Role of hydrogen bonds and weak non-covalent interactions in the supramolecular assembly of 9-hydroxyeucaliptol: crystal structure, Hirshfeld surface analysis, and DFT calculations.

The compound 1,3,3-trimethyl-2-oxabicyclo[2.2.2]octan-9-ol (9-hydroxyeucaliptol) has been prepared and characterized by single-crystal X-ray diffraction analysis, infrared, Raman, and UV-visible spectroscopies. The molecular geometry of the title compound was also investigated theoretically by density functional theory (DFT) calculations to compare with the experimental data. The substance crystallizes in the trigonal crystal system, space group P32 with Z = 9 molecules per unit cell. There are three independent molecules in the crystal asymmetric unit having the same chirality and showing some differences in the orientation of the H-atom of the hydroxyl group. The crystal structure of 9-hydroxyeucaliptol shows that the hydroxyl group presents an anti-conformation with respect to the O-atom of the ether group. The crystal packing of 9-hydroxyeucaliptol is stabilized by intermolecular O-H···O hydrogen bonds involving the hydroxyl groups of different molecules, which play a decisive role in the preferred conformation adopted in solid state. The intermolecular interactions observed in solid state were also studied through the Hirshfeld surface analysis and quantum theory of atoms in molecules (QTAIM) approaches. Energy framework calculations have also been carried out to analyze and visualize the topology of the supramolecular assembly, and the results indicate a significant contribution from electrostatic energy over the dispersion.

Characterization of the phenolic fraction from Argentine wine and its effect on viability and polysaccharide production of Pediococcus pentosaceus.

OBJECTIVES: To qualitatively and quantitatively characterize a low molecular weight phenolic fraction (LMF) of Malbec wine from Cafayate, Argentina, and evaluate its effect on viability and exopolysaccharide production of Pediococcus pentosaceus 12p, a wine spoilage bacterium. RESULTS: The phenolic compounds detected were, in general, comparable to data previously reported but hydroxycinnamic acids were detected at higher concentrations than determined in other studies. Addition of LMF at identical concentrations present in wine or a four times concentrated LMF mixture to a synthetic wine-like medium produced a diminution in bacterial viability and exopolysaccharide production in the supernatant culture. Transmission electron microscopy revealed damage of bacterial cell integrity after 96 h of incubation only in the presence of four times concentrated LMF. CONCLUSION: This is the first time a low molecular weight phenolic fraction has been characterized in Cafayate wine and it has demonstrated a marked antimicrobial effect on an exopolysaccharide-producing wine spoilage bacterium.

3-Chlorotyramine Acting as Ligand of the D2 Dopamine Receptor. Molecular Modeling, Synthesis and D2 Receptor Affinity.

We synthesized and tested 3-chlorotyramine as a ligand of the D2 dopamine receptor. This compound displayed a similar affinity by this receptor to that previously reported for dopamine. In order to understand further the experimental results we performed a molecular modeling study of 3-chlorotyramine and structurally related compounds. By combining molecular dynamics simulations with semiempirical (PM6), ab initio and density functional theory calculations, a simple and generally applicable procedure to evaluate the binding energies of these ligands interacting with the D2 dopamine receptors is reported here. These results provided a clear picture of the binding interactions of these compounds from both structural and energetic view points. A reduced model for the binding pocket was used. This approach allowed us to perform more accurate quantum mechanical calculations as well as to obtain a detailed electronic analysis using the Quantum Theory of Atoms in Molecules (QTAIM) technique. Molecular aspects of the binding interactions between ligands and the D2 dopamine receptor are discussed in detail. A good correlation between the relative binding energies obtained from theoretical calculations and experimental IC50 values was obtained. These results allowed us to predict that 3-chlorotyramine possesses a significant affinity by the D2 -DR. Our theoretical predictions were experimentally corroborated when we synthesized and tested 3-chlorotyramine which displayed a similar affinity by the D2 -DR to that reported for DA.

Catalytic and molecular properties of rabbit liver carboxylesterase acting on 1,8-cineole derivatives.

Rabbit liver carboxylesterase (rCE) was evaluated as the catalyst for the enantioselective hydrolysis of (+/-)-3-endo-acetyloxy-1 ,8-cineole [(+/-)-4], which yields (1S,3S,4R)-(+)-3-acetyloxy-1,8-cineole [(+)-4] and (1R,3R,4S)-(-)-3-hydroxy-1,8-cineole [(-)-3]. Enantioselective asymmetrization of meso-3,5-diacetoxy-1,8-cineol (5) gives (1S,3S,4R,5R)-(-)-3-acetyloxy-5-hydroxy-1,8-cineole (6), with high enantioselectivity. rCE has been chosen to perform both experiments and molecular modeling simulations. Docking simulations combined with molecular dynamics calculations were used to study rCE-catalyzed enantioselective hydrolysis of cineol derivatives. Both compounds were found to bind with their acetyl groups stabilized by hydrogen bond interactions between their oxygen atoms and Ser221.

Preparation and absolute configuration of (1R,4R)-(+)-3-oxo-, (1S,4S)-(-)-3-oxo- and (1R,3S,4R)-(+)-3-acetyloxy-5-oxo-1 ,8-cineole.

Enantiomerically pure (1S,4S)-(-)-3-oxo-1,8-cineole (-)-2 and (1R,4R)-(+)-3-oxo-1,8-cineole (+)-2 were prepared for the first time and their absolute configurations assigned by vibrational circular dichroism (VCD) measurements. Thus, treatment of cineole 1 with chromyl acetate gave rac-2 which after sodium borohydride reduction and acetylation provided racemic 3-endo-acetyloxy-1,8-cineole, rac-4. Enantioselective hydrolysis using porcine liver esterase (PLE) gave a mixture of 3-endo-hydroxy-1,8-cineole (-)-3 and 3-endo-acetyloxy-1,8-cineole (+)-4. After chromatographic separation, (-)-3 was oxidized to (+)-2, while (+)-4 was hydrolysed to (+)-3 and then oxidized to (-)-2. The absolute configuration of either ketone 2 was established by VCD spectroscopy in combination with density functional theory (DFT) calculations at the B3LYP/DGDZVP level of theory, from where it followed that the (+)-2 enantiomer corresponds to (1R,4R)-1,3,3-trimethyl-5-oxo-2-oxabicyclo[2.2.2]octane and the (-)-2 enantiomer to the (1S,4S) molecule which is also in agreement with the absolute configuration deduced by the Mosher method for the starting chiral alcohols. Some literature inconsistencies are clarified. In addition, the enantiomerically pure monoester (1S,3S,4R,5R)-(-)-3-acetyloxy-5-hydroxy-1,8-cineole 6 and the ketoester (1R,3S,4R)-(+)-3-acetyloxy-5-oxo-1,8-cineole 7 were prepared from meso-diacetate 5 by enantioselective asymmetrization also using PLE.