Structure and absolute configuration of secondary metabolites from two strains of Streptomyces chartreusis associated with attine ants

Abstract

The antibiotic streptazolin (1), its E-isomer (2), along with the stereoisomers strepchazolin A (3) and strepchazolin B (4) and the inorganic compound cyclooctasulfur (5) were produced in solid culture by Streptomyces chartreusis ICBG377, which was isolated from the fungal garden of the leaf-cutter ant Acromyrmex subterraneus brunneus. This is the first time compound 2 is reported as a natural product. Compound 5, which showed antagonist activity against the specialized pathogenic fungus Escovopsis sp., was also produced by Streptomyces chartreusis ICBG323, isolated from the exoskeleton of winged male of Mycocepurus goeldii. The absolute configurations of 3 and 4 were confirmed by the combination of vibrational circular dichroism (VCD) spectroscopy and density functional theory (DFT) calculations. These results clearly demostrate the power of VCD to tell apart epimeric natural products. Compounds 1, 3 and 4 were produced by geographically distant but phylogenetically close strains, S. chartreusis ICBG 377 isolated in Brazil, and S. chartreusis NA02069, a marine sediment strain isolated in China.