Electrochemical Oxidation of Catechols in the Presence of Triethyl Phosphite

The mechanism of electrochemical oxidation of catechol and some of its derivatives have been studied in the presence of triethyl phosphite as a nucleophile in aqueous solution. Voltammetric studies indicate that the quinones derived from catechol, and its derivatives, participate in Michael addition reaction with triethyl phosphite. The reaction mechanism consists of electron transfer followed by a chemical reaction which is named as an EC mechanism. The homogeneous rate constants (k_obs) were estimated by comparing the experimental cyclic voltammograms with the digitally simulated voltammograms based on EC mechanism. Also the effects of nucleophile concentration and substituted group of catechols on voltammetric behavior and the rate constants of chemical reactions were examined.     

Electrochemical Oxidation of Catechols in the Presence of Pyrimidine-2-thiol: Application to Electrosynthesis

The electrooxidation of catechols (1a–d) in the presence of pyrimidine-2-thiol (3) as a nucleophile in aqueous solution is described. The mechanistic investigations using cyclic voltammetry and controlled potential coulometry indicate that the quinone derived from catechols participates in a Michael addition reaction with pyrimidine-2-thiol to form corresponding catechol derivatives of 6a–d (ECEC). The efficient electrosynthesis of 6a–d has been performed at carbon rod electrodes in an undivided cell in good yield and purity.     

Electrochemical Study of Catechol in the Presence of Dibuthylamine and Diethylamine in Aqueous Media: Part 1. Electrochemical Investigation

Electrochemical oxidation of catechol has been studied in the presence of secondary amines as nucleophiles in aqueous solution with various pH values using cyclic voltammetry and differential pulse voltammetry. Cyclic voltammetry of catechol in pure buffered solution (2.00 pH<9.00) shows one anodic and corresponding cathodic peak which relates to the transformation of catechol to corresponding o‐benzoquinone and vice versa within a quasi‐reversible two electron transfer process. Also, a little amount of o‐benzoquinone undergoes polymerization reaction. Cyclic voltammogram of catechol in the presence of nucleophilic amines, show one anodic peak in the first scan of potential but on the reverse scan the corresponding cathodic peak disappear and new peak is observed at less positive potential. In the second scan of potential also a new anodic peak is observed. On the other hand at high concentration of amines the redox peak attributable to formed polymer disappear showing that in this condition the polymerization reaction occurs at non‐measurable extent. On the basis of these observations we propose an ECE mechanism for the electrochemical oxidation of catechol in the presence of secondary amines.     

Electro-oxidation of catechols in the presence of benzenesulfinic acid. Application to electro-organic synthesis of new sulfone derivatives

The mechanism of electrochemical oxidation of catechol (1a), 3-methylcatechol (1b) and 3-methoxycatechol (1c) in the presence of benzenesulfinic acid (3) as a nucleophile has been studied in an aqueous solution using cyclic voltammetry and controlled-potential coulometry. The results indicate that the catechol derivatives (1a–1c) are converted to sulfone derivatives (4a–4c) through Michael addition of benzenesulfinate to anodically generated o-quinones (2a–2c). The electrochemical synthesis of 4a–4c has been successfully performed in an undivided cell in good yields and purity.     

Synthesis of some heterocyclic compounds derived from indole as antimicrobial agents

Recently, indoles are considered interesting heterocyclic compounds due to their wide range of biological activities such as antimicrobial activity. Herein, some new indole derivatives containing heterocyclic moieties were synthesized using 3-chloro-1H-Indole-2-carbaldehyde (1) as a starting material, then allowed to react with compounds containing active methylene under Knoevenagel condensation and afforded the corresponding compounds (2, 3, 9). Also, the compound (1) when allowed to react with hydrazine derivatives gave the corresponding thiosemiccarbazone, semicarbazone, and hydrazone derivatives (4, 5, 6). Reaction of thiosemicarbazone derivatives with α-halognated carbonyl compounds gave the thiazolyl indole derivatives (10, 12a–b). Cyclic chalcones (11a–c) were obtained when compound (10) reacted with different aromatic aldehydes. The structures of all new synthesized compounds were confirmed on the basis of spectral analysis, IR, 1H NMR, 13C NMR, and MS spectroscopy. All synthesized compounds were evaluated for their antimicrobial activity. Compounds (2, 5, 7, 8, 11a, 12a) showed high antibacterial activity and compounds (3, 6, 9, 10, 11a, 12a) showed high antifungal activity.     

Electrochemical study of catechol and some 3-substituted catechols in the presence of 4-hydroxy coumarin: application to the electro-organic synthesis of new coumestan derivatives

Electrochemical oxidation of catechol (1d), 3-methylcatechol (1a), 3-methoxycatechol (1b) and 2,3-dihydroxybenzoic acid (1c) in the presence of 4-hydroxycoumarin as nucleophile in aqueous solution has been studied using cyclic voltammetry and controlled-potential coulometry. The results indicate that (1a–1d) participating in a 1,4 (Michael) addition reaction convert to coumestan derivatives (5a–5d). The electrochemical synthesis of 5a–5d has been successfully performed in an undivided cell in good yield and purity.     

Electrochemical study of catechol and some of 3-substituted catechols in the presence of 1,3-diethyl-2-thio-barbituric acid. Application to the electro-organic synthesis of new dispirothiopyrimidine derivatives

Electrochemical oxidation of catechol (1a), 3-methylcatechol (1b) and 3-methoxycatechol (1c) in the presence of 1,3-diethyl-2-thiobarbituric acid (3) as a nucleophile in aqueous solution has been studied using cyclic voltammetry and controlled-potential coulometry. The results indicate that (1a–1c) participating in a 1,4 (Michael) addition reaction converts to dispirothiopyrimidine derivatives (6a–6c). The electrochemical synthesis of 6a–6c has been successfully performed in an undivided cell in good yield and purity.     

Dapson in Heterocyclic Chemistry,Part II: Antimicrobial and Antitumor Activities of Some Novel Sulfone Biscompounds Containing Biologically Active Thioureido,Carbamothioate, Quinazoline,Imidazolidine, and Thiazole Moieties

The reaction of 4,4′-diisothiocyanato-1,1-diphenylsulfone 2 with aromatic amines and phenol derivatives afforded the corresponding thioureio derivatives 3–9 , respectively. Also, the reaction of 2 with catechol gave the corresponding carbamothioate derivative 11. Quinazoline derivatives 14 and 15 were obtained in good yield via reaction of 2 with anthranlic acid derivatives. Imidazolidine biscompounds 16 and 17 were readily synthesized from the reaction of 2 with N-(4-substituted-phenyl)cyanothioformanilides. The structure of the products was confirmed from elemental analysis as well as spectral data. Most of the synthesized compounds showed remarkable antimicrobial activity compared with chloramphenicol and Grisofluvine as positive controls. Compound 6 was almost as active an antitumor agent as the reference drug Doxorubicin.     

Synthesis and Antimicrobial Evaluation of Some New 4,5′‐Bisthiazoles

Thiazole and bisthiazole derivatives represent a prevalent scaffold in the antimicrobial drug discovery. Therefore, we have decided to synthesize some new series of 4,5′‐bisthiazoles. A total of 17 compounds were synthesized, their structural elucidation being based on elemental analysis (C,H,N,S) and spectroscopic data (MS and ¹H NMR). Their in vitro antimicrobial activities were assessed against several Gram‐positive and Gram‐negative bacteria strains and also against one fungal strain (Candida albicans) using the difusimetric method. Some of the compounds showed modest to good antibacterial activity against Gram‐negative Escherichia coli and Salmonella typhimurium and Gram‐positive Staphylococcus aureus and Bacillus cereus bacterial strains. All of the synthesized compounds showed moderate to very good antifungal activity against C. albicans.     

Synthesis and in vitro antimicrobial activity of new 3-(2-morpholinoquinolin-3-yl) substituted acrylonitrile and propanenitrile derivatives

A series of new 3-(2-morpholinoquinolin-3-yl)acrylonitrile derivatives (IVa-IVf) has been synthesised by the base-catalysed condensation reaction of 2-morpholinoqionoline-3-carboxaldehydes (IIa-IIc) and 2-cyanomethylbenzimidazoles (IIIa-IIIb). Subsequent regiospecific reduction of the C—C double bond in acrylonitrile moiety afforded 3-(2-morpholinoquinolin-3-yl)propanenitrile derivatives (Va-Vf). All the compounds synthesised were subjected to in vitro antimicrobial screening against some representatives of bacteria and fungi. The majority of the compounds were found to be active against Gram-positive bacteria Bacillus subtilis and Clostridium tetani as well as against the fungal pathogen Candida albicans.     

Electrochemical oxidation of catechol in the presence of 2-thiouracil: application to electro-organic synthesis

The electrochemical oxidation of catechol in the presence of 2-thiouracil (as a nucleophile) has been studied in aqueous solutions using cyclic voltammetry and controlled-potential coulometric techniques. The results indicate that catechol participating in a 1,4 (Michael) addition reaction converts to a new thiadiazafluorenone compound. The electrochemical synthesis of this compound has been successfully performed in an undivided cell in a good yield and purity and was characterized by IR, ¹H and ¹³C NMR, mass spectrometry and elemental analysis.     

Ultrasound‐assisted Synthesis of Novel Pyrazole and Pyrimidine Derivatives as Antimicrobial Agents

Herein, we report a convenient and facile methodology for the synthesis of new series of pyrazole and pyrimidine derivatives 2a – f and 3a – f under ultrasound irradiation. Pyrazole and pyrimidine derivatives have been synthesized in better yields and shorter reaction times compared with the conventional method. The chemical structures of all the synthesized compounds were elucidated by their IR, ¹H NMR, ¹³C NMR, MS, and elemental analysis. Further, the target compounds were screened for their antimicrobial activity against four bacteria (Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa) and two fungi (Candida albicans, Aspergillus niger). In particular, compounds 2a , 2d , 2e , 3a , 3e , and 3f exhibited potent antimicrobial activity.     

An Efficient Synthesis and Antibacterial Activity of Pyrido[2,3‐d]Pyrimidine,Chromeno[3,4‐c]Pyridine,Pyridine, Pyrimido[2,3‐c]Pyridazine,Enediamines, and Pyridazine Derivatives

A series of Pyrido[2,3‐d]pyrimidine have been synthesized through a reaction of cyanoacetylurea derivatives with aromatic aldehydes or Arylidines. Reaction of compound 1 with aromatic arylidine derivatives or arylhydrazones gave Chromeno[3,4‐c]pyridine, Pyridine, Pyrimido[2,3‐c]pyridazine, Enediamines, and Pyridazine derivatives. All the synthesized compounds were confirmed by spectral studies and screened for their in antibacterial activity against Staphylococcus aureus (Gram positive) and Escherichia coli (Gram negative) bacterial strains. All the compounds were weak to good active against the tested bacterial strains on comparing with the standard drug gentamicin.     

Synthesis,characterization and antimicrobial screening of quinoline based quinazolinone-4-thiazolidinone heterocycles

In an attempt to find new pharmacologically active molecules, we report here the synthesis and in vitro antimicrobial activity of various 2-(2-chloro-6-methyl(3-quinolyl))-3-[2-(4-chlorophenyl)-4-oxo(3-hydroquinazolin-3-yl)]-5-[(aryl)methylene]-1,3-thiazolidin-4-ones. In vitro antimicrobial activity of the title compounds are screened against two Gram positive bacteria (Staphylococcus aureus, Streptococcus pyogenes), two Gram negative bacteria (Escherichia coli, Pseudomonas aeruginosa) and three strains of fungi (Candida albicans, Aspergillus niger, Aspergillus clavatus) using broth micro dilution method. Some derivatives bearing chloro or hydroxy group exhibited very good antimicrobial activity.     

In vitro pharmacological screening of three newly synthesised pyrimidine derivatives

The antibacterial and antifungal activities of three new pyrimidine derivatives, namely, 2,6-bis(4,6-dimethylpyrimidin-2-ylthio)benzene-1,4-diol (1),3,5-bis(4,6-dimethylpyrimidin-2-ylthio)-2-methylbenzene-1,4-diol (2) and 3,5-bis(4,6-dimethylpyrimidin-2-ylthio)-2-methoxybenzene-1,4-diol (3), synthesised by electrochemical method are presented here. The compounds were screened for their activities against Gram-positive and Gram-negative bacteria, Bacillus subtilis, Staphylococcusaureus, Escherichia coli and a pathogenic fungus Aspergillus niger. The results show that these compounds have significant activity against these bacteria and fungus. The minimum inhibitory concentration of compound 1 was determined as 62.5 μg/mL against B. subtilis, 125 μg/mL against E. coli and 250 μg/mL against S. aureus establishing its promising activities higher than susceptible ranges.     

Convenient synthesis,antimicrobial evaluation and molecular modeling of some novel quinoline derivatives

α, β-Unsaturated carbonyl compounds 2a, 2b, 3, and 4 were synthesized by the Knoevenagel condensation between 2-substituted quionoline-3-carboxaldehyde 1a and/or 1b with active methylene compounds. In addition, the synthesis of azlactone is achieved starting from 1a and N-acetylglycine. Synthesis of pyridine, pyrene, and pyrimidine derivatives 6–8 were accomplished via one-pot multicomponent reaction of 1b with acetyl acetone, malononitrile, and ammonium acetate; acetophenone, malononitrile, and NaOH; or acetyl acetone and urea in acidic medium. The new synthesized compounds showed good antimicrobial activities. The DFT calculations have been used to predict the electronic properties of the studied compounds.     

Investigation of the electro-oxidation and oxidation of catechol in the presence of sulfanilic acid

The electrochemical oxidation of catechol (1) in the presence of sulfanilic acid (2) was investigated. Some electrochemical (EC) techniques such as cyclic voltammetry and controlledpotential coulometry were used. The oxidation reaction of catechol (1) with periodate in the presence of sulfanilic acid (2) was also investigated spectrophotometrically. The results indicate that the o-quinone derived from catechol participate in Michael addition reaction with sulfanilic acid (2). In addition, according to the ECE mechanism, the observed homogeneous rate constant (k _obs) for the reaction ofo-quinone derived from catechol (1) with sulfanilic acid (2) has been estimated by digital simulation of cyclic voltammograms.     

Synthesis and Antimicrobial Properties of New Thiosemicarbazide, 1,2,4-Triazole,and 1,3,4-Thiadiazole Derivatives of Sulfanylacetic Acid

Abstract

1,2,4-triazole and 1,3,4-thiadiazole derivatives are still considered a viable lead structure for the synthesis of more efficient antimicrobial agents having a broad spectrum of activity. This study presents the synthesis and antimicrobial evaluation of a new series of substituted 1,2,4-triazole and 1,3,4-thiadiazole derivatives. Reaction of 4-phenyl-5-(pyridin-3-yl)-4H-1,2,4-triazole-3-thione with ethyl bromoacetate yields the corresponding ethyl acetate (1). In the subsequent reaction with 100% hydrazine hydrate, the hydrazide (2) was obtained, which was converted with isothiocyanates to new acyl derivatives of thiosemicarbazide (3a–l). The cyclization of these compounds in alkaline media resulted in the formation of new derivatives of 1,2,4-triazole (4a–i), whereas in acidic media new derivatives of 1,3,4-thiadiazole (5a,b,g) were obtained. All synthesized compounds were screened for their in vitro antimicrobial activities.     

Microwave assisted synthesis and antimicrobial evaluation of novel substituted thiosemicarbazide derivatives of pyrimidine

A new series of antimicrobial thiosemicarbazide substituted pyrimidine derivatives were synthesized by using thiosemicarbazide and ethyl 2-((2-amino-5-carbamoyl-6-[substituted benzyl] pyrimidin-4-yl)oxy)acetate derivatives and subsequent addition of acetaldehyde and acetone. The designed compounds were screened for Antibacterial activity against Staphylococcus aureus, Staphylococcus epidermidis, Micrococcus luteus, Bacillus cereus, Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumonia in comparison with the standard drugs Ciprofloxacin and antifungal effect against Aspergillus niger and Aspergillus fumigates in comparison with the standard drug Ketoconazole reveal the potency of synthesized derivatives. In accordance with the data obtained from antimicrobial activity, all the synthesized derivatives have shown good activity against the tested microbes. Among them, compound bearing 2-hydroxy and 3-chloro derivatives of thiosemicarbazide substituted pyrimidine has shown good activity against all the tested organisms.     

Antimicrobial and antiquorum-sensing activity of Ricinus communis extracts and ricinine derivatives

Ricinine (1), a known major alkaloid in Ricinus communis plant, was used as a starting compound for the synthesis of six ricinine derivatives; two new and four known compounds. The new derivatives; 3-amino-5-methyl-1H-pyrazolo[4,3-c]pyridin-4(5H)-one (2), and 3-amino-5-methyl-1-(phenylsulfonyl)-1H-pyrazolo[4,3-c]pyridin-4(5H)-one (3), as well as the previously prepared derivatives (4–7) were subjected for antimicrobial and antiquorum-sensing evaluation in comparison to different R. communis extracts. Acetyl ricininic acid derivative (5) showed the highest antimicrobial activity among all tested derivatives against Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeuroginosa and Candida albicans. However, compound 7 (4-methoxy-1-methyl-2-oxo-1,2-dihydropyridine-3-carboxamide) showed the highest antiquorum-sensing activity among all tested compounds and extracts. These findings proved the usefulness of ricinine as a good scaffold for the synthesis of new antimicrobial and antiquorum-sensing derivatives in spite of its poor contribution to the antimicrobial activity of the plant extracts.