A Single‐Scan Ultraselective Heteronuclear Polarization Transfer Method for Unambiguous Complex Structure Assignment

Complex nuclear magnetic resonance (NMR) signals of organic compounds containing multiple analogous substructures or mixtures pose a significant challenge to structural identification, thus resulting in frequent misassignment of structures. The GEMSTONE method, a single‐scan technique that selectively excites a specific proton signal among the crowded NMR signals, was recently proposed as a solution. However, its extension to the polarization transfer method for heteronuclear spin systems was unsuccessful. Herein, we present an extension method that addresses the altered heteronuclear polarization transfer efficiency and enables the acquisition of ultraselective 13C and 1H‐13C correlation NMR subspectra with hertz‐level signal selectivity in both dimensions. We demonstrate the effectiveness of this technique in the structural analysis of a chromopeptide pharmaceutical and a diastereomeric mixture of a fungicide. A single‐scan ultraselective heteronuclear polarization transfer (UHPT) NMR method is presented. When applied to chromopeptide pharmaceuticals and a diastereomeric mixture of a fungicide with highly complex NMR signals in both the 1H and 13C dimension, this method provided accurate 1H‐13C correlation and 13C NMR spectra of individual subunits, which enabled unambiguous structure assignment.