Off-Line NMR Improves Traditional Chinese Medicine Analysis

Researchers at Zhejiang University, China, have developed a new method combining liquid chromatography-mass spectrometry (LC-MS) and off-line nuclear magnetic resonance (NMR) to analyze the constituents within traditional Chinese medicines (TCMs).¹ This new method addresses the limitations of conventional phytochemical and solely LC-MS-based approaches. 

In recent years research into TCMs has increased dramatically as their potential as a source for novel pharmaceutical agents has been recognized. However, conventional phytochemical methods used to distinguish chemical constituents proved ineffective as a result of TMCs being comprised of multiple crude drugs. This has resulted in LC-MS gaining importance as a method for identifying chemical components. While LC-MS-based research has proven effective, limitations have arisen from solely using LC-MS as distinguishing isomers generally cannot be accomplished with only MS data, and the structures of unknown compounds cannot be confirmed.

This phenomenon has arisen within the literature before with notable studies by Zheng et al.² and Yen et al.³ failing to gather structural data on isomers uncovered in studies focused upon TCMs. To address this Shufang Wang and her team developed an LC guided method that uses NMR spectroscopy. The team performed LC-ion trap MS (LC-IT-MS) and LC-quadrupole time-of-flight MS (LC-QTOF-MS) to assign the compounds to one particular crude drug and followed this with semi-preparative LC guided by LC-MS to prepare target isomers in micro-scale for off-line NMR analysis. 

This approach was applied to two TCM formulae taken from Shang-Han-Lun, a medical classic by Zhongjing Zhang from the Eastern Han dynasty of China. Zhi-Zi-Gan-Cao-Chi-Tang (ZZGCCT) is used to treat restlessness, sleeplessness, and weak breathing caused by typhoid; Zhi-Zi-Bai-Pi-Tang (ZZBPT) is used to treat typhoid and fever.   

Lead author of the study Shufang Wang told The Column: “Nowadays, it is becoming more and more difficult to find new chemical entities with the paradigm of single-compound-single-target, while the concept of multi-compound-multi-target drugs is [being] paid increasing attention. Considering that their therapeutic effects have been demonstrated and proved by broad clinical practice for thousands of years, TCMs would be a valuable resource to develop new multi-compound-multi-target drugs.”

The research identified 119 constituents in total including two new triterpene saponins and one new flavonoid glycoside. Structural identification was performed on these as well as on five previously known triterpenoid glycosides, which were completely assigned. 

These results indicate that the approach developed is reliable and effective for the identification of constituents in TCM formulae, particularly for isomers that could not be distinguished by MS data. The team responsible for this research are currently focusing on the identification of active constituents from multiple TCM formulae. - L.B. 

References

S. Wang et al., J. Pharm. Biomed. Anal. 117, 255-265 (2016).

C.N. Zheng et al., J. Mass Spectrom.44, 230-244 (2009).

Y. Yan et al., J. Pharm. Biomed. Anal.80, 192-202 (2013).