Russian Chemical Bulletin最新文献

Computational modeling of dihydropyrene derivatives bearing 4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl-3-oxide (1), tert-butyl nitroxide (2), and fluorenyl (3) radical groups, as well as various substituents (H, CN, Me) at the C(15) and C(16) atoms was carried out in terms of the density functional theory (DFT) at the B3LYP-D3BJ/6-311++G(d,p) level and using the SA-CASSCF/NEVPT2 method. It was established that isomerization of compounds 3 is accompanied by a spin-state switchng, which manifests itself as a transition from the diamagnetic cyclic dihydropyrene (dhp) form to the paramagnetic open (cyclophanediene, cpd) one. Time-dependent DFT calculations of the electronic spectra of the dhp and cpd isomers of the compounds bearing fluorenyl groups revealed the presence of non-overlapping bands. The results obtained give grounds to expect that photo-controlled spin-state changes in dihydropyrenes 3 are feasible and these systems can be considered as molecular magnetic switches.

This mini-review covers the methods for obtaining enantiomers of the anticoagulant Warfarin and its closest analogs, including Acenocoumarol, Fumarin, and Coumachlor. The methods are based on the use of enzymes, metal complexes with chiral ligands, and enantiomerically pure organocatalysts. A comparison of the efficiency and practical applicability was carried out for the proposed strategies in terms of their possible use in the pharmaceutical industry.

This paper presents data from a study on the one-pot consecutive double arylation of monosubstituted alkenes with two competing aryl halides. The joint analysis of patterns of the reaction differential selectivity for the products of mono- and double arylation of alkene by the competing aryl halides was carried out. The obtained results cannot be explained in the framework of the commonly accepted linear mechanism that assumes the consecutive activation of aryl halide and alkene in one catalytic cycle. The observed patterns are consistent with the hypothesis of the cooperative nonlinear mechanism of catalysis that suggests the activation of alkene and aryl halide in two coexisting catalytic cycles conjugated by the nonlinear elementary step of interaction of two palladium-containing intermediates.

Convenient syntheses of functionalized PCHNH-containing amines have been developed based on the nucleophilic addition of trivalent phosphorus acid esters to various imines. Subsequent acylation of these amines at the NH fragment opens the way to promising types of amides and sulfonamides of functionalized aminomethyl-substituted organophosphorus acids. The resulting compounds contain polar amide (sulfonylamide) and phosphoryl moieties, have potential biological activity, and are also of interest as effective extractants and polydentate chelating ligands.

The synthesis of a mixture of polyprenyl monoesters of 1,2,4,5-benzenetetracarboxylic (pyromellitic) acid, potential inhibitors of pathogenic viruses replication, was described for the first time. A more efficient protocol for obtaining a mixture of (±)-2,3-dihydropoly-prenylpyromellitates was proposed compared to the previously described one.

Two accesses to N-Boc-(S)-prolinonitrile (tert-butyl (S)-2-cyanopyrrolidine-1-carboxylate) from (S)-l-proline, namely, a three-step procedure that involves synthesis of intermediate N-Boc-l-Pro-NH₂ and a six-step procedure that excludes the synthesis of this intermediate, were compared. The second approach despite more steps is easier to accomplish and provides the target compound in 47% yield based on the starting l-proline.

A new mechanism of singlet-triplet conversion of electron pairs of diamagnetic substrates in the active sites of enzymes is proposed to explain the effect of nuclear spins and strong magnetic fields on the enzymatic synthesis of adenosine triphosphate (ATP) in vitro and in vivo. It is shown that the Fermi contact interaction, inducing a redistribution of electron density in enzyme-substrate complexes ²⁵Mg-ADP—ATPase, enables a decrease of the negative charge on the terminal groups of ADP. Thus, the nuclear spin of the ²⁵Mg isotope decreases the Coulomb repulsion of the negatively charged fragments of the substrates and increases the rate of the enzymatic formation of ATP. The theoretical results explain the experimentally observed effect of the nuclear spin of the ²⁵Mg isotope on the intracellular synthesis of ATP in Escherichia coli bacteria in strong magnetic fields.

Analysis of absorption and fluorescence spectra at 293 and 77 K, as well as fluorescence excitation spectra of bis(aza-18-crown-6)-containing dibenzylidenecyclohexanone (CD6) and its complexes confirms the presence of photorecoordination in CD6•(Mⁿ⁺)₂ (M = Ba²⁺, Sr²⁺, Ca²⁺, K⁺). The process is completely blocked in low-temperature butyronitrile glass. Coordination of the metal cation to the carbonyl group of the CD6 molecule is accompanied by fluorescence enhancement, while coordination of the cations to the aza-18-crown-6 ether residues, on the contrary, leads to its quenching. In the case of the complexes CD6•(Mⁿ⁺)₂, correlations were observed between the stability constants, the values of the blue shifts in the absorption spectra, the red shifts in the fluorescence spectra, and the diameters of the cations. The CD6 dienone forms complexes with the compositions CD6•Mⁿ⁺, CD6•(Mⁿ⁺)₂, and Mⁿ⁺•CD6•(Mⁿ⁺)₂ with the cations Mg²⁺, Li⁺, and Na⁺. A correlation of the above-mentioned parameters with the cation surface charge density was observed for the complexes Mⁿ⁺•CD6•(Mⁿ⁺)₂. The possibility of influencing the efficiency of complexation and the degree of photorecoordination by varying the nature of the central acceptor fragment in the dye series CD4, CD5, CD6 (CD4 and CD5 are dyes similar to CD6 with central cyclobutanone (CD4) and cyclopentanone (CD5) fragments, respectively) was determined.

Along with 4-acetoxybenzoic acid (4-ABA) and O-acetylvanillic acid (AVA), the syringic acid derivative O-acetylsyringic acid (ASA) can be used as an AB-type comonomer in polycondensation reactions. All three monomers have comparable polycondensation rates, and therefore the copolycondensation of 4-ABA, ASA, and AVA in the melt is expected to yield copolyesters with a random or nearly random macromolecular structure. From a mixture of ASA, 4-ABA, and 4′-acetoxybiphenyl-4-carboxylic acid (4-ABCA), a ternary thermotropic copolyester with a “liquid crystal glass” structure was synthesized. This copolyester has a lower softening temperature and a higher glass transition temperature compared to similar ternary copolyesters based on 4-ABA and 4-ABCA.