Characterisation of diarylheptanoid- and flavonoid-type phenolics in Corylus avellana L. leaves and bark by HPLC/DAD-ESI/MS.

Introduction: The leaves of Corylus avellana L. (common hazel, Betulaceae), a plant with a wide distribution in Europe, have been used in folk medicine for various diseases, but phytochemical exploration of C. avellana is still incomplete. To the best of our knowledge there is no previous report concerning diarylheptanoids in C. avellana, although these compounds show a frequent occurrence among Betulaceae plants.

Objective: To improve existing online chromatographic methods for the investigation of the phenolic compounds in C. avellana leaves and bark, focusing on diarylheptanoid-type molecules.

Methods: Dried and powdered leaves and bark of C. avellana were extracted with increasing polarity solvents (n-hexane, chloroform, ethyl acetate and methanol) in Soxhlet extractor apparatus. For the characterisation of the phenolic compounds in the ethyl acetate and methanolic extracts, UV spectral data, obtained by LC with a diode-array detector (DAD), accurate molecular mass and formula, acquired by LC and electrospray ionisation (ESI) with time-of-flight (TOF) MS and fragmentation pattern, given by LC-ESI/MS/MS analyses were used. Quantitation of the compounds was performed by LC-MS/MS.

Results: In the methanolic and ethyl acetate extracts of C. avellana bark four flavonoid glycosides and a caffeoyl hexoside derivative were detected and characterised, while in C. avellana leaves, seven diarylheptanoid-type molecules were tentatively identified in addition to six flavonoid components. As far as we know this is the first study where the presence of diarylheptanoids in C. avellana is reported.

Conclusion: The improved HPLC/DAD-ESI/MS method was successfully utilised for the characterisation and quantitation of the phenolic compounds in C. avellana bark and leaves extracts.