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.     

Antibacterial Activity of a Promising Antibacterial Agent: 22-(4-(2-(4-Nitrophenyl-piperazin-1-yl)-acetyl)-piperazin-1-yl)-22-deoxypleuromutilin

A novel pleuromutilin derivative, 22-(4-(2-(4-nitrophenyl-piperazin-1-yl)-acetyl)-piperazin-1-yl)-22-deoxypleuromutilin (NPDM), was synthesized in our laboratory and proved excellent antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA). In this study, more methods were used to further study its preliminary pharmacological effect. The antibacterial efficacy and toxicity of NPDM were evaluated using tiamulin as the reference drug. The in vitro antibacterial activity study showed that NPDM is a potent bactericidal agent against MRSA that induced time-dependent growth inhibition and a concentration-dependent post-antibiotic effect (PAE). Toxicity determination showed that the cytotoxicity of NPDM was slightly higher than that of tiamulin, but the acute oral toxicity study proved that NPDM was a low-toxic compound. In an in vivo antibacterial effect study, NPDM exhibited a better therapeutic effect than tiamulin against MRSA in a mouse thigh infection model as well as a mouse systemic infection model with neutropenia. The 50% effective dose (ED₅₀) of NPDM in a Galleria mellonella infection model was 50.53 mg/kg. The pharmacokinetic properties of NPDM were also measured, which showed that NPDM was a rapid elimination drug in mice.     

Synthesis and antimicrobial activity of Schiff bases and 2-azetidinones derived from quinazolin-4(3H)-one

A series of 2-oxo-azetidinyl-quinazolin-4(3H)-ones 5a–k have been synthesized from Schiff bases 4a–k. Schiff bases were synthesized by the condensation reaction of compound 3 with substituted aromatic aldehydes. The benzoxazinone 2 was prepared by the cyclization reaction of acid chloride 1 with 5-bromo anthranilic acid. Further reaction of benzoxazinone 2 with hydrazine hydrate yielded compound 3. The structures of the synthesized compounds were elucidated on the basis of elemental analyses as well as IR and NMR spectral data. Schiff bases 4a–k and 2-azetidinones 5a–k were screened for antibacterial and antifungal activities in vitro. Compounds having chloro and methoxy groups exhibited good antimicrobial activity.     

Antibacterial potential of N-(2-furylmethylidene)-1, 3, 4-thiadiazole-2-amine: Experimental and theoretical investigations

Recently, a lot of interest has been attributed to the Schiff base compound because of its wide range of biological activities which include: antibacterial, antifungal, antima larial, including; antiproliferative, antiviral, and antipyretic. In this research work, N-(2-furylmethylidene)-1, 3, 4-thiadiazole- 2-amine gotten from o-phenylenediamine and 5- methoxysalicaldehyde was produced and characterized using UV–Visible, FT-IR, ¹H NMR, ¹³C NMR, and GC-MS along with molecular modeling using density functional theory (DFT) and molecular docking approach. The results obtained indicated that the Schiff base exhibited antimicrobial action against all the tested microbes except Candidaalbicans isolate, which exhibited zero diameter zone of inhibition. The theoretical investigations of the synthesized compounds were computed applying density functional theory at the B3LYP/6–31++G (d, p) level of theory and in silico molecular docking simulation. In comparing binding affinity energies and binding poses of the studied compound and the standard drug (ampicillin), the deduction that the molecular docking analysis results are in good agreement with in vitro analysis of the synthesized compounds can be made.     

Synthesis,spectral analysis,antibacterial activity,quantum chemical studies and supporting molecular docking of Schiff base (E)-4-((4-bromobenzylidene) amino)benzenesulfonamide

A new Schiff base (E)-4-((4-bromobenzylidene) amino) benzenesulfonamide (M2) was synthesized by the reaction between 4-bromobenzaldehyde and sulfanilamide followed by characterization using IR, Raman, UV–Visible, ¹HNMR, and ¹³CNMR spectral techniques. This was followed by electronic structure studies using DFT and TD-DFT. We simulated the IR spectrum using B3LYP/6-31+G(d,p) level of theory, followed by a comparison with experimental spectra and detailed potential energy distribution and vibrational assignment analysis. The comparison of experimental UV and simulated UV spectrum using TD-DFT B3LYP/6-31+G(d,p) in DMSO solvent atmosphere gave good agreement. As Schiff bases are biologically active, we checked for the potential activity of the synthesized compound with the help of ADMET prediction and found it to be active. Wavefunctions related properties like ELF, LOL, and ELF are also reported. Prediction of biological activity spectrum study indicated possible antibacterial activity against bacteria, which is supported by molecular docking against Staphylococcus aureus (3U2D) protein with a docking score of ?7.1 kcal/mol. Experimental antibacterial study using the compound and standard drugs confirmed this prediction.     

Synthesis and Antimicrobial Activity of Quinazolin-4(3H)-ones Incorporating Sulfonamido-4-thiazolidinone

Some new derivatives 7‐chloro‐2‐[2‐(2,6‐dichlorophenyl)amino]benzyl‐3‐[4‐(2‐substituted phenyl‐4‐oxo‐ thiazolidin‐3‐yl)phenyl]sulfonamido‐quinazolin‐4(3H)‐ones 5a – 5l were synthesized from 2‐[2‐(2,6‐dichloro‐phenyl)amino]phenyl acetic acid via acid chloride, benzoxazinone, amino quinazolin‐4(3H)‐one and Schiff base formation. The synthesized compounds were screened for in vitro antibacterial and antifungal activities by broth micro dilution method. Some of the Schiff base as well as 4‐thiazolidinone derivatives showed promising antibacterial activity while pronounced antifungal activity was observed against C. albicans.     

Europium and terbium Schiff base peptide complexes as potential antimicrobial agents against <Emphasis Type="Italic">Salmonella typhimurium</Emphasis> and <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis>

Eu(III) and Tb(III) Schiff base complexes are applicable in various fields such as sensing, assays, screening protocols in vitro, and imaging studies in vitro or in vivo. Fluorescent europium and terbium complexes and their interaction with cell penetrating peptide (KKKRKC) can represent an excellent key for understanding pathway of peptide transportation though cell membrane and the application of Schiff base complexes as potential antibacterial drugs. The Schiff base–metal complexes and its conjugates with peptide were tested for their antibacterial activity against Pseudomonas aeruginosa and Salmonella typhimurium. Schiff base–metal complexes conjugated with peptide show minor toxicity in normal human PNT1A cells and high antibacterial activity against P. aeruginosa and S. typhimurium, where IC50 down to 125.9 and/or 36.1 µM were found for P. aeruginosa and S. typhimurium, respectively. Our results strongly suggest that Schiff base–metal complexes conjugated with peptide have great potential to be developed into highly effective antibacterial drug.     

Synthesis of 3-[4-(1-Benzofuran-2-yl)-1,3-thiazol-2-yl]-2-(4-aryl)-1,3-thiazolidin-4-one Derivatives as Biological Agents

A protocol for the synthesis of 3-[4-(1-benzofuran-2-yl)-1,3-thiazol-2-yl]-2-(4-aryl)-1,3-thiazolidin-4-one derivatives (5a–e) has been developed from 1-(1-benzofuran-2-yl)-2-bromoethanone (2),which served as a key intermediate for the synthesis of the title compounds. The reaction of compound 2 with thiourea furnished 4-(1-benzofuran-2-yl)-1,3-thiazol-2-amine 3, which upon further reaction with various aromatic aldehydes, gave Schiff bases 4a–e. These Schiff bases, when treated with thioacetic acid in the presence of catalytic amount of anhydrous ZnCl₂, yielded thiazolidinone derivatives 5a–e. All the newly synthesized compounds have been characterized by analytical and spectral data and screened for their antimicrobial and analgesic activity.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Magnetically recoverable nano-zirconium(IV) complex: enhancement of antibacterial activity

In this study, antibacterial activity of a zirconium(IV)–Schiff base ligand [Schiff base = N,N′-bis(3-salicylidenaminopropyl)amine] was examined via the paper disk diffusion method against Escherichia coli (gram-negative bacterium) and Bacillus subtilis (gram-positive bacterium). In the next step, a magnetically recoverable analog of this compound was synthesized by covalent grafting of the Schiff base ligand onto modified silica-coated magnetic nanoparticles. The synthesis was accomplished by the complexation of these magnetically recoverable nanoparticles with Zr(acac)₄. The newly synthesized particles were characterized by FT-IR, XRD, TGA–DSC, XRF, TEM, FE-SEM, and VSM, and then screened against bacteria. The results indicated the significant increased activity of zirconium complex grafted onto nanomagnetite particles. Moreover, as the particles were superparamagnetic, they could be easily recovered from the reaction matrix by use of a permanent magnet.     

Lipase-mediated kinetic resolution of (RS)-1-bromo-3-[4-(2-methoxy-ethyl)-phenoxy]-propan-2-ol to (R)-1-bromo-3-(4-(2-methoxyethyl) phenoxy) propan-2-yl acetate

A novel biocatalytic method for the enantioselective synthesis of (R)-bromo-3-[4-(2-methoxy-ethyl) phenoxy]-2-propanol [(R)-BMEPP], a precursor for the synthesis of (S)-metoprolol, an anti hypertensive drug is described. We have developed kinetic resolution of rac-BMEPP by transesterification using Candida rugosa lipase and vinyl acetate as the acyl donor affording the product with excellent conversion (49%) and ee (>99%). Various reaction parameters (source of enzyme, reaction media, and concentration of substrate and acylating agent) for the enzymatic kinetic resolution have been reported.     

Synthesis,crystal structures,and antibacterial activity of copper(II) and cobalt(III) complexes derived from 2-[(2-dimethylaminoethylimino)methyl]-4-methylphenol

A new tetranuclear copper(II) complex (I) and a new mononuclear cobalt(III) complex (II) have been synthesized from the Schiff base compound 2-[(2-dimethylaminoethylimino)methyl]-4-methylphenol. The complexes have been characterized by physico-chemical and spectroscopic methods, as well as single crystal X-ray determination (CIF files CCDC nos. 1447778 (I) and 1447779 (II)). The Cu atoms in complex I are in square pyramidal coordination, and the Co atom in complex II is in octahedral coordination. Crystal structures of the complex are stabilized by hydrogen bonds and π···π interactions. The complexes and the Schiff base compound were assayed for antibacterial activities against three Gram-positive bacterial strains (B. subtilis, S. aureus, and St. faecalis) and three Gram-negative bacterial strains (E. coli, P. aeruginosa, and E. cloacae) by MTT method. As a result, the complexes showed effective antimicrobial activity against the microorganisms tested.     

Synthesis, characterization and antimicrobial activity of some new 1-(fluorobenzoyl)-3-(fluorophenyl)thioureas

Synthesis of a variety of new 1-(isomeric fluorobenzoyl)-3-(isomeric fluorophenyl)thioureas (1a-t) was accomplished in two steps. The synthetic route involves the reaction of equimolar quantities of isomeric fluorobenzoyl chlorides with potassium thiocyanate in anhydrous acetone to afford the corresponding isothiocyantes in situ, followed by treatment with equimolar quantities of isomeric fluoroanilines. All of the synthesized compounds (1a-t) were screened for their in vitro antibacterial activity using Gram-positive bacteria (Staphylococcus aureus, Bacillus subtilis) and Gram-negative bacteria (Escherichia coli, Pseudomonas aureginosa). The minimum inhibitory concentration (MIC) was also determined for the most active compounds. In vitro antifungal activity was also determined against the five fungal species (Rhizopus oryzae, Aspergillus tereus, Fusarium oxysporum, Aspergillus niger, Aspergillus fumigatus). In general, the antifungal activity of compounds was better than their antibacterial activity.     

Synthesis and antibacterial evaluation of novel Schiff base derivatives containing 4(3<Emphasis Type="Italic">H</Emphasis>)-quinazolinone moiety

A series of novel Schiff base derivatives containing 4(3H)-quinazolinone moiety were synthesised and their antibacterial activities against tobacco and tomato bacterial wilts evaluated in vitro. Out of the synthesised compounds, 5g, 5j, 5n, 5m and 5p exhibited excellent antibacterial activities against tobacco bacterial wilt, with half maximal effective concentrations (EC50): 160.34, 158.03, 125.94, 148.09 and 133.67 (all in εg mL^?1), respectively, which were better than the EC50 of thiodiazole–copper (216.70 εg mL^?1). Compounds 5j, 5n and 5o also showed good antibacterial activities against tomato bacterial wilt, with EC50 of 95.20, 90.03 and 83.21 (all in εg mL^?1) respectively, which were better than the EC50of thiodiazole–copper (99.80 εg mL^?1). These compounds may prove to be useful as potential antibacterial agents.     

Synthesis of magnetically recyclable Fe3O4@[(EtO)3Si–L1H]/Pd(II) nanocatalyst and application in Suzuki and Heck coupling reactions

A Pd(II) Schiff base complex as an efficient and highly heterogeneous catalyst was developed by immobilization of a palladium complex on the surface of modified Fe₃O₄ magnetite nanoparticles. These surface‐modified nanoparticles were characterized using various techniques such as transmission electron microscopy, X‐ray diffraction, thermogravimetric analysis, vibrating sample magnetometry, elemental analysis and Fourier transform infrared spectroscopy. The palladium catalyst exhibited efficient catalytic activity in Suzuki and Heck coupling reactions. This method has notable advantages such as excellent chemoselectivity, mild reaction conditions, short reaction times and excellent yields. The yields of the products were in the range 85–100%. Also, the nanocatalyst can be easily recovered with a permanent magnet and reused at least five times without noticeable leaching or loss of its catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis of 2-(4-chlorobenzylamino)-1-(4-nitrophenyl)ethanol and its chemical transformations

By the ring cleavage of p-nitrophenyloxirane with p-chlorobenzylamine the corresponding chlorobenzyl- and nitrophenyl-substituted aminoethanol was obtained that was brought into reactions of glycosylation, reduction and substitution aimed at the preparation and designing of new structures containing pharmacalogically active functional groups. Among the synthesized compounds a compound is revealed possessing moderately expressed antibacterial and antifungal activity.     

A modern technique for preparation of zinc(II) and nickel(II) nanometric oxides using Schiff base compounds: synthesis,characterization, and antibacterial properties

The purpose of the work reported in this paper was the preparation and characterization of Zn(II) and Ni(II) nanometric oxides by using a simple Schiff compound as precursor for complexation then thermal degradation at 600 °C. Metal complexes [Ni(L)₂(Cl)₂] and [Zn(L)₂](NO₃)₂, where L is the Schiff base formed by condensation of 2-thiophenecarboxaldehyde with phenylhydrazine, were prepared and characterized by elemental analysis and by magnetic and spectroscopic measurements (infrared, Raman, X-ray powder diffraction, and scanning electron microscopy). Elemental analysis of the chelates suggests the stoichiometry is 1:2 (metal–ligand). Infrared spectra of the complexes are indicative of coordination of the nitrogen of the phenylhydrazine (–Ph–NH–) group and the sulfur atom of the thiophene ring with the central metal atom. Magnetic susceptibility data and electronic and ESR spectra suggest a distorted octahedral structure for the Ni(II) complex and tetrahedral geometry for the Zn(II) complex. The Schiff base and its metal chelates were screened for in-vitro activity against four bacteria, two Gram-positive (Bacillus subtilis and Staphylococcus aureus) and two Gram-negative (Escherichia coli and Pseudomonas aeruginosa), and two strains of fungus (Aspergillus flavus and Candida albicans). The metal chelates were shown to have greater antibacterial activity than the free Schiff-base chelate.     

Synthesis and characterization of biologically active new Schiff bases containing 3‐functionalized 1,2,4‐triazoles and their zinc(II) complexes: crystal structure of 4‐bromo‐2‐[(E)‐(1H‐1,2,4‐triazol‐3‐ylimino)‐ methyl]phenol

Biologically active triazole Schiff bases ( L ¹  L ³ ) derived from the reaction of 3‐amino‐1,2,4‐triazole with chloro‐, bromo‐ and nitro‐ substituted salicylaldehydes and their Zn(II) complexes (1–3) have been synthesized and characterized by their physical, spectral and analytical data. Triazole Schiff bases potentially act as tridentate ligands and coordinate with the Zn(II) metal atom through salicylidene‐O, azomethine‐N and triazole‐N. The complexes have the general formula [M(L‐H)₂], where M = zinc(II) and L = ( L ¹ – L ³ ), and observe an octahedral geometry. The Schiff bases and their Zn(II) complexes have been screened for in‐vitro antibacterial, antifungal and brine shrimp bioassay. The biological activity data show the Zn(II) complexes to be more potent antibacterial and antifungal than the parent simple Schiff bases. Copyright © 2011 John Wiley & Sons, Ltd.     

Chemoenzymatic synthesis of (3R,4S)- and (3S,4R)-3-methoxy-4-methylaminopyrrolidine

An efficient and a convenient enantioselective synthesis of (3R,4S)-3-methoxy-4-methylaminopyrrolidine has been carried out by a lipase-mediated resolution protocol. This method describes the preparation of (±)-1-Cbz-cis-3-azido-4-hydroxypyrrolidine starting from commercially available diallylamine followed by ring-closing metathesis (RCM) via S_N2 displacement reactions. Pseudomonas cepacia lipase immobilized on diatomaceous earth (Amano PS-D) provides (3R,4S)-11 and (3S,4R)-12 in an excellent enantiomeric excess.     

Microwave solid phase synthesis, characterization, and antimicrobial activities of one mononuclear manganese(II) complex with 4-chlorobenzoic acid 4-[3-(4-chlorophenyl)-3-hydroxyacryloyl]-3-hydroxyphenyl ester

One mononuclear complex has been designed and synthesized by a β-dikertone ligand 4-chlorobenzoic acid 4-[3-(4-chlorophenyl)-3-hydroxyacryloyl]-3-hydroxyphenyl ester (L) with MnCl₂ · 4H₂O in microwave radiation assistance. The complex was characterized by X-ray crystallography, confirming that the central manganese(II) atom was coordinated by four oxygens from two L and two oxygens from two water. The complex was assayed for in vitro antibacterial (B. subtilis, S. aureus, S. faecalis, P. aeruginosa, E. coli, and E. cloacae) activities and showed better antimicrobial activity against Gram positive strains than Gram negative strains.     

Synthesis and antimicrobial activity of new 2-((1-furan-2-yl)ethylidene)hydrazono)-4-phenylthiazol-3(2H)-amine derivatives and their schiff bases with 4-nitrobenzaldehyde

Abstract

A new series of 2-((1-furan-2-yl)ethylidene)hydrazono)-4-substitutedphenylthiazol-3(2H)-amines (2a–2o) and their Schiff bases (3a–3o) from 4-nitrobenzaldehyde were synthesized. The chemical structures of all the synthesized compounds were confirmed by their IR, ¹H-NMR, ¹³C-NMR spectroscopy and mass spectrometry. They were screened for their antimicrobial and antifungal activities. Additionally, in vitro cytotoxic acivity of the most active antifungal compound (3o) and ketoconazole was determined in NIH/3T3 cells by MTT assay. Compound 2i (4-{3-Amino-2-[(1-(furan-2-yl)ethylidene)hydrazono]-2,3-dihydrothiazol-4-yl}phenol) showed the greatest antifungal activity among the newly synthesized derivatives. Schiff bases (3c-3n) displayed an undeniable fungicidal action against Candida parapsilosis ATCC 22019 as intense as the reference ketoconazole. In addition, the most active Schiff base 3o (2-[(1-(Furan-2-yl)ethylidene)hydrazono]-N-(4-nitrobenzylidene)-4-(2,3,4-trichloro phenyl)thiazol-3(2H)-amine) showed the highest antifungal activity against both Candida krusei ATCC 6258 and Candida parapsilosis ATCC 22019, and was as potent as ketoconazole. Moreover, compound 3o was found to be non-cytotoxic against NIH/3T3 cells.