3 research outputs found
Analysis of ergonomics problems contact-centers
The analysis of the ergonomic problems
of the contact center. It allocates main factors of
influence on man- operator
Nature of Amide Carbonyl−Carbonyl Interactions in Proteins
Nature of Amide Carbonyl−Carbonyl Interactions in Protein
Synthesis of 5-Fluoro- and 5-Hydroxymethanoprolines via Lithiation of <i>N</i>-BOC-methanopyrrolidines. Constrained C<sup>γ</sup>-Exo and C<sup>γ</sup>-Endo Flp and Hyp Conformer Mimics
Proline derivatives with a C<sup>γ</sup>-exo pucker
typically
display a high amide bond trans/cis (<i>K</i><sub>T/C</sub>) ratio. This pucker enhances n→π* overlap of the amide
oxygen and ester carbonyl carbon, which favors a trans amide bond.
If there were no difference in n→π* interaction between
the ring puckers, then the correlation between ring pucker and <i>K</i><sub>T/C</sub> might be broken. To explore this possibility,
proline conformations were constrained using a methylene bridge. We
synthesized discrete gauche and anti 5-fluoro- and 5-hydroxy-<i>N</i>-acetylmethanoproline methyl esters from 3-syn and 3-anti
fluoro- and hydroxymethanopyrrolidines using directed α-metalation
to introduce the α-ester group. NBO calculations reveal minimal
n→π* orbital interactions, so contributions from other
forces might be of greater importance in determining <i>K</i><sub>T/C</sub> for the methanoprolines. Consistent with this hypothesis,
greater trans amide preferences were found in CDCl<sub>3</sub> for
anti isomers en-MetFlp and en-MetHyp (72–78% trans) than for
the syn stereoisomers ex-MetFlp and ex-MetHyp (54–67% trans).
These, and other, <i>K</i><sub>T/C</sub> results that we
report here indicate how substituents on proline analogues can affect
amide preferences by pathways other than ring puckering and n→π*
overlap and suggest that caution should be exercised in assigning
enhanced pyrrolidine C<sup>γ</sup>-exo ring puckering based
solely on enhanced trans amide preference