4.6 Article

Pseudocyclic Form of 4-Hydroxypyrrolidine-2-carboxanilide Podands with Trioxyethylene Chain: Modeling, Conformational Search, and NMR Analysis

Journal

JOURNAL OF PHYSICAL CHEMISTRY A
Volume 125, Issue 28, Pages 6029-6041

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/acs.jpca.1c02613

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Funding

  1. Ministry of Science and Higher Education of the Russian Federation [075-15-2020-777]

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The 4-hydroxypyrrolidine-2-carboxanilide podand salt displays catalytic activity in the asymmetric Biginelli reaction. A novel algorithm for generation and selection of conformers based on molecular dynamics and clustering in the space of principal components was proposed to identify the major structural factors of the podand, revealing its tendency to form a pseudocyclic structure.
The 4-hydroxypyrrolidine-2-carboxanilide podand salt demonstrates catalytic activity in asymmetric Biginelli reaction. The systematic search for prevalent conformational state of the cation was carried out by computer simulations in combination with one- and two-dimensional NMR experiments. For that purpose, we proposed a novel algorithm for the generation and selection of conformers based on molecular dynamics and clustering in the space of principal components. The search had found an important trend of the podand to form a pseudocyclic structure with a horseshoe-shaped conformation of the oligooxyethylene fragment. This conformation is stabilized by different types of intramolecular hydrogen bonds between the acidic and basic centers of the two 4-hydroxypyrrolidine-2-carboxanilide residuals (branches). The proposed approach had made it possible to identify the major structural factors, providing a correlation between the calculated and experimental chemical shifts of hydrogen atoms in the H-1 NMR spectra of the protonated podand.

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