Structure verification through computer‐assisted spectral assignment of NMR spectra

Abstract

The validation of a molecular organic structure on the basis of 1D and 2D HSQC, COSY and HMBC NMR spectra is proposed as an alternative to the methods that are mainly based on chemical shift prediction. The CCASA software was written for this purpose. It provides an updated and improved implementation of the preceding computer-assisted spectral assignment software. CCASA can be downloaded freely from http://www.univ-reims.fr/LSD/JmnSoft/CASA. Two bioactive natural products, a triterpene and a benzophenone, were selected from literature data as examples. The tentative matching between the structure and the NMR data interpretation of the triterpene unexpectedly leads to the hypothesis of an incorrect structure. The LSD software was used to find an alternative structure that improved the 2D NMR data interpretation and the carbon-13 chemical shift matching between experimental values and those produced by the nmrshiftdb2 prediction tool. The benzophenone example showed that signal assignment by means of chemical shift prediction can be replaced by elementary user-supplied chemical shift and multiplicity constraints.