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Schiff bases are a vast group of compounds characterized by the presence of a double bond linking carbon and nitrogen atoms, the versatility of which is generated in the many ways to combine a variety of alkyl or aryl substituents. Compounds of this type are both found in nature and synthesized in the laboratory. For years, Schiff bases have been greatly inspiring to many chemists and biochemists. In this article, we attempt to present a new take on this group of compounds, underlining of the importance of various types of Schiff bases. Among the different types of compounds that can be classified as Schiff bases, we chose hydrazides, dihydrazides, hydrazones and mixed derivatives such as hydrazide–hydrazones. For these compounds, we presented the elements of their structure that allow them to be classified as Schiff bases. While hydrazones are typical examples of Schiff bases, including hydrazides among them may be surprising for some. In their case, this is possible due to the amide-iminol tautomerism. The carbon–nitrogen double bond present in the iminol tautomer is a typical element found in Schiff bases. In addition to the characteristics of the structure of these selected derivatives, and sometimes their classification, we presented selected literature items which, in our opinion, represent their importance in various fields well.

The increase in drug resistance and the high toxicity of current drugs have inspired the scientific community to develop new drugs for various diseases. Hydrazides have become an attractive functional group to easily obtain a plethora of novel compounds with a broad range of biological activities. This review, which contains studies in the literature from the previous five years, focuses on the synthesis methods and biological applications of hydrazides and their derivatives. Here, the details of the experimental reaction conditions used for the synthesis of hydrazides and their derivatives (hydrazide–hydrazones and heterocycle derivatives) are presented, as well as the purification methods and the biological activity of the synthesized compounds.

N–N linkages are found in many natural compounds and endow fascinating structural and functional properties. In comparison to the myriad methods for the construction of C–N bonds, chemistry for N–N coupling, especially in an intermolecular fashion, remains underdeveloped. Here, we report a nitrene-mediated intermolecular N–N coupling of dioxazolones and arylamines under iridium or iron catalysis. These reactions offer a simple and efficient method for the synthesis of various hydrazides from readily available carboxylic acid and amine precursors. Although the Ir-catalysed conditions usually give higher N–N coupling yield than the Fe-catalysed conditions, the reactions of sterically more demanding dioxazolones derived from α-substituted carboxylic acids work much better under the Fe-catalysed conditions. Mechanistic studies revealed that the nitrogen atom of Ir acyl nitrene intermediates has strong electrophilicity and can undergo nucleophilic attack with arylamines with the assistance of Cl···HN hydrogen bonding to form the N–N bond with high efficiency and chemoselectivity.Although many natural products and drug molecules contain N–N linkages, the chemistry of N–N coupling is somewhat underdeveloped. Now, a nitrene-mediated intermolecular N–N coupling of dioxazolones and arylamines that relies on iridium or iron catalysis has been developed. These reactions offer a simple and efficient method for the synthesis of hydrazides from readily available precursors.

Hydrazones have versatile properties that make them promising for a range of possible applications. In this study, we examined a library of 17 aroylhydrazones derived from nicotinic acid hydrazide (1-12) and isonicotinic acid hydrazide (A-E) created by us for their biological activity. The antiproliferative activity of the compounds was investigated on non-tumour MCF-10A cells and cancer cell lines, MCF-7 and MDA-MB-231. Four compounds were selected as most active in cell growth inhibition of the tumour cell lines. These compounds, 5, 11, C and E, were tested on four additional cell lines: non-tumour BJ and cancer cell lines, HeLa, HepG2 and HT-29. Compounds 5 and E exhibited the highest selectivity index on cancer cell lines MDA-MB-231, HeLa and HepG2. High selectivity to MCF-7 cells was demonstrated with compound 5. Compound C was very selective to HepG2 cells as well as to MDA-MB-231 but to a lesser degree. Compound 11 showed selectivity against MDA-MB-231. The obtained results allow assessing the structure-activity relationship of the compounds and provide insight into the further development of this group of aroylhydrazones as more potent and selective anti-neoplastic agents.

The study of proteins and protein complexes using chemical cross-linking followed by the MS identification of the cross-linked peptides has found increasingly widespread use in recent years. Thus far, such analyses have used almost exclusively homobifunctional, amine-reactive cross-linking reagents. Here we report the development and application of an orthogonal cross-linking chemistry specific for carboxyl groups. Chemical cross-linking of acidic residues is achieved using homobifunctional dihydrazides as cross-linking reagents and a coupling chemistry at neutral pH that is compatible with the structural integrity of most protein complexes. In addition to cross-links formed through insertion of the dihydrazides with different spacer lengths, zero-length cross-link products are also obtained, thereby providing additional structural information. We demonstrate the application of the reaction and the MS identification of the resulting cross-linked peptides for the chaperonin TRiC/CCT and the 26S proteasome. The results indicate that the targeting of acidic residues for cross-linking provides distance restraints that are complementary and orthogonal to those obtained from lysine cross-linking, thereby expanding the yield of structural information that can be obtained from cross-linking studies and used in hybrid modeling approaches.

In this study, new amino heterocyclic cellulose derivatives were prepared. Dialdehyde cellulose was functionalized by Schiff base reaction with (E)-2-(4-(dimethylamino) benzylidene)-4-oxo-4-phenylbutanehydrazide, (E)-2-((1,3-diphenyl-1H-pyrazol-4-yl)-4-oxo-4-phenylbutane hydrazide, and thiophene-2-carbohydrazide. The prepared derivatives were characterized and confirmed by Fourier-transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray, and Thermo gravimetric analysis. Additionally, antimicrobial activity of all derivatives was assessed as well as antitumor activity. Results revealed that, all derivatives have potential antimicrobial activity against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Bacillus subtilis, Candida albicans, Cryptococcus neoformance, Aspergillus niger, A. fumigatus. Additionally, (E)-2-(4-(dimethylamino) benzylidene)-4-oxo-4-phenylbutanehydrazide and (E)-2-((1,3-diphenyl-1H-pyrazol-4-yl)-4-oxo-4-phenylbutanehydrazide cellulose compounds have good antitumor activities against Hep G2 and MCF7 cancerous cell lines without any effects on Wi38 normal cell line. Molecular dynamics study revealed that (E)-2-(4-(dimethylamino) benzylidene)-4-oxo-4-phenylbutanehydrazide and (E)-2-((1,3-diphenyl-1H-pyrazol-4-yl)-4-oxo-4-phenylbutanehydrazide cellulose derivatives have selectively target the ATP binding pocket residues. Identification of these ATP binding site residues and their crucial roles could provide the structure basis for understanding c-Kit kinase auto-inhibition

A series of hydrazones bearing 6-methyluracil and hydrazone pharmacophoric units were synthesized by the direct reaction of 6-methyluracil-5-carboxaldehyde and either carboxylic acid hydrazides or hydrazines. It was found that E configuration of the C=N double bond is preferable for some of the synthesized compounds.

Eight new N -acylhydrazones were synthesized from betulin diacetate by its low-temperature ozonolysis to obtain 3β,3,28-diacetoxyoxy-20-oxo-29-norlupan and condensation of the latter with capric, cyclohexanoic, benzoic, o -hydroxy-, p -hydroxy-, p -methoxybenzoic, isonicotinic, and nicotinic hydrazides. The synthesized compounds were tested for in vitro cytotoxic activity against a number of cancer cell lines. The derivatives of salicylic, isonicotinic, and nicotinic hydrazides showed moderate activity against HepG2 human hepatocellular carcinoma, HTC-116 human colon cancer, THP-1 leukemia, and Jurkat acute T-cell leukemia cells.

Glutathione remains one of the most efficient antioxidant compounds in living systems, and the biological abilities of hydrazides have been well documented in literature. This study highlights the phytochemical constituents of garlic and the separation of the bioactive benzoic acid, 4-chloro- 1-(4-methoxyphenyl) hydrazide (BA4C) using gas chromatography-mass spectroscopy (GC–MS) technique. Preliminary phytochemical screening reveals the presence of alkaloids, saponins, flavonoids, tannins, terpenoids, steroids and phenols. Computationally, compound BA4C was optimized using the B3LYP/aug-cc-PVDZ DFT method. Spectroscopic studies of the compound involved analysis of the vibrational FT-IR frequencies and the modes of vibrations. Frontier molecular orbitals analysis records an energy gap of 4.3391 eV; NBO studies reveal that the compound has strong perturbation energies of 246 kcal/mol and 269 kcal/mol among its intramolecular interactions such as π *C 12 – C 13 to π *C 14 – C 15 and π *C 11 – C 16 to π *C 14 – C 15 , respectively. According to the visualization of non-covalent interactions, steric repulsions were observed at the core of the phenyl and benzene rings. However, other regions of the compound depict a significant balance of forces between steric repulsions and van der Waals forces. To significantly deduce the reducing power of compound BA4C, electrons were found to be highly localized at the methoxy and hydrazide moieties significantly implying their propensity to donate electrons to oxidized systems. Furthermore, ADMET analysis reveals that the compound has two hydrogen donors. Most significantly, the compound binds to NADPH dehydrogenase (5V4P) and glutathione reductase (1XAN) with binding energies of − 6.0 kcal/mol and − 8.0 kcal/mol showing considerable favourable binding feasibility as well as forming plural hydrogen bonds with the amino acid residues. Notably, BA4C was bonded at the active site of 1XAN, which implies the ability of the compound for the reduction of oxidized glutathione. Graphical Abstract

Main conclusionAmmonium sulfate is well known to salt out proteins at high concentrations. The study revealed that it can serve to increase by 60% the total number of identified carbonylated proteins by LC–MS/MS.Protein carbonylation is a significant post-translational modification associated with reactive oxygen species signaling in animal and plant cells. However, the detection of carbonylated proteins involved in signaling is still challenging, as they only represent a small subset of the proteome in the absence of stress. In this study, we investigated the hypothesis that a prefractionation step with ammonium sulphate will improve the detection of the carbonylated proteins in a plant extract. For this, we extracted total protein from the Arabidopsis thaliana leaves and subjected the extract to stepwise precipitation with ammonium sulfate to 40%, 60%, and 80% saturation. The protein fractions were then analyzed by liquid chromatography–tandem mass spectrometry for protein identification. We found that all the proteins identified in the non-fractionated samples were also found in the prefractionated samples, indicating no loss was incurred during the prefractionation. About 45% more proteins were identified in the fractionated samples compared to the non-fractionated total crude extract. When the prefractionation steps were combined with the enrichment of carbonylated proteins labeled with a fluorescent hydrazide probe, several carbonylated proteins, which were unseen in the non-fractionated samples, became visible in the prefractionated samples. Consistently, the prefractionation method allowed to identify 63% more carbonylated proteins by mass spectrometry compared to the number of carbonylated proteins identified from the total crude extract without prefractionation. These results indicated that the ammonium sulfate-based proteome prefractionation can be used to improve proteome coverage and identification of carbonylated proteins from a complex proteome sample.