Structure and absolute configuration of ginkgolide B characterized by IR‐ and VCD spectroscopy |
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Authors: | Niels H Andersen Niels Johan Christensen Peter R Lassen Teresa BN Freedman Laurence A Nafie Kristian Strømgaard Lars Hemmingsen |
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Institution: | 1. Department of Physics, Quantum Protein Center (QuP), Technical University of Denmark, Kgs. Lyngby, Denmark;2. Department of Food Science, Quality and Technology, Faculty of Life Sciences, University of Copenhagen, Frederiksberg, Denmark;3. Department of Chemistry, Syracuse University, New York;4. Department of Medicinal Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, Copenhagen, Denmark;5. Department of Basic Sciences and Environment, Faculty of Life Sciences, University of Copenhagen, Frederiksberg, Denmark |
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Abstract: | Experimental and calculated (B3LYP/6‐31G(d)) vibrational circular dichroism (VCD) and IR spectra are compared, illustrating that the structure and absolute configuration of ginkgolide B (GB) may be characterized directly in solution. A conformational search for GB using MacroModel and subsequent DFT optimizations (B3LYP/6‐31G(d)) provides a structure for the lowest energy conformer which agrees well with the structure determined by X‐ray diffraction. In addition, a conformer at an energy of 7 kJ mol?1 (B3LYP/6‐311+G(2d,2p)) with respect to the lowest energy conformer is predicted, displaying different intramolecular hydrogen bonding. Differences between measured and calculated IR and VCD spectra for GB at certain wavenumbers are rationalized in terms of interactions with solvent, intermolecular GB‐GB interactions, and the potential presence of more than one conformer. This is the first detailed investigation of the spectroscopic fingerprint region (850?1300 cm?1) of the natural product GB employing infrared absorption and VCD spectroscopy. Chirality, 2010. © 2009 Wiley‐Liss, Inc. |
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Keywords: | ginkgolides vibrational circular dichroism DFT calculations conformational analysis fingerprint region |
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