Design, synthesis, and structure–affinity relationship studies in NK1 receptor ligands based on azole-fused quinolinecarboxamide moieties

Imidazoquinoline Derivatives as Potential Inhibitors of InhA Enzyme and Mycobacterium tuberculosis

Tuberculosis is a serious public health problem worldwide. The search for new antibiotics has become a priority, especially with the emergence of resistant strains. A new family of imidazoquinoline derivatives, structurally analogous to triazolophthalazines, which had previously shown good antituberculosis activity, were designed to inhibit InhA, an essential enzyme for Mycobacterium tuberculosis survival. Over twenty molecules were synthesized and the results showed modest inhibitory efficacy against the protein. Docking experiments were carried out to show how these molecules could interact with the protein's substrate binding site. Disappointingly, unlike triazolophthlazines, these imidazoquinoline derivatives showed an absence of inhibition on mycobacterial growth.

Trifluoromethyl Rhodium-Carbynoid in [2+1+2] Cycloadditions

Trifluoromethyl cationic carbyne (CF3 C+ :) possessing dual carbene-carbocation behavior emulated as trifluoromethyl metal-carbynoid (CF3 C+ =M) has not been explored yet, and its reaction characteristics are unknown. Herein, a novel α-diazotrifluoroethyl sulfonium salt was prepared and used in Rh-catalyzed three-component [2+1+2] cycloadditions for the first time with commercially available N-fused heteroarenes and nitriles, yielding a series of imidazo[1,5-a] N-heterocycles that are of interest in medicinal chemistry, in which the insertion of trifluoromethyl Rh-carbynoid (CF3 C+ =Rh) into C=N bonds of N-fused heteroarenes was involved. This strategy demonstrates synthetic applications in late-stage modification of pharmaceuticals, construction of CD3 -containing N-heterocycles, gram-scale experiments, and synthesis of phosphodiesterase 10A inhibitor analog. These highly valuable and modifiable imidazo[1,5-a] N-heterocycles exhibit good antitumor activity in vitro, thus demonstrating their potential applications in medicinal chemistry.

Diversity-Oriented Metal-Free Synthesis of Nitrogen-Containing Heterocycles Using Atropaldehyde Acetals as a Dual C3/C2-Synthon

A highly efficient and elegant diversity-oriented reaction paradigm employing atropaldehyde acetals as new dual C2/C3 synthons was developed under metal-free conditions using glycine esters as the counterpart reagents, which allowed rapid synthesis of two important nitrogen-containing heterocycles, pyrrolo[1,2-a]quinolines and 3,5-diarylpyridines. The divergent products are subtly controlled by the manipulation of the substitutional groups of glycine esters. When a N-arylglycine ester was used, pyrrolo[1,2-a]quinolines can be formed through cascade oxidative C-C cleavage/multiple cyclization. Instead, N-benzylglycine ester as the counter-reagent led to the synthesis of 3,5-diarylpyridines via two key C-N cleavages. Mild conditions, broad substrate scope, scalability and environmentally acceptable organic solvents rendered this method practical and attractive.

Electrochemical [4 + 1] Tandem sp3(C-H) Double Amination for the Direct Synthesis of 3-Acyl-Functionalized Imidazo[1,5-a]pyridines

3-Acyl imidazo[1,5-a]pyridines, featured pharmaceutical moieties that were prepared by a three-step reaction conventionally, could be obtained in one step by an electrochemical tandem sp³ (C-H) double amination of acetophenones with pyridine ethylamines using ammonium iodide as a redox mediator.

CBr4 Mediated [4 + 1] Dehydrocyclization for the Synthesis of Functionalized Imidazo[1,5-a]heterocycles from Pyridin-2-ylmethanamines and Aldehydes

A CBr₄ mediated [4 + 1] dehydrocyclization was developed for the synthesis of imidazo[1,5-a]heterocycles from pyridin-2-ylmethanamines and aldehydes. This method was highly practical with the advantages of wide substrate scope, functional group tolerance, and mild reaction conditions.

Calcium-Catalyzed Stereoselective Tandem [4+2] and [3+2] Annulation Reaction for the Synthesis of Dihydropyrrolo[1,2-a]quinolines

Calcium-catalyzed highly facile one-pot, A⁴ annulation of aldehyde, amine, alkene, and alkyne to form fused 4,5-dihydropyrrolo[1,2-a]quinolines with exclusive syn diastereoselectivity is reported. This selectivity arises from an inverse electron demand [4+2] aza-Diels-Alder cycloaddition, and the adduct further undergoes a formal [3+2] cyclization with activated alkynes. This diversity-oriented protocol is highly general and furnishes the dihydropyrrolo[1,2-a]quinoline derivatives with a broad substrate scope in good to excellent yields.

Synthesis of pyrrolo[1,2-a]quinolines by formal 1,3-dipolar cycloaddition reactions of quinolinium salts

Quinolinium salts, Q+-CH2-CO2Me Br- and Q+-CH2-CONMe2 Br- (where Q = quinoline), were prepared from quinolines. Deprotonation of these salts with triethylamine promoted the reaction of the resulting quinolinium ylides (formally azomethine ylides) with electron-poor alkenes by conjugate addition followed by cyclization or by [3 + 2] dipolar cycloaddition. The pyrroloquinoline products were formed as single regio- and stereoisomers. These could be converted to other derivatives by Suzuki-Miyaura coupling, reduction or oxidation reactions.

Metal-free synthesis of imidazo[1,5-a]pyridines via elemental sulfur mediated sequential dual oxidative Csp3-H amination

A simple and efficient approach has been developed for the synthesis of imidazo[1,5-a]pyridines using the elemental sulfur mediated sequential dual oxidative Csp3-H amination of 2-pyridyl acetates and amines under metal- and peroxide-free conditions. Broad substrate scope, operational simplicity and gram-scale ability make this chemistry very practical.

The synthesis of imidazo[1,5-a]quinolinesviaa decarboxylative cyclization under metal-free conditions

An iodine-mediated decarboxylative cyclization was developed from α-amino acids and 2-methyl quinolines under metal-free conditions, affording a variety of imidazo[1,5-a]quinolines with moderate to good yields.

An iodine-mediated decarboxylative cyclization was developed from α-amino acids and 2-methyl quinolines under metal-free conditions, affording a variety of imidazo[1,5-a]quinolines with moderate to good yields.

Design, Synthesis, and Biological Evaluation of Imidazo[1,5-a]quinoline as Highly Potent Ligands of Central Benzodiazepine Receptors

A series of imidazo[1,5-a]quinoline derivatives was designed and synthesized as central benzodiazepine receptor (CBR) ligands. Most of the compounds showed high CBR affinity with Ki values within the submicromolar and subnanomolar ranges with interesting modulations in their structure-affinity relationships. In particular, fluoroderivative 7w (Ki = 0.44 nM) resulted in the most potent ligand among the imidazo[1,5-a]quinoline derivatives described so far. Overall, these observations confirmed the assumption concerning the presence of a large though apparently saturable lipophilic pocket in the CBR binding site region interacting with positions 4 and 5 of the imidazo[1,5-a]quinoline nucleus. The in vivo biological characterization revealed that compounds 7a,c,d,l,m,q,r,w show anxiolytic and antiamnestic activities without the unpleasant myorelaxant side effects of the classical 1,4-BDZ. Furthermore, the effect of 7l,q,r, and 8i in lowering lactate dehydrogenase (LDH) release induced by ischemia-like conditions in rat brain slices suggested neuroprotective properties for these imidazo[1,5-a]quinoline derivatives.

Isonitrile alkylations: a rapid route to imidazo[1,5-a]pyridines

Metalated arylmethylisonitriles readily add to 2-chloropyridines to afford imidazo[1,5-a]pyridines. Analogous additions to imidoyl chlorides and a chloroquinoline provide imidazoles and an imidazo[1,5-a]quinolone which, like imidazo[1,5-a]pyridines, are valuable heterocycles for pharmaceutical synthesis.

Iodine-promoted sequential dual oxidative Csp3–H amination/Csp3–H iodination reactions: efficient synthesis of 1-iodoimidazo[1,5-a]pyridines

An iodine-promoted sequential dual oxidative C_sp3–H amination of aryl methyl ketones and C_sp3–H iodination of pyridin-2-ylmethanamines have been realized for the first time. This simple and efficient approach constructed 1-iodoimidazo[1,5-a]pyridines in moderate to good yields.

Construction of benzo-fused indolizines, pyrrolo[1,2-a]quinolines via alkyne–carbonyl metathesis

The strategic use of a sequential Sonogashira coupling/intramolecular alkyne–carbonyl metathesis process for the synthesis of a pyridine ring from 1-(2-haloaryl)-1H-pyrrole-2-carbaldehydes allowed ready access to diverse novel benzo-fused indolizines, pyrrolo[1,2-a]quinolines, in good to excellent yields.

Cerium(iii)-catalyzed cascade cyclization: an efficient approach to functionalized pyrrolo[1,2-a]quinolines

A general and practical route to the synthesis of multisubstituted pyrrolo[1,2-a]quinolines has been described from 2-alkylazaarenes and nitroolefins using cerium chloride as a catalyst via a tandem Michael addition, cyclization and aromatization.

Targeting the Akt1 allosteric site to identify novel scaffolds through virtual screening

Preclinical data and tumor specimen studies report that AKT kinases are related to many human cancers. Therefore, identification and development of small molecule inhibitors targeting AKT and its signaling pathway can be therapeutic in treatment of cancer. Numerous studies report inhibitors that target the ATP-binding pocket in the kinase domains, but the similarity of this site, within the kinase family makes selectivity a major problem. The sequence identity amongst PH domains is significantly lower than that in kinase domains and developing more selective inhibitors is possible if PH domain is targeted. This in silico screening study is the first time report toward the identification of potential allosteric inhibitors expected to bind the cavity between kinase and PH domains of Akt1. Structural information of Akt1 was used to develop structure-based pharmacophore models comprising hydrophobic, acceptor, donor and ring features. The 3D structural information of previously identified allosteric Akt inhibitors obtained from literature was employed to develop a ligand-based pharmacophore model. Database was generated with drug like subset of ZINC and screening was performed based on 3D similarity to the selected pharmacophore hypotheses. Binding modes and affinities of the ligands were predicted by Glide software. Top scoring hits were further analyzed considering 2D similarity between the compounds, interactions with Akt1, fitness to pharmacophore models, ADME, druglikeness criteria and Induced-Fit docking. Using virtual screening methodologies, derivatives of 3-methyl-xanthine, quinoline-4-carboxamide and 2-[4-(cyclohexa-1,3-dien-1-yl)-1H-pyrazol-3-yl]phenol were proposed as potential leads for allosteric inhibition of Akt1.

Natural α-amino acids applied in the synthesis of imidazo[1,5-a]N-heterocycles under mild conditions

A facile iodine-mediated decarboxylative cyclization from α-amino acids and N-heterocyclic carbaldehydes was developed. By virtue of this method, a series of imidazo[1,5-a]N-heterocycles can be synthesized efficiently under mild conditions. A tentative reaction mechanism was proposed based on the experimental results and previous reports.

Non-peptide NK1 receptor ligands based on the 4-phenylpyridine moiety

The quinoline nucleus of the previously described 4-phenylquinoline-3-carboxamides NK(1) receptor ligands 7 has been transformed into either substituted or azole-(i.e., triazole or tetrazole) fused pyridine moieties of compounds 9 and 10, respectively, in order to obtain NK(1) receptor ligands showing lower molecular weight or higher hydrophilicity. The program of molecular manipulations produced NK(1) receptor ligands showing affinity in the nanomolar range. In particular, 4-methyl-1-piperazinyl derivative 9j showed an IC(50) value of 4.8 nM and was proved to behave as a NK(1) antagonist blocking Sar(9)-SP-sulfone induced proliferation and migration of microvascular endothelial cells. Therefore, compound 9j has been labeled with [(11)C]CH(3)I (t(1/2)=20.4 min, β(+)=99.8%) starting from the corresponding des-methyl precursor 9i using with a radiochemical yield of about 10% (not decay corrected) and a specific radioactivity>1 Ci/μmol in order to be used as a radiotracer in next PET studies.

Isocyanides in the synthesis of nitrogen heterocycles

Isocyanides have long proved themselves to be irreplaceable building blocks in modern organic chemistry. The unique features of the isocyano group make isocyanides particularly useful for the synthesis of a number of important classes of nitrogen heterocycles, such as pyrroles, indoles, and quinolines. Several cocyclizations of isocyanides via zwitterions and radical intermediates as well as transition-metal-catalyzed syntheses of different types of heterocycles have recently been developed. Methods starting from isocyanides often have distinct advantages over alternative approaches to the same heterocycles because of their enhanced convergence, the great simplicity of most of the operations with them, and the great variety of isocyanides readily available for use. Isocyanides have also been used in some enantioselective syntheses of chiral heterocyclic compounds, including natural products as well as precursors thereof.

7-[4-(4-Fluorophenyl)-2-methylsulfanyl-1H-imidazol-5-yl]tetrazolo[1,5-a]pyridine

The crystal structure of the title compound, C₁₅H₁₁FN₆S, forms a three-dimensional network stabilized by π–π inter­actions between the imidazole core and the tetra­zole ring of the tetra­zolopyridine­unit; the centroid–centroid distance is 3.627 (1) Å. The crystal structure also displays bifurcated N—H⋯(N,N) hydrogen bonding and C—H⋯F inter­actions. The former involve the NH H atom of the imidazole core and the tetra­zolopyridine N atoms, while the latter involve a methyl H atom, of the methyl­sulfanyl group, and the 4-fluoro­phenyl F atom. In the mol­ecule, the imidazole ring makes dihedral angles of 40.45 (9) and 17.09 (8)°, respectively, with the 4-fluoro­phenyl ring and the tetra­zolopyridine ring mean plane.

Ethyl 2,6-dichloro-4-phenyl-quinoline-3-carboxyl-ate

In the title compound, C₁₈H₁₃Cl₂NO₂, the quinoline ring system is almost planar (r.m.s. deviation 0.009 Å), and the phenyl and carboxyl­ate planes are twisted away from it by 59.2 (1) and 65.9 (2)°, respectively.