Phytoecdysteroids are known to exert a broad range of biological activities in mammals accounting for a general strengthening, adaptogenic, and anabolic activity. Our research group has recently reported the synthesis of various autoxidized bioactive metabolites of 20-hydroxyecdysone (20E) [1]. Time dependency of the oxidation was monitored by HPLC after neutralizing the pH, and the above-mentioned metabolites were also detected when biomimetic oxidation of 20E using the Fenton reaction was performed and the product mixture was monitored by HPLC after sample pre-purification by solid phase extraction on silica [2]. In contrast with HPLC, capillary electrophoresis (CE) does not require sample pre-treatment, and it is also less time and solvent consuming.
The aim of the present study was to compare results obtained by HPLC and CE in order to gain insight on possible effects of the pre-purification concerning (i) the monitoring of base-catalysed autoxidation of 20E and (ii) the analysis of the crude Fenton reaction.
Oxidation of 20E through base-catalysis or by Fenton reagent was performed similarly as before, and direct analysis of the crude reaction mixtures was achieved by CE without sample preparation. Autoxidation showed a similar qualitative fingerprint and time dependency to that found before [1], with a significantly higher maximum possible yield of 14,15-dihydro-14α-hydroxycalonysterone and isocalonysterone than before, i.e.70% and 50%, respectively. Concerning the Fenton reaction, however, none of the autoxidized metabolites could be identified by CE, suggesting that the previous observation on the formation of these compounds [2] was an artefact arising from subsequent oxidation during the sample preparation.
This work was supported by the NKFIH, Hungary (K119770), the EU-funded Hungarian grant EFOP-3.6.1 – 16 – 2016 – 00008, and GINOP-2.3.2 – 15 – 2016 – 00012. A.H. acknowledges the János Bolyai fellowship of the Hungarian Academy of Sciences and the Kálmán Szász Prize.
[1] Csábi J et al. J Nat Prod 2015; 78: 2339 – 2345.
[2] Dankó B et al. Planta Med 2015; 81: SL2C_02.
