A 15N nuclear magnetic resonance study of the biosynthesis of quinoxaline antibiotics

Uniformly ¹⁵N-labelled triostin A and echinomycin have been prepared by growing the producing organisms on enriched media and their ¹⁵N nuclear magnetic resonance spectra partially assigned by a combination of nuclear Overhauser effect and scalar coupling constant measurements. Selective feeding experiments using unlabelled L-tryptophan-supplemented media have shown that N-1 and N-4 of the quinoxaline rings have their origins in the indole and amino groups of tryptophan, respectively.