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Keywords:

  • HPLC–ESI/QTOF/MS/MS;
  • diterpenoids;
  • Rhododendron molle

Introduction

‘Naoyanghua’, composed of the flowers of Rhododendron molle G. Don, is a traditional Chinese medicine that is widely known for its toxicity. Grayanane-type diterpenoids are the main active ingredients in R. molle, as well as possibly their toxicity: they are, however, difficult to isolate and analyse using common chromatographic methods, due to their small amounts and absence of conjugated groups, such as phenyl and α, β-unsaturated ketone.

Objective

To establish a highly sensitive, selective and reliable method for the qualitative evaluation of trace diterpenoids in the flowers of R. molle by using tandem solid-phase extraction followed by high-performance liquid chromatography with electrospray ionisation quadrupole-time-of-flight mass spectrometry (HPLC–ESI/QTOF/MS/MS).

Methods

Tandem solid phase extraction (SPE) was undertaken using a polyamide cartridge and a C18E cartridge in succession to enrich the trace diterpenoids. HPLC–ESI/QTOF/MS/MS was used to determine the fragmentation patterns of diterpenoids and to tentatively characterise their fragmentation pathways.

Results

HPLC–ESI/QTOF/MS/MS detected a total of 14 diterpenoids, eight of which were identified by comparison with literature sources and six based on fragmentation analysis. Among the latter six, rhodojaponin VI-3-glucoside was tentatively identified as a new diterpenoid glycoside and rhodojaponin VII, rhodojaponin IV and rhodojaponin I were reported from R. molle for the first time.

Conclusion

By qualitative research of diterpenoids in this plant by HPLC–ESI/QTOF/MS/MS, a reliable methodology for the analysis of these active constituents of R. molle was established for the first time. Copyright © 2014 John Wiley & Sons, Ltd.