Domino Cyclization Reaction of o-Diisocyanoarenes for the Synthesis of Imidazo[1,2-a]pyridinobenzimidazole Backbones.

An efficient procedure to access a variety of connected imidazo[1,2-a]pyridine and benzimidazole skeletons through the C-N bond was described as a new type of Buchwald-Hartwig reaction. Furthermore, the bis(imidazo[1,2-a]pyridin-3-yl)aryl-1,2-diamine scaffolds were obtained by changing the equivalent ratio of the starting materials. Some advantages of the protocol are the formation of four new bonds (C═C, C-N), a transition-metal-free reaction, a broad substrate scope, high yields, and mild reaction conditions. The reaction mechanism was confirmed on the basis of DFT calculations.

Substrate-Controlled Three-Component Synthesis of Diverse Fused Heterocycles.

A chemoselective strategy toward a variety of fused heterocyclic scaffolds relying on a three-component condensation of heterocyclic ketene aminals (HKAs) or corresponding thioaminals with aryl glyoxals and cyclic 1,3-dicarbonyl compounds has been developed and explored. Depending on the applied combination of substrates, the strategy can be tuned to provide straightforward access to imidazo[1,2-a]quinoline, pyrrolo[1,2-a]imidazole, and pyrrolo[2,1-b]thiazole frameworks.

Versatile Diazomethane Sulfonamide for Expedited Exploration of Azole-Based Carbonic Anhydrase Inhibitors via [3+2] Cycloaddition.

A newly introduced diazo reagent, 1-diazo-N,N-bis(4-methoxybenzyl)methanesulfonamide, enables access to a range of azole-based primary sulfonamides via [3+2] cycloaddition followed by protecting group removal. Such compounds are representative of the sulfonamide chemical space highly relevant but hitherto not investigated in the context of inhibition of therapeutically relevant isoforms of carbonic anhydrase enzyme. Using this reagent, three sets of primary sulfonamides based on pyrazole, 1,2,3-triazole and tetrazole cores were synthesized and profiled for inhibition of tumor-associated hCA IX and XII isoforms as well as abundant cytosolic hCA I and II isoforms. Using virtual library design and docking prioritization tool of the Schrödinger suite, one of the promising leads was evolved into a dual hCA IX/XII inhibitor with excellent selectivity over off-target hCA I and II. The new synthetic strategy to access azole-based primary sulfonamides will support the discovery of novel, isoform-selective inhibitors of carbonic anhydrase within the poorly explored azole chemical space.

Periphery Exploration around 2,6-Diazaspiro[3.4]octane Core Identifies a Potent Nitrofuran Antitubercular Lead.

A small set of twelve compounds of a nitrofuran carboxamide chemotype was elaborated from a readily available 2,6-diazaspiro[3.4]octane building block, exploring diverse variants of the molecular periphery, including various azole substituents. The in vitro inhibitory activities of the synthesized compounds were assessed against Mycobacterium tuberculosis H37Rv. As a result, a remarkably potent antitubercular lead displaying a minimal inhibitory concentration of 0.016 µg/mL was identified.

Dual PTP1B/TC-PTP Inhibitors: Biological Evaluation of 3-(Hydroxymethyl)cinnoline-4(1H)-Ones.

Dual inhibitors of protein phosphotyrosine phosphatase 1B (PTP1B)/T-cell protein phosphotyrosine phosphatase (TC-PTP) based on the 3-(hydroxymethyl)-4-oxo-1,4-dihydrocinnoline scaffold have been identified. Their dual affinity to both enzymes has been thoroughly corroborated by in silico modeling experiments. The compounds have been profiled in vivo for their effects on body weight and food intake in obese rats. Likewise, the effects of the compounds on glucose tolerance, insulin resistance, as well as insulin and leptin levels, have been evaluated. In addition, the effects on PTP1B, TC-PTP, and Src homology region 2 domain-containing phosphatase-1 (SHP1), as well as the insulin and leptin receptors gene expressions, have been assessed. In obese male Wistar rats, a five-day administration of all studied compounds led to a decrease in body weight and food intake, improved glucose tolerance, attenuated hyperinsulinemia, hyperleptinemia and insulin resistance, and also compensatory increased expression of the PTP1B and TC-PTP genes in the liver. The highest activity was demonstrated by 6-Chloro-3-(hydroxymethyl)cinnolin-4(1H)-one (compound 3) and 6-Bromo-3-(hydroxymethyl)cinnolin-4(1H)-one (compound 4) with mixed PTP1B/TC-PTP inhibitory activity. Taken together, these data shed light on the pharmacological implications of PTP1B/TC-PTP dual inhibition, and on the promise of using mixed PTP1B/TC-PTP inhibitors to correct metabolic disorders.

Diazo Tetramic Acids Provide Access to Natural-Like Spirocyclic Δα,ß-Butenolides through Rh(II)-Catalyzed O-H Insertion/Base-Promoted Cyclization.

3-Diazotetramic acids were found to be valid substrates for the recently discovered approach toward natural-like Δα,ß-spirobutenolides via Rh(II)-catalyzed O-H insertion into propiolic acids followed by base-promoted intramolecular Michael addition. The target Δα,ß-spirobutenolides were obtained in generally high yields and, in the case of chiral 5-monosubstituted 3-diazotetramic acids, high diastereoselectivity. The synthesis of Δα,ß-spirobutenolides that we report here was virtually insensitive to the structure of the propiolic acids though it was somewhat sensitive to the structure of the 3-diazotetramic acids, thereby demonstrating quite a large scope. Thus, a new class of α-diazocarbonyl compounds suitable for the realization of the approach outlined above was identified.

Synthesis and Antibacterial Evaluation of Ciprofloxacin Congeners with Spirocyclic Amine Periphery.

The synthesis of novel fluoroquinolones, congeners of ciprofloxacin, which was inspired by earlier work on spirocyclic ciprofloxacin, is described. An antibacterial evaluation of the 11 fluoroquinolone compounds synthesized against the ESKAPE panel of pathogens in comparison with ciprofloxacin revealed that the more compact spirocycles in the fluoroquinolone periphery resulted in active compounds, while larger congeners gave compounds that displayed no activity at all. In the active cohort, the level of potency was comparable to that of ciprofloxacin. However, the spectrum of antibacterial activity was quite different, as the new compounds showed no activity against Pseudomonas aeruginosa. Among the prepared and tested compounds, the broadest range of activity (five pathogens of the six in the ESKAPE panel) and the highest level of activity were demonstrated by 1-yclopropyl-7-[8-(4-cyclopropyl-4H-1,2,4-triazol-3-yl)-6-azaspiro[3.4]oct-6-yl]-6-fluoro-4-oxo-1,4-dihydroquinoline-3-carboxylic acid, which is the lead compound nominated for further characterization and development.

A Series of Trifluoromethylisoxazolyl- and Trifluoromethylpyrazolyl- Substituted (Hetero)aromatic Sulfonamide Carbonic Anhydrase Inhibitors: Synthesis, and Convenient Prioritization Workflow for Further In Vivo Studies.

AIMS: To synthesize novel sulfonamide inhibitors of carbonic anhydrase and develop in vitro prioritization workflow to select compounds for in vivo evaluation. BACKGROUND: Carbonic anhydrase (CA) inhibitors gain significant attention in the context of drug discovery research for glaucoma, hypoxic malignancies, and bacterial infections. In previous works, we have successfully used direct sulfochlorination approach to develop diverse heterocyclic primary sulfonamides with remarkable activity and selectivity against therapeutically relevant CA isoforms. OBJECTIVE: Synthesis and investigation of the CA inhibitory properties of novel trifluoromethylisoxazolyl- and trifluoromethylpyrazolyl-substituted (hetero)aromatic sulfonamides. METHODS: Thirteen trifluoromethylisoxazolyl- and thirteen trifluoromethylpyrazolyl-substituted (hetero) aromatic sulfonamides were synthesized by direct sulfochlorination of hydroxyisoxazolines and pyrazoles followed by reaction with ammonia. The compound structures were confirmed by 1H and 13C NMR as well as element analysis. The obtained compounds were evaluated, using the CA esterase activity assay, for their potential to block the catalytic activity of bovine CA (bCA). RESULTS: Eight most potent compounds selected based on the esterase activity assay data were tested for direct affinity to the enzyme using the thermal shift assay (TSA). These compounds displayed Kd values (measured by TSA) in the double-digit nanomolar range, thus showing comparable activity to the reference drug acetazolamide. CONCLUSION: Coupling the bCA esterase activity assay with thermal shift assay represents a streamlined and economical strategy for the prioritization of sulfonamide CA inhibitors for subsequent evaluation in vivo.

Synthesis of novel glutarimide ligands for the E3 ligase substrate receptor Cereblon (CRBN): Investigation of their binding mode and antiproliferative effects against myeloma cell lines.

To expand the chemical toolkit for targeted protein degradation, we report the generation of a new series of non-thalidomide Cereblon (CRBN) ligands. Readily available 2-methylidene glutarimide was converted to a series of 2-((hetero)aryl(methyl))thio glutarimides via the thio-Michael addition reaction. The compounds thus synthesized were evaluated for their affinity to the thalidomide-binding domain of human CRBN and their binding modes studied via X-ray crystallography. This helped identify several promising glutarimide derivatives which bind stronger to CRBN compared to thalidomide and contain a functional group which permits further chemical conjugation. Oxidation of the sulfur atom in a select group of 2-((hetero)aryl(methyl))thio glutarimides produced the respective sulfones which were found to possess a markedly stronger antiproliferative profile against multiple myeloma cell lines and a sophisticated structural binding mode with additional hydrogen bonding interactions. The newly identified Cereblon ligands form the basis for the synthesis of novel PROTAC protein degraders.

A novel bis-triazole scaffold accessed via two tandem [3 + 2] cycloaddition events including an uncatalyzed, room temperature azide-alkyne click reaction.

The previously described α-acetyl-α-diazomethanesulfonamide was employed in a three-component reaction with azide-containing benzaldehydes and propargylamines. Besides the initial formation of the triazole core, the reaction proceeded further, in uncatalyzed fashion at room temperature and yielded, after intramolecular azide-alkyne click reaction novel, structurally intriguing bistriazoles.

One-Pot Sequence of Staudinger/aza-Wittig/Castagnoli-Cushman Reactions Provides Facile Access to Novel Natural-like Polycyclic Ring Systems.

Realization of the one-pot Staudinger/aza-Wittig/Castagnoli-Cushman reaction sequence for a series of azido aldehydes and homophthalic anhydrides is described. The reaction proceeded at room temperature and delivered novel polyheterocycles related to the natural product realm in high yields and high diastereoselectivity. The methodology has been extended to three other cyclic anhydrides. These further unravel the potential of the Castagnoli-Cushman reaction in generating polyheterocyclic molecular scaffolds.

The Use of Aryl-Substituted Homophthalic Anhydrides in the Castagnoli-Cushman Reaction Provides Access to Novel Tetrahydroisoquinolone Carboxylic Acid Bearing an All-Carbon Quaternary Stereogenic Center.

Novel aryl-substituted homophthalic acids were cyclodehydrated to the respective homophthalic anhydrides for use in the Castagnoli-Cushman reaction. With a range of imines, this reaction proceeded smoothly and delivered hitherto undescribed 4-aryl-substituted tetrahydroisoquinolonic acids with remarkable diastereoselectivity, good yields and no need for chromatographic purification. These findings significantly extend the range of cyclic anhydrides employable in the Castagnoli-Cushman reaction and signify access to a novel substitution pattern around the medicinally relevant tetrahydroisoquinolonic acid scaffold.

A novel spirocyclic scaffold accessed via tandem Claisen rearrangement/intramolecular oxa-Michael addition.

A straightforward access to novel spiro[benzofuran-2,3'-pyrrolidine]-2',5'-diones based on the Rh2(esp)2-catalyzed insertion of carbenes derived from diazo arylidene succinimides (DAS) into the O-H bond of phenols is described. The initial adducts underwent a thermally promoted Claisen rearrangement followed by DABCO-catalyzed intramolecular 5-exo-trig oxa-Michael addition.

In situ generation of imines by the Staudinger/aza-Wittig tandem reaction combined with thermally induced Wolff rearrangement for one-pot three-component ß-lactam synthesis.

A new efficient protocol for diastereoselective three-component one-pot lactam synthesis involving the in situ generation of imines via the Staudinger/aza-Wittig tandem reaction combined with the Wolff-rearrangement and ketene-imine cycloaddition was developed to produce a series of 24 novel structurally diverse ß-lactam- or 1,3-oxazine-products. It was shown that this synthesis can be performed both as a two step-procedure and true MCR with simultaneous loading of all reactants. The intramolecular version of the 1st step provided facile access to seven-membered cyclic imines, which allowed further preparation of a series of rare tricyclic ß-lactams. For the intermolecular version of the 1st step (acyclic imine generation), it was shown that the outcome of the synthesis is different from that using pre-synthesized and isolated imines. Additionally, this is the first example of the implementation of the Staudinger/aza-Wittig tandem reaction for the preparation of four-membered heterocycles.

Extending the Scope of the New Variant of the Castagnoli-Cushman Cyclocondensation onto o-Methyl Benzoic Acids Bearing Various Electron-Withdrawing Groups in the α-Position.

Based on the previously reported involvement of homophthalic acid monoesters in the Castagnoli-Cushman reaction-type cyclocondensation with imines, we tested a number of other o-methyl benzoic acids bearing various electron-withdrawing groups in the α-position. The majority of these substrates delivered the expected tetrahydroisoquinolone adducts on activation with CDI or acetic anhydride. Homophthalic acid mononitriles displayed the highest promise as substrates for the new reaction, both in terms of scope and product yields. Homophthalic acid monoamides either gave low yields or failed to react with imines. Sulfonyl-substituted substrates gave the desired (and hitherto unknown) type of tetrahydroisoquinolines. Despite the low yields, this approach to sulfonyl-substituted tetrahydroisoquinolines appears practical as alternative syntheses based on the traditional, carboxylic acid CCR adducts would presumably be cumbersome and multistep. The azido- and nitro-substituted o-methyl benzoic acids failed to react with imines.

Discovery of Trace Amine Associated Receptor 1 (TAAR1) Agonist 2-(5-(4'-Chloro-[1,1'-biphenyl]-4-yl)-4H-1,2,4-triazol-3-yl)ethan-1-amine (LK00764) for the Treatment of Psychotic Disorders.

A focused in-house library of about 1000 compounds comprising various heterocyclic motifs in combination with structural fragments similar to ß-phenethylamine (PEA) or tyramine was screened for the agonistic activity towards trace amine-associated receptor 1 (TAAR1). The screening yielded two closely related hits displaying EC50 values in the upper submicromolar range. Extensive analog synthesis and testing for TAAR1 agonism in a BRET-based cellular assay identified compound 62 (LK00764) with EC50 = 4.0 nM. The compound demonstrated notable efficacy in such schizophrenia-related in vivo tests as MK-801-induced hyperactivity and spontaneous activity in rats, locomotor hyperactivity of dopamine transporter knockout (DAT-KO) rats, and stress-induced hyperthermia (i.p. administration). Further preclinical studies are necessary to evaluate efficacy, safety and tolerability of this potent TAAR1 agonist for the potential development of this compound as a new pharmacotherapy option for schizophrenia and other psychiatric disorders.

Discovery and In Vivo Efficacy of Trace Amine-Associated Receptor 1 (TAAR1) Agonist 4-(2-Aminoethyl)-N-(3,5-dimethylphenyl)piperidine-1-carboxamide Hydrochloride (AP163) for the Treatment of Psychotic Disorders.

Starting from a screening hit, a set of analogs was synthesized based on a 4-(2-aminoethyl)piperidine core not associated previously with trace amine-associated receptor 1 (TAAR1) modulation in the literature. Several structure-activity relationship generalizations have been drawn from the observed data, some of which were corroborated by molecular modeling against the crystal structure of TAAR1. The four most active compounds (EC50 for TAAR1 agonistic activity ranging from 0.033 to 0.112 µM) were nominated for evaluation in vivo. The dopamine transporter knockout (DAT-KO) rat model of dopamine-dependent hyperlocomotion was used to evaluate compounds' efficacy in vivo. Out of four compounds, only one compound (AP163) displayed a statistically significant and dose-dependent reduction in hyperlocomotion in DAT-KO rats. As such, compound AP163 represents a viable lead for further preclinical characterization as a potential novel treatment option for disorders associated with increased dopaminergic function, such as schizophrenia.

New reagent space and new scope for the Castagnoli-Cushman reaction of oximes and 3-arylglutaconic anhydrides.

The Castagnoli-Cushman reaction of oximes, discovered originally for homophthalic anhydride, stimulated the search for other cyclic anhydrides that would be workable in that reaction. Finally, 3-arylglutaconic acid anhydrides were identified as displaying the right reactivity towards a wide range of oximes (including those which did not react with homophthalic anhydride, such as derivatives of aliphatic aldehydes or ketones and substrates with nucleophilic side groups) and delivering, after 18 h at 110 °C in DMSO, ß,γ-unsaturated N-hydroxylactam products lacking the carboxylic acid functionality as the result of decarboxylation accompanying the cyclocondensation process. The reaction was found to be scalable to gram quantities of the starting anhydrides. The products were shown to be easily amenable to post-condensational double-bond transposition or reduction. As expected from cyclic hydroxamic acids, the reaction products were shown to bind Fe(III) and Cu(II) ions (selectively out of a panel of 16 metal cations) and potentially serve as fluorescent metal sensors.

Facile and diastereoselective arylation of the privileged 1,4-dihydroisoquinolin-3(2H)-one scaffold.

A practically convenient and streamlined protocol for the trans-diastereoselective introduction of an aryl substituent at position 4 of the 1,4-dihydroisoquinol-3-one (1,4-DHIQ) scaffold is presented. The protocol involves direct Regitz diazo transfer onto readily available 3(2H)-isoquinolones followed by TfOH-promoted hydroarylation by an arene molecule. Screening of the novel 1,2,4-trisubstituted 1,4-DHIQs against cancer cell lines confirmed high cytotoxicity of selected analogs, which validates this new chemotype for further investigations as anticancer cytotoxic agents.

Novel 5-Nitrofuran-Tagged Imidazo-Fused Azines and Azoles Amenable by the Groebke-Blackburn-Bienaymé Multicomponent Reaction: Activity Profile against ESKAPE Pathogens and Mycobacteria.

A chemically diverse set of 13 5-nitrofuran-tagged heterocyclic compounds has been prepared via the Groebke-Blackburn-Bienaymé multicomponent reaction. The testing of these compounds against the so-called ESKAPE panel of pathogens identified an apparent lead compound-N-cyclohexyl-2-(5-nitrofuran-2-yl)imidazo[1,2-a]pyridine-3-amine (4a)-which showed an excellent profile against Enterobacter cloacae, Staphylococcus aureus, Klebsiella pneumoniae, and Enterococcus faecalis (MIC 0.25, 0.06, 0.25 and 0.25 µg/mL, respectively). Its antibacterial profile and practically convenient synthesis warrant further pre-clinical development. Certain structure-activity relationships were established in the course of this study which were rationalized by the flexible docking experiments in silico. The assessment of antitubercular potential of the compounds synthesized against drug sensitive H37v strain of Mycobacterium tuberculosis revealed little potential of the imidazo-fused products of the Groebke-Blackburn-Bienaymé multicomponent reaction as chemotherapeutic agents against this pathogen.