Multiple Ultrafast, Broadband 2D NMR Spectra of Hyperpolarized Natural Products

The combination of ex situ dynamic nuclear polarization (DNP) with nuclear magnetic resonance (NMR) leads to signal-to-noise enhancements of 10(3)-10(4) compared to conventional NMR. Ex situ DNP, however, is ill-suited for collecting the array of transients needed in 2D NMR spectroscopy. Spatially encoded single-scan 2D NMR methods can circumvent this drawback, yet these ultrafast experiments can cover spectral, ranges of only approximate to 20 ppm using conventional hardware. To deal with this limitation, we discuss here new spatial/spectral encoding strategies capable of folding C-13 resonances into the desired spectral windows. This new approach allows one to obtain -following a single hyperpolarization process- multiple 2D heteronuclear correlations arising from different C-13 regions. In combination with ex situ DNP, these principles enable the acquisition of HMBC and HSQC 2D NMR spectra on approximate to 1 mM mixtures of natural products, characterizing with a high resolution sites spread over nearly 100 ppm bandwidths.