Nuclear magnetic resonance (NMR) spectroscopy is extensively used at FMC to confirm the chemical structures of molecules synthesized by Organic Chemists and chemicals from commercial libraries shown to have interesting biological activity. Determination of the correct regioisomer in monosubstituted 1,2,3-thiadiazoles by NMR is challenging due to the scarcity of ring protons and presence of multiple heteroatoms. A rapid two-dimensional NMR method to correctly determine the site of substitution in such molecules has been developed. This method is based on a standard 1H/15N-HMBC experiment with an optimized long-range JHN value that allows discrimination between the 4- and 5-substitution sites.
