Copper-catalyzed synthesis of 3-substituted-5-amino-1,2,4-thiadiazoles via intramolecular N–S bond formation

A chromatography-free one-pot, two-step synthesis of 1,2,4-thiadiazoles from primary amides via thiolation and oxidative dimerization under solvent-free conditions: a greener approach

An efficient and practical one-pot, two-step synthesis of 1,2,4-thiadiazoles from primary amides with Lawesson reagent (LR) and tert-butyl hydrogen peroxide (TBHP) without solvent is demonstrated for the first time. This groundbreaking and environmentally friendly approach utilises readily available starting materials and eliminates the use of traditional solvents in the reaction process. The broad substrate scope, excellent functional group tolerance in mild and metal-free conditions, quick conversion, and excellent yields are essential features of this methodology. All the compounds were purified without column chromatography.

Directed evolution of Escherichia coli surface-displayed Vitreoscilla hemoglobin as an artificial metalloenzyme for the synthesis of 5-imino-1,2,4-thiadiazoles

Artificial metalloenzymes (ArMs) are constructed by anchoring organometallic catalysts to an evolvable protein scaffold. They present the advantages of both components and exhibit considerable potential for the in vivo catalysis of new-to-nature reactions. Herein, Escherichia coli surface-displayed Vitreoscilla hemoglobin (VHbSD-Co) that anchored the cobalt porphyrin cofactor instead of the original heme cofactor was used as an artificial thiourea oxidase (ATOase) to synthesize 5-imino-1,2,4-thiadiazoles. After two rounds of directed evolution using combinatorial active-site saturation test/iterative saturation mutagenesis (CAST/ISM) strategy, the evolved six-site mutation VHbSD-Co (6SM-VHbSD-Co) exhibited significant improvement in catalytic activity, with a broad substrate scope (31 examples) and high yields with whole cells. This study shows the potential of using VHb ArMs in new-to-nature reactions and demonstrates the applicability of E. coli surface-displayed methods to enhance catalytic properties through the substitution of porphyrin cofactors in hemoproteins in vivo.

Synthesis of 3,5-Disubstituted-1,2,4-thiadiazoles via NaH-DMF-Promoted Dehydrogenative Intramolecular N-S Bond Formation

A facile transition-metal-free synthesis of 3,5-bis(het)aryl/arylaminothiadiazoles has been reported. The overall protocol involves base-mediated tandem thioacylation of amidines with dithioesters or aryl isothiocyanates in DMF solvent and subsequent in situ intramolecular dehydrogenative N-S bond formation of thioacylamidine intermediates under an inert atmosphere. A probable mechanism involving a carbamoyl anion, generated by deprotonation of DMF, acting as a radical initiator has been suggested.

External oxidant-free and transition metal-free synthesis of 5-amino-1,2,4-thiadiazoles as promising antibacterials against ESKAPE pathogen strains

A new route to 5-amino-1,2,4-thiadiazole derivatives via reaction of N-chloroamidines with isothiocyanates has been proposed. The advantages of this method are high product yields (up to 93%), the column chromatography-free workup procedure, scalability and the absence of additive oxidizing agents or transition metal catalysts. The 28 examples of 5-amino-1,2,4-thiadiazole derivatives obtaining via the proposing protocol were evaluated in vitro against ESKAPE pathogens strains (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter cloacae). It was found that compounds 5ba, 5bd, 6a, 6d and 6c have potent antibacterial activity (MIC values 0.09-1.5 μg mL^-1), which is superior to the activity of commercial antibiotics such as pefloxacin (MIC 4-8 μg mL^-1) and streptomycin (MIC 2-32 μg mL^-1). The additional cytotoxic assay of hit compounds on PANC-1 cell line demonstrated the low or non-cytotoxicity activity at the same level of concentrations. Thus, these 5 compounds are promising starting point for further antimicrobial drug development.

Metal- and Oxidant-Free Green Three-Component Desulfurization and Deamination Condensation Approach to Fully Substituted 1H-1,2,4-Triazol-3-amines and Their Photophysical Properties

A metal- and oxidant-free three-component desulfurization and deamination condensation of amidines, isothiocyanates, and hydrazines for the synthesis of structurally diverse fully substituted 1H-1,2,4-triazol-3-amines is described. The reaction proceeds without the requirement of any external catalysts, metals, ligands, or oxidants. This [2 + 1 + 2] cyclization strategy involves C-N and C-S bond cleavage and the formation of new C-N bonds in one pot. This transformation provides a series of full substituted 1H-1,2,4-triazol-3-amines with advantages of a broad substrates scope, mild reaction conditions, environmental friendliness, and easy gram-scale applications. The fluorescence and aggregation-induced emission (AIE) properties of selected products were further tested. These synthesized 1H-1,2,4-triazol-3-amines may be worth investigating for further applications in the fields of organic chemistry, medicinal chemistry, and optical materials.

Transition-metal-free S–N bond formation: synthesis of 5-amino-1,2,4-thiadiazoles from isothiocyanates and amidines

A novel and green method for the synthesis of 5-amino-1,2,4-thiadiazoles has been developed by the reaction of isothiocyanates with amidines.

Copper-Catalyzed Aerobic Oxidative [3+2] Annulation for the Synthesis of 5-Amino/Imino-Substituted 1,2,4-Thiadiazoles through C-N/N-S Bond Formation

A copper-catalyzed aerobic oxidative annulation reaction of 2-aminopyridine/amidine with isothiocyanate has been reported. This strategy involving C-N/N-S bond formations provides various 5-amino/imino-substituted 1,2,4-thiadiazole derivatives under a Cu/O₂ catalytic system. This method has demonstrated high reactivity, mild reaction conditions, and a broad substrate scope. Furthermore, the synthetic utilities of the approach are demonstrated by further modifications.

A Novel and Convenient Synthesis of 3-Amino-2H-1,2,4-Triazoles from Isoselenocyanates and Hydrazine Hydrate

A novel and convenient one-pot synthesis of 3-amino-2 H-1,2,4-triazoles from two molecules of isoselenocyanates and hydrazine hydrate via cyclodeselenisation was developed. Various 3-amino-2 H-1,2,4-triazoles were obtained in moderate to good yields (33–45%, based on isoselenocyanates). The selenium powder and aromatic amine side products during the reaction could be recycled for efficient preparation of isoselenocyanates, which improved the atom economy. A plausible mechanism was proposed for the formation of the target products.

Direct synthesis of N-sulfenylimines through oxidative coupling of amines with disulfides/thiols over copper based metal–organic frameworks

A highly porous metal–organic framework based on supramolecular building blocks with pcu-topology has been tested for the oxidative coupling of amines and disulfides to afford the N-sulfenylimines directly in good yields.

Synthesis of the 1,2,4-thiadiazole alkaloids polycarpathiamines A and B

Synthesis of the 1,2,4-thiadiazole alkaloids polycarpathiamines A and B is described. The heteroaromatic core of the natural products was assembled using a one-pot benzylic oxidation–oxidative heterocyclization process.