Bioassay-Guided Isolation of Antibacterial Metabolites from Emericella sp. TJ29

J Nat Prod. 2017 Sep 22;80(9):2399-2405. doi: 10.1021/acs.jnatprod.7b00077. Epub 2017 Sep 13.

Abstract

Bioassay-guided isolation of metabolites from cultures of the plant-derived fungus Emericella sp. TJ29 yielded three new terpene-polyketide hybrid meroterpenoids, emervaridones A-C (1-3), two new polyketides, varioxiranediols A and B (5 and 6), and three known analogues (4, 7, and 8). The structures and absolute configurations of these new compounds were elucidated by spectroscopic analyses, single-crystal X-ray diffraction, Mo2(OAc)4-induced electronic circular dichroism (ECD) data, and ECD calculations. To date, only one compound (4) bearing the emervaridone-type carbocyclic skeleton has been reported. The structures of emervaridones A-C (1-3) are new members of this type of natural product, and 1 features the first example of an α-directional H-7' in this structural category. Compounds 1 and 5 were active against five drug-resistant microbial pathogens [methicillin-resistant Staphylococcus aureus (MRSA), Enterococcus faecalis, extended-spectrum β-lactamase-producing Escherichia coli (ESBL-producing E. coli), Pseudomonas aeruginosa, and Klebsiella pneumoniae] with minimum inhibitory concentration (MIC) values in the micrograms per milliliter range. Notably, the inhibitory effect of emervaridone A (1) against ESBL-producing E. coli was comparable to that of the clinically used antibiotic amikacin, with an MIC value of 2 μg/mL. Compounds 1 and 5, both with low toxicities to mammalian cells, were bacteriostatic and bactericidal, respectively. Importantly, these two compounds may provide novel chemical scaffolds for the discovery of antibacterial agents for drug-resistant microbial pathogens.

MeSH terms

  • Anti-Bacterial Agents / chemistry
  • Anti-Bacterial Agents / isolation & purification*
  • Anti-Bacterial Agents / pharmacology*
  • Biological Assay
  • Emericella
  • Enterococcus faecalis / drug effects*
  • Escherichia coli / drug effects*
  • Klebsiella pneumoniae / drug effects*
  • Methicillin-Resistant Staphylococcus aureus / drug effects*
  • Microbial Sensitivity Tests
  • Molecular Structure
  • Polyketides / chemistry
  • Polyketides / pharmacology*
  • Pseudomonas aeruginosa / drug effects*
  • Terpenes / chemistry
  • Terpenes / isolation & purification*
  • Terpenes / pharmacology*
  • beta-Lactamases / chemistry*
  • beta-Lactamases / metabolism

Substances

  • Anti-Bacterial Agents
  • Polyketides
  • Terpenes
  • emervaridone A
  • emervaridone B
  • emervaridone C
  • beta-Lactamases