Heteroaromatic rings of the future

Iridium-Catalysed C-H Borylation of Heteroarenes: Balancing Steric and Electronic Regiocontrol

The iridium-catalysed borylation of aromatic C-H bonds has become the preferred method for the synthesis of aromatic organoboron compounds. The reaction is highly efficient, tolerant of a broad range of substituents and can be applied to both carbocyclic and heterocyclic substrates. The regioselectivity of C-H activation is dominated by steric considerations and there have been considerable efforts to develop more selective processes for less constrained substrates. However, most of these have focused on benzenoid-type substrates and in contrast, heteroarenes remain much desired but more challenging substrates with the position and/or nature of the heteroatom(s) significantly affecting reactivity and regioselectivity. This review will survey the borylation of heteroarenes, focusing on the influence of steric and electronic effects on regiochemical outcome and, by linking to current mechanistic understandings, will provide insights to what is currently possible and where further developments are required.

Catalytic Asymmetric 1,3-Dipolar Cycloaddition of α,β-Unsaturated Amide and Azomethine Imine

α,β-Unsaturated amides were incorporated as viable dipolarophiles in a catalytic asymmetric 1,3-dipolar cycloaddition of azomethine imines. The use of a 7-azaindoline auxiliary was essential to acquire sufficient reactivity with excellent diastereoselectivity, likely due to the chelating activation of the amide by the In(III)/bishydroxamic acid complex. Although the enantioselectivity remains unsatisfactory, this work is an important step toward the development of an asymmetric catalysis utilizing stable and low-reactive substrates.

Diastereoselective Rhodium-Catalyzed Hydrogenation of 2-Oxindoles and 3,4-Dihydroquinolones

The benzene ring of indolin-2-ones (2-oxindoles) and 3,4-dihydroquinol-2-ones was converted to a saturated cyclohexane ring by hydrogenation in the presence of the rhodium complex ^Cy(CAAC)Rh(cod)Cl. The stereoselectivity of the process was found to be high with respect to both external substituent R¹ within the saturated part of the heterocyclic ring and substituent X on the benzene ring. Twenty-one hexahydroindolin-2(3H)-ones (70-99% yield, dr = 83/17 to >99/1) and twelve octahydro-2(1H)-quinolinones (87-96% yield, dr = 64/36 to >99/1) were obtained with the major diastereoisomer exhibiting the hydrogen atoms in an all-cis arrangement. The high tolerance toward functional groups and the compatibility with existing stereogenic centers are key features of the hydrogenation protocol presented here.

Heterocyclization Reagents for Rapid Assembly of N-Fused Heteroarenes from Alkenes

N-Fused heterocycles are of particular use and upmost importance in multiple fields. Herein, we disclose a conceptually new approach for the rapid assembly of N-fused heteroarenes from alkenes. A portfolio of strategically designed heterocyclization reagents are readily prepared for the cascade reaction. A plethora of N-fused heteroarenes including seven types of heterocyclic core are furnished. The protocol features a broad functional-group compatibility and high product diversity, and provides a practical tool for late-stage heteroarene elaboration.

Deep learning and generative methods in cheminformatics and chemical biology: navigating small molecule space intelligently

The number of 'small' molecules that may be of interest to chemical biologists - chemical space - is enormous, but the fraction that have ever been made is tiny. Most strategies are discriminative, i.e. have involved 'forward' problems (have molecule, establish properties). However, we normally wish to solve the much harder generative or inverse problem (describe desired properties, find molecule). 'Deep' (machine) learning based on large-scale neural networks underpins technologies such as computer vision, natural language processing, driverless cars, and world-leading performance in games such as Go; it can also be applied to the solution of inverse problems in chemical biology. In particular, recent developments in deep learning admit the in silico generation of candidate molecular structures and the prediction of their properties, thereby allowing one to navigate (bio)chemical space intelligently. These methods are revolutionary but require an understanding of both (bio)chemistry and computer science to be exploited to best advantage. We give a high-level (non-mathematical) background to the deep learning revolution, and set out the crucial issue for chemical biology and informatics as a two-way mapping from the discrete nature of individual molecules to the continuous but high-dimensional latent representation that may best reflect chemical space. A variety of architectures can do this; we focus on a particular type known as variational autoencoders. We then provide some examples of recent successes of these kinds of approach, and a look towards the future.

Three cheers for nitrogen: aza-DKPs, the aza analogues of 2,5-diketopiperazines

Nitrogen-containing heterocycles represent a major source of pharmacological probes and drug candidates. To extend their molecular diversity and their potential biological activities, it is of importance to design and synthesize new N-heterocyclic scaffolds. Therefore, aza-diketopiperazines (aza-DKPs), the aza analogues of well-known 2,5-diketopiperazines (DKPs), emerged as a promising new scaffold. Although the first synthesis of an aza-DKP dates from 1951, significant developments have been made during the last decade. This feature article summarizes the different synthetic strategies to access and functionalise aza-DKPs. Their biological properties and potential applications in medicinal chemistry and drug discovery are discussed as well.

Co-Catalyzed Transannulation of Pyridotriazoles with Isothiocyanates and Xanthate Esters

An efficient radical transannulation reaction of pyridotriazoles with isothiocyanates and xanthate esters was developed. This method features conversion of pyridotriazoles into two N-fused heterocyclic aromatic systems-imino-thiazolopyridines and oxo-thiazolopyridine derivatives-via one-step Co(II)-catalyzed transannulation reaction proceeding via a radical mechanism. The synthetic usefulness of the developed method was illustrated in the synthesis of amino acid derivatives and further transformations of obtained reaction products.

Explicit Representation of Cation-π Interactions in Force Fields with 1/r4 Nonbonded Terms

The binding energies for cation-π complexation are underestimated by traditional fixed-charge force fields owing to their lack of explicit treatment of ion-induced dipole interactions. To address this deficiency, an explicit treatment of cation-π interactions has been introduced into the OPLS-AA force field. Following prior work with atomic cations, it is found that cation-π interactions can be handled efficiently by augmenting the usual 12-6 Lennard-Jones potentials with 1/r⁴ terms. Results are provided for prototypical complexes as well as protein-ligand systems of relevance for drug design. Alkali cation, ammonium, guanidinium, and tetramethylammonium were chosen for the representative cations, while benzene and six heteroaromatic molecules were used as the π systems. The required nonbonded parameters were fit to reproduce structure and interaction energies for gas-phase complexes from density functional theory (DFT) calculations at the ωB97X-D/6-311++G(d,p) level. The impact of the solvent was then examined by computing potentials of mean force (pmfs) in both aqueous and tetrahydrofuran (THF) solutions using the free-energy perturbation (FEP) theory. Further testing was carried out for two cases of strong and one case of weak cation-π interactions between druglike molecules and their protein hosts, namely, the JH2 domain of JAK2 kinase and macrophage migration inhibitory factor. FEP results reveal greater binding by 1.5-4.4 kcal/mol from the addition of the explicit cation-π contributions. Thus, in the absence of such treatment of cation-π interactions, errors for computed binding or inhibition constants of 10¹-10³ are expected.

Identification of Novel Thiazolo[5,4-b]Pyridine Derivatives as Potent Phosphoinositide 3-Kinase Inhibitors

A series of novel 2-pyridyl, 4-morpholinyl substituted thiazolo[5,4-b]pyridine analogues have been designed and synthesized in this paper. These thiazolo[5,4-b]pyridines were efficiently prepared in seven steps from commercially available substances in moderate to good yields. All of these N-heterocyclic compounds were characterized by nuclear magnetic resonance (NMR) and high-resolution mass spectrometry (HRMS) analysis and tested for phosphoinositide 3-kinase (PI3K) enzymatic assay. The results indicated that these N-heterocyclic compounds showed potent PI3K inhibitory activity, and the IC₅₀ of a representative compound (19a) could reach to 3.6 nm. The structure−activity relationships (SAR) study showed that sulfonamide functionality was important for PI3Kα inhibitory activity, and 2-chloro-4-florophenyl sulfonamide (19b), or 5-chlorothiophene-2-sulfonamide (19c) showed potent inhibitory activity with a nanomolar IC₅₀ value. The pyridyl attached to thiazolo[5,4-b]pyridine was another key structural unit for PI3Kα inhibitory potency, and replacement by phenyl lead to a significant decrease in activity. Enzymatic Inhibition results showed that compound 19a inhibited PI3Kα, PI3Kγ, or PI3Kδ with a nanomolar IC₅₀ value, but its inhibitory activity on PI3Kβ was approximately 10-fold reduced. Further docking analysis revealed that the N-heterocyclic core of compound 19a was directly involved in the binding to the kinase through the key hydrogen bonds interaction.

Computational generation of an annotated gigalibrary of synthesizable, composite peptidic macrocycles

Peptidomimetic macrocycles have the potential to regulate challenging therapeutic targets. Structures of this type having precise shapes and drug-like character are particularly coveted, but are relatively difficult to synthesize. Our laboratory has developed robust methods that integrate small-peptide units into designed scaffolds. These methods create macrocycles and embed condensed heterocycles to diversify outcomes and improve pharmacological properties. The hypothetical scope of the methodology is vast and far outpaces the capacity of our experimental format. We now describe a computational rendering of our methodology that creates an in silico three-dimensional library of composite peptidic macrocycles. Our open-source platform, CPMG (Composite Peptide Macrocycle Generator), has algorithmically generated a library of 2,020,794,198 macrocycles that can result from the multistep reaction sequences we have developed. Structures are generated based on predicted site reactivity and filtered on the basis of physical and three-dimensional properties to identify maximally diverse compounds for prioritization. For conformational analyses, we also introduce ConfBuster++, an RDKit port of the open-source software ConfBuster, which allows facile integration with CPMG and ready parallelization for better scalability. Our approach deeply probes ligand space accessible via our synthetic methodology and provides a resource for large-scale virtual screening.

Vibrational, spectroscopic, chemical reactivity, molecular docking and in vitro anticancer activity studies against A549 lung cancer cell lines of 5-Bromo-indole-3-carboxaldehyde

Spectroscopic investigations are performed for 5-Bromo-1H-indole-carboxaldehyde by using experimental (FT-IR, FT-Raman) and theoretical (DFT) calculations. Vibrational assignments of the fundamental modes were assigned on the basis of Potential energy distribution (PED) calculations. Electron Localization Function (ELF) and Local Orbital Localizer (LOL) studies were performed to visualize the electron delocalization in the molecule. Frontier molecular orbitals (FMOs) and related molecular properties were computed. The electron-hole distribution of the molecule was also computed using Multiwfn 3.3.9 software to predict the charge transfer within the molecule. The total and partial density of states (TDOS and PDOS) and also the overlap population density of states (OPDOS) spectra were simulated. UV-Vis spectrum of the compound was also recorded. The reactive sites of the compound were studied from the MEP and Fukui function analysis. The charge delocalization and stability of the title molecule were investigated using natural bond orbital (NBO) analysis. The lung cancer activity of the title compound against p53 tumor suppressor proteins was studied using molecular docking analysis. The in-vitro cytotoxic activity of the molecule against human pulmonary lung cancer cell lines (A549) was determined by MTT assay.

DeepGraphMolGen, a multi-objective, computational strategy for generating molecules with desirable properties: a graph convolution and reinforcement learning approach

We address the problem of generating novel molecules with desired interaction properties as a multi-objective optimization problem. Interaction binding models are learned from binding data using graph convolution networks (GCNs). Since the experimentally obtained property scores are recognised as having potentially gross errors, we adopted a robust loss for the model. Combinations of these terms, including drug likeness and synthetic accessibility, are then optimized using reinforcement learning based on a graph convolution policy approach. Some of the molecules generated, while legitimate chemically, can have excellent drug-likeness scores but appear unusual. We provide an example based on the binding potency of small molecules to dopamine transporters. We extend our method successfully to use a multi-objective reward function, in this case for generating novel molecules that bind with dopamine transporters but not with those for norepinephrine. Our method should be generally applicable to the generation in silico of molecules with desirable properties.

Analysis of Benzenoid Substitution Patterns in Small Molecule Active Pharmaceutical Ingredients

Previous analyses have revealed that benzenoid rings are prevalent scaffolds in active pharmaceutical ingredients (APIs). Here, we analyze the substitution patterns of benzenoid rings in small molecule APIs approved by the FDA through 2019 and show that only a few substitution patterns (1-, 1,2-, 1,4-, and 1,2,4-) prevail, and the distribution has remained relatively constant over time. We postulate the connection between available synthetic methods and the occurrence of a few benzenoid substitution patterns by providing an overview of synthetic methods that elaborate existing substitution patterns and those that create new substitution patterns, including those of the former that are favored by medicinal chemists. Finally, we calculated medicinal chemistry properties of benzenoid containing APIs that are often used by practitioners as design elements, including "druglikeness", shape, complexity, and similarity/diversity and discuss these properties in the context of synthesis.

A Predictive Model Towards Site-Selective Metalations of Functionalized Heterocycles, Arenes, Olefins, and Alkanes using TMPZnCl⋅LiCl

The development of a predictive model towards site-selective deprotometalation reactions using TMPZnCl⋅LiCl is reported (TMP=2,2,6,6-tetramethylpiperidinyl). The pKa values of functionalized N-, S-, and O-heterocycles, arenes, alkenes, or alkanes were calculated and compared to the experimental deprotonation sites. Large overlap (>80 %) between the calculated and empirical deprotonation sites was observed, showing that thermodynamic factors strongly govern the metalation regioselectivity. In the case of olefins, calculated frozen state energies of the deprotonated substrates allowed a more accurate prediction. Additionally, various new N-heterocycles were analyzed and the metalation regioselectivities rationalized using the predictive model.

Experimental and theoretical study on structure-tautomerism among edaravone, isoxazolone, and their heterocycles derivatives as antioxidants

Edaravone is a heterocyclic pyrazolone compound. It has pronounced effect against free radicals, however renal and hepatic disorders have been reported. Isoxazolones are considered bioisosteric analogues of pyrazolones and may have comparable properties. Thus, we investigated the structural and electronic influences for edaravone, isoxazolone, and their tautomers on antioxidant process. Structure and tautomerism study among edaravone, isoxazolone and their heterocycles derivatives were related to antioxidant mechanisms by using the hybrid DFT method B3LYP with the basis sets 6-31++G(2d,2p). The C—H tautomer was the most stable and energetically favored among them. Intramolecular N—H—N hydrogen bonds and polar medium were responsible for the low energy differences among all possible tautomers. N—H tautomers in both systems proved to be better antioxidant by SET (single electron transfer), while O—H tautomers were better antioxidant on HAT (homolytic hydrogen atom transfer) mechanism. Theoretical calculation showed that edaravone is more potent than phenylisoxazolone, however, both has similar antioxidant scavenging on experimental DPPH. The carbonyliminic system played a very important role in the antioxidant activity for both studied classes.

"Ring Breaker": Neural Network Driven Synthesis Prediction of the Ring System Chemical Space

Ring systems in pharmaceuticals, agrochemicals, and dyes are ubiquitous chemical motifs. While the synthesis of common ring systems is well described and novel ring systems can be readily and computationally enumerated, the synthetic accessibility of unprecedented ring systems remains a challenge. "Ring Breaker" uses a data-driven approach to enable the prediction of ring-forming reactions, for which we have demonstrated its utility on frequently found and unprecedented ring systems, in agreement with literature syntheses. We demonstrate the performance of the neural network on a range of ring fragments from the ZINC and DrugBank databases and highlight its potential for incorporation into computer aided synthesis planning tools. These approaches to ring formation and retrosynthetic disconnection offer opportunities for chemists to explore and select more efficient syntheses/synthetic routes.

A Photochemical Organocatalytic Strategy for the α-Alkylation of Ketones by using Radicals

Reported herein is a visible‐light‐mediated radical approach to the α‐alkylation of ketones. This method exploits the ability of a nucleophilic organocatalyst to generate radicals upon S_N2‐based activation of alkyl halides and blue light irradiation. The resulting open‐shell intermediates are then intercepted by weakly nucleophilic silyl enol ethers, which would be unable to directly attack the alkyl halides through a traditional two‐electron path. The mild reaction conditions allowed functionalization of the α position of ketones with functional groups that are not compatible with classical anionic strategies. In addition, the redox‐neutral nature of this process makes it compatible with a cinchona‐based primary amine catalyst, which was used to develop a rare example of enantioselective organocatalytic radical α‐alkylation of ketones.

Amide Synthesis by Nickel/Photoredox-Catalyzed Direct Carbamoylation of (Hetero)Aryl Bromides

Herein, we report a one‐electron strategy for catalytic amide synthesis that enables the direct carbamoylation of (hetero)aryl bromides. This radical cross‐coupling approach, which is based on the combination of nickel and photoredox catalysis, proceeds at ambient temperature and uses readily available dihydropyridines as precursors of carbamoyl radicals. The method's mild reaction conditions make it tolerant of sensitive‐functional‐group‐containing substrates and allow the installation of an amide scaffold within biologically relevant heterocycles. In addition, we installed amide functionalities bearing electron‐poor and sterically hindered amine moieties, which would be difficult to prepare with classical dehydrative condensation methods.

An efficient, stereocontrolled and versatile synthetic route to bicyclic partially saturated privileged scaffolds

A simple, high yielding and scalable synthesis for diastereoselective access to privileged fused bicyclic heteroaromatic scaffolds.

Cycloaddition Strategies for the Synthesis of Diverse Heterocyclic Spirocycles for Fragment-Based Drug Discovery

In recent years the pharmaceutical industry has benefited from the advances made in fragment-based drug discovery (FBDD) with more than 30 fragment-derived drugs currently marketed or progressing through clinical trials. The success of fragment-based drug discovery is entirely dependent upon the composition of the fragment screening libraries used. Heterocycles are prevalent within marketed drugs due to the role they play in providing binding interactions; consequently, heterocyclic fragments are important components of FBDD libraries. Current screening libraries are dominated by flat, sp2-rich compounds, primarily owing to their synthetic tractability, despite the superior physicochemical properties displayed by more three-dimensional scaffolds. Herein, we report step-efficient routes to a number of biologically relevant, fragment-like heterocyclic spirocycles. The use of both electron-deficient and electron-rich 2-atom donors was explored in complexity-generating [3+2]-cycloadditions to furnish products in 3 steps from commercially available starting materials. The resulting compounds were primed for further fragment elaboration through the inclusion of synthetic handles from the outset of the syntheses.

Converting SMILES to Stacking Interaction Energies

Predicting the strength of stacking interactions involving heterocycles is vital for several fields, including structure-based drug design. While quantum chemical computations can provide accurate stacking interaction energies, these come at a steep computational cost. To address this challenge, we recently developed quantitative predictive models of stacking interactions between druglike heterocycles and the aromatic amino acids Phe, Tyr, and Trp (DOI: 10.1021/jacs.9b00936 ). These models depend on heterocycle descriptors derived from electrostatic potentials (ESPs) computed using density functional theory and provide accurate stacking interactions without the need for expensive computations on stacked dimers. Herein, we show that these ESP-based descriptors can be reliably evaluated directly from the atom connectivity of the heterocycle, providing a means of predicting both the descriptors and the potential for a given heterocycle to engage in stacking interactions without resorting to any quantum chemical computations. This enables the rapid conversion of simple molecular representations (e.g., SMILES) directly into accurate stacking interaction energies using a freely available online tool, thereby providing a way to rank the stacking abilities of large sets of heterocycles.

Are We Opening the Door to a New Era of Medicinal Chemistry or Being Collapsed to a Chemical Singularity?

The paradigm of "drug-like-ness" dramatically altered the behavior of the medicinal chemistry community for a long time. In recent years, scientists have empirically found a significant increase in key properties of drugs that have moved structures closer to the periphery or the outside of the rule-of-five "cage". Herein, we show that for the past decade, the number of molecules claimed in patent records by major pharmaceutical companies has dramatically decreased, which may lead to a "chemical singularity". New compounds containing fragments with increased 3D complexity are generally larger, slightly more lipophilic, and more polar. A core difference between this study and recently published papers is that we consider the nature and quality of sp³-rich frameworks rather than sp³ count. We introduce the original descriptor MCE-18, which stands for medicinal chemistry evolution, 2018, and this measure can effectively score molecules by novelty in terms of their cumulative sp³ complexity.

Functionalised bicyclic tetramates derived from cysteine as antibacterial agents

Routes to bicyclic tetramates derived from cysteine permitting ready incorporation of functionality at two different points around the periphery of a heterocyclic skeleton are reported. This has enabled the identification of systems active against Gram-positive bacteria, some of which show gyrase and RNA polymerase inhibitory activity. In particular, tetramates substituted with glycosyl side chains, chosen to impart polarity and aqueous solubility, show high antibacterial activity coupled with modest gyrase/polymerase activity in two cases. An analysis of physicochemical properties indicates that the antibacterially active tetramates generally occupy physicochemical space with MW of 300-600, clog D7.4 of -2.5 to 4 and rel. PSA of 11-22%. This work demonstrates that biologically active 3D libraries are readily available by manipulation of a tetramate skeleton.

A visible-light mediated three-component radical process using dithiocarbamate anion catalysis

A three-component radical process is reported that, by coupling alkyl chlorides, maleimides, and heteroaromatic fragments, installs multiple biologically relevant heterocycles within complex cascade products. This method, which generates radicals via an S_N2-based photochemical catalytic mechanism, activates substrates incompatible with or inert to classical radical-generating strategies.

We report a photoinduced three-component radical process, which couples readily available alkyl chlorides, maleimides, and heteroaromatic fragments to rapidly generate complex chiral products with high diastereocontrol. This method generates radicals via an S_N2-based photochemical catalytic mechanism, which is not reliant on the redox properties of the precursors. It therefore grants access to open-shell intermediates from substrates that would be incompatible with or inert to classical radical-generating strategies. The redox-neutral conditions of this process make it tolerant of redox-sensitive substrates and allow the installation of multiple biologically relevant heterocycles within the cascade products.

3D Heterocycles from Sulfonimidamides by Sequential C-H Bond Alkenylation/Aza-Michael Cyclization

Starting from NH-sulfonimidamides, rhodium-catalyzed C-H bond alkenylation followed by aza-Michael cyclization leads to unprecedented benzoisothiazole 1-oxides. The applicability and robustness of the method is demonstrated in 25 examples with yields up to 95 %. The resulting scaffolds are partly saturated, 3D heterocycles with potential significance for medicinal and agricultural chemistry.

Copper-catalyzed cross-dehydrogenative coupling between quinazoline-3-oxides and indoles

A novel and simple protocol for the synthesis of 4-(indole-3-yl)quinazolines via cross-dehydrogenative coupling of quinazoline-3-oxides and indoles under an air atmosphere has been developed.

Application of Virtual Screening to the Identification of New LpxC Inhibitor Chemotypes, Oxazolidinone and Isoxazoline

This report summarizes the identification and synthesis of novel LpxC inhibitors aided by computational methods that leveraged numerous crystal structures. This effort led to the identification of oxazolidinone and isoxazoline inhibitors with potent in vitro activity against P. aeruginosa and other Gram-negative bacteria. Representative compound 13f demonstrated efficacy against P. aeruginosa in a mouse neutropenic thigh infection model. The antibacterial activity against K. pneumoniae could be potentiated by Gram-positive antibiotics rifampicin (RIF) and vancomycin (VAN) in both in vitro and in vivo models.

Discovery of High-Affinity Cannabinoid Receptors Ligands through a 3D-QSAR Ushered by Scaffold-Hopping Analysis

Two 3D quantitative structure–activity relationships (3D-QSAR) models for predicting Cannabinoid receptor 1 and 2 (CB₁ and CB₂) ligands have been produced by way of creating a practical tool for the drug-design and optimization of CB₁ and CB₂ ligands. A set of 312 molecules have been used to build the model for the CB₁ receptor, and a set of 187 molecules for the CB₂ receptor. All of the molecules were recovered from the literature among those possessing measured K_i values, and Forge was used as software. The present model shows high and robust predictive potential, confirmed by the quality of the statistical analysis, and an adequate descriptive capability. A visual understanding of the hydrophobic, electrostatic, and shaping features highlighting the principal interactions for the CB₁ and CB₂ ligands was achieved with the construction of 3D maps. The predictive capabilities of the model were then used for a scaffold-hopping study of two selected compounds, with the generation of a library of new compounds with high affinity for the two receptors. Herein, we report two new 3D-QSAR models that comprehend a large number of chemically different CB₁ and CB₂ ligands and well account for the individual ligand affinities. These features will facilitate the recognition of new potent and selective molecules for CB₁ and CB₂ receptors.

New N,C-Diaryl-1,2,4-triazol-3-ones: Synthesis and Evaluation as Anticancer Agents

BACKGROUND

A set of 2,5-diaryl-1,2,4-triazol-3-ones was synthesized in two steps and evaluated as regards their activity in some relevant biological targets related to cancer.

OBJECTIVE

This study is focused on the synthesis and the biological evaluation of 2,5-diaryl-1,2,4- triazol-3-ones. In this sense, the effect of the synthetic triazolones on the proliferation of HT-29 and A549 cancer cells and on HEK non-cancer cells has been measured. In addition, the effects of triazolones on the expression of hTERT, c-Myc and PD-L1 genes and on the production of c-Myc and PD-L1 proteins have also been evaluated.

METHOD

A set of 2,5-diaryl-1,2,4-triazol-3-ones was synthesized in two steps. Firstly, N- (aminocarbonyl)-3-methoxybenzamide was prepared by coupling 3-methoxybenzoic acid and cyanamide followed by aqueous HCl hydrolysis. Then, the 2,5-diaryl-1,2,4-triazol-3-ones were obtained upon reaction of N-(aminocarbonyl)-3-methoxybenzamide with arylhydrazines in decaline at 170ºC. The ability of the triazolones to inhibit cell proliferation was measured against two human carcinoma cell lines (colorectal HT-29 and lung A549), and one non-tumor cell line (HEK- 293) by MTT assay. The downregulation of the synthetic triazolones on the expression of the hTERT, c-Myc and PD-L1 genes was measured by an RT-qPCR analysis. Their ability to regulate the expression of the c-Myc and PD-L1 proteins, as well as their direct interaction with c-Myc protein, was determined by the ELISA method. Finally, the direct interaction of triazolones with PD-L1 protein was assessed by the thermal shift assay.

RESULTS

Ten 2,5-diaryl-1,2,4-triazol-3-ones were synthesized and characterized by spectroscopic methods. A thorough study by 1H, 13C, 15N and 19F NMR spectroscopy showed that all the synthetic compounds exist as 4H-triazolones and not as hydroxytriazoles or 1H-triazolones. Some triazolones showed relatively high activities together with very poor toxicity in non-tumor cell line HEK-293. 2-(2-fluorophenyl)-5-(3-methoxyphenyl)-2,4-dihydro-3H-1,2,4-triazol-3-one (4) was particularly active in downregulating c-Myc and PD-L1 gene expression although 2-(4- chloro-2-fluorophenyl)-5-(3-methoxyphenyl)-2,4-dihydro-3H-1,2,4-triazol-3-one (8) is the one that combines the best downregulatory activities in the three genes studied. Considering protein expression, the most active compounds are 2-(4-fluorophenyl)-5-(3-methoxyphenyl)-2,4-dihydro- 3H-1,2,4-triazol-3-one (5) and 2-(2,4,6-trifluorophenyl)-5-(3-methoxyphenyl)-2,4-dihydro-3H- 1,2,4-triazol-3-one (10) (c-Myc expression) and 2-(2,3,5,6-tetrafluorophenyl)-5-(3-methoxyphenyl)- 2,4-dihydro-3H-1,2,4-triazol-3-one (11) and (8) (PD-L1 expression).

CONCLUSION

Some of the triazolones studied have shown relevant activities in the inhibition of the hTERT, c-Myc and PD-L1 genes, and in the inhibition of c-Myc and PD-L1 protein secretion, the 2-(4-chloro-2-fluorophenyl)-5-(3-methoxyphenyl)-2,4-dihydro-3H-1,2,4-triazol-3-one (8) was found to be a particularly promising lead compound.

Quantifying intermolecular interactions for isoindole derivatives: substituent effect vs. crystal packing

The aim of the study was to examine noncovalent interactions in considerably different crystal packings of three isoindole compounds. Their structures were compared to three other closely-related derivatives described earlier in the literature. Here we discuss the crystal structures in the context of the hydrogen-bonded motifs and other weak interactions. The hierarchy of investigated intermolecular interactions was examined in a quantitative manner through pairwise interaction energies and energy framework analysis.

Asymmetric Reaction of p-Quinone Diimide: Organocatalyzed Michael Addition of α-Cyanoacetates

Hitherto unknown catalytic enantioselective transformation of p-quinone diimides is achieved using chiral bifunctional organic molecules. Bifunctional thiourea compounds catalyze the Michael addition of cyanoacetates with excellent yields and enantioselectivities. The initially formed Michael adducts undergo cyclization to yield functionally rich, fused cyclic imidines bearing a quaternary benzylic chiral center. Density functional theory calculations of the competing transition states (TSs) were carried out to explain the observed stereochemical outcome.