Synergistic Combination of NAPROC-13 and NMR 13C DFT Calculations: A Powerful Approach for Revising the Structure of Natural Products.

This article describes the structure revision of nine triterpenoids that have been reported corresponding to the same 13C NMR data set. In addition, 13C NMR calculation shows that some chemical shift assignments must be swapped. Our analysis improves the fit between the experimental and calculated data. Correcting misassigned structures and correctly assigning each signal is essential for elucidating new structurally related compounds. Furthermore, the ambiguity of several compounds, the structure of which differs in the literature and the Sci-Finder database, has been eliminated. Misassigned structures were found by chemical shift searches in NAPROC-13, and the results provide two or more different compounds with the same 13C NMR data. The process to determine the correct, most likely structural proposal in agreement with the experimental 13C NMR data was carried out by DFT calculations.

Computational Structural Revision of Elaeophorbate and Other Triterpenoids with the Help of NAPROC-13. A New Strategy for Structural Revision of Natural Products.

A considerable number of natural products have been published in recent years with misassigned structure, even though they had been correctly elucidated in the past. The availability of databases containing revised structures can prevent the amplification of errors in structural elucidation. NAPROC-13, a dereplication tool based on the 13C chemical shift, has been used to search for substances that, possessing the same chemical shifts, have been described with different structures. The correct structure of these different structural proposals is verified by computational chemistry. This paper reports the structural revision of nine triterpenoids following this methodology.