Structure Elucidator:  A Versatile Expert System for Molecular Structure Elucidation from 1D and 2D NMR Data and Molecular Fragments

Abstract

StrucEluc is an expert system that allows the computer-assisted elucidation of chemical structures based on the inputs of a series of spectral data including 1D and 2D NMR and mass spectra. The system has been enabled to allow a chemist to utilize fragments stored in a fragment database as well as user-defined fragments submitted by the chemist in the structure elucidation process. The association of fragments in this way has been shown to dramatically speed up the process of structure generation from 2D NMR data and has helped to minimize or eliminate the need for user intervention thereby further enabling the vision of automated elucidation. The use of fragments has frequently transformed very difficult 2D NMR elucidation challenges into easily solvable tasks. A strategy to utilize molecular fragments has been developed and optimized based on specific challenging examples. This strategy will be described here using real world examples. Experience gained by solving more than 150 structure elucidation problems from a variety of literature sources is also reviewed in this work.

Elucidação estrutural de substâncias orgânicas com auxílio de computador: evoluções recentes

“…Este programa, que está na versão 8.0 58 , foi desenvolvido para a elucidação estrutural automatizada de estruturas químicas. O programa possui uma moderna interface com o usuário e é necessária pouca interferência do químico.…”

The application of empirical methods of 13C NMR chemical shift prediction as a filter for determining possible relative stereochemistry

“…A strategy based on combining all mentioned methods was suggested. [5,6] It allows selection of the most probable structure from the output file of an expert system developed for the molecular structure elucidation.…”

“…Our experiences in the field of computer-aided structure elucidation have shown [22] that the d A ( 1 H) deviation is a less reliable criterion compared with d C and it is usually only used for additional confirmation of the most probable structural isomer. [5,6,22] The difference between the deviations d A ( 13 C) found for the second and first ranked structures is not large (0.2 ppm), but this value is frequently observed in the structure elucidation process when the 'best structure' is selected. [22] It is worthy to note that in the stereoisomers 3, 4, 6 and 9, atoms H-17 and H-19 are situated on opposite sides of the macrocycle and are unlikely to be close enough in space to show a ROESY coupling.…”

“…We investigated what results would be obtained if the problem is solved using 1D and 2D NMR spectra and the empirical chemical shift prediction methods implemented into the expert system Structure Elucidator. [5,6,22] To perform this analysis structure 1 was input into the system and all carbon and hydrogen atoms were supplied with chemical shifts in accordance with the author's assignment. Then all 2 5 = 32 streoisomers were generated by the program and depicted using conventional designations for stereobonds.…”

“…Consequently, the neural net approach can be used for preliminary ranking the stereoisomer file for subsequent spectrum prediction based on fragmental method as is common in Structure Elucidator system. [6] When NOESY/ROESY data were available from the corresponding articles, application of these data to structures presented in top sets (S r = 3-12) allowed us to conclude that the right stereoisomer is the preferred one algorithmically also. Examples of the several top ranked sets of stereoisomers are presented in the Supporting Informations.…”