Thiazolino 2-Pyridone Amide Isosteres As Inhibitors of Chlamydia trachomatis Infectivity

Bicyclic N,S-Acetals Containing Fused Cysteine-Amide System as New Heterocyclic Class Targeting Human Farnesyltransferase (FTase-h)

We report in this contribution the synthesis and in vitro biological evaluation of a novel class of chiral thiazoloisoindolinone scaffolds as potent inhibitors against human farnesyltransferase (FTase-h). The targeted products, sulfides (4), sulfoxides (5,6), and sulfones (7), containing up to three points of diversification, were obtained in a short-step sequence starting from the available and cost-effective L-cysteine hydrochloride (1), which is the source of N and S atoms and the chiral pool, and α-carbonyl benzoic acids (2), which are isoindolinone precursors. Concisely, the key ester intermediates (1) provide (a) sulfide-amides (4) by solvent-free amidation, (b) sulfoxides (5,6) by selective S-oxidation using NaIO4, and (c) sulfones (7) by oxidation using MMPP. Finally, the obtained N,S-acetal systems have shown promising inhibitory activities on FTase-h in the nanomolar range with excellent half maximal inhibitory concentration (IC50) values up to 4.0 nanomolar (for example, 25.1 nM for sulfide 4bI, 67.3 nM for sulfone 7bG, and more interesting of 4.03 nM for sulfoxide 5bG).

Imidazolone as an Amide Bioisostere in the Development of β-1,3-N-Acetylglucosaminyltransferase 2 (B3GNT2) Inhibitors

B3GNT2 is responsible for elongation of cell surface long-chain polylactosamine, which influences the regulation of the immune response, making it an attractive target for immunomodulation. In the development of amide containing B3GNT2 inhibitors guided by structure-based drug design, imidazolones were found to successfully serve as amide bioisosteres. This novel imidazolone isosteric strategy alleviated torsional strain of the amide bond on binding to B3GNT2 and improved potency, isoform selectivity, as well as certain physicochemical and pharmacokinetic properties. Herein, we present the synthesis, SAR, X-ray cocrystal structures, and in vivo PK properties of imidazol-4-ones in the context of B3GNT2 inhibition.

A Light-Promoted Innate Trifluoromethylation of Pyridones and Related N-Heteroarenes

We report a practical, light-mediated perfluoroalkylation using Langlois' reagent (sodium trifluoromethylsulfinate) that proceeds in the absence of any photocatalyst or additives. This method has allowed for the facile functionalization of pyridones and related N-heteroarenes such as azaindole. This protocol is operationally simple, uses readily available materials, and is tolerable for electron-neutral and -rich functional pyridones. Cyclic voltammetry was utilized as a mechanistic probe, and preliminary data suggest the reaction may involve an electrophilic radical mechanism.

Design, Biological Evaluation, and Computer-Aided Analysis of Dihydrothiazepines as Selective Antichlamydial Agents

Chlamydia trachomatis (CT) causes the most prevalent sexually transmitted bacterial disease in the United States. The lack of drug selectivity is one of the main challenges of the current antichlamydial pharmacotherapy. The metabolic needs of CT are controlled, among others, by cylindrical proteases and their chaperones (e.g., ClpX). It has been shown that dihydrothiazepines can disrupt CT-ClpXP. Based on this precedent, we synthesized a dihydrothiazepine library and characterized its antichlamydial activity using a modified semi-high-throughput screening assay. Then, we demonstrated their ability to inhibit ClpX ATPase activity in vitro, supporting ClpX as a target. Further, our lead compound displayed a promising selectivity profile against CT, acceptable cytotoxicity, no mutagenic potential, and good in vitro stability. A two-dimensional quantitative structure-activity relationship (2D QSAR) model was generated as a support tool in the identification of more potent antichlamydial molecules. This study suggests dihydrothiazepines are a promising starting point for the development of new and selective antichlamydial drugs.

The structure of caseinolytic protease subunit ClpP2 reveals a functional model of the caseinolytic protease system from Chlamydia trachomatis

Chlamydia trachomatis (ct) is the most reported bacterial sexually transmitted infection worldwide and the leading cause of preventable blindness. Caseinolytic proteases (ClpP) from pathogenic bacteria are attractive antibiotic targets, particularly for bacterial species that form persister colonies with phenotypic resistance against common antibiotics. ClpP functions as a multisubunit proteolytic complex, and bacteria are eradicated when ClpP is disrupted. Although crucial for chlamydial development and the design of agents to treat chlamydia, the structures of ctClpP1 and ctClpP2 have yet to be solved. Here, we report the first crystal structure of full-length ClpP2 as an inactive homotetradecamer in a complex with a candidate antibiotic at 2.66 Å resolution. The structure details the functional domains of the ClpP2 protein subunit and includes the handle domain, which is integral to proteolytic activation. In addition, hydrogen-deuterium exchange mass spectroscopy probed the dynamics of ClpP2, and molecular modeling of ClpP1 predicted an assembly with ClpP2. By leveraging previous enzymatic experiments, we constructed a model of ClpP2 activation and its interaction with the protease subunits ClpP1 and ClpX. The structural information presented will be relevant for future rational drug design against these targets and will lead to a better understanding of ClpP complex formation and activation within this important human pathogen.

Tandem Ring Opening/Intramolecular [2 + 2] Cycloaddition Reaction for the Synthesis of Cyclobutane Fused Thiazolino-2-Pyridones

Reaction of thiazoline fused 2-pyridones with alkyl halides in the presence of cesium carbonate opens the thiazoline ring via S-alkylation and generates N-alkenyl functionalized 2-pyridones. In the reaction with propargyl bromide, the thiazoline ring opens and subsequently closes via a [2 + 2] cycloaddition between an in situ generated allene and the α,β-unsaturated methyl ester. This method enabled the synthesis of a variety of cyclobutane fused thiazolino-2-pyridones, of which a few analogues inhibit amyloid β_1–40 fibril formation. Furthermore, other analogues were able to bind mature α-synuclein and amyloid β₁₋₄₀ fibrils. Several thiazoline fused 2-pyridones with biological activity tolerate this transformation, which in addition provides an exocyclic alkene as a potential handle for tuning bioactivity.

K2S2O8-mediated coupling of 6-amino-7-aminomethyl-thiazolino-pyridones with aldehydes to construct amyloid affecting pyrimidine-fused thiazolino-2-pyridones

We herein present the synthesis of diversely functionalized pyrimidine fused thiazolino-2-pyridones via K2S2O8-mediated oxidative coupling of 6-amino-7-(aminomethyl)-thiazolino-2-pyridones with aldehydes. The developed protocol is mild, has wide substrate scope, and does not require transition metal catalyst or base. Some of the synthesized compounds have an ability to inhibit the formation of Amyloid-β fibrils associated with Alzheimer's disease, while others bind to mature amyloid-β and α-synuclein fibrils.

A 2-pyridone amide inhibitor of transcriptional activity in Chlamydia trachomatis

Chlamydia trachomatis is a strict intracellular bacterium that causes sexually transmitted infections and eye infections that can lead to life-long sequelae. Treatment options are limited to broad-spectrum antibiotics that disturb the commensal flora and contribute to selection of antibiotic-resistant bacteria. Hence, development of novel drugs that specifically target C. trachomatis would be beneficial. 2-pyridone amides are potent and specific inhibitors of Chlamydia infectivity. The first generation compound KSK120, inhibits the developmental cycle of Chlamydia resulting in reduced infectivity of progeny bacteria. Here, we show that the improved, highly potent second-generation 2-pyridone amide KSK213 allowed normal growth and development of C. trachomatis and the effect was only observable upon re-infection of new cells. Progeny elementary bodies (EBs) produced in the presence of KSK213 were unable to activate transcription of essential genes in early development and did not differentiate into the replicative form, the reticulate body (RB). The effect was specific to C. trachomatis since KSK213 was inactive in the closely related animal pathogen C. muridarum and in C. caviae The molecular target of KSK213 may thus be different in C. trachomatis or non-essential in C. muridarum and C. caviae Resistance to KSK213 was mediated by a combination of amino acid substitutions in both DEAD/DEAH RNA helicase and RNAse III, which may indicate inhibition of the transcriptional machinery as the mode of action. 2-pyridone amides provide a novel antibacterial strategy and starting points for development of highly specific drugs for C. trachomatis infections.

Construction of 2-pyridones via oxidative cyclization of enamides: access to Pechmann dye derivatives

An efficient protocol for the construction of structurally diverse 2-pyridone derivatives from imines and α,β-unsaturated acid chlorides in a single operation is reported. The target compounds, including coumarin-8-oxoprotoberbine analogues and lamellarin G isomers, were prepared via thermal cyclization of the in situ generated enamides followed by thermal dehydrogenation. The cyclization of enamides was achieved by the introduction of an electron-withdrawing group on the α-carbon of acid chlorides. This methodology allows quick access to polycyclic Pechmann dyes via rare double oxidative cyclizations of dienamides under mild conditions.

Synthesis of Highly Conjugated Functionalized 2-Pyridones by Palladium-Catalyzed Aerobic Oxidative Dicarbonation Reactions of N-(Furan-2-ylmethyl) Alkyne Amides and Alkenes as Coupling Partners

A mild, step-economical method for the synthesis of highly conjugated functionalized 2-pyridones from N-(furan-2-ylmethyl) alkyne amides is reported. This method involves Pd-catalyzed aerobic oxidative dicarbonation reactions of alkynes with carbon nucleophiles of a furan ring and an acrylate or styrene as coupling partners. The UV-vis absorption spectra of some of the 2-pyridones indicated that they absorbed shortwave radiation, suggesting their potential utility for filtration of such radiation.

An efficient method for the synthesis of 2-pyridones via C-H bond functionalization

A simple and practical method to access N-substituted 2-pyridones via a formal [3+3] annulation of enaminones with acrylates based on RhIII-catalyzed C-H functionalization was developed. Control and deuterated experiments led to a plausible mechanism involving C-H bond cross-coupling and aminolysis cyclization. This strategy provides a short synthesis of structural motifs of N-substituted 2-pyridones.

Intramolecular Povarov Reactions for the Synthesis of Chromenopyridine Fused 2-Pyridone Polyheterocycles Binding to α-Synuclein and Amyloid-β Fibrils

A BF3·OEt2 catalyzed intramolecular Povarov reaction was used to synthesize 15 chromenopyridine fused thiazolino-2-pyridone peptidomimetics. The reaction works with several O-alkylated salicylaldehydes and amino functionalized thiazolino-2-pyridones, to generate polyheterocycles with diverse substitution. The synthesized compounds were screened for their ability to bind α-synuclein and amyloid β fibrils in vitro. Analogues substituted with a nitro group bind to mature amyloid fibrils, and the activity moreover depends on the positioning of this functional group.

Synthesis and Antichlamydial Activity of Molecules Based on Dysregulators of Cylindrical Proteases

Chlamydia trachomatis is the most common sexually transmitted bacterial disease globally and the leading cause of infertility and preventable infectious blindness (trachoma) in the world. Unfortunately, there is no FDA-approved treatment specific for chlamydial infections. We recently reported two sulfonylpyridines that halt the growth of the pathogen. Herein, we present a SAR of the sulfonylpyridine molecule by introducing substituents on the aromatic regions. Biological evaluation studies showed that several analogues can impair the growth of C. trachomatis without affecting host cell viability. The compounds did not kill other bacteria, indicating selectivity for Chlamydia. The compounds presented mild toxicity toward mammalian cell lines. The compounds were found to be nonmutagenic in a Drosophila melanogaster assay and exhibited a promising stability in both plasma and gastric fluid. The presented results indicate this scaffold is a promising starting point for the development of selective antichlamydial drugs.

Methyl sulfonamide substituents improve the pharmacokinetic properties of bicyclic 2-pyridone based Chlamydia trachomatis inhibitors

Methyl sulfonamide substituents effectively improve the pharmacokinetic properties of bicyclic 2-pyridones, a new class of Chlamydia trachomatis infectivity inhibitors.

Chlamydia trachomatis infections are a global health problem and new approaches to treat C. trachomatis with drugs of high specificity would be valuable. A library of substituted ring fused 2-pyridones has been synthesized and evaluated for their ability to attenuate C. trachomatis infectivity. In vivo pharmacokinetic studies were performed, with the best candidates demonstrating that a C8-methylsulfonamide substituent improved pharmacokinetic properties important for oral administration. C8-Methyl sulfonamide analogue 30 inhibited C. trachomatis infectivity in low micromolar concentrations. Further pharmacokinetic evaluation at an oral dose of 10 mg kg^–1 showed an apparent bioavailability of 41%, compared to C8-cyclopropyl and -methoxy analogues which had negligible oral uptake. In vitro ADME (absorption, distribution, metabolism and excretion) testing of solubility and Caco-2 cell permeability revealed that both solubility and permeability is greatly improved with the C8-methyl sulfonamide 30, effectively moving it from BCS (Biopharmaceutical Classification System) class IV to II.

Red Fluorescent Chlamydia trachomatis Applied to Live Cell Imaging and Screening for Antibacterial Agents

In this study, we describe the application of a transformed Chlamydia trachomatis strain constitutively expressing the red fluorescent protein mCherry, to allow real-time monitoring of the infection cycle and screening for agents that block replication of C. trachomatis. The red fluorescent C. trachomatis strain was detected autonomously without antibody staining and was equally susceptible to doxycycline as the wild type strain. A high-throughput screening assay was developed using the transformed strain and automated fluorescence microscopy. The assay was used in a pilot screen of a 349 compound library containing natural products from Australian flora and fauna. Compounds with anti-chlamydial activity were tested for dose response and toxicity to host cells and two non-toxic compounds had 50% effective concentration (EC₅₀) values in the low micromolar range. Natural products are valuable sources for drug discovery and the identified Chlamydia growth inhibition may be starting points for future drug development. Live cell imaging was used to visualize growth of the red fluorescent C. trachomatis strain over time. The screening assay reduced workload and reagents compared to an assay requiring immunostaining and could further be used to monitor the development of Chlamydia inclusions and anti-chlamydial effect in real time.

Synthesis and biological evaluation of 1-benzyl-N-(2-(phenylamino)pyridin-3-yl)-1H-1,2,3-triazole-4-carboxamides as antimitotic agents

A library of 1-benzyl-N-(2-(phenylamino)pyridin-3-yl)-1H-1,2,3-triazole-4-carboxamides (7a-al) have been designed, synthesized and screened for their anti-proliferative activity against some selected human cancer cell lines namely DU-145, A-549, MCF-7 and HeLa. Most of them have shown promising cytotoxicity against lung cancer cell line (A549), amongst them 7f was found to be the most potent anti-proliferative congener. Furthermore, 7f exhibited comparable tubulin polymerization inhibition (IC₅₀ value 2.04 µM) to the standard E7010 (IC₅₀ value 2.15 µM). Moreover, flow cytometric analysis revealed that this compound induced apoptosis via cell cycle arrest at G₂/M phase in A549 cells. Induction of apoptosis was further observed by examining the mitochondrial membrane potential and was also confirmed by Hoechst staining as well as Annexin V-FITC assays. Furthermore, molecular docking studies indicated that compound 7f binds to the colchicine binding site of the β-tubulin. Thus, 7f exhibits anti-proliferative properties by inhibiting the tubulin polymerization through the binding at the colchicine active site and by induction of apoptosis.