A facile synthesis of novel 1,4-benzoxazepin-2-one derivatives

An efficient and simple synthesis of 1,4-benzoxazepin-2-one derivatives has been achieved via the reaction of isoquinoline, activated acetylenes, and 1-(6-hydroxy-2-isopropenyl-1-benzofuran-yl)-1-ethanone in water without using any catalyst. This one-pot reaction occurs in high yields under mild conditions.     

An efficient one-pot method for the synthesis of novel ferrocene-triamide conjugates via pseudo five-component reaction

A simple and efficient one-pot synthesis of novel ferrocene-triamide conjugates from the reaction of ferrocenecarboxaldehyde with Meldrum’s acid and isocyanides in the presence of NH-containing compounds is described. This transformation proceeds through the creation of two CC bonds, two CN bonds, and one CO bond, leading to three peptide bonds, and presumably occurs via a domino sequence involving Knoevenagel condensation, [1+4] cycloaddition, deacetonation, and aminolysis reactions.     

An efficient one-pot synthesis of pyrimido[2,1-b][1,3]thiazine derivatives by reaction of activated acetylenes, thiouracils, and isocyanides

The reactive 1:1 zwitterionic intermediate, formed by the addition of isocyanides to dialkyl acetylenedicarboxylates, was trapped by thiouracils to yield a ketenimine intermediate, which cyclized and then rearranged to afford pyrimido[2,1-b][1,3]thiazines in good yields.     

Novel synthesis of alkoxy substituted oxa[9]helicenes by the reaction of helical quinone with alcohols

The reaction of helical quinone with alcohols in the presence of Brønsted acid such as para-toluenesulfonic acid (pTSA) or HCl proceeded smoothly to produce the corresponding alkoxy substituted oxa[9]helicenes in good yields.     

Theoretical study of valance photoelectron spectra of hypoxanthine, xanthine, and caffeine using direct symmetry-adapted cluster/configuration interaction methodology

UV photoelectron spectra of hypoxanthine, xanthine, and caffeine, up to 20 eV, were calculated and compared with the experimental spectra reported in literature. The calculations were performed using a novel version of the quantum mechanical symmetry-adapted cluster/configuration interaction (SAC-CI) method termed, direct SAC-CI. The Duning/Huzinaga valance double-zeta D95+(d,p) Gaussian basis set was also employed with this method. The ionization energies and intensities were calculated, and the corresponding spectral bands were assigned. Natural bonding orbital (NBO) calculations were employed for better spectral band assignment. The calculated ionization energies and intensities reasonably produced the experimental photoelectron spectra.     

Synthesis and applications of cross-linked poly(diallyldimethyl ammonium chloride) and its derivative copolymers as efficient phase transfer catalyst for nucleophilic substitution reactions

Cross-linked poly(diallyldimethylammonium chloride) and its derivative copolymers were synthesized and used as phase transfer catalyst in the nucleophilic substitution reaction especially halogen exchange reactions. In addition, the effect of hydrophilic-hydrophobic character of the polymers in the nucleophilic reactions was investigated.     

Synthesis,spectroscopy, and X-ray crystal structures of copper(II) complexes of the tridentate ONS ligand formed by condensation of 4,4,4-trifluoro-1-(2-thienyl)-2,4-butanedione with S-benzyldithiocarbazate

A new tridentate ONS ligand, H₂L, has been synthesized by condensing thenoyltrifluoroacetone(4,4,4-trifluoro-1-(2-thienyl)-2,4butaneanedione) with S-benzyldithiocarbazate and its structure determined by X-ray diffraction. In the solid state, the Schiff base exists as the ketoamine-thioketo tautomer but in solution and in the presence of copper(II), it converts to the enol-thiol form and deprotonates to give copper(II) complexes of formula, [CuL] and [CuLL¹] (L = doubly deprotonated form of the ligand; L¹ = py, bipy or phen] which have been characterized by magnetic, spectroscopic, and X-ray diffraction studies. An X-ray crystallographic analysis shows that [CuL(py)] has a square-planar geometry with the ligand coordinated to the copper(II) center via the enolate oxygen, the azomethinic nitrogen and the thiolate sulfur, the fourth coordination position being occupied by pyridine. The [CuL(bipy)] complex is five-coordinate with a structure close to square-pyramidal in which the Schiff base acts as a doubly deprotonated tridentate ONS ligand and bipy is bidentate.     

Ferric hydrogensulphate as a recyclable catalyst for the synthesis of fluorescein derivatives

Polycondensation reactions of phenols with phthalic anhydride were carried out in the presence of ferric hydrogensulphate under melt conditions. The reactions proceeded in short reaction times by using a catalytic amount of Fe(HSO₄)₃ and the corresponding fluorescein derivatives were obtained in high yields. The simplicity, scale-up, along with the use of an inexpensive, non-toxic, recyclable catalyst of an environmentally benign nature, are other remarkable features of the procedure. The absorption and emission properties of these fluorescein derivatives were studied.     

Self-assembly of tissue transglutaminase into amyloid-like fibrils using physiological concentration of Ca2+

Tissue transglutaminase (tTG or TG2) is a member of the transglutaminase family that catalyzes calcium dependent formation of isopeptide bonds. It has been shown that the expression of TG2 is elevated in neurodegenerative diseases such as Parkinson's, Huntington's, and Alzheimer's. We have investigated the self-assembly of TG2 in vitro. First, using software, hot spots, which are prone for aggregation, were identified in domain 2 of the enzyme. Next we expressed and purified recombinant TG2 and its truncated version that contains only the catalytic domain, and examined their amyloidogenic behavior in various conditions including different temperatures and pHs, in the presence of metal ions and Guanosine triphosphate (GTP). To analyze various stages leading to TG2 fibrillation, we employed various techniques including Thioflavin T (ThT) binding assay, Congo-Red, birefringence, Circular Dichroism (CD), 8-anilino-1-naphthalene sulfonic acid (ANS) binding, Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM). Our results indicated that using low concentrations of Ca(2+), TG2 self-assembled into amyloid-like fibrils; this self-assembly occurred at the physiological temperature (37 °C) and at a higher temperature (57 °C). The truncated version of TG2 (domain 2) also forms amyloid-like fibrils only in the presence of Ca(2+). Because amyloid formation has occurred with domain 2 alone where no enzymatic activity was shown, self-cross-linking by the enzyme was ruled out as a mechanism of amyloid induction. The self-assembly of TG2 was not significant with magnesium and zinc ions, indicating specificity of the self-assembly for calcium ions. The calcium role in self-assembly of TG2 into amyloid may be extended to other proteins with similar biophysical properties to produce novel biomaterials.     

Chemical wave studies in the bromate–pyrocatechol beads system

We studied the chemical wave activity of the pyrocatechol‐acidic bromate system in the presence of ferroin‐loaded beads. The wave activity lasted for more than 24 h while meandering spirals continued for up to 10 h. Rigid and meandering spiral waves were investigated. We have analyzed the wave propagation speed and spiral tip trajectory versus the initial concentrations of all reagents as well as the age of the solution. Wave velocity depends on [H⁺] and [BrO] concentrations by the relationship v=k[H⁺]^1/2[BrO]^1/2, which is in agreement with other studies. This system is ideal to study wave activity and spiral waves as it does not produce precipitates under the studied conditions. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 198–203, 2011