Andrei A. Gakh

Fluorine as an NMR probe for structural studies of chemical and biological systems

Applications of fluorine NMR to probe long‐range interactions in rigid organic molecules, namely cubanes, and to study structures and dynamics of proteins and other biological systems, are presented. 19F NMR parameters, especially long‐range coupling constants are shown to reveal intrinsic features of the molecules. Correlations between long‐range (more than three‐bond) couplings involving fluorine and other chemical and physico‐chemical properties of the compounds are demonstrated, and examples of unusual couplings which cannot be explained by existing theories of ‘through‐bond’ and ‘through‐space’ mechanisms are discussed. Recent applications of fluorine labeling of aromatic and aliphatic amino acids in investigating protein structures and dynamics are highlighted. The potential of using 19F NMR parameters, such as large spin–spin coupling constants observed for organic compounds, for structural analysis of biological macromolecules is outlined. Copyright

Neural network-graph theory approach to the prediction of the physical properties of organic compounds

A new computational scheme is developed to predict physical properties of organic compounds on the basis of their molecular structure. The method uses graph theory to encode the structural information which is the numerical input for a neutral network. Calculated results for a series of saturated hydrocarbons demonstrate average accuracies of 1--2% with maximum deviations of 12--14%.

‘Fluorine dance’ on the fullerene surface

Abstract A facile fluorine migration process (‘fluorine dance’) leads to the formation of the most thermodynamically stable isomers during the high temperature fluorination of [60]fullerene.

N-fluorination with cesium fluoroxysulfate

Abstract Cesium fluoroxysulfate was proved to be a N-fluorinating agent for some nitrogen compounds. Yields of products obtained mainly monofluoro-derivatives, depend on structures of initial nitrogen compounds. The ability of cesium fluoroxysulfate for N-fluorination is much inferior to that of elemental fluorine and fluoromethylhypofluoride (CF 3 OF) but superior to that of perchlorylfluoride (FClO 3 ).

Highly fluorinated fullerenes as oxidizers and fluorinating agents

Contrary to the chemistry of “standard” fluorocarbons, highly fluorinated fullerenes (C60F44 - C60F46) display distinct oxidizing and fluorinating properties. They liberate iodine from NaI solutions, oxidize isopropanol to acetone, and fluorinate aromatic compounds in the presence of acid catalysts such as BF3·Et2O. Fluoroaromatic products are also generated in the reaction of these fluorofullereness with organolithium reagents. Even the relatively unreactive heterocycle pyridine is fluorinated by the higher fluorofullerenes. Reaction mechanisms are proposed to explain these observations.

Hetarylation of C-nucleophiles: a new course for the reaction of N-fluoropyridiniun salts with carbanions.

Abstract The N-fluoropyridinium tetrafluoroborate reactions with carbanions were found either to follow the cine -(tele)-AEa-substitution or go through possible formation of a carbenic (cationic) intermediate; as a result 2- or 4-pyridyl derivatives are formed.

Prediction of Complexation Properties of Crown Ethers Using Computational Neural Networks

A computational neural network method was used for the prediction of stability constants of simple crown ether complexes. The essence of the method lies in the ability of a computer neural network to recognize the structure-property relationships in these host-guest systems. Testing of the computational method has demonstrated that stability constants of alkali metal cation (Na+, K+, Cs+)-crown ether complexes in methanol at 25 °C can be predicted with an average error of ±0.3 log K units based on the chemical structure of the crown ethers alone. The computer model was then used for the preliminary analysis of trends in the stabilities of the above complexes.

Regioselective synthesis and S-derivatization reactions of 4- and 6-trifluoromethyl-3-cyano-2(1H)-pyridinethiones

Abstract The regioselective synthesis of the title compounds was developed on the basis of condensation reactions of trifluoroacetylacetone and its methyl enacetal with cyanothioacetamide in the presence of bases. Thus, the condensation of trifluoroacetyl-acetone with cyanothioacetamide yields predominantly 4-trifluoromethyl-6-methyl-3-cyano-2(1H)-pyridinethiones, whereas the methyl enacetal of trifluoroacetylacetone gives exclusively the 6-trifluoromethyl-4-methyl isomer. S-Alkylation of the trifluoromethyl-pyridinethione salts can be achieved using methyl iodide or bromoacetophenone in DMF-water. Bromoacetophenone derivatives can be further transformed into 3-aminothieno-[2,3-b]pyridines in the presence of excess KOH.

Dihydro-resveratrol—A potent dietary polyphenol

Dihydro-resveratrol (dihydro-R), a prominent polyphenol component of red wine, has a profound proliferative effect on hormone-sensitive tumor cell lines such as breast cancer cell line MCF7. We found a significant increase in MCF7 tumor cells growth rates in the presence of picomolar concentrations of this compound. The proliferative effect of dihydro-R was not observed in cell lines that do not express hormone receptors (MDA-MB-231, BT-474, and К-562).

Molecular gears : Structures of (9,10-triptyceno) crown ethers

AbstractThe incorporation of 9,10-triptycene unit in a crown ether is examined from a structural perspective. Insertion of a triptycene group into 18-crown-6 stretches the crown into an ellipse, as seen in structures presented here of 9,10-triptyceno-22-crown-6 and its thallium complex. Symmetric addition of two triptycene groups into 18-crown-6 results in the sterically congested bis(9,10-triptyceno)-26-crown-6, whose crown cavity is filled with the π-clouds of two arene groups. The larger bis(9,10-triptyceno)-32-crown-8 is more sterically relaxed. The structures of these bis(triptyceno)crown ether molecules are the first with two triptycene groups simultaneously linked through their 9 and 10 positions, thereby forming a simple molecular gearing mechanism. The compound 9,10-triptyceno-22-crown-6 (1) crystallizes in the orthorhombic space group Pbca with a = 10.7962(7), b = 15.826(3), c = 31.147(5) Å, V = 5321.8(12) Å3, and Z = 8; its complex with TlNO3 (Tl-1) crystallizes in the monoclinic space group P21/c with a = 8.1884(14), b = 19.552(2), c = 20.575(4) Å, β = 97.062(8)°, V = 3269.2(9) Å3, and Z = 4; bis(9,10-triptyceno)-26-crown-6 (2) crystallizes in the triclinic space group P