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)
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
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
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