Assignment of 1H signals in complex overlapping spectral regions using proton-detected 2D heteronuclear shift correlation spectroscopy

The application of a heteronuclear 2D pulse sequence is demonstrated which correlates chemical shifts of carbons with directly bound protons and with remote protons belonging to the same coupled spin system by using the effect of Hartmann—Hahn cross polarization among protons. The enhanced spectral resolution obtained by spreading individual proton subsystems into the carbon domain and the option for multiplicity discrimination makes these kind of experiments most suitable for proton and carbon signal assignments of natural products as alkaloids and steroids with strongly overlapping proton resonances. With the application to a steroid we want to demonstrate that such unambiguous signal assignments are the prerequisite and the basis for detailed structural investigations using additional, more conventional NMR experiments.