3 research outputs found

    On Stability, Chirality Measures, and Theoretical VCD Spectra of the Chiral C<sub>58</sub>X<sub>2</sub> Fullerenes (X = N, B)

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    The stability of all 23 C<sub>58</sub>N<sub>2</sub> and C<sub>58</sub>B<sub>2</sub> heterofullerenes in the singlet and triplet states was determined at the B3LYP/6-31G** level. In equilibrium mixture the achiral (1,4) C<sub>58</sub>N<sub>2</sub> isomer would be populated in ca. 95.8%, the chiral (1,16) one in ca. 3.3%, and the achiral (1,4) C<sub>58</sub>B<sub>2</sub> in 100%, whereas all triplet state isomers are less stable. Fourteen out of 23 C<sub>58</sub>X<sub>2</sub> are chiral. Four different chirality measures were calculated by our own CHIMEA program: pure geometrical, labeled, mass, and charge. Intercorrelations between the measures for all chiral compounds indicate that the pure geometrical chirality measure is unstable and should not be used in QSAR predictions of the other molecular properties, while the labeled and mass-weighted ones are promising QSAR descriptors. For each chiral C<sub>58</sub>N<sub>2</sub> molecule, some very strong VCD bands, of intensity comparable with that in the IR spectra, can serve in identification and characterization of the isomers

    Exploring the Sponge Consortium <i>Plakortis symbiotica–Xestospongia deweerdtae</i> as a Potential Source of Antimicrobial Compounds and Probing the Pharmacophore for Antituberculosis Activity of Smenothiazole A by Diverted Total Synthesis

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    Fractionation of the bioactive CHCl<sub>3</sub>–MeOH (1:1) extracts obtained from two collections of the sponge consortium <i>Plakortis symbiotica</i>–<i>Xestospongia deweerdtae</i> from Puerto Rico provided two new plakinidone analogues, designated as plakinidone B (<b>2</b>) and plakinidone C (<b>3</b>), as well as the known plakinidone (<b>1</b>), plakortolide F (<b>4</b>), and smenothiazole A (<b>5</b>). The structures of <b>1</b>–<b>5</b> were characterized on the basis of 1D and 2D NMR spectroscopic, IR, UV, and HRMS analysis. The absolute configurations of plakinidones <b>2</b> and <b>3</b> were established through chemical correlation methods, VCD/ECD experiments, and spectroscopic data comparisons. When assayed in vitro against <i>Mycobacterium tuberculosis</i> H<sub>37</sub>Rv, none of the plakinidones <b>1</b>–<b>3</b> displayed significant activity, whereas smenothiazole A (<b>5</b>) was the most active compound, exhibiting an MIC value of 4.1 μg/mL. Synthesis and subsequent biological screening of <b>8</b>, a dechlorinated version of smenothiazole A, revealed that the chlorine atom in <b>5</b> is indispensable for anti-TB activity

    Chirality Measures of α-Amino Acids

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    To measure molecular chirality, the molecule is treated as a finite set of points in the Euclidean <i>R</i><sup>3</sup> space supplemented by <i>k</i> properties, <i>p</i><sub>1</sub><sup>(<i>i</i>)</sup>, <i>p</i><sub>2</sub><sup>(<i>i</i>)</sup>, ..., <i>p</i><sub><i>k</i></sub><sup>(<i>i</i>)</sup> assigned to the <i>i</i>th atom, which constitute a point in the Property <i>P</i><sup><i>k</i></sup> space. Chirality measures are described as the distance between a molecule and its mirror image minimized over all its arbitrary orientation-preserving isometries in the <i>R</i><sup>3</sup> × <i>P</i><sup><i>k</i></sup> Cartesian product space. Following this formalism, different chirality measures can be estimated by taking into consideration different sets of atomic properties. Here, for α-amino acid zwitterionic structures taken from the Cambridge Structural Database and for all 1684 neutral conformers of 19 biogenic α-amino acid molecules, except glycine and cystine, found at the B3LYP/6-31G** level, chirality measures have been calculated by a CHIMEA program written in this project. It is demonstrated that there is a significant correlation between the measures determined for the α-amino acid zwitterions in crystals and the neutral forms in the gas phase. Performance of the studied chirality measures with changes of the basis set and computation method was also checked. An exemplary quantitative structure–activity relationship (QSAR) application of the chirality measures was presented by an introductory model for the benchmark Cramer data set of steroidal ligands of the sex-hormone binding globulin
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