Abstract: The main impurity of the new antiviral drug candidate MJJ was studied.The structure was elucidated by LC-MS and comparison with literature data.Impurity was prepared by alkali-destroying MJJ and its structure was determined by NMR spectroscopy.The synthesized impurity was used as reference compound in quality control of MJJ.The result of biological activity test showed that the impurity had certain antitumor activity.It was believed that this is a new strategy for related substances in bulk drug,and the experimental data were valuable for the determination of the impurity and quality control of MJJ.

Key words: diethyl tectoridingenin, MJJ, impurity, LC-MS, quality control