Respective Schiff Bases Research Articles

Synthesis of Manganese(II), Iron(III), and Vanadium(IV) Complexes with New Schiff Bases and their Spectroscopic and Thermal Studies and Evaluation of their Antimicrobial Activity

Heterocyclic 3-acetyl coumarin with hydrazide derivatives and their metal complexes are a substantial family of pharmaceutical drugs used to treat infection, anti-inflammatory issues, diabetes, and neurological disorders in the field of medicinal chemistry. Cyclization of 5- floro-2-furaldehyde, ethyl acetoacetate, and urea or thiourea by LaCl3.7H2O, addition of hydrazine to form amine derivatives were performed, and respective Schiff base derivatives (L1, L2) were produced by adding acetyl coumarin in an ethanolic solution at ambient temperature. New ligands and its complexes of the V (IV), Fe (III) and Mn (II) ions were characterized using (FT-IR, UV, MS) and nuclear magnetic resonance (1H-NMR) as well as elemental analysis (CHN). The synthesized complexes chelate with ligands L1, L2 via (N, O2) atoms. The structural geometry of the complexes was illustrated in the solid phase using FT-IR and UV-VIS spectroscopy, elemental analysis (CHNS), and flame atomic absorption, in addition to magnetic susceptibility and conductivity measurement. The antibacterial activity of the newly prepared ligands and their metal complexes was evaluated against Pseudonomous aerugionosa as a gram negative and Bacillus subtilis as a gram positive microorganism. Moreover, the antifungal activity against two fungi Aspergillus flavus, and Saccharomyces cerevisiae was studied for all compounds. The coordinated ligands significantly increased their bactericidal and fungicidal action compared to the free ligands, which did not exhibit any activity against the selected fungal and bacterial strains. The results focused on the synergetic relationship between the metal ion and the ligand, in addition to the structural variation.

Ru/Pd Complex and Its Monometallic Fragments as Catalysts for Norbornene Polymerization via ROMP and Addition

The [Ru(PPh3)2Cl-piperidine(4-aminomethyl)] complex (mono-Ru) was synthesized from [Ru(PPh3)3Cl2] and 4-(aminomethyl)piperidine, whereas the [(PPh3)PdCl(Shiff-pip)] complex (mono-Pd) was obtained by reacting [Pd(PPh3)2Cl2] with its respective Schiff base ligand, both at a 1:1 molar ratio. The heterobimetallic [RuCl2(PPh3)2](μ-Schiff)Pd(PPh3)Cl] complex (Ru/Pd) was synthesized via a one-pot, three-component reaction of mono-Ru, [(Pd(PPh3)2Cl2] and salicylaldehyde. All complexes were fully characterized by FTIR, UV-Vis, and NMR spectroscopy, as well as elemental analysis, MALDI-TOF mass spectrometry, cyclic voltammetry, and computational studies. Ru/Pd was able to polymerize norbornene (NBE) by two different mechanisms: ROMP and vinyl polymerization. The Ru fragment was active for ROMP of NBE, reaching yields of 68 and 31% for mono-Ru and Ru/Pd, respectively, when the [NBE]/[Ru] = 3000 molar ratio and 5 μL EDA addition were employed at 50 °C. The poly(norbornene) (polyNBE) obtained presented an order of magnitude of 104 g mol−1 and Ð values between 1.48 and 1.79. For the vinyl polymerization of NBE, the Pd fragment was active using MAO as a cocatalyst, reaching a yield of 47.0% for Ru/Pd and quantitative yields for mono-Pd when [Al]/[Pd] = 2500 and [NBE]/[Pd] = 20,000 molar ratios were employed, both at 60 °C.

Synthesis, spectral studies and antimicrobial evaluation of transition metal complexes of bidentate Schiff base ligands derived from 4-amino quinoline

Coordination compounds of Co(II) , Ni(II), Cu(II) and Zn(II) of the type [M(L1-2)2(H2O)2] were obtained from Schiff base ligands [HL1-2] by the condensation reaction of 5-bromosalicyldehyde/5-chlorosalicyldehyde with 4-amino quinoline using methanol as a solvent in (1:1) molar ratio. The metal complexes were synthesized by reacting the aqueous methanolic solution of metal acetates M(CH3COO)2xH2O with the hot methanolic solution of their respective Schiff base ligands in (1:2) molar ratio. Various physicochemical techniques i.e. elemental analysis, molar conductance measurements, magnetic moment studies and different spectral studies (1H NMR, 13C NMR, UV–Vis, FT-IR, ESR) and mass spectrometry were used for characterization of compounds. The spectral data confirmed the bidentate nature (NO) of Schiff base ligands coordinating through nitrogen atom of azomethine group and oxygen atom of hydroxyl group resulting in the formation of octahedral geometry of all metal complexes. The Schiff base ligands and their transition metal complexes were screened against two gram-positive bacterial species i.e. (S. aureus, B. subtilis), two-gram negative bacterial species i.e. (E. coli, P. aeruginosa) and two fungal species (A. niger and C. albicans) using serial dilution method with ciprofloxacin and fluconazole as reference drug. The results obtained from antimicrobial studies showed that metal complexes are more active than their respective Schiff base ligands. Complex 5 and 6 are potent antimicrobial agent.

Efficient Catalytic Reduction of 4-Nitrophenol Using Copper(II) Complexes with N,O-Chelating Schiff Base Ligands.

The reduction of 4-nitrophenol to 4-aminophenol by sodium borohydride was used as a model to test the catalytic activity of copper(II) complexes containing N,O-chelating Schiff base ligands. In this study, a series of copper(II) complexes containing respective Schiff base ligands, N′-salicylidene-2-aminophenol (1), N′-salicylidene-2-aminothiazole (2), and N,N′-bis(salicylidene)-o-phenylenediamine (3), were synthesized and characterized by elemental analysis, Fourier transform infrared (FT-IR), UV-Visible (UV-Vis) and electron paramagnetic resonance (EPR) spectroscopies. The results from the 4-nitrophenol reduction showed that 3 has the highest catalytic activities with 97.5% conversion, followed by 2 and 1 with 95.2% and 90.8% conversions, respectively. The optimization of the catalyst amount revealed that 1.0 mol% of the catalyst was the most optimized amount with the highest conversion compared to the other doses, 0.5 mol% and 1.5 mol%. Recyclability and reproducibility tests confirmed that all three complexes were active, efficient, and possess excellent reproducibility with consistent catalytic performances and could be used again without a major decrease in the catalytic activity.

Synthesis, crystal structure and antibacterial activity of manganese(III) and cobalt(III) complexes containing pentadentate Schiff bases of a common amine and thiocyanate

Four new mononuclear Schiff base manganese(III) and cobalt(III) complexes viz. [Mn(L1)(NCS)] (1), [Mn(L2)(NCS)] (2), [Co(L3)(NCS)] (3), and [Co(L4)(NCS)]·0.5CH3OH·0.5H2O (4), containing thiocyanate as a common pseudohalide ion are reported. The pentadentate Schiff base ligands H2L1, H2L2, H2L3, and H2L4 were obtained by the condensation of substituted salicylaldehydes with N-(3-aminopropyl)-N-methylpropane-1,3-diamine. The syntheses of the complexes have been achieved by the reaction of manganese(II) perchlorate or cobalt(II) perchlorate with the respective Schiff bases in the presence of thiocyanate in methanol medium. Complexes 1–4 have been characterized by microanalytical, spectroscopic, single-crystal X-ray diffraction and other physicochemical studies. Structural studies reveal that 1–4 adopt nearly similar structures containing the MN4O2 (M = Mn, Co) chromophore in which each central M(III) ion adopts a distorted octahedral geometry. Weak intermolecular H-bonding interactions are operative in these complexes to bind the molecular units. The antibacterial activity of 1–4 and their constituent Schiff bases has been tested against some common bacteria.

Copper(II)-faciliated synthesis of substituted thioethers and 5-substituted 1H-tetrazoles: Experimental and theoretical studies

Benzoylhydrazine based Schiff base-ligated two new copper(II) complexes, [Cu(L1)2] (1) and [Cu(L2)2] (2) were synthesized by the reaction of Cu(CH3COO)2·H2O with respective Schiff base ligand 1-[(4-nitrophenyl)ethylidene] benzohydrazide (HL1) or 1-[(4-methoxyphenyl)ethylidene] benzohydrazide (HL2). Both complexes were isolated as greenish solid and fully characterized by elemental analysis, FT-IR, EPR, thermo-gravimetric (TG) analysis and Cyclic Voltammetry. The molecular structures of both complexes have also been determined by single crystal X-ray crystallography, which confirmed the coordination of Schiff base ligands through N, O donor atoms and distorted square planar geometry around the Cu(II) ion. Both complexes were found to be good homogeneous catalysts for the synthesis of a wide range of substituted thioethers and 5-substituted 1H-tetrazoles in 92% and 93% yield, respectively, at a low catalyst loading (0.5 mol%). The bond angles and distances, as discerned from the DFT calculations, commusurated with the experimental findings. The energy difference between the HOMO and the LUMO, calculated from DFT studies, was found to be 5.645 eV and 6.459 eV for complex 1 and complex 2, respectively. These results are in harmony with the observed higher catalytic activity of complex 1.

Synthesis, characterization, biological and DFT studies of new 4-substituted phthalonitriles

Herein, we describe the synthesis, characterization and computational studies of novel 4-substituted phthalonitriles: (1) 4-(4-((benzothiazole)methyleneamino)phenoxy)phthalonitrile, (2) 4-(4-(3-phenylallylideneamino)phenoxy)phthalonitrile and (3) 4-(4-(4-isopropylbenzylideneamino)phenoxy)phthalonitrile. Compound 1 was obtained from the equimolar condensation reaction of 4-(4-aminophenoxy)phthalonitrile with benzothiazole-2-carboxaldehyde while compounds 2 and 3 were isolated from the reactions of 4-aminophenol with either cinnamaldehyde or cuminaldehyde followed by the nucleophilic substitution reactions of their respective Schiff bases and 4-nitrophthalonitrile. The spectral characterization of 1–3 was done using 1H NMR, IR and UV–Vis spectroscopy, while structural confirmation could be affirmed from single TOF mass spectrometry and single crystal X-ray crystallography (for 1 and 2). Molecular geometry optimizations were conducted using the DFT method and the simulated IR frequencies data concurred well with the experimental data and the respective vibrational assignments. Similarly, TD-DFT studies provided an interesting perspective on the nature of the intra-ligand electronic transitions found within the experimental electronic spectra of the respective Schiff base phthalonitriles. Compound 3 showed the highest Human African sleeping sickness trypanocidal potency.

Tautomerism aspect of thione-thiol combined with spectral investigation of some 4-amino-5-methyl-1,2,4-triazole-3-thione Schiff's bases

Reaction of 4-amino-3-methyl-1,2,4-triazole-5-thione with some substituted benzaldehydes in presence of catalytic amount of hydrochloric acid afforded the respective Schiff's bases 3a-e. Computational studies using DFT incorporating the B3LYP/6-311G(d,p) level of theory is used to predict the stability of the possible tautomers. Molecular modeling, natural charge calculations, NMR, Frontier molecular orbitals and electronic spectra were investigated. Analysis of the thermodynamic parameters of the thione-thiol tautomeric reactions of these derivatives was used to predict the tautomers stability. The thione tautomer is the most favored form in gas phase and in solution whatever the nature of solvent used. The electronic spectra were assigned based on the TD-DFT calculations. The GIAO NMR chemical shifts correlated well with the experimental data.

Design and Synthesis of Some Novel Schiff's Base Aryl Imidazole Derivatives, Characterization, Docking and Study of their Anti-Microbial Activity

A growing threat of resistance to antibiotics by various microorganisms, an attempt has been made to identify the potent Aryl imidazole derivatives for its antimicrobial activities. A series of Aryl imidazole derivatives were synthesized by the condensation of various primary aromatic amines with aromatic aldehyde to form respective schiff's base which on further undergone reaction with ammonium acetate and Isatin in presence of glacial acetic acid to form the title compounds. The structures of the synthesized compounds were characterized by FT-IR, 1H-NMR and 13C-NMR spectral studies. Based on AutoDock score, the potent aryl imidazole derivatives were selected for their Antimicrobial study. The screened compounds showed moderate to good antibacterial activity against Staphylococcus aureus, Bacillus cereus, E.coli, Salmonella typhi when compared to standard (Ciprofloxacin-30mcg/disc). In the antifungal study among the screened compounds, JG3 only showed moderate antifungal activity against Candida albicans when compared to standard (Clotrimazole-30mcg).

Bis(μ-tetrazolato-NN′) bridged dinuclear nickel(II) Schiff base complexes: Tandem synthesis, structure and self assembly

Two new bis(μ-tetrazolato-NN′) bridged dinuclear nickel(II) Schiff base complexes [Ni2L12(PTZ)2]·2(CH3)2SO·2.69H2O (1) and 2[Ni2L22(PTZ)2]·3H2O (2) (HL1 and HL2 are Schiff bases, HL1=2-((2-(dimethylamino)ethylimino)methyl)phenol, HL2=2-((2-(methylamino)ethylimino)methyl)-6-methoxyphenol and HPTZ is 5-pyrazinyltetrazole) have been synthesized via [3+2] cyclo-addition of 2-cyanopyrazine and sodium azide in presence of nickel(II) acetate tetrahydrate and the respective Schiff bases. The structures of the complexes are confirmed by single crystal X-ray diffraction analysis. Both complexes show fluorescence. The change in the denticity of the Schiff base blocking ligand is shown to have no effect in controlling the molecular structures of the complexes. The supramolecular self assemblies are also explored.

Synthesis, Structures, and Antibacterial Activities of Cobalt(III) and Copper(II) Complexes with Schiff Bases

A mononuclear cobalt(III) complex, [Co(L1)3] (1), and a dinuclear copper(II) complex, [Cu2Cl2(L2)2] (2), where L1 and L2 are the monoanionic form of 2-(cyclopropyliminomethyl)-4-fluorophenol and 4-fluoro-2-[(pyridin-2-ylmethylimino)methyl]phenol, respectively, have been prepared and structurally characterized by elemental analyses, infrared spectra, and single-crystal X-ray determination. Crystallographic data for 1: monoclinic, P21, a = 10.6154(7) Å, b = 20.019(2) Å, c = 13.693(1) Å, β = 100.914(2)°, V = 2857.2(4) Å3, Z = 4, R1 = 0.0701, wR2 = 0.2033. The Co atom is in an octahedral coordination. Crystallographic data for 2: monoclinic, P21/c, a = 12.543(2) Å, b = 14.895(3) Å, c = 7.078(2) Å, β = 102.089(3)°, V = 1293.1(5) Å3, Z = 2, R1 = 0.1032, wR2 = 0.2179. The Cu atom is in a square pyramidal coordination. The antibacterial activities of the complexes and their respective Schiff bases have been tested against Gram(+) and Gram(–) bacteria.

Synthesis, crystal structure and antibacterial activity of a group of mononuclear manganese(II) Schiff base complexes

Five mononuclear complexes of manganese(II) of a group of the general formula, [MnL(NCS)2] where the Schiff base L=N,N′-bis[(pyridin-2-yl)ethylidene]ethane-1,2-diamine (L1), (1); N,N′-bis[(pyridin-2-yl)benzylidene]ethane-1,2-diamine (L2), (2); N,N′-bis[(pyridin-2-yl)methylidene]propane-1,2-diamine (L3), (3); N,N′-bis[(pyridin-2-yl)ethylidene]propane-1,2-diamine (L4), (4) and N,N′-bis[(pyridin-2-yl)benzylidene]propane-1,2-diamine (L5), (5) have been prepared. The syntheses have been achieved by reacting manganese chloride with the corresponding tetradentate Schiff bases in presence of thiocyanate in the molar ratio of 1:1:2. The complexes have been characterized by IR spectroscopy, elemental analysis and other physicochemical studies, including crystal structure determination of 1, 2 and 4. Structural studies reveal that the complexes 1, 2 and 4 adopt highly distorted octahedral geometry. The antibacterial activity of all the complexes and their respective Schiff bases has been tested against Gram(+) and Gram(−) bacteria.

Synthesis and pharmacological studies on some phthalimidoxy substituted quinoline derivatives

Synthesis of novel N'-[2-(4-substitutedphenyl)-3-N-ethoxyphthalimido-5-oxoimidazolidene-1-yl]-2-(quinoline-8-yloxy)acetamide derivatives (6a-e) with potential biological activities were carried out by adopting the reaction scheme given below. Compound ethyl-(quinoline-8-yloxy)acetate (2) was synthesized by refluxing 8-hydroxyquinoline with ethylchloroacetate in presence of K 2 CO 3 . Ethyl-(quinoline-8-yloxy)acetate (2) was converted to corresponding hydrazide (3) on treatment with hydrazine hydrate which on further condensation with various araldehydes gave respective Schiff's bases (4a-e). These on cyclisation with glycine yielded corresponding oxoimidazolidenes (5a-e). Active H of imidazolidinones (5a-e) was replaced by ethoxy phthalimide to yield final products (6a-e).

Synthesis, 11C labeling and biological properties of derivatives of the tyrphostin AG957

Four analogues of AG957, a known inhibitor of the tyrosine kinase p210 bcr-abl , have been synthesized and tested for their growth inhibitory effect against the BCR/ABL-positive FDrv210C cells as well as the epidermal growth factor (EGF) receptor-positive Baf/ERX cells. All compounds that can undergo oxidation to the corresponding quinone demonstrated inhibition of FDrv210C cells and Baf/ERX cells. Compounds that cannot become oxidized showed significantly less inhibition of BCR/ABL- or EGF receptor-mediated cell proliferation. The 11C-labeled compounds were prepared by labeling 4-aminobenzoic acid using [ 11C]CH 3I, which afforded the corresponding 11C-labeled methyl ester in excellent yields. Subsequent condensation of the amino group with an appropriately substituted hydroxy benzaldehyde formed the respective Schiff base. Reduction of this compound with NaBH 3CN gave the 11C-labeled inhibitors in an overall radiochemical yield of 17.3±2.1% ( n=3; not decay corrected) and an average specific radioactivity of 40 GBq/µmol (1.1 Ci/µmol) at the end of synthesis. The total synthesis time from EOB including HPLC purification and formulation was 45 min.

Synthesis and Catalytic Activity of Spaced Ferrocene Oxazolines

Chiral 2-[{N-aryl-N-(ferrocenylmethyl)amino}methyl]-4-(1-methylethyl)-4,5-dihydroxazoles with various substituents at the aryl ring were prepared by alkylation of N-(ferrocenylmethyl)anilines, FcCH2NHC6H4R (Fc = ferrocenyl), with (S)-2-(chloromethyl)-4-(1-methylethyl)-4,5-dihydrooxazole. The oxazoles, substituted anilines, and the precursors of the latter, the respective Schiff bases FcCH=NC6H4R, were characterized by standard methods and further studied by mass spectrometry. The oxazoles were further tested as chiral auxiliaries in the addition of diethylzinc to benzaldehyde but showed only negligible asymmetric induction (ee ca 10%), most likely due to steric hindrance of the nitrogen donor centres. This steric restriction seems to be lowered upon replacement of the substituted phenyl group with a benzyl substituent; compounds FcCH2NHCH2Ph and (R)-FcCH2NHCH(Me)Ph are easily alkylated yielding [FcCH2NMe2(CH2Ph)]I (9) and 2-[{N-(1-phenylethyl)-N-(ferrocenylmethyl)amino}methyl]-4-(1-methylethyl)-4,5-dihydroxazole (10), respectively. Solid-state structures of FcCH2NHC6H4R (R = 2-Me and 4-Cl), 9, and 10 have been determined by single-crystal X-ray diffraction.

11C labelling of AG957—a potential tyrphostin radiotracer for PET

AbstractCarbon‐11 labelled 4‐(N‐2,5‐dihydroxybenzyl)amino methyl benzoate (AG957), a potential radiotracer for imaging bcr–abl receptors was synthesized. [11C]AG957 was prepared by labelling 4‐aminobenzoic acid using [11C]CH3I, which affords the corresponding [11C] methyl ester in excellent yields. Subsequent condensation of the amino group with 2,5‐dihydroxy‐benzaldehyde formed the respective Schiff base. Reduction of this compound with NaBH3CN gave [11C]AG957 in overall decay corrected radiochemical yield of 65–75% (based on 11CH3I) with an average specific radioactivity of 40 GBq/μmol (1.1 Ci/μmol). The total synthesis time from EOB including formulation was 45 min. At physiological pH, the compound was found to be sufficiently stable for in vitro and in vivo investigations. Copyright © 2002 John Wiley & Sons, Ltd.

ChemInform Abstract: Stereochemical Studies. Part 133. Saturated Heterocycles. Part 137. Synthesis and Steric Structure of Stereoisomeric 2‐p‐Nitrophenylperhydroquinazolin‐4‐ones.

AbstractFrom cis‐ and trans‐amino ester (I) the respective Schiff base (III) is obtained which on reaction with ammonia and methylamine (IV) in the cis‐case (IIIa) gives mainly all‐cis products (Va) but exclusively isomers (VIb) in the trans‐case (IIIb); the amides (VII) are produced as well.

Synthesis of certain 3-aminoquinazolinone Schiff's bases structurally related to some biologically active compounds.

The condensation of 2-methyl-3-amino-4(3H)-quinazolinone and 2-phenyl-3-amino-4(3H)-quinazolinone with different aldehydes is described. Reacting equimolecular amounts of these two amino compounds with p-nitrobenzaldehyde, p-hydroxybenzaldehyde, cinnamaldehyde and 5-nitro-2-furfuraldehyde diacetate afforded the respective Schiff's bases. Condensation of benzaldehyde, anisaldehyde, p-dimethylaminobenzaldehyde and o-nitrobenzaldehyde with the former quinazolinone afforded the corresponding condensation products while with the latter no condensation took place. Furthermore, condensation of cinnamaldehyde with methylaminoquinazolinone in pyridine and in glacial acetic acid afforded the mono- and di-condensation products respectively while furfural, thiophenaldehyde, resorcinaldehyde, protocatechualdehyde, veratraldehyde, and salicylaldehyde, the condensation ended in failure.

Polymeric Schiff Bases. XV. The Synthesis of Cross-Linked Polymeric Azomethines from Amino Aryl Ketones

Abstract A number of polymeric azomethines were synthesized to determine the influence on char yields by the deliberate introduction of cross links in their structures. The linear reference polymer, was synthesized from H2NC6H4COCH3 and was considered as having a cross-link density,p, of zero. Two series were prepared with p values between zero and 1, using an equimolar mixture of 1,3,5-C6H3(COCH3)3 and 1,3, 5-C6H3(NH2)3, or their respective Schiff bases, as the cross-linking agents.

Detection of protein-bound amino groups in plant tissue by Schiff base formation and azo coupling.

This account pertains to the detection of protein-bound amino groups in fresh, freehand sections of bean cotyledons. Two separate reagents were used: (A) p-aminobenz-aldehyde and (B) p-dimethylaminobenzaldehyde. Both of these compounds, by virtue of their free aldehyde groups, condensed with native amino groups to form their respective Schiff bases. The free amino groups of the resultant Schiff base with reagent A were diaz-otized and coupled with an arylamine, whereas the Schiff base produced in the sections treated with reagent B was treated with nitrous acid to yield its nitroso derivative which was finally coupled with H acid to produce a purple-red dye.