Ismail I. Althagafi

Allosteric Inhibitory Molecular Recognition of a Photochromic Dye by a Digestive Enzyme: Dihydroindolizine makes α-chymotrypsin Photo-responsive.

The structural-functional regulation of enzymes by the administration of an external stimulus such as light could create photo-switches that exhibit unique biotechnological applications. However, molecular recognition of small ligands is a central phenomenon involved in all biological processes. We demonstrate herein that the molecular recognition of a photochromic ligand, dihydroindolizine (DHI), by serine protease α-chymotrypsin (CHT) leads to the photo-control of enzymatic activity. We synthesized and optically characterized the photochromic DHI. Light-induced reversible pyrroline ring opening and a consequent thermal back reaction via 1,5-electrocyclization are responsible for the photochromic behavior. Furthermore, DHI inhibits the enzymatic activity of CHT in a photo-controlled manner. Simultaneous binding of the well-known inhibitors 4-nitrophenyl anthranilate (NPA) or proflavin (PF) in the presence of DHI displays spectral overlap between the emission of CHT-NPA or CHT-PF with the respective absorption of cis or trans DHI. The results suggest an opportunity to explore the binding site of DHI using Förster resonance energy transfer (FRET). Moreover, to more specifically evaluate the DHI binding interactions, we employed molecular docking calculations, which suggested binding near the hydrophobic site of Cys-1-Cys-122 residues. Variations in the electrostatic interactions of the two conformers of DHI adopt unfavorable conformations, leading to the allosteric inhibition of enzymatic activity.

Synthesis, characterization, POM analysis and antifungal activity of novel heterocyclic chalcone derivatives containing acylated pyrazole

A series of heterocyclic chalcone derivatives (4a–h) were synthesized and characterized by IR, 1H and 13C NMR as well as MS. All the synthesized compounds were evaluated for their antifungal activity on Candida albicans and Aspergillus niger. The assay revealed that compounds 3d and 4f showed significant activity against both tested fungal strains. POM analyses showed that the compounds are highly lipophyllic but present a potential bioactivity. Moreover, they have no NH–O or N–HO intramoleculcular interaction which is a crucial parameter controlling solubility of compounds possessing these encouraging pharmaceutical properties. This series gives us an important lesson in drug design: We should take the balance of hydrosolubility/lipophilicity into consideration. POM analyses were in agreement with the idea of coexistence of two combined antifungal N,O and O,S-pharmacophore sites for series 4a–h. On the other hand, two coexistents and identical N,Cl-pharmacophore sites have been identified for Fluconazole.Graphical Abstract

A convenient regioselective synthesis of spirooxindolinopyrrolizidines incorporating the pyrene moiety through a [3 + 2]-cycloaddition reaction

Abstract A facile one-pot synthesis of spirooxindolinopyrrolizidines incorporating the pyrene moiety was accomplished in good yields through a 1,3-dipolar cycloaddition reaction of 3-aryl-1-(pyren-1-yl)prop-2-en-1-one derivatives with in situ-generated azomethine ylides.

Kinetics and Mechanistic Approach to Palladium (II)-Catalyzed OxidativeDeamination and Decarboxylation of Leucine and Isoleucine byAnticancer Platinum (IV) Complex in Perchlorate Solutions

Oxidations of two aliphatic α-amino acids (AA), namely, leucine and isoleucine by hexachloroplatinate (IV) as an anticancer platinum (IV) complex has been studied using a spectrophotometric technique in perchlorate solutions in the presence of palladium (II) catalyst at a constant ionic strength of 1.0 mol dm-3 and at 25°C. The reactions did not proceed in the absence of the catalyst. The reactions of both amino acids showed a first order dependence on both [PtIV] and [PdII], and less than unit order dependences with respect to both [AA] and [H+]. Increasing ionic strength and dielectric constant of the reactions medium increased the rates of the reactions. A probable oxidations mechanism has been suggested and the rate law expression has been derived. Both spectral and kinetic evidences revealed formation of 1:1 intermediate complexes between AA and PdII before the rate-controlling step. The oxidation products of the investigated amino acids were identified as the corresponding aldehyde, ammonium ion and carbon dioxide. The activation parameters of the second order rate constants were evaluated and discussed

Precursor directed regioselective synthesis of partially reduced benzo[e]indene through oxidative cyclization and benzo[h]quinolines

We have reported a simple, unprecedented base promoted synthesis of 7-substituted-1-(2-cyano-phenyl/phenyl)-3-sec amino-4,5-dihydro-1H-benz[e]indene-1,2-dicarbonitriles by reaction of 2-oxo-4-sec amino-5,6-dihydro-2H-benzo[h]chromene-3-carbonitriles and 2-cyanomethyl-benzonitrile/phenyl-acetonitrile under basic conditions at 100 °C. This reaction involves ring opening of 2-oxo-4-sec amino-5,6-dihydro-2H-benzo[h]chromene-3-carbonitrile by a carbanion generated in situ from 2-cyanomethylbenzonitrile/phenyl-acetonitrile followed by oxidative cyclization to afford the desired product. Alternatively, reaction of 6-aryl-4-sec amino-2H-pyran-2-one-3-carbonitriles and 2-cyanomethyl-benzonitrile under basic conditions provides functionalized benzo[h]quinolines. The structure of the synthesized compound was confirmed by single crystal X-ray.

Kinetics and Mechanism of Oxidation of Vanillin by Chromium(VI) inSulfuric Acid Medium

The kinetics of oxidation of vanillin (VAN) by chromium(VI) in sulfuric acid medium was studied by a spectrophotometric technique. The reaction exhibited a first order dependence with respect to [Cr(VI)] and fractionalfirst orders with respect to [VAN] and [H+]. Varying ionic strength or dielectric constant of the reaction medium had no significant effect on the oxidation rate. The proposed mechanism includes an intermediate complex formation between vanillin and chromium(VI) before the rate-determining step. The final oxidation product of vanillin was identified by both spectral and chemical analysis as vanillic acid. The suitable rate law has been deduced. The reaction constants included in the various steps of the suggested mechanism have been evaluated. The activation parameters of the rate constant of the rate-determining step of the mechanism and the thermodynamic quantities of the equilibrium constant have been evaluated and discussed.

Microwave-assisted and thermal synthesis of nanosized thiazolyl-phenothiazine derivatives and their biological activities

Efficient synthesis of a series of nanosized phenothiazine derivatives incorporating thiazole moiety was achieved using microwave irradiation as well as thermal conditions. Reaction of 2-(1-(10H-phenothiazin-2-yl)ethylidene)hydrazine-1-carbothioamide with various types of hydrazonoyl halide or α-haloketone afforded corresponding thiazolyl phenothiazines in good to excellent yield. Mass, 1H and 13C nuclear magnetic resonance (NMR), ultraviolet–visible (UV–Vis), X-ray diffraction (XRD), and elemental analyses confirmed the structure of all the new derivatives. The reaction progressed under microwave irradiation in shorter reaction time with higher yield compared with the conventional method. The antimicrobial and antitumor activities of selected derivatives were investigated, revealing that some of them showed high potency compared with standard references.

Synthesis of Pyrazolone Derivatives and Their Nanometer Ag(I) Complexes and Physicochemical, DNA Binding, Antitumor, and Theoretical Implementations

Four pyrazolone derivatives and their corresponding silver complexes were synthesized and characterized. Based on elemental analysis, 1 : 2 (M : L) molar ratio was suggested for all inspected complexes. 1H, 13C NMR, mass, UV-Vis, TGA, and IR were the spectral tools used for describing the formulae. Moreover, XRD patterns and SEM pictures were used to evaluate the particle sizes which appeared strongly in nanometer range. CT-DNA study is the major consideration in this study, to test the interacting ability of all synthesized cationic complexes towards cell DNA. Each binding constant was computed and correlated with the Hammett sigma constant. Antitumor activity was examined upon three carcinoma cell lines (MCF-7, HepG2, and HCT116). The high efficiency was recorded towards MCF-7 (breast carcinoma) cell line. Kinetic studies yield essential parameters to assert on the rule of metal atom on thermal feature of organic compounds. Molecular modeling was implemented to optimize the structures of compounds. Also, molecular docking was achieved to obtain a clear view about proposed drug behavior within the affected cells. This was achieved through comparing the calculated internal energy values of all docking complexes. All the tested compounds displayed a significant interaction with breast cancer protein (strong matching with practical result) followed by DNA polymerase protein.

Cholinesterase Inhibitory Activity of Some semi-Rigid Spiro Heterocycles: POM Analyses and Crystalline Structure of Pharmacophore Site

BACKGROUND Cholinesterase family consists of two sister enzymes; acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) which hydrolyze acetylcholine. Since deficit of acetylcholine has been evidenced in patients of Alzheimers disease (AD), cholinesterase inhibitors are currently the most prescribed drugs for the treatment of AD. OBJECTIVE our aim in this article was to investigate the inhibitory potential of five known compounds (2-6) with spiro skeleton against AChE and BChE using ELISA microplate assays. In addition to their ChE inhibitory effect, their physico-chemical properties were also calculated. Moreover, the present work aims at investigating the charge/geometrical effect of a hypothetical pharmacophore or bidentate site in a bioactive group, on the inhibition efficiency of spiro compounds 2-6 by using Petra/Osiris/ molinspiration (POM) and X-ray analyses. METHOD In the present study, five compounds (2-6) with spiro skeleton have been synthesized and tested in vitro for their inhibitory potential against AChE and BChE using ELISA microtiter plate assays at 25 µg/mL. RESULTS Results revealed that three of the spiro compounds tested exert more than 50% inhibition against one of cholinesterases. Compound 5 displayed 68.73 ± 4.73% of inhibition toward AChE, whereas compound 6 showed 56.17 ± 0.83% of inhibition toward BChE; these two previously synthesized compounds have been the most active hits. CONCLUSIONS Our data obtained from screening of compounds 2-6 against the two cholinesterases indicate that three of these show good potential to selectively inhibit AChE or BChE. Spiro compounds 2, 5, and 6 exhibited the most potent activity of the series against AChE or BChE with inhibition values in the range 55-70%.

Novel pyridine-based Pd(II)-complex for efficient Suzuki coupling of aryl halides under microwaves irradiation in water

Suzuki C–C cross-coupling of aryl halides with aryl boronic acids using new phosphene-free palladium complexes as precatalysts was investigated. A pyridine-based Pd(II)-complex was used in open air under thermal as well as microwave irradiation conditions using water as an eco-friendly green solvent.