A review on bis-hydrazonoyl halides: Recent advances in their synthesis and their diverse synthetic applications leading to bis-heterocycles of biological interest

Palladium-Catalyzed Multicomponent Carbonylation of Halides to Acylhydrazones

The current methods for synthesizing acylhydrazones are limited by their multistep processes, narrow substrate scope, low selectivities, and poor yields. Herein, a fundamentally novel approach to bioactive acylhydrazones was developed based on the palladium-catalyzed multicomponent tandem condensation carbonylation of halides with aldehydes and hydrazines. This method provides a useful and efficient strategy for generating grams of various acylhydrazones in a one-pot manner. Mechanistic studies provided evidence of facile carbonylation of halides with the weak nucleophile hydrazones facilitated by a base.

The (E, Z) Isomerization of C-methoxycarbonyl-N-aryl Chlorohydrazones

Since chlorohydrazones are planar molecules, it is in principle possible to distinguish between their E and Z stereoisomers. Chlorohydrazones are known to preferentially assume the Z configuration around the C=N double bond, and their (E, Z) isomerization is almost suppressed at room temperature. The lack, or rather the difficulty, of such an isomerization has been conveniently addressed by the in-depth theoretical study of seven C-methoxycarbonyl-N-aryl chlorohydrazones (aryl = phenyl, 4-chlorophenyl, 4-bromophenyl, 4-iodophenyl, 2-chlorophenyl, 2-bromophenyl, and 2-iodophenyl). DFT ωB97M-D4/cc-pVTZ calculations of these C-methoxycarbonyl-N-aryl chlorohydrazones, supported by the XRD determination of the molecular structure, provided a complete picture of the isomerization processes in the studied compounds. The analysis of the energetics, molecular geometry, and electronic structure (the latter in the framework of the Quantum Theory of Atoms In Molecules) showed that the Z isomers are thermodynamically favored because, within the low-energy planar isomers with extensive π conjugation, the electrostatic interactions between the dipoles of the C–O, C–Cl, and N–H bonds overcome the stabilization induced by the N–H ··· O bond present in the E isomers. We confirmed that the (E, Z) isomerization occurs by the umklapp mechanism, in which the –NHAr moiety rotates in the molecular plane towards a linear C=N–N configuration and then proceeds to the other isomer. The (E, Z) isomerization is very slow at room temperature because the umklapp interconversion has high barriers (≈110 kJ/mol) despite the extended π electron delocalization present in the transition state.

Synthesis and biological evaluation of new 1,3,4-thiadiazole derivatives as potent antimicrobial agents

A series of 1,3,4-thiadiazole derivatives were designed and synthesized using N-(4-nitrophenyl)acetohydrazonoyl bromide and 1-[3,5-dimethyl-1-(4-nitrophenyl)-1H-pyrazol-4-yl]ethan-1-one as starting materials. The treatment of 1-[3,5-dimethyl-1-(4-nitrophenyl)-1H-pyrazol-4-yl]ethan-1-one with methyl hydrazinecarbodithioate or hydrazinecarbothioamide afforded 2-[1-[5-methyl-1-(4-nitrophenyl)-1H-pyrazol-4-yl]ethylidene]hydrazine derivatives. The targeted 1,3,4-thiadiazolyl derivatives were prepared by the reaction of 2-[1-[5-methyl-1-(4-nitrophenyl)-1H-pyrazol-4-yl]ethylidene]hydrazine derivatives with hydrazonoyl chloride derivatives. The reaction of N-(4-nitrophenyl)acetohydrazonoyl bromide with 2-[(methylthio)carbonthioyl]hydrazones in absolute ethanol in the presence of triethylamine afforded the corresponding 1,3,4-thiadiazole derivatives. The newly synthesized compounds were fully characterized by 1H NMR, 13C NMR, IR, MS, and elemental analysis. Moreover, the antimicrobial activity of the synthesized 1,3,4-thiadiazole derivatives were tested against E. coli, B. mycoides, and C. albicans. Four compounds outperformed the other produced compounds in terms of antimicrobial activity.

Graphical abstract

Cu-Catalyzed tandem cyclization and coupling of enynones with enaminones for multisubstituted furans & furano-pyrroles

A synthetic strategy that efficiently constructs complex molecular diversity in a few steps will always be embraced by organic chemists. Here, we report a cascade reaction of enynones with enaminones via carbene insertion and aryl migration to engineer distinctive multisubstituted furans with an all-carbon quaternary center, and could extend the protocol in the same pot towards furano-pyrrole bis-heterocycles. Heterogeneity of this protocol was proved with the upshot of divergent chemical space under a relatively mild reaction environment.

Copper-catalyzed synthesis of 1-(2-benzofuryl)-N-heteroarenes from o-hydroxy-gem-(dibromovinyl)benzenes and N-heteroarenes

An efficient method for the synthesis of 1-(2-benzofuryl)-N-heteroarenes is developed from o-hydroxy-gem-(dibromovinyl)benzenes and N-heteroarenes under copper-catalyzed tandem reaction conditions. This methodology displayed a broad substrate scope and high yields in the preparation of a variety of 1-(2-benzofuryl)-N-heteroarenes. Further, 1-(2-benzofuryl)-N-heteroarenes were also applied in the synthesis of polycyclic benzofuro-indolo-pyridine scaffolds under palladium-catalyzed dehydrogenative coupling conditions. Overall, the present tandem approach is general, synthetically advantageous and avoids air-sensitive reagents.

Hydrazonoyl bromide precursors as DHFR inhibitors for the synthesis of bis-thiazolyl pyrazole derivatives; antimicrobial activities, antibiofilm, and drug combination studies against MRSA

Microbial resistance is a big concern worldwide, making the development of new antimicrobial drugs difficult. The thiazole and pyrazole rings are important heterocyclic compounds utilized to produce a variety of antimicrobial medications. As a result, a series of new bis-thiazolyl-pyrazole derivatives 3, 4a-c, 5a, b, and 6a-c was synthesized by reacting bis hydrazonoyl bromide with several active methylene reagents in a one-pot reaction. The assigned structure was characterized entirely based on elemental and spectral analyses. The antimicrobial activity represented by MIC was performed using a resazurin-based turbidimetric (TB) assay. The results exhibited good antimicrobial activity against gram-positive strains, especially S. aureus (ATCC6538) while showing poor to moderate activity against gram-negative and fungal strains. Furthermore, the most active derivatives 3, 4a, 4c, and 5b were evaluated for MIC, MBC, antibiofilm, hemolytic assay, and drug combination testing against two S. aureus (ATCC6538) and MRSA (ACL18) strains. Additionally, bis-thiazolyl pyrazole 3, 4c, and 5b exhibited more potent inhibitory activity for DHFR with IC₅₀ values (6.34 ± 0.26, 7.49 ± 0.28, and 3.81 ± 0.16 µM), respectively, compared with Trimethoprim (8.34 ± 0.11 µM). The bis-1-(substituted-thiazol-2-yl)-1H-pyrazole-4-carbonitrile derivative 5b was the most active member with MIC values ranging from (0.12-0.25 µM) compared to Vancomycin (1-2 µM), and MBC values ranging from (0.5-1 µM) for S. aureus (ATCC6538) and MRSA (ACL18). Surprisingly, compound 5b displayed bactericidal behavior, synergistic effect with three commercial antibiotics, and inhibited DHFR with 2.1 folds higher than Trimethoprim. Finally, good findings were obtained from in silico investigations incorporating toxicity prediction and molecular docking simulation.

An Overview of the Synthesis and Antimicrobial, Antiprotozoal, and Antitumor Activity of Thiazole and Bisthiazole Derivatives

Thiazole, a five-membered heteroaromatic ring, is an important scaffold of a large number of synthetic compounds. Its diverse pharmacological activity is reflected in many clinically approved thiazole-containing molecules, with an extensive range of biological activities, such as antibacterial, antifungal, antiviral, antihelmintic, antitumor, and anti-inflammatory effects. Due to its significance in the field of medicinal chemistry, numerous biologically active thiazole and bisthiazole derivatives have been reported in the scientific literature. The current review provides an overview of different methods for the synthesis of thiazole and bisthiazole derivatives and describes various compounds bearing a thiazole and bisthiazole moiety possessing antibacterial, antifungal, antiprotozoal, and antitumor activity, encouraging further research on the discovery of thiazole-containing drugs.

Retro Diels Alder protocol for regioselective synthesis of novel [1,2,4]triazolo[4,3-a]pyrimidin-7(1H)-ones

Reactions of diastereochemically varied norbornene-condensed 2-thioxopyrimidin-4-ones 6 and 10 with variously functionalized hydrazonoyl chlorides 2a-h gave regioselectively angular norbornene-based [1,2,4]triazolo[4,3-a]pyrimidin-7(1H)-ones 7a-h and 11a,c-e, respectively. Thermal retro Diels-Alder (RDA) reaction of 7a-h and 11a,c-e resulted in the target compounds 4a-h as single products. On the other hand, reactions of thiouracil 1 and hydrozonoyl chlorides 2a-e gave regioselectively [1,2,4]triazolo[4,3-a]pyrimidinone-5(1H)-ones 3a-e. The opposite regioselectivity of thiouracil 1 and norbornene-condensed 2-thioxopyrimidin-4-ones 6 and 10 was attributed to electronic factors according to DFT calculations. The angular structure of norbornene based [1,2,4]triazolo[4,3-a]pyrimidin-7(1H)-ones was confirmed by single crystal X-ray crystallography.

Synthesis of Novel Bis-pyrazole Derivatives as Antimicrobial Agents

BACKGROUND

Bis-heterocycles especially those containing pyrazole moiety display much better antibacterial activity than mono heterocycles.

OBJECTIVE

Herein, we synthesised a series of new bis-pyrazoles and investigated their antimicrobial agents.

METHODS

A novel series of bis-pyrazole derivatives have been synthesized in good yield by coupling reaction of cyanoacetic acid {4-[(2-cyano-acetyl)-hydrazonomethyl]-benzylidene}-hydrazide with a number of diazonium salts of aromatic amines in DMF in the presence of NaOH. Refluxing of the produced hydrazones with hydrazine-hydrate in ethanolic solution afforded the respective bis-pyrazoles. On the other hand, the reaction of bis(cyanoacetic acid hydrazide) derivative with a diversity of hydrazonoyl chlorides in dioxane under reflux gave bis-pyrazoles.

RESULTS

The structures of all the products were discussed and assured from all possible spectral data as well as for the elemental analysis. In addition, the results of the antimicrobial activity examination of selected derivatives revealed a high strength of some tested compounds compared to standard bactericides and fungicides utilized. Molecular docking of the newly synthesized compounds into the Enoyl ACP reductase active site supported the in vitro antimicrobial activity. All the tested compounds could fit in the enzyme binding pocket with significant binding affinities (-7.040 to -9.141 Kcal/mol).

CONCLUSION

The good results of the antimicrobial examination of the newly synthesized bis-pyrazoles comprise the considerable evidence of the importance of bis-heterocyclic compounds which encourages us to continue designing and synthesising a novel series with potent biological activity in the future.