| The synthesis, characterization, the antioxidative activity and antibacterial activity of 9 novel heterocyclic Schiff base derivatives were studied in this paper,based on the lead compound 2-hydroxy-4-methoxy benzaldehyde condensation with heterocyclic amines. The molecular structure of the compound A~I were characterized by UV-Vis, IR, fluorescence spectroscopy, 1H NMR and X-ray single crystal diffraction method.1. By the lead compound 2-hydroxy-4-methoxy benzaldehyde condensed with 9types of heterocyclic amines: 2-amino-5-methylthiazol(a), 5-aminoindazole(b), 4, 5-dicyan-2-aminoimidazole(c), 2-amino-5-thiol-1, 3, 4-thiadiazole(d), 2-(amino methyl)pyridine(e), 4-(aminomethyl)pyridine(f), 3-amino-4-cyanpyrazole(g), 2-amino-6-chloropyrazine(h), 2-amino-5-brominepyrazine(i), 9 types of heterocyclic Schiff base derivations: 5-methoxy-2-[(E)-(5-methylthiazol-2-ylimino) methyl]phenol(A),5-methoxy-2-[(E)-(1H-indazol-5-ylimino)methyl]phenol(B), 2-[(E)-2-hydroxy-4-methoxybenzylideneamino]-1H-imidazole-4, 5-dicyan(C), 5-methoxy-2-[(E)-(5-thiol-1, 3, 4-thiadiazole-2-ylimino) methyl]phenol(D), 5-methoxy-2-[(pyridine-2-methyl imino)methyl]phenol(E), 5-methoxy-2-[(pyridine-4-methyl imino)methyl]phenol(F),3-(2-hydroxy-4-methoxybenzylideneamino)-1H-pyrazole-4-cyan(G), 5-methoxy-2-[(E)-(6-chloropyrazine-2-ylimino)methyl]phenol(H), 5-methoxy-2-[(E)-(5-bromine pyrazine-2-ylimino)methyl]phenol(I) were synthesized.By orthogonal experimental and single factor experiments, the optimum reaction conditions of compound A and B were determined. The reaction yield was 84.72 %under 1: 2 molar ratio of 2-amino-4-methylthiazol and 2-hydroxy-4-methoxy benzaldehyde, reacted at the temperature of 75 ℃ for 2.5 h in methanol. The maximum yield 86.37 % of compound B was obtained by the reaction of 1: 1.75 molar ratio of 5-aminoindazole with 2-hydroxy-4-methoxy benzaldehyde in ethanol under the temperature of 75 ℃ for 5 h.2. The UV-Vis spectra showed that the enol-keto tautomerism was observed obviously for compound B. With the increasing ratio of water in the methanol-water solution, the absorption peaks in 344 nm of enolamine were decreased and the absorption peaks in 418 nm of ketoamine were increased.The fluorescence spectra showed that compound A~I had blue or violet fluorescence in methanol solution.The crystal structures of compound A, B, D, E, and F were characterized by single X-ray single crystal diffraction. Compound A, D, E and F crystallize in the monoclinic system, with space group P2(1)/n, C2/c, P2(1)/c and P2(1)/c; Compound B crystallize in the orthorhombic system, with space group P212121.3. The antioxidative activity of the compound A~I wre tested by 1, 1-diphenyl-2-picrylhydrazyl(DPPH) free radical scavenging method. The results showed that compound A~I had some scavenging activity on DPPH free radical. Compound D had the strongest scavenging activity, the scavenging activity was 95.74 % under the concentration 200 mg·L-1. The scavenging activity of compound A~I on DPPH free radical was linear with its concentration in the range of 10~200 mg·L-1.4. The antibacterial activity of the compound A~I against Staphylococs aureus ATCC 25923, Escherichia coli DH5 a, Pseudomonas aeruginosa ATCC 27853 were tested by filter paper method and trace serial dilution method. The results showed that compound A~F and H had antibacterial activity against Staphylococs aureus,minimum inhibitory concentration(MIC) were 1.0? 10-5 mol·L-1, 1.0 ? 10-6 mol·L-1,1.0?10-7 mol·L-1, 1.0?10-6 mol·L-1, 1.0?10-7 mol·L-1, 1.0?10-7 mol·L-1 and 1.0?10-6mol·L-1, respectively. Compound A, C, E, F, H and I had antibacterial activity against Escherichia coli, minimum inhibitory concentration were 1.0?10-6 mol·L-1, 1.0?10-6mol·L-1, 1.0?10-6 mol·L-1, 1.0?10-6 mol·L-1, 1.0?10-6 mol·L-1 and 1.0?10-6 mol·L-1,respectively. Compound F and G had antibacterial activity against Pseudomonas aeruginosa, minimum inhibitory concentration were 1.0?10-6 mol·L-1 and 1.0?10-6mol·L-1. While the compound C had the strongest antibacterial activity against Staphylococs aureus. |
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