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Synthesis of Small Combinatorial Libraries of Natural Products: Identification and Quantification of New Long-chain 3-Methyl-2-alkanones from the Root Essential Oil of Inula helenium L. (Asteraceae)

Authors

  • Niko S. Radulović,

    Corresponding author
    1. Department of Chemistry, Faculty of Science and Mathematics, University of Niš, Niš, Serbia
    • Correspondence to: N. S. Radulović, Department of Chemistry, Faculty of Science and Mathematics, University of Niš, Višegradska 33, 18000 Niš, Serbia. E-mail: nikoradulovic@yahoo.com

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  • Marija S. Denić,

    1. Department of Chemistry, Faculty of Science and Mathematics, University of Niš, Niš, Serbia
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  • Zorica Z. Stojanović-Radić

    1. Department of Biology and Ecology, Faculty of Science and Mathematics, University of Niš, Niš, Serbia
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ABSTRACT

Introduction

Recently, a potent anti-staphylococcal activity of Inula helenium L. (Asteraceae) root essential oil was reported. Also, bioassay guided fractionation of the oil pointed to eudesmane sesquiterpene lactones and a series of unidentified constituents as the main carriers of the observed activity.

Objective

To identify nine new constituents (long-chain 3-methyl-2-alkanones) from a fraction of this root essential oil with a low minimum inhibitory concentration value (0.8 µg/mL) by employing a synthetic methodology that leads to the formation of a small combinatorial library of these compounds.

Methods

The identity of these constituents was inferred from mass spectral fragmentation patterns and GC retention data. A library of 3-methyl-2-alkanones (C11–C19 homologous series) was synthesised in three steps starting from methyl acetoacetate and the corresponding alkyl halides. The synthetic library was also screened for in vitro anti-microbial activity.

Results

Gas chromatographic analyses of I. helenium essential oil samples with spiked compounds from the synthesised library corroborated the tentative identifications of the long-chain 3-methyl-2-alkanones. The availability of these anti-microbial compounds from this library made it possible to construct GC/FID calibration curves and determine their content in the plant material: 0.08 − 24.2 mg/100 g of dry roots.

Conclusion

The small combinatorial library approach enabled the first unequivocal identification of long-chain 3-methyl-2-alkanones as plant secondary metabolites, and, also, allowed determination of not only a single compound and biological properties, but those of a group of structurally related compounds. Copyright © 2013 John Wiley & Sons, Ltd.

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