Direct metabolic fingerprinting by NMR spectroscopy as a new method for the analysis of herbal tinctures

In natural product chemistry, NMR spectroscopy has traditionally been used for identification of pure compounds, while recent efforts have focused on the use of NMR for fingerprinting in combination with multivariate data analysis [1]. Here we describe the application of an NMR-based approach for direct fingerprinting herbal tinctures. This method does not need the evaporation of the solvent; only the addition of 10% of deuterated water to the tinctures was necessary for the acquisition of the spectra. Compared to the HPLC approach [2], this method does not require the optimization of the conditions for each specific herbal tincture. In fact, the same NMR experiments were here successfully applied for fingerprinting tinctures prepared from different medicinal plants. Simple proton spectra of the herbal tinctures show practically exclusively the intense signals of the solvents (ethanol and water). However, using different NMR experiments, such as 1D-DOSY and the 1D-NOESY pulse sequence with suppression of water and ethanol signals [3], it was possible to reduce the intensity of the solvent signals in the spectra and a better resolution of the metabolic profiles was then achieved. Tinctures of Cannabis (prepared in our lab), Ginkgo and Echinacea (commercial products) were successfully analyzed with this rapid and versatile method. The major limitation for this NMR approach is due to variation of the chemical shifts that occur when a component is dissolved in different solvents, and tinctures containing different amount of alcohol must be compared carefully.

Acknowledgment: We thank the European Commission for financial support under the FP6 (COOP-CT-2004–512696).

References: [1] Sumner, L.W., et al. (2003) Phytochemistry, 62: 817–836. [2] Bilia, A.R., et al. (2001) Chromatographia, 53: 210–215. [3] Duarte I., et al. (2002) J. Agric. Food Chem. 50: 2475–2481.