Preparation and Antibacterial Activity of Some New 4-( 2-Heterylidenehydrazinyl )-7-chloroquinoline Derivatives

N-(4-Substituted phenyl)acetamides, which were prepared from acetic anhydride and p-substituted anilines, were utilized as precursors for reactions to Vilsmeier-Haack reagent to form 6-substituted-2-chloroquinoline-3-carbaldehydes 3a–c. Meanwhile, a similar reagent was applied to 1-[1-(4-substituted phenyl)ethylidene]-2-phenylhydrazines as substrates, which were synthesized from phenylhydrazine hydrochloride and p-substituted acetophenones, and 1,3-diarylpyrazole-4-carbaldehydes 3d–f were observed as a result. Reactions between the aldehydes 3a–f and 7-chloro-4-hydrazinylquinoline 2, obtained from reaction of 4,7-dichloroquinoline 1 and hydrazine hydrate, formed six new hydrazone compounds, namely, 4-{2-[(6-substituted-2chloroquinolin-3-yl)methylidene]hydrazinyl}-7-chloroquinolines 4a–c and 4-(2-{[3-(4-substituted phenyl)-1-phenyl-1H-pyrazol4-yl]methylene}hydrazinyl)-7-chloroquinolines 4d–f.The chemical structures of all synthesized compounds were elucidated by the analysis of IR, H, C-NMR, and HRMS spectral data. Additionally, all of the synthesized hydrazones were evaluated in terms of cytotoxic activity against four strains of bacteria and four strains of fungus at several concentrations of substrates. As a result, three of them, 4a–c, possess the good ability as growth inhibitor of Bacillus subtilis andAspergillus niger at the concentration of 25 μg/mL and 50 μg/mL, respectively, while compound 4e only shows a cytotoxic activity against Aspergillus niger at the concentration of 25 μg/mL.


Introduction
Quinoline derivatives, which widely occur in nature, especially alkaloids, have become an important skeleton in synthetic chemistry due to their variety of applications in medicinal, bioorganic, and industrial chemistry.Some hydrazone derivatives possessing a quinoline moiety have been well known as having a broad spectrum of biological activities such as antibacterial [1], anticancer [2], antitubercular [3][4][5], antifungal [6], anti-inflammatory [7], antimalarial [8], and antimicrobial [9,10].According to Ferreira et al. [11], hydrazone derivatives, which were prepared from the reaction of 7-chloro-4-hydrazinylquinoline and heteroaromatic aldehydes, showed a good antimycobacterial activity in comparison with some drugs such as ethambutol and rifampicin.Additionally, some hydrazones being born from 2-chloroquinoline-3-carbaldehyde possessed a moderate to good antibacterial activity against both Gram-positive and Gram-negative bacteria [12].

Materials and Methods
All chemicals were purchased from Merck or Aldrich and solvents were commercial and were used without any further purification.
Melting points were determined with a Gallenkamp digital Melting-point apparatus 5A-6797 and were uncorrected.
The IR absorption spectra were scanned on Shimadzu FTIR 8400S spectrum using potassium bromide (KBr) pellets.
All the 1 H, 13 C-NMR, HSQC, and HMBC spectra were recorded on a Bruker Advance 500 MHz model spectrometer using DMSO-d 6 as solvents and internal standard.The spinspin coupling constants (J) are given in Hz.Peak multiplicity is reported as s (singlet), d (doublet), dd (double-doublet), t (triplet), q (quartet), m (multiplet), and br (broad).
Mass spectrometric data were recorded on a micrOTOF-QII Bruker.
The synthesis of the hydrazones containing quinoline heterocycles was performed following the steps shown in Scheme 1.
2-Chloroquinoline-3-carbaldehydes 3a-c were prepared according to the literature [16].p-Substituted aniline was added to the solution of acetic anhydride in acetic acid, following by being refluxed in 2 hours.Consequently, cooling to room temperature and pouring into ice water were performed to collect N-(4-substituted phenyl)acetamide derivatives, which then reacted to the mixture of dimethylformamide and phosphoryl chloride (Vilsmeier-Haack reagent) to form 2chloroquinoline-3-carbaldehyde derivatives a-c.

Preparation of 4-(2-Heterylidenehydrazinyl)-7-chloroquinoline
Compounds 4a-f .Appropriate 2-chloroquinoline-3carbaldehyde derivatives a-c or 1,3-diphenylpyrazole-4carbaldehyde derivatives d-f (1 mmol) were dissolved in absolute ethanol (10 mL) with a few drops of glacial acetic acid.This mixture was stirred for 10 minutes and then compound (0.19 g, 1 mmol) was added in.The reaction mixture was refluxed for 3 hours.At the completion of reaction, the mixture was cooled to room temperature to separate the solid, which was filtered and recrystallized from suitable solvent to give products a-f, respectively.
All the synthesized hydrazones were evaluated to in terms of antimicrobial activities against microorganism.The method for these experiences was based on the literature [18,19].Theoretically, H and H usually appear as doublet signals due to having spin-spin coupling together.However, in our case, the ring system may lead to them becoming hydroxylic protons, and, so, the broad signals were obtained.

Result and Discussion
Compound was utilized as a precursor for preparation of six new hydrazones according to Scheme The reaction of and some heteroaromatic a-f occurred easily and may be observed clearly by both changing color of reaction solution and the appearance of precipitates in the progress of reaction.In IR spectra, the specific vibration of amino group (-NH 2 , double peak) at 3255-3258 cm −1 disappeared while the sharpness peak of N-H bonds still appeared around 3200 cm −1 ; the stretching bands of the C=N bonds were recognized at 1555-1582 cm −1 .These data are similar to those of the 7-chloro-4-quinolinylhydrazone compounds described in literature [3].
The physical properties and IR spectral data of the a-f compounds were presented in Table 1.
The structures of the hydrazones were further confirmed by the HRMS data.Molecular ion peaks in the mass spectra of the products were in conformity with desired molecular formulas of them (see Tables 2 and 3).

7 -
Chlorohydrazinylquinoline was prepared from the reaction of 4,7-dichloroquinoline and hydrazine hydrate.Its 1 H-NMR spectrum (S2 from Supplementary materials) showed two broad singlet signals of hydrazine group (-NHNH 2 ) at  H 8.6 and 4.5.Additionally, there were a doublet signal at  H 8.16 with spin-spin coupling of 9.0 Hz attributed to H and a double-doublet signal at 7.39 attributed to H .Meanwhile, H gave a singlet signal at  H 7.76.Two signals appearing at  H 8.39 and 6.87 were attributed to H and H , respectively.

Table 1 :
The physical properties and IR spectral data of the a-f compounds.

Table 2 :
1 H, 13 C-NMR, and HR-MS spectral data of compounds a-c.