Two-dimensional concurrent HMQC-COSY as an approach for small molecule chemical shift assignment and compound identification

Abstract

Chemical shift assignment is the first step toward the structure elucidation of natural products and other chemical compounds. We propose here the use of 2D concurrent HMQC-COSY as an experiment for rapid chemical shift assignment of small molecules. This experiment provides well-dispersed 1H–13C peak patterns that are distinctive for different functional groups plus 1H–1H COSY connectivities that serve to identify adjacent groups. The COSY diagonal peaks, which are phased to be absorptive, resemble 1H–13C HMQC cross peaks. We demonstrate the applicability of this experiment for rapidly and unambiguously establishing correlations between different functional groups through the analysis of the spectrum of a metabolite (jasmonic acid) dissolved in CDCl3. In addition, we show that the experiment can be used to assign spectra of compounds in a mixture of metabolites in D2O.