Structural assignment of newly synthesized compounds or validation of newly assignednatural products with close isomeric relationships can be quite challenging, especially when the variations in the carbon framework configuration or stereochemistry is epimeric. Here we present a streamlined protocol for calculating and analyzing 13C chemical shifts of close structurally related compounds. The calculated chemical shifts are then compared with experimental 13C NMR values to determine and validate the correct structural assignment. The steps in the protocol are as follows: 1) conduct conformational search using LowModeMD, 2) refine conformations using a QM method (e.g. Gaussian), 3) calculate shieldings for each conformation with Gaussian and convert to chemical shifts, 4) determine the weighted Boltzmann distribution for 13C chemical shifts, 5) compare the calculated 13C NMR chemical shifts of multiple compound candidates with experimentally derived 13C values to identify the best match using the NMR Spectral Analysis application in MOE.<br/>.

Protocol for validating small molecule structure assignment using calculated 13C NMR chemical shifts with quantum mechanics and moe

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