• Macrooxazoles A-D, New 2,5-Disubstituted Oxazole-4-Carboxylic Acid Derivatives from the Plant Pathogenic Fungus .

      Matio Kemkuignou, Blondelle; Treiber, Laura; Zeng, Haoxuan; Schrey, Hedda; Schobert, Rainer; Stadler, Marc; HZI,Helmholtz-Zentrum für Infektionsforschung GmbH, Inhoffenstr. 7,38124 Braunschweig, Germany. (MDPI, 2020-11-24)
      In our ongoing search for new bioactive fungal metabolites, four previously undescribed oxazole carboxylic acid derivatives (1-4) for which we proposed the trivial names macrooxazoles A-D together with two known tetramic acids (5-6) were isolated from the plant pathogenic fungus Phoma macrostoma. Their structures were elucidated based on high-resolution mass spectrometry (HR-MS) and nuclear magnetic resonance (NMR) spectroscopy. The hitherto unclear structure of macrocidin Z (6) was also confirmed by its first total synthesis. The isolated compounds were evaluated for their antimicrobial activities against a panel of bacteria and fungi. Cytotoxic and anti-biofilm activities of the isolates are also reported herein. The new compound 3 exhibited weak-to-moderate antimicrobial activity as well as the known macrocidins 5 and 6. Only the mixture of compounds 2 and 4 (ratio 1:2) showed weak cytotoxic activity against the tested cancer cell lines with an IC50 of 23 µg/mL. Moreover, the new compounds 2 and 3, as well as the known compounds 5 and 6, interfered with the biofilm formation of Staphylococcus aureus, inhibiting 65%, 75%, 79%, and 76% of biofilm at 250 µg/mL, respectively. Compounds 5 and 6 also exhibited moderate activity against S. aureus preformed biofilm with the highest inhibition percentage of 75% and 73% at 250 µg/mL, respectively.
    • Synthesis of the fungal macrolide berkeleylactone A and its inhibition of microbial biofilm formation.

      Schriefer, Manuel G; Schrey, Hedda; Zeng, Haoxuan; Stadler, Marc; Schobert, Rainer; HZI,Helmholtz-Zentrum für Infektionsforschung GmbH, Inhoffenstr. 7,38124 Braunschweig, Germany. (Royal Society of Chemistry, 2021-05-03)
      The fungal macrolide berkeleylactone A was synthesised in 13 steps and 24% yield using (R)-propylene oxide and an asymmetric Noyori hydrogenation of a β-ketoester to install the stereogenic centres. A domino addition-Wittig olefination of a 13-hydroxytetradecanal intermediate with the cumulated ylide Ph3PCCO closed the macrocyle by establishing the α,β-unsaturated ester group, necessary for the attachment of the sidechain thiol via a thia-Michael reaction. The synthetic berkeleylactone A inhibited the formation of Staphylococcus aureus biofilms and showed significant dispersive effects on preformed biofilms of Candida albicans by at least 45% relative to untreated controls at concentrations as low as 1.3 μg mL-1.