The solution conformation of the peptide antibiotic thiostrepton: a 1H NMR study.

The majority of the 84 protons in the 1H NMR spectrum of thiostrepton at 300 MHz were unambiguously assigned on the basis of double resonance experiments under different conditions of solvent, temperature and 2H-exchange by comparison with the known crystal structure determined by Anderson et al.1) Evidence is presented to suggest that the side chain, the nature of which remained undefined on X-ray analysis, is comprised of two dehydroalanine residues which supports the conclusions reached by Tori et al.2) on the basis of 13C NMR spectroscopy. These two residues are missing in thiostrepton A2, a minor artifact. All available 1H NMR evidence suggests thiostrepton to have a similar conformation in deuterochloroform solution to that found in the crystal form.