Multi-purpose functionality for the structural elaboration of the piperazine-2,5-dione motif

Mild methods for controlled C- and N-alkylation of 3-benzyloxycarbonylpiperazine-2,5-diones are reported. The benzyloxylcarbonyl substituent can also serve as latent functionality for N-acyliminium ion formation and subsequent trapping enables installation of new carbon and/or heteroatom substituents.     

Synthesis of biindolyls via palladium-catalyzed reactions

An unprecedented synthesis of a range of high value homo- and heterobiindolyls is presented. The one-pot Miyaura borylation and subsequent Suzuki-Miyaura coupling sequence allows for the construction of the highly sterically congested C-C bond between two bromoindoles in modest to good overall yields.     

Preconditioned iterative methods for coupled discretizations of fluid flow problems

Computational fluid dynamics, where simulations require largecomputation times, is one of the areas of application of highperformance computing. Schemes such as the SIMPLE (semi-implicitmethod for pressure-linked equations) algorithm are often usedto solve the discrete Navier-Stokes equations. Generally theseschemes take a short time per iteration but require a largenumber of iterations. For simple geometries (or coarser grids)the overall CPU time is small. However, for finer grids or morecomplex geometries the increase in the number of iterationsmay be a drawback and the decoupling of the differential equationsinvolved implies a slow convergence of rotationally dominatedproblems that can be very time consuming for realistic applications.So we analyze here another approach, DIRECTO, that solves theequations in a coupled way. With recent advances in hardwaretechnology and software design, it became possible to solvecoupled Navier-Stokes systems, which are more robust but implyincreasing computational requirements (both in terms of memoryand CPU time). Two approaches are described here (band blockLU factorization and preconditioned GMRES) for the linear solverrequired by the DIRECTO algorithm that solves the fluid flowequations as a coupled system. Comparisons of the effectivenessof incomplete factorization preconditioners applied to the GMRES(generalized minimum residual) method are shown. Some numericalresults are presented showing that it is possible to minimizeconsiderably the CPU time of the coupled approach so that itcan be faster than the decoupled one.     

Preparation, structural analysis and dielectric properties of Bi x La1−x FeO3 perovskite

Rare earth element substituted bismuth ferrites (BiFeO₃) are of enormous importance as magnetoelectric materials. The polycrystalline samples of Bi _x La_1−x FeO₃ (x=0, 0.2, 0.4, 0.6, 0.8) were prepared by solid-state reaction using standard ceramic method. The single-phase formation of these compounds was confirmed by X-ray diffraction (XRD) studies. The samples with x=0, 0.2, 0.4, 0.6 are found to be orthorhombic while the sample with x=0.8 is triclinic. The dielectric constant (ε′) and dissipation factor (tan δ) were measured in the frequency range 100 Hz to 1 MHz at room temperature and as a function of temperature at certain fixed frequencies (1 kHz, 10 kHz, 100 kHz, 1 MHz). All the samples showed dielectric dispersion. The dielectric constant with temperature shows a broad peak; the peak temperature shifts with frequency which reflects the relaxor-type behavior. The peak above 600 K in the measured temperature range corresponds to antiferromagnetic ordering temperature (Néel temperature). The broadness of the peak changes with composition. The ac conductivity as well as ε′ are found to be maximum for the sample x=0.2 at room temperature.     

Concise, efficient and practical assembly of bromo-5,6-dimethoxyindole building blocks

A concise, efficient and simple route to a series of bromoindole building blocks is described. The synthetic routes are highlighted by purification-free preparation of o-nitrocinnamate intermediates and clean, modified Cadogan indole syntheses. The scope of this indole synthesis has been explored and expanded through the use of a range of solvents and easily removable phosphine reagents.     

The synthetic versatility of alkoxycarbonyl- and hydroxymethyl-piperazine-2,5-diones

Alkoxycarbonylpiperazine-2,5-diones are versatile precursors for the α-functionalisation of piperazine-2,5-diones. The alkoxycarbonyl group activates the α-carbon position to alkylation reactions and this provides a mild and selective method for the extension of the carbon framework of piperazine-2,5-diones. In addition, the alkoxycarbonyl group can be converted to the carboxy group, which in turn can be ‘deleted’ or manipulated for the installation of carbon and/or heteroatom substituents where desired, the latter via N-acyliminium chemistry. We also demonstrate that hydroxymethylpiperazine-2,5-diones complement carboxypiperazinediones as precursors for the generation of N-acyliminium ions.     

Impurity analysis of gentamicin bulk samples by improved liquid chromatography-ion trap mass spectrometry

Several gentamicin bulk samples from different origins were investigated using an LC/MS method.LC equipped with ion trap MS with positive ionization was performed on a Capcell Pak C18(AQ) column with the mobile phase containing 50 mM trifluoroacetic(TFA) and methanol.Impurities present in batches of gentamicin bulk samples were elucidated and compared according to their fragmentation behavior.In total seventeen impurities present in samples,five impurities were not elucidated and two compounds were identifi...     

Highly efficient catalytic routes to spiroketal motifs

The versatile and efficient synthesis of a variety of spiroketal motifs via the double intramolecular hydroalkoxylation of aliphatic and aromatic alkyne diols was achieved using simple and readily accessible Ir(I) and Rh(I) cyclooctadiene complexes as catalysts.