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Mar. Drugs 2018, 16(10), 388; https://doi.org/10.3390/md16100388

For a Correct Application of the CD Exciton Chirality Method: The Case of Laucysteinamide A

Department of Chemistry and Industrial Chemistry, University of Pisa, Via G. Moruzzi 13, 56124 Pisa, Italy
Received: 21 September 2018 / Revised: 10 October 2018 / Accepted: 15 October 2018 / Published: 16 October 2018
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Abstract

The circular dichroism (CD) exciton chirality method (ECM) is a very popular approach for assigning the absolute configuration (AC) of natural products, thanks to its immediacy and ease of application. The sign of an exciton couplet (two electronic CD bands with opposite sign and similar intensity) can be directly correlated with the molecular stereochemistry, including the AC. However, a correct application of the ECM necessitates several prerequisites: knowledge of the molecular conformation; knowledge of transition moment direction; and preeminence of the exciton coupling mechanism with respect to other sources of CD signals. In recent years, by using quantum-chemical CD calculations, we have demonstrated that some previous applications of ECM were wrong or based on incorrect assumptions. In a recent publication of this journal (Mar. Drugs, 2017, 15(4), 121), the ECM was employed to assign the AC of a marine metabolite, laucysteinamide A. This is a further case of incorrect application of the method, where none of the aforementioned prerequisites is fully met. Using this example, we will discuss the criteria required for a correct application of the ECM. View Full-Text
Keywords: electronic circular dichroism; absolute configuration; molecular conformation; electric transition dipole moment; exciton coupling; TDDFT calculations electronic circular dichroism; absolute configuration; molecular conformation; electric transition dipole moment; exciton coupling; TDDFT calculations
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Pescitelli, G. For a Correct Application of the CD Exciton Chirality Method: The Case of Laucysteinamide A. Mar. Drugs 2018, 16, 388.

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