Developmental changes in the composition of five anthraquinones from Rheum palmatum as quantified by (1) H-NMR

Introduction: Rheum palmatum is an important traditional Chinese medicine featuring anthraquinones with several activities. Generally, rhein, emodin, aloe-emodin, physcion and chrysophanol are used as chemical markers for the quality control of rhubarb products.

Objective: To develop a simple protocol for the quantification of rhein, emodin, aloe-emodin, physcion and chrysophanol in R. palmatum collected at different developmental stages.

Methods: (1) H-NMR spectra were measured on samples dissolved in acetone-d6 , quantification was carried out using the signals of H-4 of rhein (δH 8.36), H-7 of emodin (δH 6.68), CH2 OH of aloe-emodin (δH 4.81), OCH3 of physcion (δH 4.02) and CH3 of chrysophanol (δH 2.50), which were well separated from other signals. Quantitative analysis was based on the relative ratio of the intensity of each compound to the known amount of internal standard maleic acid.

Results: The quantitative (1) H-NMR (qHNMR) method developed showed good precision, trueness, linearity, repeatability and stability for the quantification of rhein, emodin, aloe-emodin, physcion and chrysophanol. This method was applied successfully to explore the seasonal variations of the five major anthraquinones in R. palmatum, and provided quantitative results in reasonable agreement with those obtained by the HPLC-UV method.

Conclusion: Compared with the conventional HPLC-based methods, the qHNMR analysis is rapid, reference-free and convenient with less sample pre-treatment. This technique should be a feasible choice for the quality control of R. palmatum.