A novel process related impurity and forced degradation study of synthetic wogonin: Development of a liquid chromatographic method for purity control

Although the chemical synthesis of wogonin (5,7-dihydroxy-8-methoxy-2-phenyl-4H-chromen-4-one) has been established, the impurity profile of this pharmaceutical agent is still not fully understood. In this study, a novel process related impurity present in the synthetic wogonin was isolated by preparative HPLC. Its structure elucidation was unambiguously carried out by NMR, HRMS and IR spectra, and it was characterized as 6-chloro-5,7-dihydroxy-8-methoxy-2-phenyl-4H-chromen-4-one (imp-1), a new compound which had never been reported before. Moreover, forced degradation studies were also carried out, and wogonin was shown to undergo isomerzation under basic stress condition to form a major degradant, 5,7-dihydroxy-6-methoxy-2-phenyl-4H-chromen-4-one (imp-2) using HPLC–Q-TOF–MS/MS technique. Finally, a selective and simple routine HPLC method was developed for simultaneous quantification of wogonin and the two related compounds. The proposed method is useful for purity control during the process development of wogonin and laboratory-prepared preparations. Their formation pathways were also discussed.

► An unknown process related impurity in synthetic wogonin crude drugs was confirmed as 6-chloro-5,7-dihydroxy-8-methoxy-2-phenyl-4H-chromen-4-one.
► A major degradation product formed during basic stress conditions was also identified as 5,7-dihydroxy-6-methoxy-2-phenyl-4H-chromen-4-one by HPLC-Q-TOF-MS/MS technique.
► A selective and simple routine HPLC method was developed for simultaneous quantification of wogonin and the two related compounds.