A Structure Elucidation System Using 1H-NMR and H-H COSY Spectra
Organic Synthesis Research Laboratory, Sumitomo Chemical Co., Ltd.; Tsukahara, Takatsuki-shi 569-1093 Japan
Valuable information from 2D-NMR spectra should be used for structure elucidation. A system named “Spec2D” as a structure elucidation system has been developed in order to propose plausible structures for unknown compounds using H-H COSY spectral information. A knowledge base for the system has been constructed beforehand. It consists of information about correlation between chemical shifts of 1H-NMR spectra and the corresponding substructures represented by HYPER code. The knowledge base is incorporated with networks of spin-spin coupling information from cross peaks in the H-H COSY spectral data which have been derived from fully assigned 1H-NMR data in our databases. For the structure elucidation the system requires information of chemical shifts, the number of protons of each signal, and signal connections derived from the cross peak information of H-H COSY spectrum of an unknown compound. The system does not require any molecular formula. The requisite information is only 1H-NMR and H-H COSY spectra of the unknown compound in question. The system extracts substructures consistent with input spectral data from the knowledge base. A small number of consistent substructures should be survived by means of the cross peak information and the extracted large fragments of the substructures. Furthermore, the substructures are combined into larger substructures using coupling information of the cross peaks. Referring to the assignments of the substructures, these are combined into complete structures in the final combination procedure. In a verification module the system predicts the chemical shifts and the cross peaks for every candidate structure proposed in the structure generation step and compares them with the input spectrum of the unknown compound. The system calculates scores of the predicted spectra representing similarities of chemical shifts and cross peaks. The most plausible structure for the unknown compound is ranked at the higher position in the list of candidate structures. Finally, the system proposes the plausible candidate structures.
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