Antimycobacterial pyridine carboxamides: From design to in vivo activity

Tuberculosis is the number one killer of infectious diseases caused by a single microbe, namely Mycobacterium tuberculosis (Mtb). The success rate of curing this infection is decreasing due to emerging antimicrobial resistance. Therefore, novel treatments are urgently needed. As an attempt to develop new antituberculars effective against both drugs-sensitive and drug-resistant Mtb, we report the synthesis of a novel series inspired by combining fragments from the first-line agents isoniazid and pyrazinamide (series I) and isoniazid with the second-line agent 4-aminosalicylic acid (series II). We identified compound 10c from series II with selective, potent in vitro antimycobacterial activity against both drug-sensitive and drug-resistant Mtb H37Rv strains with no in vitro or in vivo cytotoxicity. In the murine model of tuberculosis, compound 10c caused a statistically significant decrease in colony-forming units (CFU) in spleen. Despite having a 4-aminosalicylic acid fragment in its structure, biochemical studies showed that compound 10c does not directly affect the folate pathway but rather methionine metabolism. In silico simulations indicated the possibility of binding to mycobacterial methionine-tRNA synthetase. Metabolic study in human liver microsomes revealed that compound 10c does not have any known toxic metabolites and has a half-life of 630 min, overcoming the main drawbacks of isoniazid (toxic metabolites) and 4-aminosalicylic acid (short half-life).

Hybridization Approach Toward Novel Antituberculars: Design, Synthesis, and Biological Evaluation of Compounds Combining Pyrazinamide and 4-Aminosalicylic Acid

Apart from the SARS-CoV-2 virus, tuberculosis remains the leading cause of death from a single infectious agent according to the World Health Organization. As part of our long-term research, we prepared a series of hybrid compounds combining pyrazinamide, a first-line antitubercular agent, and 4-aminosalicylic acid (PAS), a second-line agent. Compound 11 was found to be the most potent, with a broad spectrum of antimycobacterial activity and selectivity toward mycobacterial strains over other pathogens. It also retained its in vitro activity against multiple-drug-resistant mycobacterial strains. Several structural modifications were attempted to improve the in vitro antimycobacterial activity. The δ-lactone form of compound 11 (11') had more potent in vitro antimycobacterial activity against Mycobacterium tuberculosis H37Rv. Compound 11 was advanced for in vivo studies, where it was proved to be nontoxic in Galleria mellonella and zebrafish models, and it reduced the number of colony-forming units in spleens in the murine model of tuberculosis. Biochemical studies showed that compound 11 targets mycobacterial dihydrofolate reductases (DHFR). An in silico docking study combined with molecular dynamics identified a viable binding mode of compound 11 in mycobacterial DHFR. The lactone 11' opens in human plasma to its parent compound 11 (t_1/2 = 21.4 min). Compound 11 was metabolized by human liver fraction by slow hydrolysis of the amidic bond (t_1/2 = 187 min) to yield PAS and its starting 6-chloropyrazinoic acid. The long t_1/2 of compound 11 overcomes the main drawback of PAS (short t_1/2 necessitating frequent administration of high doses of PAS).

Synthesis of functionalized benzo[1,3]dioxin-4-ones from salicylic acid and acetylenic esters and their direct amidation

Direct synthesis of 4H-benzo[d][1,3]dioxin-4-one derivatives from salicylic acids and acetylenic esters (both mono- and disubstituted) has been described. The reaction is mediated by CuI and NaHCO₃ in acetonitrile. Room temperature amidation of the synthesized 1,3-benzodioxinones with primary amines readily afforded the corresponding salicylamides in moderate to good yields.

An efficient method for the synthesis of the active core 4H-benzo[d][1,3]dioxin-4-one followed by its direct room temperature amidation is reported.

Green Synthesis of 3-Substituted-4-arylmethylideneisoxazol-5(4H)-one Derivatives Catalyzed by Salicylic Acid

Background:

4-Arylmethylideneisoxazol-5(4H)-ones are a class of organic compounds with a variety of applications in the agriculture, filter dyes, photonic devices, and pharmaceutical industries. They are also used as synthetic precursors for the synthesis of other organic compounds. As a result, efforts are being made to search new and available catalyst and green methods toward their synthesis.

Objective:

The aim of this work is to investigate the catalytic activity of salicylic acid as an inexpensive, easy to handle, and safe catalyst to synthesis of some derivatives of isoxazole-5(4H)-ones in water medium.

Methods:

To aqueous solution of equal amounts of aryl/heteroaryl aldehydes, β-ketoesters, and hydroxylamine hydrochloride; salicylic acid (15 mol%) was added and the reaction mixture was stirred at room temperature for a specified periods. The precipitated product was filtered and washed with water to obtain 3-substituted-4-arylmethylideneisoxazol-5(4H)-ones. The reaction conditions were also optimized and extended to synthesis other isoxazol-5(4H)-ones.

Results:

The salicylic acid is found to possess acceptable catalytic activity for the promotion of three-component cyclocondensation of aryl/heteroaryl aldehydes, β-ketoesters, and hydroxylamine hydrochloride. The three-component reaction led to construction of 3-substituted-4-arylmethylideneisoxazol- 5(4H)-ones in good to high isolated reaction yields.

Conclusion:

The efficient and environmental friendliness procedure for the synthesis of isoxazol- 5(4H)-ones is introduced. The reaction also carried out smoothly in water as a cost-effective, simple, green, and non-toxic solvent at room temperature without using heating, microwave, and ultrasound sources.

Highly efficient synthesis of benzodioxins with a 2-site quaternary carbon structure by secondary amine-catalyzed dual Michael cascade reactions

Employing salicylic acids and substituted 3-butyn-2-ones as the substrates, a morpholine catalyzed tandem dual Michael addition afforded a benzodioxin skeleton.

Palladium-Catalyzed Cyclization of Alkynoic Acids To Form Vinyl Dioxanones Bearing a Quaternary Allylic Carbon

A palladium-catalyzed intramolecular reaction of carboxylic acids and alkynes in a novel cyclization manner was developed. This unique cyclization efficiently provided a wide range of complex ring systems-vinyl dioxanones bearing a quaternary allylic carbon. Mechanistic studies suggest an allenyl carboxylate as an intermediate.

Copper-catalyzed synthesis of benzo[d][1,3]dioxin-4-ones via tandem Ar–halogen bond hydroxylation and dichloromethane-based double Williamson etherification

The copper-catalyzed tandem reactions of o-halobenzoic acids, dichloromethane and KOH giving benzo[d][1,3]dioxin-4-ones via tandem Ar–X hydroxylation and double Williamson etherification are reported.

Oxidative cyclization of alkenoic acids promoted by AgOAc

Alkenoic acids derived from salicylic acid and analogues undergo an unexpected oxidative cyclization process triggered by AgOAc leading to 4H-benzo[d][1,3]dioxin-4-ones. The process is affected by the substitution on the aryl and the allyl units.