Antibiotics from Gliding Bacteria, LXXVI. Vioprolides: New Antifungal and Cytotoxic Peptolides from Cystobacter violaceus

The antifungal and cytotoxic metabolites vioprolides A‐D ( 1 – 4 ) were obtained from the myxobacterium Cystobacter violaceus strain Cb vi35 by fermentation in the presence of the adsorber resin XAD‐1180. Peptolide structures 1–4 composed of eight amino acids and a glyceric acid were determined by spectroscopic methods and total hydrolysis. The absolute configurations of the building blocks were established by GC analysis on chiral stationary phases. Common building blocks of 1–4 are l ‐Ala, l ‐Cys, D ‐Leu, l ‐Thr, l ‐MeVal, ( E )‐dehydrobutyrine ( E ‐Dhb), and l ‐glyceric acid ( l ‐Gla). Two variable positions are occupied by l ‐Pro or l ‐Homopro and l ‐Pro or trans ‐(2 S ,4 R )‐4‐methylazetidinecarboxylic acid [(2 S ,4 R )‐Maz]. Two defined isomers of 1 were detected in CDCl 3 in a ratio of 3 : 2 (2D‐ 1 H NOESY) and assigned to rotational isomers at the amide bond of ThrMeVal.