| Abstract
| - The HPLC-SPE-NMR technique, supported by HPLC-MS measurements, was used to determine structures of major aswell as some minor constituents of ethanol and petroleum ether extracts of Harpagophytum procumbens (Devil's claw)roots. This method was also shown to be applicable for rapid and precise on-line identification of secondary metabolitespresent in commercial herbal products of H. procumbens. A total of 15 compounds (1−14 and 17) were identified fromthe ethanol and petroleum ether extracts, including a novel Diels−Alder dimer 14. Optimization of the HPLC-SPE-NMR experiments included quantitative 1H NMR measurements, determination of trapping and elution efficiency, effectof multiple trapping of analytes, use of various deuterated solvents for SPE cartridge elution, and effect of post-columndilution ratio of eluent with water. Linear accumulation of apolar and relatively polar analytes was demonstrated for atleast 8−10 repeated trappings, resulting in greatly improved signal-to-noise ratios in NMR spectra and reduced acquisitiontimes. Thus, the HPLC-SPE-NMR technique provides an efficient means of identification of multiple components ofcrude extracts. By allowing on-line generation of high-quality 2D NMR data without traditional purification of extractcomponents, the HPLC-SPE-NMR methodology represents a paradigm shift in natural products research with respectto structure elucidation.
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