Synthesis,characterization, and antioxidant activity of heterocyclic Schiff bases

Schiff base derivatives have gained great importance due to revealing a great number of biological properties. Schiff bases were synthesized by treatment of 4-amino-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one ( 1 ) with various aldehydes in methanol at reflux. In addition, diamine was reacted with an aldehyde to yield the corresponding Schiff bases. The structures of synthesized Schiff bases were elucidated by spectroscopic methods such as microanalysis, ¹H-NMR, ¹³C-NMR, and FTIR. Antioxidant activities of synthesized Schiff bases were carried out using different antioxidant assays such as 1,1-diphenyl-2-picryl-hydrazyl free radical (DPPH^•) scavenging, 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical scavenging, and reducing power activity. (E)-4-((1H-indol-3-yl)methyleneamino)-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one ( 3 ), (E)-1,5-dimethyl-4-((2-methyl-1H-indol-3-yl)methyleneamino)-2-phenyl-1H-pyrazol-3(2H)-one ( 5 ), (E)-1,5-dimethyl-2-phenyl-4-(thiophen-2-ylmethyleneamino)-1H-pyrazol-3(2H)-one ( 7 ), (E)-1,5-dimethyl-2-phenyl-4-(quinolin-2-ylmethyleneamino)-1H-pyrazol-3(2H)-one ( 9 ), (1S,2S,N1,N2)-N1,N2-bis((1H-indol-3-yl)methylene)cyclohexane-1,2-diamine ( 11 ), and (1S,2S,N1,N2)-N1,N2-bis((2-methyl-1H-indol-3-yl)methylene)cyclohexane-1,2-diamine ( 12 ) were synthesized in high yields. Compound 5 displayed a good ABTS^•+ activity. Compound 3 revealed the outstanding activity in all assays. Compound 7 has the best-reducing power ability in comparison to other synthesized compounds. Although compounds 5, 11, 12 are new, compounds 3, 7, 9 are known. Due to revealing a good antioxidant activity, the synthesized compounds ( 3, 5, 7 ) have the potential to be used as synthetic antioxidant agents.     

N-多氟烷基取代和葡萄糖基取代的1,2,4-三唑-5-硫酮类席夫碱的合成及其杀虫活性

为改善三唑类化合物的生物活性, 以3-苯基-4-氨基-1,2,4-三唑-5-硫酮为原料, 将其与芳香醛在冰醋酸体系中反应, 得到3-苯基-4-芳基亚甲氨基-1,2,4-三唑-5-硫酮类席夫碱(4a～4i). 在此基础上, 化合物4a～4i分别与多氟烷基碘代烷和溴代乙酰基葡萄糖反应合成了一系列1,2,4-三唑-5-硫酮类席夫碱的多氟烷基取代物5a～5r和葡萄糖基取代物6a～6d, 并用¹H NMR, ¹⁹F NMR, IR和MS谱以及元素分析表征了它们的结构. 初步生物活性测试结果表明, 部分目标化合物具有明显的杀虫活性.     

Microwave-assisted synthesis and biological activity of new Schiff bases derived from dimers of 4-amino-3-[3-(1-benzyl)indole]-5-thiomethyl-1,2,4-triazole

An expeditious method with microwave irradiation has been developed for synthesis of novel Schiff bases from dimers of 4-amino-3-[3-(1-benzyl)indole]-5-thiomethyl-1,2,4-triazole. Its distinct advantages are short reaction times and good conversion. The structures of these new Schiff bases were established by ¹H NMR, IR, and mass spectroscopy, and elemental analysis. The antibacterial activity of ten novel Schiff bases against three bacterial strains was studied by the disk diffusion method. Preliminary results indicated that some of the compounds had strong antibacterial activity.     

Synthesis,Structures, and Fungitoxicity of Novel Organophosphorus Compounds

Abstract

A series of biologically active organophosphorus compounds have been synthesized by the reactions of O,O-diethylchlorophosphate with Schiff bases derived from 5-(phenyl/substituted phenyl)-2-hydrazino-1,3,4-oxadiazole and salicylaldehyde/2-hydroxyacetophenone. The compounds have been characterized on the basis of analyses and spectral (IR, ¹H, ¹³C NMR) data. Fungicidal activities of these derivatives against Colletotrichum falcatum, Fusarium oxysporum, and Curvularia pallescence have been evaluated. All compounds showed moderate to significant antifungal activity.     

3-取代苯氧甲基-4-氨基-1,2,4-三唑-5-硫酮席夫碱的合成、结构表征和生物活性研究

以醋酸为反应溶剂和催化剂,用自制的4-氨基-4,5-二氢-3-取代苯氧甲基-1,2,4-三唑-5-硫酮与4-氟苯甲醛反应合成了5个4-氨基-4,5-二氢-3-取代苯氧甲基-1,2,4-三唑-5-硫酮席夫碱化合物,通过1HNMR、IR和元素分析对所有化合物进行了结构表征.初步生物活性测试结果表明所有化合物具有优良的杀菌活性,并对席夫碱结构与活性的关系进行了探讨.     

Experimental and theoretical studies of the products of addition–elimination reactions between benzil dihydrazone and three isomeric chlorobenzaldehydes

A series of mono‐ and di‐Schiff bases formed between benzil dihydrazone {BDH; systematic name: (1Z)‐[(2E)‐2‐hydrazinylidene‐1,2‐diphenylethylidene]hydrazine} and three isomeric chlorobenzaldehydes were designed and synthesized to be used as model compounds to help to explain the reaction mechanisms for the formation of Schiff bases. These compounds are 1‐(2‐chlorobenzylidene)‐2‐{2‐[2‐(2‐chlorobenzylidene)hydrazin‐1‐ylidene]‐1,2‐diphenylethylidene}hydrazine (BDHOCB), and the 3‐chloro (BDHMCB) and 4‐chloro (BDHPCB) analogues, all having the formula C₂₈H₂₀Cl₂N₄. Surprisingly, only di‐Schiff bases were obtained; our attempts to push the reaction in favour of the mono‐Schiff bases all failed. Density functional theory (DFT) calculations were performed to explain the trend in the experimental results. In the case of the systems studied, the type of Schiff base produced exhibits a clear dependence on the HOMO–LUMO energy gaps (ΔE_HOMO–LUMO), i.e. the product is mainly governed by its stability. The compounds were characterized by single‐crystal X‐ray diffractometry, elemental analysis, melting point, ¹H NMR and ¹³C NMR spectroscopy. The structural features of the three new Schiff bases are similar. For instance, they have the same chemical formula, all the molecules have a symmetrical double helix structure, with each Ph—C=N—N=C—Ph arm exhibiting an anti conformation, and their supramolecular interactions include intermolecular π–π and weak C—H...π stacking interactions. The crystal systems are different, however, viz. triclinic (space group P) for BDHPCB, monoclinic (space group P2₁/n) for BDHOCB and orthorhombic (space group Pnna) for BDHMCB.     

Stereoselective synthesis of trans-3-functionalized-4-pyrazolo[5,1-b]thiazole-3-carboxylate substituted β-lactams: Potential synthons for diverse biologically active agents

Abstract

An efficient protocol for the stereoselective synthesis of pyrazolo[5,1-b]thiazole-3-carboxylate tethered β-lactam conjugates 8a–j from novel pyrazolo [5,1-b]thiazole-3-carboxylate substituted Schiff’s bases 6a–f is reported here. The reaction between various ketene precursors and novel Schiff’s bases 6a–f afforded exclusive formation of trans-β-lactams 8a–j. The substrate scope of this approach was investigated extensively by varying different groups (R, Z). All the novel compounds were characterized using various spectroscopic techniques, such as FT-IR, ¹H NMR, ¹³C NMR, elemental analysis, ¹³C NMR (DEPT-135), and mass spectrometry in representative cases. Single crystal X-ray crystallographic study of trans-ethyl 7-(1-(4-methoxyphenyl)-4-oxo-3-phenoxyazetidin-2-yl)-6-methyl-2-(methylthio)pyrazolo[5,1-b]thiazole-3-carboxylate 8a has confirmed the molecular structure and the stereochemical outcome. To the best of our knowledge, the synthesis of such types of Schiff’s bases and β-lactam conjugates has not been reported so far.     

Synthesis,characterization, and biological properties of Ni(II), Co(II), and Cu(II) complexes of Schiff bases derived from 4-aminobenzylamine

New Schiff bases, N,N′-bis(salicylidene)-4-aminobenzylamine (H₂L¹), N,N′-bis(3-methoxysalicylidene)-4-aminobenzylamine (H₂L²), and N,N′-bis(4-hydroxysalicylidene)-4-aminobenzylamine (H₂L³), with their nickel(II), cobalt(II), and copper(II) complexes have been synthesized and characterized by elemental analyses, electronic absorption, FT-IR, magnetic susceptibility, and conductance measurements. For the ligands, ¹H and ¹³C NMR and mass spectra were obtained. The tetradentate ligands coordinate to the metal ions through the phenolic oxygen and azomethine nitrogens. The keto-enol tautomeric forms of the Schiff bases H₂L¹, H₂L², and H₂L³ have been investigated in polar and apolar solvents. All compounds were non-electrolytes in DMSO (～10^?3 M) according to the conductance measurements. Antimicrobial activities of the Schiff bases and their complexes have been tested against Acinobacter baumannii, Pseudomonas aeruginosa, Micrococcus luteus, Bacillus megaterium, Corynebacterium xerosis, Staphylococcus aureus, Escherichia coli, Candida albicans, Rhodotorula rubra, and Kluyveromyces marxianus by the disc diffusion method; biological activity increases on complexation.     

Cobalt(II) and nickel(II) chelates of some 5-pyrazolone-based,Schiff-base ligands

The cobalt(II) and nickel(II) chelates of Schiff bases, derived by condensing 4-butyryl-3-methyl-1-phenyl-2-pyrazolin-5-one (BMPP) with o-, m-, p-phenylenediamine, benzidine, and ethylenediamine have been synthesized and characterized by elemental analyses, thermogravimetric analyses (TGA), conductance data, magnetic measurements, IR, ¹H NMR, ¹³C NMR, mass, and electronic spectroscopies. Each of the Schiff bases was an ONNO donor to metal forming chelates formulated as [M(L)(H₂O)₂] _n with M = Ni(II) and Co(II) and L is the di-anion of the Schiff base. The monomeric (n = 1) and dimeric (n = 2) species of these metal chelates, based on available evidence, are suggested.     

A new azo‐Schiff base: Synthesis,characterization, biological activity and theoretical studies of its complexes

A new Azo‐Schiff base ligand L was prepared by reaction of m‐hydroxy benzoic acid with (Schiff base B) of 3‐[2‐(1H–indol‐3‐yl)‐ethylimino]‐1.5‐dimethyl‐2‐phenyl‐2,3‐dihydro‐1H‐pyrazol‐4‐ylamine. This synthesized ligand was used for complexation with different metal ions like Ni(II), Co(II), Pd(II) and Pt(IV) by using a molar ratio of ligand: metal as 1:1. Resulted compounds were characterized by NMR (¹H and ¹³C), UV–vis spectroscopy, TGA, FT‐IR, MS, elemental analysis, magnetic moment and molar conductivity studies. The activation thermodynamic parameters, such as ΔE*, ΔH^*, ΔS^*, ΔG^*and K are calculated from the TGA curves using Coats ‐ Redfern method. Hyper Chem‐8 program has been used to predict structural geometries of compounds in gas phase. The biological activities of Schiff base and its complexes had been tested in vitro against, two Gram positive bacteria (Bacillus subtillis and Staphylococcus aureus) and two Gram negative bacteria (Escherichia coli and Pseudomonas aeruguinosa).     

New Schiff Bases Containing Silicon and Their Co(II) and Cu(II) Complexes: Synthesis,Complexation, Characterization,and Antimicrobial and Electrochemical Properties

Two novel Schiff base ligands, 4-((3-(trimethoxysilyl)propylimino)methyl)benzene– 1,2,3-triol (L¹H) and 4-((3-(triethoxysilyl)propylimino)methyl)benzene–1,2,3-triol (L²H), have been synthesized by the reaction of 2,3,4-trihydroxybenzaldehyde with 3-aminopropyltrimethoxysilane and 3-aminopropyltriethoxysilane, respectively. The mononuclear Co^II and Cu^II complexes of these Schiff bases were prepared. The complexes of the Schiff bases are formed by coordination of N, O atoms of the ligands. The proposed structures were confirmed by elemental analyses, FT-IR, and UV-visible spectroscopy, magnetic susceptibility, and conductance measurements; the ¹H NMR spectra of the ligands were also recorded. The analytical data show that the metal to ligand ratio in the complexes containing silicon is 1:2. The electrochemical properties of the complexes have been investigated at 100 mVs^?1 scan rate in DMSO. In addition, the antimicrobial activity of L¹H and L²H Schiff ligands, and their [M(L¹)2] and [M(L²)2] type coordination compounds, were investigated.     

4-Hydroxy-2-quinolones 166*. Synthesis,isomerism, and antitubercular activity of 3-arylaminomethylene-quinoline-2,4-(1H,3H)-diones

Condensation of 4-hydroxy-2-oxo-1,2-dihydroquinoline-3-carbaldehydes, thioglycolic acid (or methyl thioglycolate), and anilines does not lead to the synthesis of the corresponding thiazolidinylquinolones because the Schiff bases so formed exist exclusively in a form inert to enamine thioglycolates. ¹H NMR spectroscopy showed that the main components of the isolated 3-arylaminomethylenequinoline-2,4-(1H,3H)-diones are E-isomers. The results of a study of the antitubercular properties of the compounds obtained are presented.     

Serine and Threonine Schiff Base Esters React with β-Anomeric Peracetates in the Presence of BF3·Et2O to Produce β-Glycosides

Improved procedures are reported for the glycosylation of L-serine and L-threonine utilizing activated Schiff base glycosyl acceptors, which are less expensive and more efficient alternatives to published methods. L-serine or L-threonine benzyl ester hydrochloride salts were reacted with the diarylketimine bis-(4-methoxyphenyl)-methanimine in CH₃CN at rt to form the more nucleophilic Schiff bases 3a and 3b in excellent yield. These Schiff bases exhibited ring-chain tautomerism in CDCl₃ as shown by ¹H NMR. Schiff bases 3a and 3b, acting as glycosyl acceptors, reacted at rt with simple sugar peracetate donors with BF₃·OEt₂ promotion to provide the corresponding L-serine and L-threonine O-linked glycosides in excellent yields and purities. The dipeptide ester Schiff base Ar₂C = N-Ser-Val-OCH₃ 3e also reacted to provide β-glycosides in excellent yields, and without epimerization. With microwave irradiation the reactions were complete in 2 to 5 min. To investigate this reaction further, classical AgOTf-promoted Koenigs-Knorr reaction of D-glucopyranosyl, lactosyl, and maltosyl bromides were examined, providing the β-glycosides with yields ranging from 35% to 68%. The difference in reactivity between α- and β-carbohydrate peracetate donors was remarkable. The less configurationally stable D-xylopyranosyl tetra-acetate (a pentose) showed no selectivity (αvsβ-configuration) toward the Schiff bases.     

Ultrasonic Assisted Synthesis of Naphthalene Substituted Schiff Base Derivatives and Their Antioxidant Activity Studies

New Schiff base derivatives, 2,2′‐[naphthalene‐2,7‐diylbis(oxy)]bis[N′‐substituted acetohydrazide] ( 4a‐m ) were synthesized by the acid catalyzed condensation of aryl/hetero aromatic aldehydes with 2,2′‐ [naphthalene‐2,7‐diylbis(oxy)]diacetohydrazide ( 3 ) under reflux temperature and ultrasonic irradiation. These Schiff base derivatives were confirmed through spectral characterization using IR, ¹H NMR, ¹³C NMR and mass spectra. All the synthesized compounds were screened for their antioxidant activity using DPPH free radical scavenging method.     

α-Cyclodextrin compounds containing benzoic,acetylsalicylic, and 2-(4-isobutylphenyl)propionic acid residues

Selectively substituted derivatives of α-cyclodextrin and hexa-O-tert-butyldimethylsilyl-α-cyclodextrin containing a definite number of acylated primary or secondary hydroxy groups were synthesized using benzoic, acetylsalicylic, and 2-(4-isobutylphenyl)propionic acid chlorides in various solvents in the presence of different bases. The acyl residues were assigned to the C², C³, or C⁶ atoms in the carbohydrate fragments on the basis of ¹³C NMR data. Desilylation of the silyl derivatives with ammonium fluoride in methanol gave the corresponding O-acyl derivatives having free primary hydroxy groups in the α-cyclodextrin skeleton.     

Synthesis,Characterization, Antibacterial,and Antifungal Activity of Novel 2‐(2‐hydroxy‐5‐((aryl)‐diazenyl)phenyl)‐3‐(4‐hydroxyphenyl)‐thiazolidin‐4‐one

A series of novel thiazolidinones, that is, 2‐(2‐hydroxy‐5‐((aryl)‐diazenyl)phenyl)‐3‐(4‐hydroxyphenyl)‐thiazolidin‐4‐one, have been synthesized by reaction of various Schiff bases 2‐(4‐hydroxyphenylimino)methyl)‐4‐(aryl)diazenyl)phenol with ethanolic thioglycolic acid. Schiff bases were obtained by the reactions of 4‐amino phenol with 2‐hydroxy‐5‐((aryl)diazenyl)benzaldehyde. The structures of the newly synthesized compounds were confirmed by IR, ¹H NMR, mass spectra, and C, H, N elemental analysis. The thiazolidinone derivatives were evaluated for their antibacterial and antifungal activity.     

Spectroscopic,thermal and antimicrobial properties of the copper(II) complex of Schiff base derived from 2‐(salicylidene) aminopyridine

Schiff bases and their complex combinations with metallic ions represent a class of compounds with antimicrobial activity. A ligand was prepared by condensation of the salicylaldehyde with 2‐aminopyridine obtaining 2‐(salicylidene) aminopyridine (SB) with a high capacity for complexing Cu(II) ions. The new compound has been characterized by physical constants (melting point, solubility, stability) and the chemical structure was confirmed by elemental, spectral (IR, UV–visible, ¹H NMR and ¹³C‐NMR) and thermal analyses. The elemental analysis gives a coordination ratio of 1:2 metal:Schiff base. Lethal dose 50 (DL₅₀) values of new Schiff base and their complex with metallic ions were established. The antimicrobial activity of this complex was tested in comparison with the activity of the corresponding Schiff base on strains of Staphylococcus aureus, Bacillus cereus, Bacillus subtilis, Escherichia coli, Candida albicans, and Klebsiella. These were compared with the activity of the reference drugs (chloramphenicol, tetracycline, ofloxacin and nystatin) on the above‐mentioned strains. It has been established that all compounds tested were very active against both Gram‐positive and Gram‐negative bacteria. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis,characterization and cytotoxicity of platinum(II) complexes containing reduced amino acid ester Schiff bases

Nine platinum(II) complexes containing reduced amino acid ester Schiff bases were synthesized and characterized using spectroscopy (¹H NMR, ¹³C NMR, infrared), elemental analysis and molar conductivity. The interaction of these complexes with salmon sperm DNA was investigated by means of ultraviolet and circular dichroism spectroscopies. The potential antitumor activity of all compounds was tested in vitro on HeLa and A549 tumor cell lines. Almost all the complexes exhibited better cytotoxic activity than cisplatin against these cell lines.     

Heterocyclic compounds from 4h‐3,1‐benzoxazin‐4‐one derivatives as anticancer agent

Behaviour of 2‐(4‐oxo‐4H‐benzo[d][l,3]oxazin‐2‐yl)‐benzoic acid (1) towards nitrogen nucleophiles namely, hydrazine hydrate, in different solvents, ammonium acetate, and o‐phenylenediamine has been investigated to give aminoquinazolin‐4‐one, benzotriazepinone, spiro‐type compound, and nitrogen bridgehead compounds 3‐5 , respectively. Also, reactivity of the aminoquinazolin‐4‐one 2 towards carbon elec‐trophiles such as ethyl acetoacetate, ethyl phenylacetate, ethyl chloroacetate, and aromatic aldehydes has been discussed. Reaction of Schiff s base 8 with sulfur nucleophiles namely o‐aminothiophenol and/or thio‐glycolic acid afforded Michael type adducts. Structural assignments, of products 1‐24 have been confirmed by elemental analysis and spectral data (¹H‐ and ¹³C ‐NMR and MS fragmentation). The bioassay indicates that some of the target compounds obtained have good selective anticancer activity.     

Synthesis,spectroscopic studies,and antioxidant activities of novel thio/carbohydrazones and bis-isatin derivatives from terephthalaldehyde

New bis(isatins-thio/carbohydrazones) based on Schiff bases were prepared from terephthalaldehyde biscarbohydrazone and 5-substituted isatins in the presence of a drop of sulfuric acid under reflux in ethanol. Terephthalaldehyde bis(thio/carbohydrazone) was synthesized by the reaction of (thio)/carbohydrazide and terephthalaldehyde in the presence of a few drops of acetic acid under reflux in ethanol. The structures of these synthesized compounds were determined using IR, ¹H NMR, and ¹³C NMR spectroscopy and elemental analysis. The in vitro antioxidant activity of all the compounds was determined by the 1,1-diphenyl-2-picryl hydrazyl (DPPH.) free radical scavenging method. Compound 2 showed the best antioxidant activity.