LC-NMR coupling technology: recent advancements and applications in natural products analysis
Exarchou, V. ; Krucker, M. ; Beek, T.A. van; Vervoort, J.J.M. ; Gerothanassis, I.P. ; Albert, K. - \ 2005
Magnetic Resonance in Chemistry 43 (2005)9. - ISSN 0749-1581 - p. 681 - 687.
nuclear-magnetic-resonance - performance liquid-chromatography - solid-phase extraction - high-resolution nmr - tandem mass-spectrometry - crude plant-extracts - dad-spe-nmr - hplc-nmr - naphthylisoquinoline alkaloids - solvent-suppression
An overview of recent advances in nuclear magnetic resonance (NMR) coupled with separation technologies and their application in natural product analysis is given and discussed. The different modes of LC-NMR operation are described, as well as how technical improvements assist in establishing LC-NMR as an important tool in the analysis of plant-derived compounds. On-flow, stopped-flow and loop-storage procedures are mentioned, together with the new LC-SPE-NMR configuration. The implementation of mass spectrometry in LC-NMR is also useful on account of the molecular weight and fragmentation information that it provides, especially when new plant species are studied. Cryogenic technology and capillary LC-NMR are the other important recent developments. Since the plant kingdom is endless in producing potential drug candidates, development and optimization of LC-NMR techniques convert the study of natural products to a less-time-consuming task, speeding up identification
LC-UV-solid-phase extraction-NMR-MS combined with a cryogenic flow probe and its application to the identification of compounds present in Greek oregano
Exarchou, V. ; Godejohann, M. ; Beek, T.A. van; Gerothanassis, I.P. ; Vervoort, J.J.M. - \ 2003
Analytical Chemistry 75 (2003)22. - ISSN 0003-2700 - p. 6288 - 6294.
magnetic-resonance-spectroscopy - performance liquid-chromatography - high-resolution nmr - tandem mass-spectrometry - to-noise ratio - hplc-nmr - solvent-suppression - natural-products - plant-extracts - constituents
Structure elucidation of natural products usually relies on a combination of NMR spectroscopy with mass spectrometry whereby NMR trails MS in terms of the minimum sample amount required. In the present study, the usefulness of on-line solid-phase extraction (SPE) in LC-NMR for peak storage after the LC separation prior to NMR analysis is demonstrated. The SPE unit allows the use of normal protonated solvents for the LC separation and fully deuterated solvents for flushing the trapped compounds to the NAIR probe. Thus, solvent suppression is no longer necessary. Multiple trapping of the same analyte from repeated LC injections was utilized to solve the problem of low concentration and to obtain 2D heteronuclear NMR spectra. In addition, a combination of the SPE unit with a recently developed cryoflow NMR probe and an MS was evaluated. This on-line LC-UV-SPE-NMR-MS system was used for the automated analysis of a Greek oregano extract. Combining the data provided by the UV, MS, and NMR spectra, the flavonoids taxifolin, aromadendrin, eriodictyol, naringenin, and apigenin, the phenolic acid rosmarinic acid, and the monoterpene carvacrol were identified. This automated technique is very useful for natural product analysis, and the large sensitivity improvement leads to significantly reduced NAIR acquisition times.