Efficient Synthesis and Discovery of Schiff Bases as Potent Cholinesterase Inhibitors.

BACKGROUND: The search for new cholinesterase inhibitors is still a promising approach for management of Alzheimer`s disease. Schiff bases are considered as important class of organic compounds, which have wide range of applications including as enzyme inhibitors. In the present study, a new green ionic liquid mediated strategy was developed for convenient synthesis of two series of Schiff bases 3(a-j) and 5(a-j) as potential cholinesterase inhibitors using aromatic aldehydes and primary amines in [bmim]Br. METHODS: The synthesized compounds were evaluated for their acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory potential by modified Ellman's method. The molecular interactions between the most active compound and the enzyme were analyzed by molecular docking. RESULTS: Among them, 3j displayed higher inhibitory activities than reference drug, galanthamine, with IC50 values of 2.05 and 5.77 µM, for AChE and BChE, respectively. Interestingly, all the compounds except 3b displayed higher BChE inhibitions than galanthamine with IC50 values ranging from 5.77 to 18.52 µM. Molecular docking of compound 3j inside the TcAChE and hBChE completely coincided with the inhibitory activities observed. The compound forms strong hydrogen bonding at the peripheral anionic site of AChE whereas on BChE, it had hydrophobic and mild polar interactions. CONCLUSION: An efficient and eco-friendly synthetic methodology has been developed to synthesize Schiff bases in a very short reaction time and excellent yields in ionic solvent, whereby the compounds from series 3 showed promising cholinesterase inhibitory activity.

Ionic liquid mediated synthesis and molecular docking study of novel aromatic embedded Schiff bases as potent cholinesterase inhibitors.

Novel aromatic embedded Schiff bases have been synthesized in ionic liquid [bmim]Br and evaluated in vitro for their acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes inhibitory activities. Among the newly synthesized compounds, 5f, 5h and 7j displayed higher AChE enzyme inhibitory activities than standard drug, galanthamine, with IC50 values of 1.88, 2.05 and 2.03µM, respectively. Interestingly, all the compounds except for compound 5c displayed higher BChE inhibitories than standard with IC50 values ranging from 3.49 to 19.86µM. Molecular docking analysis for 5f and 7j possessing the most potent AChE and BChE inhibitory activities, disclosed their binding interaction templates to the active site of AChE and BChE enzymes, respectively.

Synthesis of isatin thiosemicarbazones derivatives: in vitro anti-cancer, DNA binding and cleavage activities.

New derivatives of thiosemicarbazone Schiff base with isatin moiety were synthesized L1-L6. The structures of these compounds were characterized based on the spectroscopic techniques. Compound L6 was further characterized by XRD single crystal. The interaction of these compounds with calf thymus (CT-DNA) exhibited high intrinsic binding constant (k(b)=5.03-33.00×10(5) M(-1)) for L1-L3 and L5 and (6.14-9.47×10(4) M(-1)) for L4 and L6 which reflect intercalative activity of these compounds toward CT-DNA. This result was also confirmed by the viscosity data. The electrophoresis studies reveal the higher cleavage activity of L1-L3 than L4-L6. The in vitro anti-proliferative activity of these compounds against human colon cancer cell line (HCT 116) revealed that the synthesized compounds (L3, L6 and L2) exhibited good anticancer potency.

Flow injection analysis of mercury using 4-(dimethylamino) benzaldehyde-4-ethylthiosemicarbazone as the ionophore of a coated wire electrode.

A flow injection analysis (FIA) incorporating a thiosemicarbazone-based coated wire electrode (CWE) was developed method for the determination of mercury(II). A 0.1 M KNO(3) carrier stream with pH between 1 and 5 and flow rate of 1 mL·min(-1) were used as optimum parameters. A linear plot within the concentration range of 5 × 10(-6)­0.1 M Hg(II), slope of 27.8 ± 1 mV per decade and correlation coefficient (R2) of 0.984 were obtained. The system was successfully applied for the determination of mercury(II) in dental amalgam solutions and spiked environmental water samples. Highly reproducible measurements with relative standard deviation (RSD < 1% (n = 3)) were obtained, giving a typical throughput of 30 samples·h(-1).

(Z)-N-Ethyl-2-(5-fluoro-2-oxoindolin-3-yl-idene)hydrazinecarbothio-amide.

In the title compound, C(11)H(11)FN(4)OS, an intra-molecular N-H⋯O hydrogen bond generates an S(6) ring. In the crystal, mol-ecules form chains through N-H⋯O hydrogen bonds, which are extended by N-H⋯S hydrogen bonds into an infinite three-dimensional network.

(E)-4-Hy-droxy-N'-(2-hy-droxy-4-meth-oxy-benzyl-idene)benzohydrazide.

In the title compound, C(15)H(14)N(2)O(4), the dihedral angle between the benzene rings is 40.59 (4)° and an intra-molecular O-H⋯N hydrogen bond generates an S(6) ring. In the crystal, N-H⋯O, O-H⋯O and C-H⋯O inter-actions link the mol-ecules into a three-dimensional network.

(E)-4-Hy-droxy-N'-(2-meth-oxy-benzyl-idene)benzohydrazide.

In the title compound, C(15)H(14)N(2)O(3), the dihedral angle between the benzene rings is 66.56 (5)°. In the crystal, N-H⋯O, O-H⋯O and C-H⋯O inter-actions link the mol-ecules into a three-dimensional network. A π-π inter-action, with a centroid-centroid distance of 3.628 (6) Å, helps to establish the packing.

(Z)-N-Methyl-2-(5-nitro-2-oxoindolin-3-yl-idene)hydrazinecarbothio-amide.

In the title compound, C(10)H(9)N(5)O(3)S, an intra-molecular N-H⋯O hydrogen bond generates an S(6) ring motif. In the crystal, mol-ecules are linked via N-H⋯S hydrogen bonds into a zigzag chain along the b axis. C-H⋯O inter-actions are observed between the chains.

(Z)-N-Methyl-2-(5-methyl-2-oxoindolin-3-yl-idene)hydrazinecarbothio-amide.

In the title compound, C(11)H(12)N(4)OS, an intra-molecular N-H⋯O hydrogen bond generates an S(6) ring motif. In the crystal, the mol-ecules form a helical chain along the a axis through an N-H⋯O hydrogen bond. These chains are extended by an N-H⋯S hydrogen bond and a C-H⋯π inter-action into a three-dimensional network.

(Z)-2-(2-Oxoindolin-3-yl-idene)-N-phenylhydrazinecarbothio-amide.

In the title compound, C(15)H(12)N(4)OS, the dihedral angle between the nine-membered indolin-2-one ring system and the phenyl ring is 2.72 (7)°. Intra-molecular cyclic N-H⋯O and C-H⋯S hydrogen-bonding inter-actions [graph set S(6)] are present, as are weak N-H⋯N inter-actions [graph set S(5)]. In the crystal, mol-ecules form centrosymmetric cyclic dimers through pairs of N-H⋯O hydrogen bonds [graph set R(2) (2)(8)] and these are extended by C-H⋯S inter-actions. The crystal structure also features weak C-H⋯π inter-actions.

Bis[2-(2-oxoindolin-3-yl-idene)-N-phenylhydrazinecarbothio-amidato-κ(3)O,N(2),S]nickel(II) dimethyl-formamide monosolvate.

The asymmetric unit of the title compound, [Ni(C(15)H(11)N(4)OS)(2)]·C(3)H(7)NO, contains one Ni(II) complex mol-ecule and one disordered dimethyl-formamide solvent mol-ecule. The Ni(II) ion is six-coordinated in a distorted octa-hedral geometry by two N, two O and two S atoms. An intra-molecular C-H⋯S hydrogen bond generates an S(6) ring motif. In the crystal, mol-ecules are linked through inter-molecular N-H⋯S, N-H⋯O, C-H⋯N, C-H⋯O and C-H⋯S hydrogen bonds into infinite two-dimensional network parallel to the ab plane. The structure is further stablized by weak C-H⋯π inter-actions. The dimethylformamide solvent molecule is disordered over two sets of sites in a 0.514 (15):0.486 (15) ratio.

(Z)-2-(5-Chloro-2-oxoindolin-3-yl-idene)-N-methyl-hydrazinecarbothio-amide.

In the title compound, C(10)H(9)ClN(4)OS, an intra-molecular N-H⋯O hydrogen-bonding inter-action and an N-H⋯N inter-action generate ring motifs [graph sets S(6) and S(5), respectively]. In the crystal, mol-ecules form a chain through N-H⋯O hydrogen bonds, and these are extended by N-H⋯S hydrogen-bonding inter-actions into an infinite three-dimensional network. The crystal structure also exhibits weak C-H⋯π inter-actions.

(Z)-2-(5-Fluoro-2-oxoindolin-3-yl-idene)-N-phenyl-hydrazinecarbothio-amide.

The title compound, C(15)H(11)FN(4)OS, crystallizes with three independent mol-ecules (A, B and C) in the asymmetric unit. The dihedral angles between the nine-membered 5-fluoro-indolin-2-one ring system and the benzene ring are 22.14 (11), 12.56 (11) and 3.70 (11)° in mol-ecules A, B and C, respectively. In all three mol-ecules, intra-molecular cyclic N-H⋯O and C-H⋯S hydrogen-bonding inter-actions [graph set S(6)] are present in the N-N-C-N chain between the ring systems. In the crystal, the A mol-ecules form centrosymmetric cyclic dimers through inter-molecular N-H⋯O hydrogen bonds, which are linked into a supramolecular chain along [100] via C-H⋯F interactions; each type of hydrogen bond has graph set graph set R(2) (2)(8). A similar chain stabilised by similar interactions and also along [100] but, comprising alternating molecules of B and C is found. The latter chains are connected via C-H⋯S interactions, forming a layer with a zigzag topology parallel to (001).

(Z)-2-(5-Chloro-2-oxoindolin-3-yl-idene)-N-phenyl-hydrazinecarbothio-amide.

In the title compound, C(15)H(11)ClN(4)OS, the dihedral angle between the nine-membered 5-chloro-indolin-2-one ring system and the benzene ring is 10.00 (6)°. Intra-molecular cyclic N-H⋯O and C-H⋯S hydrogen-bonding inter-actions [graph set S(6)] are present in the N-N-C-N chain between the ring systems. In the crystal, mol-ecules form centrosymmetric cyclic dimers through inter-molecular N-H⋯O hydrogen bonds [graph-set R(2) (2)(8)] and are extended by C-H⋯Cl inter-actions into infinite chains which propagate along [100].

(Z)-2-(5-Methyl-2-oxoindolin-3-yl-idene)-N-phenyl-hydrazinecarbothio-amide.

In the title compound, C(16)H(14)N(4)OS, the dihedral angle between the nine-membered 5-methyl-indolin-2-one ring system and the benzene ring is 10.21 (7)°. Intra-molecular cyclic N-H⋯O and C-H⋯S hydrogen-bonding inter-actions [graph set S(6)] are present within the N-N-C-N chain between the ring systems. In the crystal, mol-ecules form centrosymmetric cyclic dimers through pairs of N-H⋯O hydrogen bonds [graph set R(2) (2)(8)].

Hydrazone-based ligands for micro-solid phase extraction-high performance liquid chromatographic determination of biogenic amines in orange juice.

Eight hydrazone-based ligands were synthesized, trapped in a silica sol-gel matrix, and were subsequently used in the micro-solid phase extraction (µ-SPE) of biogenic amines (BAs). The BAs investigated were tryptamine, phenylethylamine, putrescine, histamine, tyramine and spermidine. Prior to the extraction, dansyl chloride was added to the samples which were heated to 70°C for 10 min. The samples were extracted with µ-SPE, after which analytes were desorbed using acetonitrile via ultrasonication. The extracts were analysed by high performance liquid chromatography (HPLC) with ultraviolet detection. Of the eight ligands investigated as sorbents, benzophenone 2,4-dinitrophenylhydrazone was found to be the most promising. The enhanced π-π interaction between the analytes and the ligand facilitated the adsorption process. Under the most suitable extraction conditions, the method demonstrated good linearity with correlation coefficient of more than 0.985 over a concentration range of 1-50 µg L(-1). Satisfactory repeatability with relative standard deviations of 7.43-11.30% (n=3) were obtained. Detection limits ranged from 3.8 to 31.3 ng L(-1). The µ-SPE method exhibited lower recoveries (71.5-87.4%) when compared to the solid phase extraction technique (79.7-95.0%), but enrichment factors of 94-460 were obtained. The proposed µ-SPE-HPLC method was applied to the determination of BAs in orange juice purchased from local supermarkets, with satisfactory results. The orange juices were characterized by the presence of relatively high levels of putrescine (range, 550-2210 µg L(-1)) but tryptamine and phenylethylamine were not detected in any of the tested samples.

A synthetic hydrazone derivative acts as an apoptotic inducer with chemopreventive activity on a tongue cancer cell line.

One of the main aims of cancer chemopreventive studies is to identify ideal apoptotic inducers, especially examples which can induce early apoptotic activity. The present investigation focused on chemopreventive effects of a hydrazone derivative using an in vitro model with tongue cancer cells. Alteration in cell morphology was ascertained, along with stage in the cell cycle and proliferation, while living-dead status of the cells was confirmed under a confocal microscope. In addition, cytotoxicity test was performed using normal mouse skin fibroblast cells. The results showed that the compound inhibited the growth of tongue cancer cells with an inhibitory concentration (IC50) of 0.01 mg/ml in a dose and time-dependent manner, with a two-fold increase in early apoptotic activity and G0G1 phase cell cycle arrest compared to untreated cells. Exposure to the compound also resulted in alterations of cell morphology including vacuolization and cellular shrinkage. Confocal microscope analysis using calcein and ethidium staining confirmed that the compound caused cell death, whereas no cytotoxic effects on normal mouse skin fibroblast cells were observed. In conclusion, the findings in this study suggested that the hydrazone derivative acts as an apoptotic inducer with anti-proliferative chemopreventive activity in tongue cancer cells.

A 4-hydroxy-N'-[(E)-(2-hydroxyphenyl)methylidene]benzohydrazide-based sorbent material for the extraction-HPLC determination of biogenic amines in food samples.

A sorbent material based on a newly synthesized hydrazone ligand, 4-hydroxy-N'-[(E)-(2-hydroxyphenyl)methylidene]benzohydrazide was prepared by immobilizing the ligand into a silica sol-gel matrix. The capability of the sorbent material for the extraction of seven biogenic amines (BAs), i.e., tryptamine (TRY), beta-phenylethylamine (PEA), putrescine (PUT), cadaverine (CAD), histamine (HIS), tyramine (TYR), and spermidine (SPD) was studied. Under the adopted conditions, the sorbent showed good selectivity towards PUT, CAD, HIS and SPD (% extraction (%E)>96) while %E for TYR, TRY and PEA were 82.0, 78.9 and 46.4%, respectively. The sorbent could be used up to six extraction cycles for SPD, CAD and PUT and was applied to the determination of food samples ("budu", ketchup, orange juice, soy sauce) that were spiked with 20 mg L(-1) of the BAs. The extracted analytes were derivatized with dansyl chloride before the HPLC determination. With the exception of HIS and TYR in "budu" sample, reasonable recoveries were found for the other analytes in all the tested food samples.

Ethyl 4-(1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinolin-2-yl)benzoate.

The title compound, C(21)H(15)NO(4), was synthesized by reducing the Schiff base obtained from acenaphthenequinone and ethyl-4-aminobenzoate. The dihedral angle between the essentially planar 1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinoline ring system [maximum deviation = 0.061 (2) Å] and the benzene ring is 75.08 (10)°. In the crystal, mol-ecules are connected via weak inter-molecular C-H⋯O hydrogen bonds, forming a two-dimensional network. The ethyl group is disordered over two sets of sites with a refined occupancy ratio of 0.502 (12):0.498 (12).

(E)-4-Hy-droxy-N'-(4-hy-droxy-3-meth-oxy-benzyl-idene)benzohydrazide.

In the title compound, C(15)H(14)N(2)O(4), the N=C double bond has an E configuration. The two benzene rings make a dihedral angle of 28.59 (6)°. In the crystal, mol-ecules are linked into a three-dimensional network by inter-molecular N-H⋯O, O-H⋯O and C-H⋯O hydrogen bonds and stabilized by weak C-H⋯π inter-actions.