Polyketides and a Dihydroquinolone Alkaloid from a Marine-Derived Strain of the Fungus Metarhizium marquandii

Dina H. El-Kashef, Georgios Daletos, Malte Plenker, Rudolf Hartmann, Attila Mándi, T. Kurtán, Horst Weber, Wenhan Lin, Elena Ancheeva, Peter Proksch

Research output: Contribution to journalArticle

7 Citations (Scopus)

Abstract

Three new natural products (1-3), including two butenolide derivatives (1 and 2) and one dihydroquinolone derivative (3), together with nine known natural products were isolated from a marine-derived strain of the fungus Metarhizium marquandii. The structures of the new compounds were unambiguously deduced by spectroscopic means including HRESIMS and 1D/2D NMR spectroscopy, ECD, VCD, OR measurements, and calculations. The absolute configuration of marqualide (1) was determined by a combination of modified Mosher's method with TDDFT-ECD calculations at different levels, which revealed the importance of intramolecular hydrogen bonding in determining the ECD features. The (3R,4R) absolute configuration of aflaquinolone I (3), determined by OR, ECD, and VCD calculations, was found to be opposite of the (3S,4S) absolute configuration of the related aflaquinolones A-G, suggesting that the fungus M. marquandii produces aflaquinolone I with a different configuration (chiral switching). The absolute configuration of the known natural product terrestric acid hydrate (4) was likewise determined for the first time in this study. TDDFT-ECD calculations allowed determination of the absolute configuration of its chirality center remote from the stereogenic unsaturated γ-lactone chromophore. ECD calculations aided by solvent models revealed the importance of intramolecular hydrogen bond networks in stabilizing conformers and determining relationships between ECD transitions and absolute configurations.

Original languageEnglish
JournalJournal of Natural Products
DOIs
Publication statusAccepted/In press - Jan 1 2019

ASJC Scopus subject areas

  • Analytical Chemistry
  • Molecular Medicine
  • Pharmacology
  • Pharmaceutical Science
  • Drug Discovery
  • Complementary and alternative medicine
  • Organic Chemistry

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  • Cite this

    El-Kashef, D. H., Daletos, G., Plenker, M., Hartmann, R., Mándi, A., Kurtán, T., Weber, H., Lin, W., Ancheeva, E., & Proksch, P. (Accepted/In press). Polyketides and a Dihydroquinolone Alkaloid from a Marine-Derived Strain of the Fungus Metarhizium marquandii. Journal of Natural Products. https://doi.org/10.1021/acs.jnatprod.9b00125