Metabolic products of microorganisms. 245. Colabomycins, new antibiotics of the manumycin group from Streptomyces griseoflavus. II. Structure of colabomycin A.

The structure of colabomycin A (1) was elucidated by a detailed spectroscopic analysis. Two-dimensional NMR spectroscopy experiments provided assignments of the proton and carbon resonances of the tetraene carboxamide chains occurring in 1. The configurations of eight out of nine double bonds were determined by analysis of their coupling constants. The absolute configurations of C-4 (4S), C-5 (5R) and C-6 (6S) were established from the CD spectra of the parent compound and of 2-(6-oxo-2,4-hexadienoylamino)-5,6-epoxy-1,4-benzoquinone (2), which was obtained from 1 by mild chromic acid oxidation.