Extracts from Rhododendron ferrugineum Do Not Exhibit Grayanotoxin I: An Analytical Survey on Grayanotoxin I within the Genus Rhododendron

Lechtenberg M, Dierks F, Sendker J, Louis A, Schepker H, Hensel A

Abstract

For quantitative determination of grayanotoxin I(1) in plant material, a GC/MS method was devel-oped after trimethylsilyl derivatisation of theanalytes. Forskolin (5) was used as an internalstandard for quantification. ICH-compliant meth-od validation indicated sufficient specificity, pre-cision, quantitation (15μg/mL) and detection(5μg/mL) limits. Regression analysis showed thata non-linear (polynomial) model was preferableto a linear one. For isolation of grayanotoxin I ref-erence material fromRhododendron ponticumleaves, an efficient two-step fast centrifugal parti-tion chromatography isolation protocol is de-scribed. A survey of 17 different plant speciesfrom the genusRhododendronrevealed highgrayanotoxin I content forR. catawbiense, R. pon-ticum, R. degronianumsubsp.yakushimanum, R. ×sochadzeae, R. moupinense, R. galactinum,andR. mucronatumvar.ripense. The content of thiscompound in leaf material fromR. ponticumde-creased rapidly during drying process. Grayano-toxin I was not detected in different batches offresh leaves and fruits fromR. ferrugineum.Incontrast to the claims of German health author-ities, this traditionally used herb therefore cannotbe evaluated as toxic due tothe presence ofgraya-notoxin I.

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