Circular Dichroism of Marine Drugs

Dear Colleagues,

Complete characterization of the structure of a molecule requires both the evaluation of its connectivity and the determination of its stereochemistry. While in many cases the relative configuration is accessible by NMR techniques, knowledge of the absolute configuration mostly requires an X-ray structure determination. In cases where suitable crystals are not available, which is quite often the case for natural compounds, electronic CD spectroscopy (ECD) is a powerful tool to obtain the required information. Based on CD spectra the absolute configuration can be obtained in different ways. An entirely experimental approach is the comparison of the measured CD spectrum of the compound to be analyzed with the spectra of compounds of known stereochemistry. Another possibility is the application of so-called sector rules. Moreover, today modern quantum-chemical methods offer an additional possibility which is the comparison of the experimental spectrum with one calculated assuming a certain absolute configuration. In cases where the signs of the calculated and measured Cotton effects agree, the assumed stereochemistry is most likely correct. If not, the model has to be changed until coincidence between measured and calculated spectra is achieved. This might be quite laborious, especially in cases where the molecule has more than one chiral element (asymmetric atom, chiral axis, etc.) and if the molecule is flexible. In cases where the molecule has no suitable electronic chromophore vibrational CD spectroscopy (VCD) can also be applied.

Prof. Dr. Gerhard Raabe
Guest Editor

• CD spectroscopy
• ECD
• VCD
• calculated CD spectra
• sector rules
• quantum-chemical calculations