Juglorescein, Juglocombins and Juglochromans: Structure of Juglomycin Dimers from Streptomycetes

Novel juglomycin derivatives with a C28 skeleton were isolated from the Streptomyces strains 815 and GW4184. Juglorescein (1a) and juglocombin A (2a) and B (3a) are C,C dimers of juglomycin C (10) with a five membered ring between the two monomeric moieties. In the juglochromans A – D (4a, 5a, 6a, 6c), two juglomycin C (10) units are connected by C,C and C,O bonds forming a central isochroman or a chroman system. The structures of the new natural products were elucidated by detailed spectra analyses, by comparison of the NMR data with those of related compounds and by biosynthetic considerations. The new natural products were antimicrobially inactive.