Configurational Variation of a Natural Compound within Its Source Species. The Unprecedented Case of Areolal in Piptothrix areolare.

Published on Nov 21, 2019in Journal of Natural Products3.779
· DOI :10.1021/ACS.JNATPROD.9B00734
Héctor M. Arreaga-González3
Estimated H-index: 3
(UMSNH: Universidad Michoacana de San Nicolás de Hidalgo),
Gabriela Rodríguez-García5
Estimated H-index: 5
(UMSNH: Universidad Michoacana de San Nicolás de Hidalgo)
+ 5 AuthorsMario A. Gómez-Hurtado8
Estimated H-index: 8
(UMSNH: Universidad Michoacana de San Nicolás de Hidalgo)
The exceptional case of a natural compound that shows drastic absolute configuration variations within the same species was examined. Sequential samples of areolal (1) isolated from Piptothrix areolare showed dextrorotatory (ee 32%), almost racemic (ee 4%), levorotatory (ee 82%), and again dextrorotatory (ee 10%) values. Enantiomeric compositions of this epoxythymol derivative were determined from individual plant specimens collected from the same geographical location over a 46-day period, which were processed using the same extraction and isolation methods. Detection of this unusual phenomenon was possible by analysis of NMR data recorded in the presence of BINOL as a chiral solvating agent. The absolute configuration of (−)-(8S)-areolal followed from vibrational circular dichroism data of an enantiomerically enriched sample, while single-crystal X-ray diffraction and supramolecular analyses revealed interactions that diminish the crystal entropy in rac-1. These results might be related with environment...
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Since epoxythymols occur in Nature either as scalemic mixtures or as pure enantiomers, the knowledge of their chiral composition and of the absolute configuration (AC) of the dominant enantiomer turns out to be mandatory. This task has already been faced using 1,1-bis-2-naphthol (BINOL), as a chiral solvating agent in accurate 1H NMR quantifications to determine the enantiomeric ratio, and vibrational circular dichroism (VCD) to evidence the AC of the dominant enantiomer. We now explore the use ...
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