Determination of the Absolute Configurations of Natural Products via Density Functional Theory Calculations of Vibrational Circular Dichroism, Electronic Circular Dichroism, and Optical Rotation:  The Iridoids Plumericin and Isoplumericin

The absolute configurations (ACs) of the iridoid natural products, plumericin (1) and isoplumericin (2), have been re-investigated using vibrational circular dichroism (VCD) spectroscopy, electronic circular dichroism (ECD) spectroscopy, and optical rotatory dispersion (ORD). Comparison of DFT calcu...

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Bibliographic Details
Published in:Journal of organic chemistry 2007-04, Vol.72 (9), p.3521-3536
Main Authors: Stephens, P. J, Pan, J. J, Devlin, F. J, Krohn, K, Kurtán, T
Format: Article
Language:English
Subjects:
Alicyclic compounds, terpenoids, prostaglandins, steroids
Chemistry
Circular Dichroism
Exact sciences and technology
Indenes - chemistry
Iridoids - chemistry
Models, Chemical
Models, Molecular
Molecular Conformation
Molecular Structure
Optical Rotation
Optical Rotatory Dispersion
Organic chemistry
Preparations and properties
Spectrophotometry, Infrared
Terpenoids
Vibration
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Summary:The absolute configurations (ACs) of the iridoid natural products, plumericin (1) and isoplumericin (2), have been re-investigated using vibrational circular dichroism (VCD) spectroscopy, electronic circular dichroism (ECD) spectroscopy, and optical rotatory dispersion (ORD). Comparison of DFT calculations of the VCD spectra of 1 and 2 to the experimental VCD spectra of the natural products, (+)-1 and (+)-2, leads unambiguously to the AC (1R,5S,8S,9S,10S)-(+) for both 1 and 2. In contrast, comparison of time-dependent DFT (TDDFT) calculations of the ECD spectra of 1 and 2 to the experimental spectra of (+)-1 and (+)-2 does not permit definitive assignment of their ACs. On the other hand, TDDFT calculations of the ORD of (1R,5S,8S,9S,10S)-1 and -2 over the range of 365−589 nm are in excellent agreement with the experimental data of (+)-1 and (+)-2, confirming the ACs derived from the VCD spectra. Thus, the ACs initially proposed by Albers-Schönberg and Schmid are shown to be correct, and the opposite ACs recently derived from the ECD spectra of 1 and 2 by Elsässer et al. are shown to be incorrect. As a result, the ACs of other iridoid natural products obtained by chemical correlation with 1 and 2 are not in need of revision.
ISSN:0022-3263
1520-6904
DOI:10.1021/jo070155q