trans-Aconitic acid-based hetero-Diels-Alder reaction in the synthesis of thiopyrano[2,3-d][1,3]thiazole derivatives

The hetero-Diels-Alder reaction of 5-arylideneisorhodanines with trans-aconitic acid proceeds as a regio- and diastereoselective process with spontaneous decarboxylation of the [4+2]-adduct to furnish thiopyrano[2,3-d][1,3]thiazole (2) and chromeno[4′,3′:4,5]thiopyrano[2,3-d]thiazole (3) derivatives analogously to the use of itaconic acid as a dienophile. Conversely, the one-pot, three-component reaction of 5-arylideneisorhodanines, trans-aconitic acid and anilines proceeded without decarboxylation, leading to novel rel-(5′R,6′R,7′R)-5′-carboxy-7′-aryl-1-aryl-3′,7′-dihydro-2H,2′H,5H-spiro[pyrrolidin-3,6′-thiopyrano[2,3-d]thiazol]-2,2′,5-triones 4. Interestingly, the use of trans-aconitic acid trimethyl ester led to the opposite regioselectivity, yielding rel-(5R,6S,7S)-5-methyloxycarbonylmethyl-2-oxo-7-aryl-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d]thiazol-5,6-dicarboxylates 5. Selected compounds were examined for trypanocide activity against the bloodstream forms of Trypanosoma brucei where compound 4e showed the highest activity (IC₅₀ = 6.74 μM).     

Theoretical calculations: Can Gibbs free energy for intermolecular complexes be predicted efficiently and accurately?

The theoretical study has been performed to refine the procedure for calculations of Gibbs free energy with a relative accuracy of less than 1 kcal/mol. Three benchmark intermolecular complexes are examined via several quantum-chemical methods, including the second-order Moller-Plesset perturbation (MP2), coupled cluster (CCSD(T)), and density functional (BLYP, B3LYP) theories augmented by Dunnings correlation-consistent basis sets. The effects of electron correlation, basis set size, and anharmonicity are systematically analyzed, and the results are compared with available experimental data. The results of the calculations suggest that experimental accuracy can be reached only by extrapolation of MP2 and CCSD(T) total energies to the complete basis set. The contribution of anharmonicity to the zero point energy and TDeltaSint values is fairly small. The new, economic way to reach chemical accuracy in the calculations of the thermodynamic parameters of intermolecular interactions is proposed. In addition, interaction energy (De) and free energy change (DeltaA) for considered species have been evaluated by Carr-Parrinello molecular dynamics (CPMD) simulations and static BLYP-plane wave calculations. The free energy change along the reaction paths were determined by the thermodynamic integration/"Blue Moon Ensemble" technique. Comparison between obtained values, and available experimental and conventional ab initio results has been made. We found that the accuracy of CPMD simulations is affected by several factors, including statistical uncertainty and convergence of constrained forces (TD integration), and the nature of DFT (density functional theory) functional. The results show that CPMD technique is capable of reproducing interaction and free energy with an accuracy of 1 kcal/mol and 2-3 kcal/mol respectively.     

Electronic structure and bonding of {Fe(PhNO2)}6 complexes: a density functional theory study

Reduction of nitro-aromatic compounds (NACs) proceeds through intermediates with a partial electron transfer into the nitro group from a reducing agent. To estimate the extent of such a transfer and, therefore, the activity of various model ferrous-containing reductants toward NAC degradation, the unrestricted density functional theory (DFT) in the basis of paired L?wdin-Amos-Hall orbitals has been applied to complexes of nitrobenzene (NB) and model Fe(II) hydroxides including cationic [FeOH]+, then neutral Fe(OH)2, and finally anionic [Fe(OH)3]-. Electron transfer is considered to be a process of unpairing electrons (without the change of total spin projection Sz) that reveals itself in a substantial spin contamination of the unrestricted solution. The unrestricted orbitals are transformed into localized paired orbitals to determine the orbital channels for a particular electron-transfer state and the weights of idealized charge-transfer and covalent electron structures. This approach allows insight into the electronic structure and bonding of the {Fe(PhNO2)}6 unit (according to Enemark and Feltham notation) to be gained using model nitrobenzene complexes. The electronic structure of this unit can be expressed in terms of pi-type covalent bonding [Fe+2(d6, S = 2) - PhNO2(S = 0)] or charge-transfer configuration [Fe+3(d5, S = 5/2) - {PhNO2}- ((pi*)1, S = 1/2)].     

Photochromic liquid crystalline structures containing azobenzene moieties

Novel liquid crystalline photochromic materials of the type 4-R-C₆H₄-N=N-C₆H₄-O(CH₂)_n-N(CH₂CH₂OH)₂, where R is NO₂, H, CN, O-n-C₈H₁₇, phenyl, 4-O₂NC₆H₄, were prepared. Some of them are photoconductive. These materials were used for the preparation of light-sensitive polymers in which the photoactive moieties were attached to polyurethane chain. Photochromism of these compounds is based on trans-cis isomerization of azobenzene group. An example of the photochromic activity is presented on solid solution of one material (R = O-n-C₈H₁₇, n = 5) in poly(methyl methacrylate) matrix.     

Control of mosaic disease using microbial biostimulants: insights from mathematical modelling

Ricerche di Matematica - A major challenge to successful crop production comes from viral diseases of plants that cause significant crop losses, threatening global food security and the livelihoods...     

Unexpected synthesis of azepino[4,3,2-cd]indoles from 4-aminoindoles

Unexpected regioselectivity for the Skraup-Doebner-Von Miller reaction was observed during the synthesis of quinolines from 4-aminoindoles and acetone in the presence of hydrochloric acid as a catalyst. The products were unambiguously assigned as 1-alkyl-3,5,5-trimethyl-5,6-dihydro-1H-azepino[4,3,2-cd]indoles instead of 2,2,4-trimethyl-2,7-dihydro-1H-pyrrolo[2,3-h]quinolones based on NMR spectroscopy and X-ray crystallographic analysis.     

Synthesis of novel 1,2-dihydropyrrolo[1,2-a]pyrazin-1(2H)-one derivatives

The iodolactonization product obtained from methyl 7-allylpyrrolo[2,3-d]pyrimidine-6-carboxylate was used for the synthesis of novel 1,2-dihydropyrrolo[1,2-a]pyrazin-1(2H)-one derivatives, containing carboxamide- and methylamine-groups on the pyrrole ring of the heterocycle.     

Influence of aqueous electrolytes on the wetting behavior of hydrophobic solid polymers-low-rate dynamic liquid/fluid contact angle measurements using axisymmetric drop shape analysis

The interaction of inorganic ions with low-energy hydrophobic surfaces was examined using model systems of solid polymers without ionizable functional surface groups in aqueous electrolyte solutions. Low-rate dynamic contact angle measurements with captive bubbles in conjunction with axisymmetric drop shape analysis (ADSA) were performed to study the influence of electrolyte ions (in the aqueous test solutions) on the wettability of the polymers. When various types of ions were used, no significant change in advancing and receding contact angles was observed. The contact angle hysteresis was small. The zeta potential of the model polymers in aqueous electrolyte solutions was determined from streaming potential measurements. The variation of the zeta potential at different pH levels indicates preferential adsorption of hydroxyl ions at this interface. However, the presence of electrolytes at the interface between water and the different model polymers did not influence the macroscopic contact angle. The results may suggest the absence of any specific interaction between the ions and the solid polymer, as this should result in changes of hydrophobicity. Similar to the air/water interface, the composition and the potential of the polymer/water interface are obviously determined predominantly by the aqueous phase with only slight influence from the solid phase.