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Development and validation of a new HPLC-UV/Vis method for the direct determination of oxyprenylated-anthraquinones produced by Rhamnus spp.

Introduction Oxyprenylated natural products, a family of secondary metabolites that have been consider for years as biosynthetic intermediates of the most abundant C-prenyl derivatives, were shown to exert in vitro and in vivo remarkable anti-cancer and anti-inflammatory effects.1 Among the several subclasses comprised in this group of secondary metabolites, oxyprenylated anthraquinones have been characterized so far in a very limited number of species. In particular 3-isopentenyloxy-6-methyl-1, 8-dihydroxyanthraquinone, known as madagascin, has been founded in plants belonging to the genus Vismia and Psorospermum, and 3-geranyloxy-6-methyl-1, 8-dihydroxyanthraquinone has been isolated from Vismia and Cratoxylum spp.1 Methods A new HPLC-UV/Vis method for the determination in the bark of selected Rhamnus spp. of five “classic” anthraquinones and two oxyprenylated derivatives (madagascin or 3-isopentenyloxy-emodine and 3-geranyloxy-emodine), discovered for the first time in this genus, was developed and validated. Plant samples were analysed after extraction with n-hexane and methanol and the analytes were separated using a C18 column with a mobile phase composed of double distilled water (1% formic acid): methanol (1% formic acid) = 35:65 (v/v) at 0.7 mL/min flow rate in a gradient elution mode. Selective detection was performed by two different UV/Vis wavelengths, 435 nm for quantitative analyses and 288 nm for qualitative ones. Results and discussion/conclusions The limit of quantification (LOQ) was 0.5 M for all cited analytes, with the only exception geranyloxy-emodine for which the recorded value was 5.0 M, and external matrix-matched standard curves showed linearity up to 125 M. In the entire analytical range within- and between-batch precision (RSD%) values ranged from 0.2 % to 12.9 %. For all analytes within- and between-batch trueness (bias %) values ranged from 12.2 % to 12.7 %. The overall recoveries were tested by optimisation of the extraction procedure. This method showed analytical performances able to selectively identify and quantify analytes in natural sources and could be directly applied for this kind of analyses in complex matrices.

Rhamnus; oxyprenylated; anthraquinones; HPLC-UV/Vis

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