Synthesis of Schiff bases of naphtha[1,2-d]thiazol-2-amine and metal complexes of 2-(2'-hydroxy)benzylideneaminonaphthothiazole as potential antimicrobial agents

Objective： A series of 2-benzylideneaminonaphthothiazoles were designed and synthesized incorporating the lipophilic naphthalene ring to render them more capable of penetrating various biomembranes. Methods： Schiff bases were synthesized by the reaction of naphtha[1,2-d]thiazol-2-amine with various substituted aromatic aldehydes. 2-（2＇-Hydroxy）ben- zylideneaminonaphthothiazole was converted to its Co（Ⅱ）, Ni（Ⅱ） and Cu（Ⅱ） metal complexes upon treatment with metal salts in ethanol. All the compounds were evaluated for their antibacterial activities by paper disc diffusion method with Gram positive Staphylococcus aureus and Staphylococcus epidermidis and Gram negative Escherichia coli and Pseudomonas aeruginosa bacteria. The minimum inhibitory concentrations of all the Schiff bases and metal complexes were determined by agar streak dilution method. Results： All the compounds moderately inhibited the growth of Cram positive and Gram negative bacteria. In the present study among all Schiff bases 2-（2＇-hydroxy）benzylideneaminonaphthothiazole showed maximum inhibitory activity and among metal complexes Cu（Ⅱ） metal complex was found to be most potent. Conclusion： The results obtained validate the hypothesis that Schiff bases having substitution with halogens, hydroxyl group and nitro group at phenyl ring are required for the antibacterial activity while methoxy group at different positions in the aromatic ring has minimal role in the inhibitory activity. The results also indicated that the metal complexes are better antibacterial agents as compared to the Schiff bases.

Reaction of Nitrosonium (NO^+) with Schiff Bases

The reaction of nitrosonium (NO+) with Schiff bases produced diazonium salts and aldehydes in good yield. The reaction is assumed to be an electrophilic reaction of nitrosonium with imines via a four-member ring intermediate.

Synthesis, Characterization and Antibacterial Activities of Polydentate Schiff Bases, Based on Salicylaldehyde

Three Schiff bases L1, L2 and L3 were synthesized by condensing salicylaldehyde with 4-aminoantipyrine, ethylendiamine and 2-aminophenol respectively and subsequently characterized by various physicochemical investigations. All the three compounds were screened for their In-vitro antibacterial activity against two gram positive bacteria, Staphylococcus aureus (S.A), Staphylococcus epidermidis (S.E) and two gram negative bacteria Klebsiella pneumoniae (K.P) and Pseudomonas aeruginosa (P.A) by agar diffusion method. On comparing the results obtained with the activity of commercially available antibiotics such as Ciprofloxacin and Chloramphenicol, the newly synthesized compounds showed comparable antibacterial activities. The solvent methanol exhibit activity against all bacterial species with IZs ranging from 8 ± 0.25 to 17 ± 0.29 mm while the standard antibiotics Ciprofloxacin and Chloramphenicol exhibited an activities with IZs varying from 21.3 ± 0.31 to 28.3 ± 0.32 and 26.3 ± 0.24 mm to 32.3 ± 0.23 mm, respectively. However, the newly synthesized Schiff bases L1, L2 and L3 showed IZs ranging from 7.4 ± 0.23 to 32.5 ± 0.14, 3 ± 0.57 to 12 ± 0.28 and 10 ± 0.20 to 32 ± 0.36 respectively. Among the Schiff bases, L3 showed the activity (32 ± 0.36) against S.E and P.A which is higher than the activity of standard antibiotics Ciprofloxacin and Chloramphenicol against the same bacterial strains. The results obtained revealed that all the synthesized Schiff bases exhibit appreciable antibacterial activity against all the bacteria species which potentially makes them, to apply as wide range antibacterial drugs, after further in-vivo cytotoxicity investigations. Their activity can also be further modified by changing the functionality of precursors for Schiff base condensation.

The Synthesis of Tertiary Amides by theReaction of Adducts of Schiff Bases andAcyl Chlorides with Allylsamarium Bromide

Adducts of Schiff bases and acyl chlorides react with allylsamarium bromide to afford the corresponding tertiary amides.

Syntheses of Ferrocenyl Schiff Bases Using Molecular Sieves and AlCl_3 as Catalysts

In order to study the donor ability of ferrocenylimines as directing ortho metalation group（DMG） to lithium alkylide to prepare planar chiral ferrocene, a series of ferrocenyl schiff bases were synthesized by new methods using molecular sieves（0.4nm） and AlCl3 as catalysts. The reaction periods were reduced using these two catalysts in contrast with Al2O3, which was a traditional method used in the literature. In addition, as an important feature of these schiff bases, we found that they were unstable as oils in air or when filtrated through silica gel, but were stable as solids. The structures of the new compounds were confirmed by IR, ^1H NMR and HRMS.

Synthesis, Thermochromic Properties and Thermal Behavior of some Schiff Bases.Part I. p,p'-Diaminodiphenylmethane-Schiff Bases and Sulphonamide Schiff Base

p,p'-Diaminodiphenylmethane-Schiff bases (SB) of general formula (R)-phCH=N- ph-CH2-ph-N=CHph(R), where R is p-NO2, m-NO2, p-OH, o-OH, p-Cl, -H, p-OCH3, and sul- phonamide Schiff bases (SB) of general formula (R)-phCH=N-ph-SO2NH2, where R is p-NO2, m-NO2, p-OH, o-OH, p-Cl, -H, p-OCH3, were synthesized and their structure have been characterized by the melting pointing, 1HNMR, MS, and elemental analysis. They are thermolabile and undergo thermo-chromism and thermal decomposition after melting. The TG. and DSC measurement were recorded in dynamic air and interpreted.

SYNTHESIS,CHARACTERIZATION AND SELECTIVITY STUDIES OF POLY(ACRYLAMIDE) INCORPORATING SCHIFF BASES

Three novel polymers incorporating Schiff bases,derived from condensation reactions of poly(acrylamide) with 5- chloro-2-hydroxybenzaldehyde,5-bromo-2-hydroxybenzaldehyde and 5-methyl-2-hydroxybenzaldehyde,have been synthesized,and their Cu(Ⅱ) and Ni(Ⅱ) complexes have been prepared.The ~1H-NMR signals of the—CH=N—and—NH_2 groups have been utilized to determine the relative abundances of Schiff base and acrylamide groups in the polymers containing Schiff bases.Poly(acrylamide) incorporating Schiff bases and ...

Theoretical Study on the Structures, Vibrational Spectra, and the Nature of the Intermediate Hydrogen Bond of Schiff Bases

Semi-empirical method PM3 was used to study the geometry and vibrational spectrum of N-(2-hydroxy-l-naphthyl-methylene)-l-pyrenamine (NPY) with the intermediate hydrogen bond. Results are comparable to experimentations. Based on results of both NPY and its model, N-(2-hydroxy-l-naphthyl-methylene)aniline, it was found that the N-(2-hydroxy-l-naphthyl-methylene) group is principally responsible for the special hydrogen bonding through conjugation effect.

Calf Thymus DNA Intercalation by Anionic Ru（Ⅲ） Complexes Containing Tridentate Schiff Bases Derived from 5-X-Substituted Salicyladehyde and 2-Aminophenol

Sodium bis[N-2-oxyphenyl-5-substituted-salicylideneiminato-ONO]ruthenate（Ⅲ） hemitriethylamine compounds of general formula Na[Ru（N-R-5-X-salim）2]＇0.5Et3N, where, R = C6H40, X = El, Br, NO2, salim = salicylideneiminato, Et3N triethylamine, were synthesized and characterized on the basis of elemental analysis, MALDI-TOF （matrix-assisted laser desorption/ionization/time-of-flight） mass spectra, IH NMR （nuclear magnetic resonance）, electronic spectra and cyclic voltammograms. Ru（Ⅲ） is chelated with two O2N anionic tridentate Schiff bases derived from 5-X-salicyladehyde and 2-aminophenol. Spectroscopic titrations of the Ru（Ⅲ） compounds with CT DNA （calf thymus DNA） in the LMCT （ligand metal charge transfer） region have shown moderate intercalation properties of compounds with binding constants KD = 2.06-3.85 × 104 Ml. Electrochemical evidence of intercalative mode of binding is based on the decrease of current and shift of anodic and cathodic peaks towards higher values of potential with IxL-increment of CT DNA in Ru（Ⅲ） compound solution.

CHARACTERIZATION OF SOME SCHIFF BASES OF HETEROCYCLIC COMPOUNDS AND THEIR TRANSITION METAL COMPLEXES

Some new Schiff bases were synthesized by the condensation of equimolar quantities of salicylaldehyde and 2-amino-5-phenylazo-pyridine or its derivatives in dry benzene(1):Metal complexes of the type ML_2and M'L_3 where M=Cu^(2+),Co^(2+),Ni^(2+),Mn^(2+)Pd^(2+),M'=Fe^(3+)and L=different newly synthesized monobasic Schiff bases were prepared in absolute ethanolic medium(2)and characterized by elementary analysis,conductance measurements,infrared spectra,electronic spectra,magnetic moments studies.

Biological Evaluation of New Schiff Bases: Synthesized from 4-Amino-3,5-dimethyl-1,2,4-triazole, Phenathroline and Bipyridine Dicarboxaldehydes

Four new Schiff bases with promising anticancer activity have been synthesized from 4-amino-3,5-dimethyl-1,2,4-triazole and di-pyridyl-aldehydes. Structures have been established by various spectroscopic methods. The compounds were tested in vitro to study their cytotoxicity and anti-oxidative activity in human lung carcinoma (A549), breast carcinoma (BT549), prostate adenocarcinoma (PC3) and mouse preadipocytes (3T3-L1) cells. Compound 1 was found to increase Glutathione (GSH) level slightly in all four cell lines. Compound 4 showed better selectivity and cytotoxicity against both BT549 and A549 cells compared to the anticancer drug tamoxifen. With the exception of compound 4 which reduced GSH levels in A549 and BT549, all other compounds maintained GSH levels in comparison to their respective controls.

Synthesis of New Schiff Bases Containing Thiophene Moiety

Seven new Schiff bases, which are 4,4,4-trifluo-ro-1-(2-thienyl)-1-butanone-3-Z, Z =-thioseraicarbazone (a); -thiocarbohydrazone (b),-benzoic hydrazone (c), -( o-hydroxyphenyl) imine (d) ,-nicotinic hydrazone (e),-salicylic hydrazone (f), and -(p-fluoro-m-chlorophenyl) imine (g), have been synthesized by reaction of 4, 4, 4-trifluoro-1-(2-thienyl)-1,3-butanedione (TFTBD) with corresponding hy-drazides or anilines, acetic acid or p-toluence sulfonic acid as catalyst, and characterized by Elemental analysis, IR, UV-Vis,1H NMR and MS. The MS spectra confirmed that the -C3=O condensed with primary amino group. Tauto-merism of the compounds is discussed.

Dioxygen Affinity and Catalytic Performance of Bis-(furaldehyde) Schiff Bases Co(II) Complexes in Cyclohexene Oxidation

Oxygenation constants and thermodynamic parameters DeltaH degrees and DeltaS degrees of cobalt (II) complexes with bis-(furaldehyde) Schiff bases (1, 2, 3, 4)were obtained by mearsuring saturated dioxygen uptake of these complexes in pyridine at different temperature. These complexes could activate molecular oxygen and were used as catalysts in cyclohexene oxidation. The influence of ligand structure on the dioxygen affinity and catalytic activity of the complexes were discussed.

Synthesis, Structural Features and Evaluation of Antibacterial Activities of Two Schiff Bases Derived from 3,4-Dihydroxybenzhydrazide

A new Schiff base compound （I）, （E）-N＇-（2-hydroxy-3-methoxybenzylidene）-3,4-dihydroxybenzohydrazide-ethanol-water （1/1/1）, has been synthesized and characterized by elemental analysis, IR spectra, and single-crystal X-ray diffraction. The crystal belongs to monoclinic, space group P21/n with a = 7.459（4）, b = 18.316（10）, c = 13.638（7）, β = 101.585（9）o, V = 1825.2（17）3, Z = 4, μ = 0.104 mm-1, Dc = 1.333 g/cm3, F（000） = 776, the final R = 0.0635 and wR = 0.1302 for 3216 observed reflections with I 〉 2σ（I）. Another compound （Ⅱ）, （E）-N＇-（2,5-dimethoxybenzylidene）-3,4-dihydroxybenzohydrazide-ethanol-water （1/1/1）, has been synthesized and reported before. The antibacterial activities of these two compounds against seven bacteria were first evaluated, and one compound showed considerable antibacterial activity against S. aureus.

Synthesis of Pyridyl Polyheterocyclic Oxime-ether Schiff Bases Containing s-Triazole and Oxadiazole Subunits

4-Amino-5-pyridin-4-yl-s-triazole-3-thiol （1） was sequentally reacted with 3-chloro-1- phenylpropan-1-one to afford 3-（4-amino-5-pyridin-4-yl-s-triazole-3-sulfanyl）-1-phenylpropan-1- one （2） followed by oximation with hydroxylamine hydrochloride and etherification with 5-aryl-[13,4]oxadiazole-2-cbloromethanes to the corresponding oxime （3） and oxime-ethers （4a-e）, respectively. The condensation of compounds 4 with salicylaldehyde gave the title compounds （5a-e）. The antibacterial activity in vitro against Gram-postive （G^＋） and Gram negative （G） bacteria was primarily evaluated.

Efficient C_(2)-Symmetric Chiral Schiff Bases for Lanthanide-catalyzed Asymmetric Hydrogenation of Acetophenone

An array of C2-symmetric chiral Schiff bases of substituted salicylaldehyde （1R, 2R）-1, 2-cyclohexanediamine and （R）-（＋）-2, 2＇-diamino-1, 1＇-binaphthalene, incorporated with lanthanide complexes, have been applied as catalysts for asymmetric hydrogenation of acetophenone for the first time. Highly enantioselective product with 90% enantiomeric excess （e.e.） was obtained when the catalyst, hybridized by the bulky electron-donating 3, 5-di-tert-butyl substituted Schiff base （2） and SmCl3.4THF, was employed.

Antioxidative Effect of Schiff Bases with o-Hydroxybenzylidene Groupon Free Radical Induced Hemolysis of Human Red Blood Cell

The hemolysis of human red blood cells was initiated by a water soluble free radical initiator, 2,2′ azobis (2 amidinopropane hydrochloride)(AAPH), at 37 ℃ in phosphate buffered saline(pH=7.4). The respective addition of 1 [ N (o hydroxybenzylidene)amino]tetradecane(TDCA), 1,2 di[ N (o hydroxybenzylidene)amino]cyclohexane(DACH), 4 [ N (o hydroxybenzylidene)amino]benzoic acid(PABA), 4 nitro[ N (o hydroxybenzylidene)]aniline(APNA) or N (o hydroxybenzylidene)aniline(APA) can all prolong the inhibition period of hemolysis, indicating that the above Schiff bases play an antioxidative role in free radical induced hemolysis. It can be concluded that Schiff base with an alkyl group or a conjugated system in the molecule protect red blood cells against free radical induced hemolysis efficiently. This information may be useful for antioxidant drug design.

Preparation of six quinazoline schiff bases and their inhibitory effect on HHCC and Bcap-37 cells

Objective: To prepare six quinazoline schiff bases by six steps of chemistry organic synthesis and test their inhibitory effect on hepatomacellular carcinoma cells HHCC and mammary cancer cell Bcap-37, furthmore,to compare their antitumor activities on these two kinds of cells. Methods: 2-Amino-5-nitro-benzylcarbonitrile was the initial material, and it was under the reaction of hydrolysis, ring-closing, halogenation, addition, reduction and substitution in turn to get the six quinazoline schiff bases, MTT method was adopted to compare their anticancer activities against the two cancer cells. Result and Conclusion: Six 6-imine-4-halo substituted anilinoquinozolines were prepared. The anticancer activities against both HHCC and Bcap-37were found, furthermore, they have more potency that on HHCC than on Bcap-37. In the six compounds, the schiff base Ⅵ is the most potent compound.

Syntheses,Crystal Structures and Biological Activities of Three New Schiff Bases Derived from Substituted Salicylaldehyde and Tris Base

Three new o-hydroxy Schiff bases, L1, L2 and L3, were derived from the 1：1 M condensation of substituted salicylaldehyde with tris base and were characterized by FT-IR, ^1H NMR and ^13C NMR spectroscopies. The crystal structure of L1 was also determined by single-crystal X-ray analysis, and it exists as a zwitterionic form in the solid state, with the H atom of the phenol group being transferred to the imine N atom. It adopts an E-configuration about the central C=N double bond. In addition, the biological activity assay was carried out and the results show that the Schiff-base compounds have a diverse range of biological activities against the fungi tested, which suggests great potential applications in antifungal fields in the future.