A nontargeted, effect-directed screening (bioprofiling) and a subsequent highly targeted characterization of antibacterial compounds from plant matrices is demonstrated on the example of Solidago virgaurea root extracts. The procedure comprises high-performance thin-layer chromatography (HPTLC) coupled with six bacterial bioassays including two plant pathogens, a radical scavenging assay, an acetylcholinesterase assay as well as in situ and ex situ mass spectrometric analyses. In situ mass spectra were directly recorded from the adsorbent using the Direct Analysis in Real Time interface (HPTLC-DART-MS), whereas ex situ mass spectra were recorded using an elution head-based interface (HPTLC-ESI-MS). For further bioassay-guided isolation of the main antimicrobial compounds, flash chromatographic fractionation and semipreparative high-performance liquid chromatographic purification were used and nuclear magnetic resonance data allowed the identification of the unknown antimicrobial compounds as 2Z,8Z- and 2E,8Z-matricaria esters. The discovered antibacterial activity was confirmed and specified by a luminometric assay and as minimal inhibitory concentration in the liquid phase.
Comparative analysis of the full set of methylated -cyclodextrins as chiral selectors in capillary electrophoresisThe chiral separation ability of the full library of methylated--cyclodextrins towards pharmacologically significant racemic drugs including basic compounds was studied by chiral CE. The syntheses of all the methylated, single isomer -cyclodextrins were revised and optimized and the aqueous solubility of the derivatives was unambiguously established. The three most relevant commercially available methylated isomeric mixtures were also included in the screening, so a total of ten various methylated CDs were investigated. The effects of the selector concentration on the enantiorecognition properties at acidic pH were investigated. Among the dimethylated -cyclodextrins, the heptakis (2,6-di-Omethyl)--cyclodextrin isomer (2,6-DIMEB) resulted to be the most versatile chiral selector. Terbutaline was selected as a model compound for the in-depth investigation of host-guest enantiodiscrimination ability. The association constants between the two terbutaline enantiomers and 2,6-DIMEB were determined in order to support that the enantioseparation is driven by differences is host-guest binding. The migration order of the enantiomers was confirmed by performing spiking experiments with the pure enantiomers. 1D and 2D NMR spectroscopy was applied to the 2,3-, and 2,6-DIMEB/terbutaline systems to rationalize at molecular level the different enantioseparation ability of the dimethylated -cyclodextrin selectors.
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