Unique cascade ring-opening/cyclization reaction of azlactones and DBU or DBN: Synthesis of new pyrrolam A analogues

1-Azabicyclo[3.3.0]oct-3-en-2-one derivatives were synthesized efficiently through the facile cascade reaction of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) or 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) with arylidene azlactones. This research provides a straightforward procedure for the synthesis of a novel class of multicyclic semi-alkaloids which shows good antimicrobial activity. Under catalyst-free, mild, and solventless condition, a wide range of fused tricyclic derivatives was obtained in high yields.     

Tributylammonium Halochromates/silica Gel:Simple Reagents for Oxidative Coupling of Thiols to Symmetrical Disulfides

New orange solid tributylammonium halochromates, (C₄H₉)₃N⁺CrO₃X^?, TBAXC (X=F, Cl) are easily synthesized by the reaction of tributylammonium fluoride and chloride with CrO₃ in a 1:1 molar ratio in the presence of HF and HCl. Tributylammonium halochromates(VI) are versatile reagent for the effective and selective oxidation of organic substrates. Silica gel supported TBAFC and TBACC are versatile reagents for the effective and selective oxidation of organic substrates, in particular, thiols, under mild conditions. Considerable improvements are observed in the presence of the absorbent, making the work‐up much more convenient.     

Reactions of cisplatin hydrolytes, cis-[Pt(15NH3)2(H2O) 2]2+, with N-acetyl-L-cysteine

The reaction of cis-[Pt(¹⁵NH₃)2(H₂O) ₂] ²⁺ (3) with N-acetylcysteine [H₃accys] was investigated in aqueous solution. In this reaction, the ammine in the platinum complex formed was liberated. A mono-dentate sulfur-boundplatinum(II) product cis-[Pt(¹⁵NH₃)₂(H₂O)(H2accys-S)]⁺ (7) and six-membered che-late ring complex cis-[Pt(¹⁵NH₃)₂ (Haccys-S,O)] (8) were formed in solution. The dinuclear sulfur-bridged complex 9, giving a broad peak in ¹⁵N NMR, was also observed, but only present in very tiny amounts. The mass spectrometry (ES-MS) was undertaken from this re action, and the product detected was only the dinuclear sulfur bridged platinum species and species related to it by ammine loss.     

Enantioselective synthesis of bicylco[3.2.1]octan-8-ones using a tandem Michael-Henry reaction

Bicyclo[3.2.1]octan-8-ones have been prepared from a tandem Michael-Henry reaction between cyclohexane-1,2-diones and nitroalkenes using a quinine-derived thiourea as the catalyst. Although four stereogenic centers were created during the reaction, only two diastereomers were obtained in good diastereoselectivity and high enantioselectivity (92-99% ee). When 3-methylcyclohexane-1,2-dione (R¹=Me) was used as the substrate, only the regioisomeric product of the corresponding thermodynamic enolate was obtained.     

TiO2 as a Reusable Catalyst for the One‐Pot Synthesis of 3,4‐Dihydropyrimidin‐2(1H)‐ones under Solvent‐Free Conditions

An efficient solvent‐free method for the synthesis of various 3,4‐dihydropyrimidin‐2(1H)‐ones using TiO₂ as a recyclable heterogeneous catalyst is described. Compared to known methods, satisfactory results are obtained with excellent yields, short reaction times, and simplicity in the experimental procedure.     

Benign synthesis of carboxamide ligands,H2Me2bqb and H2Me2bpb. Preparation,characterization and electrochemistry of Ni(II) complexes: The crystal structure of [Ni(Me2bqb)]

A novel and highly efficient approach for the synthesis of H₂Me₂bqb and H₂Me₂bpb using ionic liquid as an environmentally benign reaction medium has been developed, eliminating the need for the pyridine as a toxic solvent. The Ni(II) complex of the dianionic ligand Me₂bqb²⁻, [Me₂bqb²⁻ = 1,2-bis(quinoline-2-carboxamide)-4,5-dimethyl-benzene dianion], has been synthesized and characterized by elemental analyses and spectroscopic methods, and the crystal and molecular structure of [Ni(Me₂bqb)] (1), has been determined by X-ray crystallography. The complex exhibits distorted square-planar NiN₄ coordination geometry with two short and two long Ni–N bonds (Ni–N ∼1.85 and ∼1.96 Å, respectively). The electrochemical behavior of [Ni(Me₂bqb)] (1), has been studied by cyclic voltammetry and compared with the analogous complex, [Ni(Me₂bpb)] (2).     

Metallation of tetradentate N<Subscript>2</Subscript>O<Subscript>2</Subscript> Schiff base with Mn(II), Co(II), Cu(II) and Zn(II): synthesis,characterization and formation constants measurement

Four Schiff base ligands, salabza-H₂ = N,N′-bis(salicylidene)-2-aminobenzylamine, were synthesized by condensation of one mole of 2-aminobenzylamine and two moles of salicylaldehyde and/or two moles of substituted salicylaldehyde (5-OMe, 5-Br, 5-NO₂). All the four Schiff bases and their Mn(II), Co(II), Cu(II) and Zn(II) complexes are characterized by UV-Vis, FT-IR, ¹H NMR spectroscopy, mass spectrometry and elemental analysis. The formation constants and the Gibbs free energies were measured spectrophotometrically for 1:1 complexes in methanol in constant ionic strength (I = 0.1 mol dm⁻³ NaClO₄) and at 25°C. The data refinement was carried out with the SQUAD program. The trend of formation constants of H₂L¹ with M(II) follows the order: Mn(II) (3.97) < Zn(II) (4.30) < Co(II) (4.89) < Cu(II) (5.73)     

Palladium-catalyzed asymmetric allylic alkylation (AAA) with alkyl sulfones as nucleophiles

An efficient palladium-catalyzed AAA reaction with a simple α-sulfonyl carbon anion as nucleophiles is presented for the first time. Allyl fluorides are used as superior precursors for the generation of π-allyl complexes that upon ionization liberate fluoride anions for activation of silylated nucleophiles. With the unique bidentate diamidophosphite ligand ligated palladium as catalyst, the in situ generated α-sulfonyl carbon anion was quickly captured by the allylic intermediates, affording a series of chiral homo-allylic sulfones with high efficiency and selectivity. This work provides a mild in situ desilylation strategy to reveal nucleophilic carbon centers that could be used to overcome the pK_a limitation of “hard” nucleophiles in enantioselective transformations.

A variety of “hard” α-sulfonyl carbanions of aryl, heteroaryl and alkyl sulfones were successfully employed as nucleophiles in palladium-catalyzed asymmetric allylic alkylation with excellent enantioselectivities.     

Vibration analysis of nanorings using nonlocal continuum mechanics and shear deformable ring theory

In this article, we use shear deformable ring theory (SDRT) for the analysis of free in-plane vibration of nanorings based on nonlocal elasticity theory. The equations of motion of the nanoring are derived for the aforementioned problem by considering the small scale effect. Analytical solutions for the natural frequencies of the nanorings are presented. It is shown that the nonlocal effects play an important role in the vibration of nanorings and cannot be neglected. The effects of the small scale on the natural frequencies considering various parameters such as the radius of the nanoring, the thickness of the nanoring and mode numbers are investigated.     

Errorless and errorful learning modulated by transcranial direct current stimulation

Background

Caspase-3 is one of the most downstream enzymes activated in the apoptotic pathway. In caspase-3 deficient mice, loss of cochlear hair cells and spiral ganglion cells coincide closely with hearing loss. In contrast with the auditory system, details of the vestibular phenotype have not been characterized. Here we report the vestibular phenotype and inner ear anatomy in the caspase-3 deficient (Casp3 ^-/- ) mouse strain.

Results

Average ABR thresholds of Casp3 ^-/- mice were significantly elevated (P < 0.05) compared to Casp3 ^+/- mice and Casp3 ^+/+ mice at 3 months of age. In DPOAE testing, distortion product 2F1-F2 was significantly decreased (P < 0.05) in Casp3 ^-/- mice, whereas Casp3 ^+/- and Casp3 ^+/+ mice showed normal and comparable values to each other. Casp3 ^-/- mice were hyperactive and exhibited circling behavior when excited. In lateral canal VOR testing, Casp3 ^-/- mice had minimal response to any of the stimuli tested, whereas Casp3 ^+/- mice had an intermediate response compared to Casp3 ^+/+ mice. Inner ear anatomical and histological analysis revealed gross hypomorphism of the vestibular organs, in which the main site was the anterior semicircular canal. Hair cell numbers in the anterior- and lateral crista, and utricle were significantly smaller in Casp3 ^-/- mice whereas the Casp3 ^+/- and Casp3 ^+/+ mice had normal hair cell numbers.

Conclusions

These results indicate that caspase-3 is essential for correct functioning of the cochlea as well as normal development and function of the vestibule.