Thermoactinoamide A, An Antibiotic Lipophilic Cyclopeptide From The Icelandic Thermophilic Bacterium Thermoactinomyces Vulgaris

The thermophilic bacterium Thermoactinomyces vulgaris strain IS CAR 2354, isolated from a coastal hydrothermal vent in Iceland, was shown to contain thermoactinoamide A (1), a new cyclic hexapeptide composed of mixed D and L amino acids, along with five minor analogues (2-6). The structure of 1 was determined by one- and two-dimensional NMR spectroscopy, high-resolution tandem mass spectrometry, and advanced Marfey's analysis of 1 and of the products of its partial hydrolysis. Thermoactinoamide A inhibited the growth of Staphylococcus aureus ATCC 6538 with an MIC value of 35 mu M. On the basis of literature data and this work, cyclic hexapeptides with mixed D/L configurations, one aromatic amino acid residue, and a prevalence of lipophilic residues can be seen as a starting point to define a new, easily accessible scaffold in the search for new antibiotic agents.