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Cherblanc F.L.,Imperial College London | Lo Y.-P.,Imperial College London | Herrebout W.A.,University of Antwerp | Herrebout W.A.,European Center for Chirality | And 4 more authors.
Journal of Organic Chemistry | Year: 2013

The stereochemistry of the desulfurization products of chiral natural and synthetic 3,6-epidithiodiketopiperazines (ETPs) is specified inconsistently in the literature. Qualitative mechanisms have been put forward to explain apparently divergent stereochemical pathways, but the quantitative feasibility of such mechanistic pathways has not been assessed. We report a computational study revealing that desulfurization of ETPs should occur universally with retention of configuration. While the majority of stereochemically assigned and reassigned cases fit this model, until now desulfurization of the synthetic gliotoxin analogue shown has remained assigned as proceeding via inversion of configuration. Through detailed chiroptical studies comparing experimentally obtained optical rotation values, electronic circular dichroism spectra, and vibrational circular dichroism spectra to their computationally simulated counterparts as well as chemical derivatization studies, we have unambiguously demonstrated that contrary to its current assignment in the literature, the desulfurization of this synthetic ETP also proceeds with retention of configuration. © 2013 American Chemical Society.

Bultinck P.,Ghent University | Bultinck P.,European Center for Chirality | Cherblanc F.L.,Imperial College London | Fuchter M.J.,Imperial College London | And 6 more authors.
Journal of Organic Chemistry | Year: 2014

Chiroptical spectroscopies, such as electronic circular dichroism (ECD) and vibrational circular dichroism (VCD), are highly sensitive techniques to probe molecular conformation, configuration, solvation, and aggregation. Here we report the application of these techniques to study the fungal metabolite brevianamide B. Comparison of the experimental ECD and VCD spectra with the density functional theory simulated counterparts establishes that VCD is the more reliable technique to assign absolute configuration due to the larger functional and dispersion dependence of computed ECD spectra. Despite a low amount of available material and a relatively unusual example of using VCD carbonyl multiplets, the absolute configuration could be reliably predicted, strengthening the case for application of VCD in the study of complex natural products. Spectral and crystallographic evidence for or against the formation of a dimeric aggregate is discussed; in solution, the VCD spectra strongly suggest only monomeric species are present. © 2015 American Chemical Society.

Debie E.,Syracuse University | Debie E.,BioTools, Inc. | De Gussem E.,Ghent University | De Gussem E.,University of Antwerp | And 10 more authors.
ChemPhysChem | Year: 2011

Spectral comparison is an important part of the assignment of the absolute configuration (AC) by vibrational circular dichroism (VCD), or equally by Raman optical activity (ROA). In order to avoid bias caused by personal interpretation, numerical methods have been developed to compare measured and calculated spectra. Using a neighbourhood similarity measure, the agreement between a computed and measured VCD or ROA spectrum is expressed numerically to introduce a novel confidence level measure. This allows users of vibrational optical activity (VOA) techniques (VCD and ROA) to assess the reliability of their assignment. of the AC of a compound. To that end, a database of successful AC determinations is compiled along with neighbourhood similarity values between the experimental spectrum and computed spectra for both enantiomers. For any new AC determination, the neighbourhood similarities between the experimental spectrum and the computed spectra for both enantiomers are projected on the database allowing an interpretation of the reliability of their assignment. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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