota. These analyses indicate that the anaerobic pathway is a more substantial contributor to TMA generation from l-carnitine in the human gut than the previously proposed aerobic pathway. The discovery and characterization of the bbu pathway provides the critical missing link in anaerobic metabolism of l-carnitine to TMA, enabling investigation into the connection between this microbial function and human disease.

Design, Synthesis and Biological Evaluation of Arylpyridin-2-yl Guanidine Derivatives and Cyclic Mimetics as Novel MSK1 Inhibitors. An Application in an Asthma Model.

Mitogen- and Stress-Activated Kinase 1 (MSK1) is a nuclear kinase, taking part in the activation pathway of the pro-inflammatory transcription factor NF-kB and is demonstrating a therapeutic target potential in inflammatory diseases such as asthma, psoriasis and atherosclerosis. To date, few MSK1 inhibitors were reported. In order to identify new MSK1 inhibitors, a screening of a library of low molecular weight compounds was performed, and the results highlighted the 6-phenylpyridin-2-yl guanidine (compound 1a, IC50~18 µM) as a starting hit for structure-activity relationship study. Derivatives, homologues and rigid mimetics of 1a were designed, and all synthesized compounds were evaluated for their inhibitory activity towards MSK1. Among them, the non-cytotoxic 2-aminobenzimidazole 49d was the most potent at inhibiting significantly: (i) MSK1 activity, (ii) the release of IL-6 in inflammatory conditions in vitro (IC50~2 µM) and (iii) the inflammatory cell recruitment to the airways in a mouse model of asthma.

Structure-Guided Identification of a Small Molecule That Inhibits Anaerobic Choline Metabolism by Human Gut Bacteria.

The anaerobic gut microbial pathway that converts choline into trimethylamine (TMA) is broadly linked to human disease. Here, we describe the discovery that betaine aldehyde inhibits TMA production from choline by human gut bacterial isolates and a complex gut community. In vitro assays and a crystal structure suggest betaine aldehyde targets the gut microbial enzyme choline TMA-lyase (CutC). In our system, we do not observe activity for the previously reported CutC inhibitor 3,3-dimethylbutanol (DMB). The workflow we establish for identifying and characterizing betaine aldehyde provides a framework for developing additional inhibitors of gut microbial choline metabolism, including therapeutic candidates.

Efficient and Mild Ullmann-Type N-Arylation of Amides, Carbamates, and Azoles in Water.

A simple, sustainable, efficient, mild, and low-cost protocol was developed for d-glucose-assisted Cu-catalyzed Ullmann reactions in water for amides, carbamates, and nitrogen-containing heterocycles. The reaction was compatible with diverse aryl/heteroaryl iodides, giving highly substituted pyridine, indole, or indazole rings. This method offers an attractive alternative to existing protocols, because the reaction proceeds in aqueous media, occurs at or near ambient temperature, and provides the N-arylated products in good to high yields.

Discovery of a Cyclic Choline Analog That Inhibits Anaerobic Choline Metabolism by Human Gut Bacteria.

The anaerobic conversion of choline to trimethylamine (TMA) by the human gut microbiota has been linked to multiple human diseases. The potential impact of this microbial metabolic activity on host health has inspired multiple efforts to identify small molecule inhibitors. Here, we use information about the structure and mechanism of the bacterial enzyme choline TMA-lyase (CutC) to develop a cyclic choline analog that inhibits the conversion of choline to TMA in bacterial whole cells and in a complex gut microbial community. In vitro biochemical assays and a crystal structure suggest that this analog is a competitive, mechanism-based inhibitor. This work demonstrates the utility of structure-based design to access inhibitors of radical enzymes from the human gut microbiota.

On water N-arylation of oxetanylamines for the preparation of N-aryl-oxetanylamines; potentially useful aryl-amide isosteres.

A Pd cross-coupling approach for the synthesis of N-aryl-oxetanylamines has been developed. This method provides new building blocks potentially useful in medicinal chemistry as amide bioisosteres. The reactions are conducted in water employing the renewable feedstock surfactant TPGS-750-M.

Design and synthesis of 3-aminophthalazine derivatives and structural analogues as PDE5 inhibitors: anti-allodynic effect against neuropathic pain in a mouse model.

Neuropathic pain is a chronic pain caused by a lesion or disease affecting the somatosensory nervous system. To date, no specific treatment has been developed to cure this pain. Antidepressants and anticonvulsant drugs are used, but they do not demonstrate universal efficacy, and they often cause detrimental adverse effects. Some studies highlighted the efficacy of sildenafil, a well-known inhibitor of phosphodiesterase 5 (PDE5, (IC50 = 3.3 nM)), in models of pain. Based on these results, we focused our attention on MY 5445, another known PDE5 inhibitor. Homologues, isosteres and structural analogues of MY 5445 were designed and all synthesized compounds were evaluated for their inhibitory activity toward PDE5. Selectivity profiles towards other PDE1-4 isoenzymes, water solubility and stability in acidic medium of the most potent PDE5 inhibitors were determined and the aminophthalazine 16h and its mimetic 41n (3-aminoindazole) were evaluated in comparison to MY 5445 (4b) in vivo in a model of neuropathic pain induced by sciatic nerve cuffing in mice (3 and 0.5 mg/kg, ip twice a day). Both compounds showed the same efficacy on neuropathic allodynia as MY 5445, and thus produced a significant relief of mechanical hypersensitivity after 12 days of treatment.

Heteroarylguanidines as Allosteric Modulators of ASIC1a and ASIC3 Channels.

Acid-sensing ion channels (ASICs) are neuronal Na+-selective ion channels that open in response to extracellular acidification. They are involved in pain, fear, learning, and neurodegeneration after ischemic stroke. 2-Guanidine-4-methylquinazoline (GMQ) was recently discovered as the first nonproton activator of ASIC3. GMQ is of interest as a gating modifier and pore blocker of ASICs. It has however a low potency, and exerts opposite effects on ASIC1a and ASIC3. To further explore the molecular mechanisms of GMQ action, we have used the guanidinium moiety of GMQ as a scaffold and tested the effects of different GMQ derivatives on the ASIC pH dependence and maximal current. We report that GMQ derivatives containing quinazoline and quinoline induced, as GMQ, an alkaline shift of the pH dependence of activation in ASIC3 and an acidic shift in ASIC1a. Another group of 2-guanidinopyridines shifted the pH dependence of both ASIC1a and ASIC3 to more acidic values. Several compounds induced an alkaline shift of the pH dependence of ASIC1a/2a and ASIC2a/3 heteromers. Compared to GMQ, guanidinopyridines showed a 20-fold decrease in the IC50 for ASIC1a and ASIC3 current inhibition at pH 5. Strikingly, 2-guanidino-quinolines and -pyridines showed a concentration-dependent biphasic effect that resulted at higher concentrations in ASIC1a and ASIC3 inhibition (IC50 > 100 µM), while causing at lower concentration a potentiation of ASIC1a, but not ASIC3 currents (EC50 ≈ 10 µM). In conclusion, we describe a new family of small molecules as ASIC ligands and identify an ASIC subtype-specific potentiation by a subgroup of these compounds.

Phenylpyridine-2-ylguanidines and rigid mimetics as novel inhibitors of TNFα overproduction: Beneficial action in models of neuropathic pain and of acute lung inflammation.

4-phenylpyridin-2-yl-guanidine (5b): a new inhibitor of the overproduction of pro-inflammatory cytokines (TNFα and Il1ß) was identified from a high-throughput screening of a chemical library on human peripheral blood mononuclear cells (PBMCs) after LPS stimulation. Derivatives, homologues and rigid mimetics of 5b were designed and synthesized, and their cytotoxicity and ability to inhibit TNFα overproduction were evaluated. Among them, compound 5b and its mimetic 12 (2-aminodihydroquinazoline) showed similar inhibitory activities, and were evaluated in vivo in models of lung inflammation and neuropathic pain in mice. In particular, compound 12 proved to be active (5 mg/kg, ip) in both models.

d-Glucose: An Efficient Reducing Agent for a Copper(II)-Mediated Arylation of Primary Amines in Water.

A copper-catalyzed Ullmann-type amination with primary amines in water with a combination of copper(II) triflate [Cu(OTf)2 ], dipivaloylmethane, and d-glucose is reported. The mild conditions and the use of an inexpensive catalyst as well as a renewable feedstock (d-glucose and the surfactant TPGS-750-M, which is derived from vitamin E) make this protocol a safe and convenient strategy for efficient C-N bond formation. This easy-to-handle procedure is extremely competitive compared to palladium-based reactions and may be used to synthesize N-containing molecules, such as drugs or organic light-emitting diodes (OLEDs).