NMR and UPLC-qTOF-MS/MS Characterisation of Novel Phenylethanol Derivatives of Phenylpropanoid Glucosides from the Leaves of Strawberry (Fragaria x ananassa cv. Jonsok)

Introduction - Strawberry (Fragaria x ananassa) is rich in polyphenols, particularly anthocyanins, flavonols, condensed tannins and ellagic tannins. In addition to the fruits, the leaves of strawberry also contain a wide range of phenolic compound classes, but have not been investigated to the same extent as the fruit. Objective - To characterise a metabolite group present in the leaves of strawberry, that was not amenable for identification based on earlier information available in the literature. Methodology - Methanolic extracts of strawberry leaves were analysed by UPLC-qTOF-MS/MS and iterative quantum mechanical NMR spectral analysis. Results - The structures of phenylethanol derivatives of phenylpropanoid glucosides Eutigoside A (F4) and its two isomeric forms 2-(4-hydroxyphenyl)ethyl-[6-O-(Z)-coumaroyl]-beta-D-glucopyranoside (F6) and 4-(2-hydroxyethyl)phenyl-[6-O-(E)-coumaroyl]-beta-D-glucopyranoside (F1) were resolved by NMR and UPLC-qTOF-MS/MS. In addition, two other derivatives of phenylpropanoid glucosides similar to Eutigoside A but possessing different phenolic acid moieties, namely Grayanoside A (F5) and 2-(4-hydroxyphenyl)ethyl-[6-O-(E)-caffeoyl]-beta-D-glucopyranoside (F14), were similarly identified. Also, accurate characteristic coupling constants for the subunits are reported and their usefulness in structural analysis is highlighted. Conclusion - Chemical analysis of the leaves of strawberry (Fragaria x ananassa cv. Jonsok) resulted in the identification of a compound class, phenylethanol derivatives of phenylpropanoid glycosides, not previously found in strawberry. Copyright (C) 2009 John Wiley & Sons, Ltd.