Structure and Absolute Configuration of Secondary Metabolites from Two Strains of Streptomyces chartreusis Associated with Attine Ants

Humberto Ortega,João Batista,Gabriela De Paula,Weilan Melo,Mônica Pupo

doi:10.21577/0103-5053.20190194

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.

Highlights

Fungus-growing ants comprise more than 230 species, all of which depend on the cultivation of fungal gardens for food
As part of the International Cooperative Biodiversity Group Program in Brazil (ICBG-Brazil),[9] we have investigated the small molecules produced by Streptomyces chartreusis ICBG377, isolated from the fungal garden of the leafcutter ant Acromyrmex subterraneus brunneus; and from
Besides reporting the isolation and structural characterization of compounds 1-5, we describe the use of vibrational circular dichroism (VCD) spectroscopy and density functional theory (DFT) calculations to confirm the absolute configuration of the stereoisomers 3 and 4

Summary

Introduction

Fungus-growing ants (tribe Attini) comprise more than 230 species, all of which depend on the cultivation of fungal gardens for food They can be divided into five distinct agricultural systems: lower agriculture; coral fungus agriculture; yeast agriculture; generalized higher agriculture; and leaf-cutter agriculture that has evolved more recently to become the dominant herbivores of the New World tropics. Several new and known biologically active compounds have been identified from actinobacteria (Streptomyces and Pseudonocardia) isolated from fungus-growing ant colonies.[4,5,6,7] The first example was the new cyclic depsipeptide dentigerumycin, produced by the symbiotic Pseudonocardia sp., isolated from the exoskeleton of the coral fungus agriculture ant Apterostigma dentigerum This compound has a selective inhibition against the specialized pathogenic fungus Escovopsis sp., found only in fungus-growing ants colonies, and a potent inhibitory activity against several Candida albicans strains.[8] As part of the International Cooperative Biodiversity Group Program in Brazil (ICBG-Brazil),[9] we have investigated the small molecules produced by Streptomyces chartreusis ICBG377, isolated from the fungal garden of the leafcutter ant Acromyrmex subterraneus brunneus; and from

Methods

Results

Conclusion