Indothiazinone, an Indolyl Thiazolyl Ketone from a
Novel Myxobacterium Belonging to the Sorangiineae
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Abstract
Indothiazinone (<b>1</b>),
an indolyl thiazolyl ketone, was discovered in cultures of novel myxobacterial
strain 706, recently isolated from compost in Germany. Molecular phylogenetic
studies based on 16S rRNA gene sequences revealed strain 706 to be
a representative of a new family of the Sorangiineae. A screening
of the culture broth for antimicrobial metabolites followed by isolation
and characterization of these compounds revealed six indole derivatives
and a 1,4-naphthoquinone derivative. The structures were determined
to be indothiazinone (<b>1</b>; 1<i>H</i>-indol-3-yl(1,3-thiazol-2-yl)methanone)
and three 3-methylbuta-1,3-dien-1-yl-substituted indoles, indolyl
ethanol <b>2</b> and the <i>E</i>- and <i>Z</i>-isomers of indolyl ethylidenehydroxylamine <b>4</b> and <b>5</b> by MS and NMR spectroscopic analyses. In the indolyl ethanol
derivative <b>3</b> the unsaturated methylene group of the butadienyl
residue was replaced by an oxygen atom to give the keto group of the
butanone side chain. Further 1<i>H</i>-indol-3-ylacetonitrile
(<b>6</b>) was identified, which was already known as a myxobacterial
metabolite. 2-Hydroxyethyl-3-methyl-1,4-naphthoquinone (<b>7</b>) was recognized during dereplication as an antibiotic previously
isolated from <i>Actinoplanes capillaceus</i>. Whereas <b>1</b>, <b>4</b>, <b>5</b>, and <b>7</b> showed
weak activity against yeasts and filamentous fungi, isomers <b>4</b> and <b>5</b> were weakly active against Gram-positive
bacteria and mouse fibroblasts. Compound <b>6</b> is volatile,
and <b>2</b> and <b>3</b> showed no activity in a number
of assays