Determination of the Relative Configuration and Conformational Analysis of Five-memberedN-Acyl-Iminosugars by Relevant3JCoupling Constants.

2016 ◽  
Vol 1 (6) ◽  
pp. 1256-1267 ◽  
Author(s):  
Didier LeNouen ◽  
Albert Defoin ◽  
Jean-Bernard Behr
Keyword(s):  
Conformational Analysis ◽  
Relative Configuration

scholarly journals MICE-PES: An Algorithm for Accurate Conformational Analysis and its Implementation to Natural Products

2021 ◽  
Author(s):  
◽  
Muhammad Ali Hashmi
Keyword(s):  
Conformational Analysis ◽  
Degrees Of Freedom ◽  
Force Fields ◽  
Flexible Structures ◽  
Chemical Properties ◽  
General Purpose ◽  
Field Methods ◽  
Relative Configuration ◽  
Incremental Construction

<p>Secondary metabolites from natural sources have revolutionized the modern drug industry by acting as lead compounds. Many commercial drugs have evolved originally from natural molecules before being synthesized in the laboratory for commercialization. Because of the importance of natural molecules, it is crucial to determine their structural properties carefully as it is essential for their synthesis and studying their pharmacological behaviour. Many natural molecules have flexible structures and can adopt many different conformations in solution at room temperature. Hence, the determination of their relative configuration is a challenging task with the available experimental techniques. For structural analysis of natural molecules and to study their properties, all conformers which might be responsible for their chemical properties have to be considered.  Theoretical chemistry has been very helpful in absolute structure determination of complex and conformationally flexible natural molecules by calculating their theoretical nuclear magnetic resonance, ultraviolet, infra red, and circular dichroism spectra etc. There are a number of software tools that offer conformational analysis by utilizing different molecular mechanics approaches. They produce a large number of possible conformers and are not general purpose, thus compromising accuracy. Apart from that, different force fields available for conformational analysis and minimization have been designed for specific molecular classes and do not produce good results beyond their scope.  In the past, there have been reports about a “build-up procedure” for predicting the low energy conformations of peptides by optimising smaller fragments of the molecule under study and then joining them while minimizing their energies using force fields. Later on, this method was extended to predict the structure of DNA from sequences. This method used force field methods and did not gain much popularity due to its various limitations.  Here, MICE-PES (Method for the Incremental Construction and Exploration of the Potential Energy Surface) is presented, an algorithm which performs a conformational analysis using high level quantum chemical calculations by building the molecule incrementally from its smallest possible analogue whose conformational degrees of freedom are very well separated than the rest of the molecule. MICE-PES has been validated through studies on known biomolecule 3-epi-xestoaminol whose absolute configuration has been determined already by experimental and theoretical methods. MICE-PES has also been used to assign the relative configuration of a natural product (meroterphenol C) whose configuration could not be established experimentally. Overall, the development of MICE-PES will be very helpful in solving problems in the study of conformationally flexible systems, in all aspects of organic chemistry.</p>

scholarly journals Synthesis of eunicellane-type bicycles embedding a 1,3-cyclohexadiene moiety

2018 ◽  
Vol 14 ◽  
pp. 2461-2467 ◽  
Author(s):  
Alex Frichert ◽  
Peter G Jones ◽  
Thomas Lindel
Keyword(s):  
Total Synthesis ◽  
Conformational Analysis ◽  
Selective Reduction ◽  
Relative Configuration ◽  
Pinacol Coupling ◽  
Low Valent ◽  
Limonene Oxide

The first synthesis of diterpenoid eunicellane skeletons incorporating a 1,3-cyclohexadiene moiety is presented. Key step is a low-valent titanium-induced pinacol cyclization that proved to be perfectly diastereoselective. Determination of the relative configuration of the diol was aided by the conversion to the diastereomer by oxidation and reduction. Conformational analysis of some of the resulting diols obtained under McMurry conditions was complicated by the presence of several conformers of similar energy. The pinacol coupling appears to start at the ketone, as indicated by the selective reduction of non-cyclizing cyclohexane systems that were synthesized from limonene oxide. The title compounds and their synthetic precursors are prone to aromatization on contact with air oxygen. Attempted synthesis of cyclohexene-containing eunicellane bicycles by elimination of water from tertiary alkynyl carbinols afforded novel allene systems. Our study may be of help towards the total synthesis of solenopodin or klysimplexin derivatives.

scholarly journals MICE-PES: An Algorithm for Accurate Conformational Analysis and its Implementation to Natural Products

2021 ◽  
Author(s):  
◽  
Muhammad Ali Hashmi
Keyword(s):  
Conformational Analysis ◽  
Degrees Of Freedom ◽  
Force Fields ◽  
Flexible Structures ◽  
Chemical Properties ◽  
General Purpose ◽  
Field Methods ◽  
Relative Configuration ◽  
Incremental Construction

<p>Secondary metabolites from natural sources have revolutionized the modern drug industry by acting as lead compounds. Many commercial drugs have evolved originally from natural molecules before being synthesized in the laboratory for commercialization. Because of the importance of natural molecules, it is crucial to determine their structural properties carefully as it is essential for their synthesis and studying their pharmacological behaviour. Many natural molecules have flexible structures and can adopt many different conformations in solution at room temperature. Hence, the determination of their relative configuration is a challenging task with the available experimental techniques. For structural analysis of natural molecules and to study their properties, all conformers which might be responsible for their chemical properties have to be considered.  Theoretical chemistry has been very helpful in absolute structure determination of complex and conformationally flexible natural molecules by calculating their theoretical nuclear magnetic resonance, ultraviolet, infra red, and circular dichroism spectra etc. There are a number of software tools that offer conformational analysis by utilizing different molecular mechanics approaches. They produce a large number of possible conformers and are not general purpose, thus compromising accuracy. Apart from that, different force fields available for conformational analysis and minimization have been designed for specific molecular classes and do not produce good results beyond their scope.  In the past, there have been reports about a “build-up procedure” for predicting the low energy conformations of peptides by optimising smaller fragments of the molecule under study and then joining them while minimizing their energies using force fields. Later on, this method was extended to predict the structure of DNA from sequences. This method used force field methods and did not gain much popularity due to its various limitations.  Here, MICE-PES (Method for the Incremental Construction and Exploration of the Potential Energy Surface) is presented, an algorithm which performs a conformational analysis using high level quantum chemical calculations by building the molecule incrementally from its smallest possible analogue whose conformational degrees of freedom are very well separated than the rest of the molecule. MICE-PES has been validated through studies on known biomolecule 3-epi-xestoaminol whose absolute configuration has been determined already by experimental and theoretical methods. MICE-PES has also been used to assign the relative configuration of a natural product (meroterphenol C) whose configuration could not be established experimentally. Overall, the development of MICE-PES will be very helpful in solving problems in the study of conformationally flexible systems, in all aspects of organic chemistry.</p>

Asymmetric Total Synthesis and Determination of the Absolute Configuration of (+)-Srilankenyne via Sequence-Sensitive Halogenations Guided by Conformational Analysis

2021 ◽  
Vol 23 (4) ◽  
pp. 1321-1326
Author(s):  
Hongjun Jang ◽  
Soo Yeon Kwak ◽  
Dongjoo Lee ◽  
Juan V. Alegre-Requena ◽  
Hyoungsu Kim ◽  
...  
Keyword(s):  
Total Synthesis ◽  
Conformational Analysis ◽  
Absolute Configuration ◽  
Asymmetric Total Synthesis ◽  
The Absolute

Determination of Relative Configuration in Organic Compounds by NMR Spectroscopy and Computational Methods

ChemInform ◽  
2007 ◽  
Vol 38 (50) ◽  
Author(s):  
Giuseppe Bifulco ◽  
Paolo Dambruoso ◽  
Luigi Gomez-Paloma ◽  
Raffaele Riccio
Keyword(s):  
Nmr Spectroscopy ◽  
Organic Compounds ◽  
Computational Methods ◽  
Relative Configuration

Determination of the Relative Configuration of β-Amino Acid Esters Based on Residual Dipolar Couplings

2015 ◽  
Vol 2015 (31) ◽  
pp. 6801-6805 ◽  
Author(s):  
Thomas Niklas ◽  
Christian Steinmetzger ◽  
Weiping Liu ◽  
Daniel Zell ◽  
Dietmar Stalke ◽  
...  
Keyword(s):  
Amino Acid ◽  
Residual Dipolar Couplings ◽  
Dipolar Couplings ◽  
Amino Acid Esters ◽  
Relative Configuration ◽  
Acid Esters

scholarly journals The use of carbonyl group anisotropy effect in determination of the relative configuration of carbapenams

ARKIVOC ◽  
2014 ◽  
Vol 2014 (3) ◽  
pp. 143-153 ◽  
Author(s):  
Olga Staszewska-Krajewska ◽  
Wojciech Bocian ◽  
Magdalena Maciejko ◽  
Piotr Szcześniak ◽  
Krzysztof Szymczak ◽  
...  
Keyword(s):  
Carbonyl Group ◽  
Relative Configuration ◽  
Anisotropy Effect
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