Proton Zero Quantum Two-Dimensional Nmr Spectroscopy: An Alternative to Proton Double Quantum Inadequate for Mapping Complex Proton Spin Systems of Natural Products

Abstract

Despite numerous potential advantages, proton zero quantum coherence (HZQC) two-dimensional (2D)-nmr spectroscopy has been totally ignored by the natural products chemists engaged in structure elucidation. The HZQC experiment is described. Application of this highly sensitive 2D-nmr experiment to strychnine as a model system is presented. Comparisons are drawn between the HZQC and proton double quantum IN-ADEQUATE(HDQC) experiment. HZQC offers considerable advantages in time and resolution but does not appear to have the abilities of HDQC in elucidating coupling pathways where aJHH is very small.

Configuration and Total Assignment of the 1H- and 13C-nmr Spectra of the Alkaloid Holstiine

“…Proton identities are labeled on the high resolution reference spectrum plotted beneath the contour plot. COSY data acquisition.-The COSY data were acquired using the normal pulse sequence and a sixteen-step phase cycle to afford quadrature detection in both frequency domains (6). The data were collected as 200 X IK complex points and were processed using sinusoidal multiplication prior to both Fourier transformations with zero filling sufficient to afford a final magnitude calculated spectrum consisting of 512 X 512 real points.…”

“…Assignment of the 'H-nmr spectrum.-As with strychnine (5,6), the aliphatic portion of the 'H-nmr spectrum of holstiine is subdivisible into four essentially isolated spin systems at 300 MHz. Constituents of these spin systems are readily established using the H-19 vinyl proton resonating at 5.51 ppm and the H-2 indole proton resonating at 4.84 ppm as starting points in the analysis of the COSY spectrum (7) of holstiine.…”

Parahydrogen induced hyperpolarization provides a tool for NMR metabolomics at nanomolar concentrations

“…thirty years ago. 18 Probably, the somewhat exotic character associated to ZQ coherence has not favoured the adoption of such experiments in conventional NMR studies.…”

Isotopological Fingerprinting Using 1H/D Scrambling Identifies the Stereochemistry of Hyperpolarization Catalysts Transferring Spin Polarization from Parahydrogen to Substrates Using Signal Amplification by Reversible Exchange

“…Fast 2D zero quantum (ZQ) spectroscopy , (Figure c) exploits the chemical shift evolution of the hydride partners, rather than the traditional J -based approach, to enable full stereochemical characterization of catalyst conformations in an NMR experiment that takes less than 1 min.…”