Mycinamicins, new macrolide antibiotics. XI. Isolation and structure elucidation of a key intermediate in the biosynthesis of the mycinamicins, mycinamicin VIII.

rubida sp. nov., which have strong antibacterial activity against Gram-positive bacteria1\ The complex consists of seven components; mycinamicins I (1), II (2), III (3), IV (4), V (5), VI (6) and VII (7)2~4). During the search for new antibiotics from the fermentation broth of mycinamicinproducing strains, we have discovered a new minor component designated mycinamicin VIII (8). Recently, the same product has been obtained in much higher yield from the fermentation ofa mutant strain C-7-1, isolated during on going mutagenic studies of M. griseorubida sp. nov. In addition, this mutant was found to accumulate protomycinolide IV (9)5). These compounds (8 and 9) are considered to be key intermediates in the biosynthesis of the mycinamicins. In this communication we describe the isolation and identification of the new metabolite, compound 8, which provided definitive information about the biosynthetic pathway from protomycinolide IV (9) to mycinamicin IV (4).