CDK1-inhibitory activity of paullones depends on electronic properties of 9-substituents

Syntheses and medicinal chemistry of azepinoindolones: a look back to leap forward

Nitrogen-containing heterocyclic scaffolds constitute nearly 75% of small molecules which favorably act as drug candidates. For the past few decades, numerous natural and synthetic indole-based scaffolds have been reported for their diverse pharmacological profiles. In particular, indole-fused azepines, termed azepinoindolones, have come under the radar of medicinal chemists owing to their synthetic and pharmacological importance. A plethora of literature reports has been generated thereof, which calls for the need for the compilation of information to understand their current status in drug discovery. Accumulating reports of evidence suggest that compounds containing this privileged scaffold display their cytotoxic effects via inhibition of kinase, topoisomerase I, mitochondrial malate dehydrogenase (mMDH), and tubulin polymerization and as DNA minor groove binding agents. Herein, we endeavor to present a closer look at the advancements of various synthetic and derivatization methods of azepinoindolone-based compounds. We have further extended our efforts to discuss the pharmacological effects of azepinoindolones in the whole range of medicinal chemistry as anti-Alzheimer, anticancer, anti-inflammatory, antidiabetic, antileishmanial, and antipyranosomal agents and as drug delivery vectors. Our analysis of recent advances reveals that azepinoindolones will continue to serve as potential pharmaceutical modalities in the years to come and their substantial pool of synthetic methods will be ever expanding.

Indole-fused azepines and analogues as anticancer lead molecules: Privileged findings and future directions

The search for new lead compounds of simple structure, displaying highest quality anti-tumor potency with new mechanisms of action and least adverse effects is the major intention of cancer drug discovery now a days. For the time being, indole-fused azepines emerged as a simple class of compounds prolifically designed with strong pharmacological significances in particular of cancer protecting ability. In the recent years from the efforts of our research group, indole-fused heteroazepines, a simple structural class achieved by fusion of indole with oxygen, sulphur and nitrogen containing heteroazepine rings, have known for its superior outcomes in cancer treatment. Surprisingly, the chemistry and biology of these unique families with an amazing role in cancer drug discovery has remained broadly unexplored. This short review is consequently an endeavor to highlight the preliminary ideas over this structural class and to draw the medical attention towards future development of indole-fused azepines and analogues for their promising function in cancer drug discovery.

10-iodo-11H-indolo[3,2-c]quinoline-6-carboxylic acids are selective inhibitors of DYRK1A

The protein kinase DYRK1A has been suggested to act as one of the intracellular regulators contributing to neurological alterations found in individuals with Down syndrome. For an assessment of the role of DYRK1A, selective synthetic inhibitors are valuable pharmacological tools. However, the DYRK1A inhibitors described in the literature so far either are not sufficiently selective or have not been tested against closely related kinases from the DYRK and the CLK protein kinase families. The aim of this study was the identification of DYRK1A inhibitors exhibiting selectivity versus the structurally and functionally closely related DYRK and CLK isoforms. Structure modification of the screening hit 11H-indolo[3,2-c]quinoline-6-carboxylic acid revealed structure-activity relationships for kinase inhibition and enabled the design of 10-iodo-substituted derivatives as very potent DYRK1A inhibitors with considerable selectivity against CLKs. X-ray structure determination of three 11H-indolo[3,2-c]quinoline-6-carboxylic acids cocrystallized with DYRK1A confirmed the predicted binding mode within the ATP binding site.

9- and 11-Substituted 4-azapaullones are potent and selective inhibitors of African trypanosoma

Trypanosomes from the "brucei" complex are pathogenic parasites endemic in sub-Saharan Africa and causative agents of severe diseases in humans and livestock. In order to identify new antitrypanosomal chemotypes against African trypanosomes, 4-azapaullones carrying α,β-unsaturated carbonyl chains in 9- or 11-position were synthesized employing a procedure with a Heck reaction as key step. Among the so prepared compounds, 5a and 5e proved to be potent antiparasitic agents with antitrypanosomal activity in the submicromolar range.

Metal-Arene Complexes with Indolo[3,2-c]-quinolines: Effects of Ruthenium vs Osmium and Modifications of the Lactam Unit on Intermolecular Interactions, Anticancer Activity, Cell Cycle, and Cellular Accumulation

Six novel ruthenium(II)- and osmium(II)-arene complexes with three modified indolo[3,2-c]quinolines have been synthesized in situ starting from 2-aminoindoloquinolines and 2-pyridinecarboxaldehyde in the presence of [M(p-cymene)Cl(2)](2) (M = Ru, Os) in ethanol. All complexes have been characterized by elemental analysis, spectroscopic techniques ((1)H, (13)C NMR, IR, UV-vis), and ESI mass spectrometry, while four complexes were investigated by X-ray diffraction. The complexes have been tested for antiproliferative activity in vitro in A549 (non-small cell lung), SW480 (colon), and CH1 (ovarian) human cancer cell lines and showed IC(50) values between 1.3 and >80 μM. The effects of Ru vs Os and modifications of the lactam unit on intermolecular interactions, antiproliferative activity, and cell cycle are reported. One ruthenium complex and its osmium analogue have been studied for anticancer activity in vivo applied both intraperitoneally and orally against the murine colon carcinoma model CT-26. Interestingly, the osmium(II) complex displayed significant growth-inhibitory activity in contrast to its ruthenium counterpart, providing stimuli for further investigation of this class of compounds as potential antitumor drugs.

3,6-Diamino-4-(2-halophenyl)-2-benzoylthieno[2,3-b]pyridine-5-carbonitriles are selective inhibitors of Plasmodium falciparum glycogen synthase kinase-3

Plasmodium falciparum is the infective agent responsible for malaria tropica. The glycogen synthase kinase-3 of the parasite (PfGSK-3) was suggested as a potential biological target for novel antimalarial drugs. Starting from hit structures identified in a high-throughput screening campaign, 3,6-diamino-4-(2-halophenyl)-2-benzoylthieno[2,3-b]pyridine-5-carbonitriles were discovered as a new class of PfGSK-3 inhibitors. Being less active on GSK-3 homologues of other species, the title compounds showed selectivity in favor of PfGSK-3. Taking into account the X-ray structure of a related molecule in complex with human GSK-3 (HsGSK-3), a model was computed for the comparison of inhibitor complexes with the plasmodial and human enzymes. It was found that subtle differences in the ATP-binding pockets are responsible for the observed PfGSK-3 vs HsGSK-3 selectivity. Representatives of the title compound class exhibited micromolar IC₅₀ values against P. falciparum erythrocyte stage parasites. These results suggest that inhibitors of PfGSK-3 could be developed as potential antimalarial drugs.

New synthetic approach to paullones and characterization of their SIRT1 inhibitory activity

A series of 7,12-dihydroindolo[3,2-d][1]benzazepine-6(5H)-ones (paullones) substituted at C9/C10 (Br) and C2 (Me, CF(3), CO(2)Me) have been synthesized by a one-pot Suzuki-Miyaura cross-coupling of an o-aminoarylboronic acid and methyl 2-iodoindoleacetate followed by intramolecular amide formation. Other approaches to the paullone scaffold based on Pd-catalyzed C-H activation were unsuccessful. In vitro enzymatic assay with recombinant human SIRT-1 indicated a strong inhibitory profile for the series, in particular the analogue with a methoxycarbonyl group at C2 and a bromine at C9. These compounds are, in general, inducers of granulocyte differentiation of the U937 acute leukemia cell line and cause a marked increase in pre-G1 of the cell cycle.

Concise synthesis and CDK/GSK inhibitory activity of the missing 9-azapaullones

A remarkably concise, chromatography-free route to the parent compound of the paullone family of cyclin-dependent kinase (CDK) inhibitors is reported. A similar strategy allowed the synthesis of the hitherto missing 9-azapaullone and its protonated, N-oxidised and N-alkylated derivatives. Screening studies identified an active and strongly selective inhibitor of CDK9/cyclin T.

Development of 5-benzylpaullones and paullone-9-carboxylic acid alkyl esters as selective inhibitors of mitochondrial malate dehydrogenase (mMDH)

A collection of paullones was tested for inhibitory activity against mitochondrial malate dehydrogenase (mMDH) as a biological target for antiproliferative activity. Based on the results of this screening, 5-benzylpaullones and paullone-9-carboxylic acid alkyl esters were developed as selective mMDH inhibitors. The new derivatives did not show noteworthy antiproliferative activity when tested on a panel of cancer cell lines, suggesting that mMDH inhibition is of minor relevance for the growth inhibition caused by paullones.

2-(3-aryl-3-oxopropen-1-yl)-9-tert-butyl-paullones: a new antileishmanial chemotype

A screening program directed to find new agents against Leishmania donovani, the parasite causing visceral leishmaniasis, revealed that paullones attenuate the proliferation of axenic amastigotes. Because these structures were not active in a test system involving infected macrophages, a structure optimization campaign was carried out. Concomitant introduction of an unsaturated side chain into the 2-position and a tert-butyl substituent into the 9-position of the parent scaffold led to compounds inhibiting also parasites dwelling in macrophages. By inclusion of the so elaborated scaffold into a chalcone substructure, the toxicity against uninfected host cells was significantly reduced. For the synthesis of this new compound class, a novel modification of the Heck-type palladium-catalyzed C,C-cross coupling strategy was used, employing a ketone Mannich base as precursor for the alkene reactant. The so-prepared compounds exhibited improved antileishmanial activity both on axenic amastigotes (GI50 < 1 microM) as well as on parasites in infected macrophages.

The First Ruthenium-Based Paullones: Syntheses, X-ray Diffraction Structures, and Spectroscopic and Antiproliferative Properties in Vitro

Two novel paullone derivatives, namely, 6-(alpha-picolylamino)-7,12-dihydroindolo[3,2-d][1]benzazepine (L1) and 9-bromo-6-(alpha-picolylamino)-7,12-dihydroindolo[3,2-d][1]benzazepine (L2), have been prepared. The reaction of cis-[RuCl2(DMSO)4] (DMSO=dimethyl sulfoxide) with L1 and L2 in a 1:1 molar ratio in dry ethanol at 50 degrees C afforded the complexes trans-[RuIICl2(DMSO)2L1] (1a) and trans-[RuIICl2(DMSO)2L2] (1b) in 26 and 30% yield, respectively. The reaction carried out from the same starting compounds in a 1:2 molar ratio at 75 degrees C led to the formation of [RuIICl(DMSO)(L1)2]Cl (2a) and [RuIICl(DMSO)(L2)2]Cl (2b) in 16 and 23% yield, correspondingly. The products were characterized by elemental analysis, one- and two-dimensional NMR spectroscopy, electrospray ionization mass spectrometry, IR spectroscopy, electronic spectra, cyclic voltammetry, and X-ray crystallography (L1, L2, 1a, and 2b). Complexes 2a and 2b exhibit remarkable antiproliferative activity in three human carcinoma cell lines, A549 (non-small cell lung carcinoma), CH1 (ovarian carcinoma), and SW480 (colon carcinoma). The novel complexes show an intercalative mode of interaction with DNA, which may render them attractive alternatives to metal compounds with a coordinative mode of interaction.

1-Aryl-4,6-dihydropyrazolo[4,3-d][1]benzazepin-5(1H)-ones: a new class of antiproliferative agents with selectivity for human leukemia and breast cancer cell lines

The synthesis of 1-aryl-4,6-dihydropyrazolo[4,3-d][1]benzazepin-5(1H)-ones by cyclization of 4-[(dimethylamino)methylidene]-3,4-dihydro-1H-[1]benzazepine-2,5-dione with arylhydrazines is reported. When tested on a panel of human cancer cell lines, the title compounds showed antiproliferative activity and a characteristic selectivity pattern of growth inhibition. Although structurally akin to established kinase inhibitors, the new compounds did not exhibit noteworthy inhibitory activity when tested on an array of cancer-related kinases.

Modeling of Cyclin-Dependent Kinase Inhibition by 1H-Pyrazolo[3,4-d]Pyrimidine Derivatives Using Artificial Neural Network Ensembles

Artificial neural network ensembles were used for modeling the cyclin-dependent kinase inhibition of 1H-pyrazolo[3,4-d]pyrimidine derivatives. The structural characteristics of these inhibitors were encoded in relevant 3D-spatial descriptors extracted by genetic algorithm feature selection. Bayesian-regularized multilayer neural networks, trained by the back-propagation algorithm, were developed using these variables as inputs. The predictive power of the model was tested by leave-one-out cross validation. In addition, for a more rigorous measure of the predictive capacity, multiple validation sets were randomly generated as members of neural network ensembles, which makes doing averaged predictions feasible. In this way, the predictive power was analyzed accounting for the averaged test set R values and test set mean-square errors. Otherwise, Kohonen self-organizing maps were used as an additional tool for the same modeling. The location of the inhibitors in a map facilitates the analysis of the connection between compounds and serves as a useful tool for qualitative predictions.