Enantioselective adsorption of dipeptides on chiral stationary phases with grafted macrocyclic antibiotics using glycylaspartic acid as an example

The chromatographic behavior and adsorption of enantiomers of glycylaspartic acid on the Nautilus-E chiral stationary phase with grafted eremomycin antibiotic were studied. Acetate buf er mixtures with variable pH prepared in a water—methanol mixed solvent (volume ratio 60 : 40) were used as acetate buf ers. The retention of Gly—Asp was found to be enantioselective and depending on the ratio of various ionic forms of dipeptide in the mobile phase. The ratio is determined by the pH. A model of adsorption equilibrium assuming independent binding of diverse ionic forms with the stationary phase, which is characteristic of energy uniformity, was proposed. This model is well consistent with the experimental data. Features of application of the equilibrium dispersion and transport dispersion dynamic elution models for the determination of the adsorption isotherms by the inverse method are discussed.

     

Marker transport in a composite vortex

Using a coloring method, the pattern of the transport of a compact spot of markers in a composite vortex created by a uniformly rotating disk, which is located on the bottom of a cylindrical tank, is investigated. The markers were formed by droplets of an aqueous solution of uranyl or ink, which fell down on the free surface of the fluid. In a quiescent fluid, the spot of the markers was transformed into a slowly sinking cascade of vortices. The markers introduced at the center of the cavity on the composite-vortex surface formed a spiral branch. For a non-central introduction of the markers, two spiral branches were formed, one growing in the direction of the fluid rotation and the other growing in the direction, opposite to the rotation. The markers penetrate into the interior of the composite vortex along isolated cylindrical surfaces. The geometrical parameters of the flow are presented.     

Tris(1-alkylindol-3-yl)methylium salts as a novel class of antitumor agents

Tris(1-alkylindol-3-yl)methanes were obtained and oxidized into tris(1-alkylindol-3-yl)methylium salts. The resulting salts are more toxic to cultured tumor cells than to non-tumor ones. The cytotoxicity of tris(1-alkylindol-3-yl)methylium salts depends on the length of the substituent at the N atom of the heterocycle, increasing from an N-unsubstituted derivative toward N-butyl- and N-pentyl derivatives. A further increase in the length of the N-alkyl substituent lowers the cytotoxicity. The cytotoxicity of tris(1-alkylindol-3-yl)methylium salts for tumor cells correlates with their antibacterial and antifungal activity. Tris(1-alkylindol-3-yl)methylium salts produced a cytocide effect on Gram-positive microorganisms and the most active compounds, on Gram-negative microorganisms as well. Similar patterns of the structure—activity relationship of N-alkylated tris(indol-3-yl)methylium derivatives, which was observed for various lines of tumor cells, bacteria, and fungi, suggest the general character of the mechanisms of the death of prokaryotic and eukaryotic cells induced by these compounds.     

Five-membered 2,3-dioxo heterocycles: XCVIII. [4 + 2]-cycloaddition of alkyl vinyl ethers to 3-aroyl-1H-pyrrolo[2,1-c][1,4]benzoxazine-1,2,4-triones. A new synthetic approach to heteroanalogs of 13(14→8)-abeo steroids

3-Aroyl-1H-pyrrolo[2,1-c][1,4]benzoxazine-1,2,4-triones reacted with alkyl vinyl ethers according to the [4 + 2]-cycloaddition pattern with formation of substituted (1S*,16R*)- and (1R*,16R*)-16-alkoxy-14-aryl-3,15-dioxa-10-azatetracyclo[8.7.0.0^1,13.0^4,9]heptadeca-4,6,8,13-tetraene-2,11,12-triones. The structure of (1S*,16R*)-7-chloro-16-ethoxy-14-phenyl-3,15-dioxa-10-azatetracyclo[8.7.0.0^1,13.0^4,9]heptadeca-4,6,8,13-tetraene-2,11,12-trione was determined by X-ray analysis. A new synthetic approach was developed to heteroanalogs of 13(14→8)-abeo steroids, substituted 3,15-dioxa-10-azatetracyclo[8.7.0.0^1,13.0^4,9]heptadecanes.     

Effect of the Composition of Initial Components and the Conditions of Activation on the Mechanochemical Synthesis of Magnesium–Aluminum Layered Double Hydroxides

The MgAl layered double hydroxides (LDHs) were prepared by two-stage synthesis, which included mechanochemical activation at the first stage and the interaction of the resulting sample with distilled water at the second stage. The influence of the material of grinding bodies (steel and ceramics), the conditions of activation (activation time and the centripetal acceleration of balls), and the nature of initial compounds on the phase composition of the resulting products was investigated. It was established that the formation of a single-phase MgAl LDH was observed upon mechanochemical activation with the use of steel grinding bodies at an acceleration of 1000 m/s² for 30 min. The samples prepared by a traditional coprecipitation method and a method that included a stage of mechanochemical activation possessed identical structural parameters. However, the mixed oxides formed upon the calcination of LDHs synthesized by mechanochemical activation were characterized by a more uniform pore space with a pore diameter of 4–5 nm with a developed specific surface.     

Divergent synthesis of (quinoxalin-2-yl)-1,3-oxazines and pyrimido[1,6-a]quinoxalines via the cycloaddition reaction of acyl(quinoxalinyl)ketenes

A facile synthetic approach towards two distinct quinoxaline-based heterocyclic scaffolds has been developed from the cycloaddition of acyl(quinoxalinyl)ketenes with carbodiimides. The described reaction represents the first example of a divergent synthesis based on acyl(quinoxalinyl)ketenes providing (quinoxalin-2-yl)-1,3-oxazines or pyrimido[1,6-a]quinoxalines depending on the type of the acyl substituent in the ketenes. The key reactants, acyl(quinoxalinyl)ketenes, are generated in situ via the thermal decarbonylation of readily available pyrroloquinoxaline oxo-derivatives. The proposed diversity-oriented synthesis provides facile access to a library of skeletally diverse pharmaceutically interesting quinoxaline-based heterocycles from inexpensive reagents.     

Solvent-free cyclopalladation on silica gel

Tertiary, secondary and primary benzylamines, as well as structurally different oxazolines readily reacted with Pd(OAc)₂ on silica gel to form cyclopalladated complexes containing a five or six-membered palladacycle with a (sp²)C-Pd or (sp³)C-Pd bond. The complexes were obtained in 45-98% yield, which is comparable with or exceeds the yields reported for preparation of the same compounds in solution. Aliphatic (sp³)C-H bond activation took place in the cyclopalladation of (S)-2-tert-butyl-4-phenyl-2-oxazoline on SiO₂ leading to the exclusive formation of the corresponding endo palladacycle, whereas two products were reported for the same reaction performed in AcOH.     

Alkoxy compounds

Twenty-six previously unreported 5-alkoxymethyl-2,5-dialkyl-1,3-dioxanes have been synthesized by the condensation of 2-alkoxymethyl-2-alkylpropane-1,3-diols with aldehydes. It has been shown by an analysis of the PMR spectra of these dioxanes that the 1,3-dioxanes considered are mixtures of two stereoisomers. In some cases these mixtures have been resolved into the individual isomers by vacuum fractionation in efficient columns. The configurations and conformations of the stereoisomeric 5-alkoxymethyl-2,5-dialkyl-1,3-dioxanes have been established by the NMR method; it has been shown that the lower-boiling isomers have the trans configuration and predominantly the chair conformation and the higherboiling isomers the cis configuration and predominantly an unsymmetrical boat conformation.For part XX, see [7].     

Magnetic anisotropy of Tb-Co amorphous films

A systematic investigation of the magnetic properties of Tb-Co amorphous films prepared using radio-frequency ion sputtering in a uniform magnetic field has been carried out. The main regularities of the change in the magnetic anisotropy parameters as a function of the composition (8–43 at % Tb), measurement temperature (5–350 K), and annealing temperature (up to 200°C) have been established. It has been shown that their interpretation can be performed within the framework of the model that takes into account the fluctuating local magnetic anisotropy of the terbium ions, columnar microstructure, and anisotropy of elastic stresses.     

The thermodynamic parameters of sorption and enantioselectivity of the chiral smectic liquid crystal 2-methylbutyl ester of 4-(4-decyloxybenzylideneamino)-cinnamic acid

The thermodynamic characteristics of sorption of n-alkanes, arenes, aldehydes, monoatomic alcohols, and optical isomers of camphene and butanediol-2,3 by a chiral smectic liquid crystal, 2-methylbutyl ester of 4-(4-decyloxybenzylideneamino)-cinnamic acid, from the gas phase were studied over the temperature range including the S*_C and S*_A mesophases and isotropic phase. The standard and excess thermodynamic functions of sorption were determined for 26 sorbates of the classes of substances specified. The S*_C and S*_A mesophases exhibited selectivity with respect to the separation of para and meta xylenes (α _p/m = 1.06–1.07, 90–108°C) and pronounced enantioselectivity (α_R/S = 1.05–1.09, 87–108°C). The helically twisted structure of the smectic liquid crystal was shown to play an important role in the mechanism of the chiral recognition of optical isomers of polar and low-polarity compounds under gas-liquid chromatography conditions.