Roimatacene: an antibiotic against Gram-negative bacteria isolated from Cystobacter ferrugineus Cb G35 (Myxobacteria).

Roimatacene (1) was isolated from the myxobacterium Cystobacter ferrugineus strain Cb G35 in a bioactivity-guided process, by following the antimicrobial activity against Escherichia coli. Since 1 was extremely sensitive to oxygen, a protective isolation and handling protocol was developed, by utilizing the free radical scavenger 4-ethoxyphenol. The structure of 1 was determined by HRMS, 1D and 2D NMR spectroscopy and chemical derivatization to acetonides and Mosher esters to finally establish the absolute configuration. Methionine and acetate were identified as building blocks in the biosynthesis of 1 by feeding experiments with differently (13)C-labeled precursors. The antimicrobial activity of 1 was determined in a broad screening revealing 1 to inhibit several Gram-negative bacteria.