1H NMR-based metabolic profiling for the quality control of Thymus vulgaris raw plant material

Conventional chromatographic methods for the characterization of Thymus vulgaris raw plant material comprise a combination of GC and LC, respectively employed for the analysis of monoterpenoids and phenolic constituents. Herein we demonstrate the suitability of ¹H NMR-based metabolic profiling for the quality control of T. vulgaris aerial parts of commercial and field culture origin. Extracts of 146 different T. vulgaris aerial parts samples were obtained by direct extraction with DMSO-d ₆ and were subsequently analyzed by ¹H NMR spectroscopy. The preliminary analysis of the acquired 600MHz ¹H NMR spectra was performed by Principal Component Analysis (PCA). A PCA model explaining 95.2% of the total variance using 5 principal components showed clear discrimination of thymol, carvacrol, and linalool chemotypes and enabled quick identification of interesting samples among the large number of samples analyzed. The use of anthracene as internal standard allowed quantification of five monoterpenoids (thymol, carvacrol, linalool, p-cymene, and γ-terpinene) and rosmarinic acid in the DMSO-d ₆ crude extracts, employing the same spectral dataset. The NMR method was validated in terms of linearity, precision, accuracy and robustness. The quantitative results were compared to those obtained with conventional chromatographic methods such as GC and HPLC and were found to be in reasonable agreement. The simultaneous analysis of monoterpenoids and rosmarinic acid, difficult to achieve with one single chromatographic technique, makes ¹H NMR an attractive method for the quality control of T. vulgaris raw plant material.

Acknowledgements: This work was financially supported by Bionorica research GmbH, 6020 Innsbruck, Austria.