The biosynthesis of AR-5 (mycinamicins) antibiotics.

Sir: AR-5 (Mycinamicins) antibiotics, 16-membered ring macrolides, are produced by Micromonospora sp. These novel macrolides are potent antibiotics with unusual activity. Structures of these compounds were independently assigned by us and a group of Japanese workers.',') The assignments of the signals in the 13C NMR spectra have been previously reported". In analogy with the origin of the carbon skeleton of the aglycone ring of rosaramicin3'4) and tylosin5), which are derived from two acetates, five propionates and one butyrate, we report here the biosynthesis of new 16-membered macrolide antibiotics. For a typical incorporation study, Micromonospora polytrota (NRRL 12066, ATCC 31584) was inoculated into a medium containing starch (50 g), distiller's solubles (5 g) and Pharmamedia (5 g) in tap water (1 liter) and the initial pH was adjusted to 7.5. After cultivation for 48 hours at 30°C, the 14C or 13C labeled precursors, [l-13C] Na-acetate, [2-13C] Na-acetate, [1-13C] Na-propionate, [1-13C] Na-butyrate and L-[methyl-13C] methionine were added to the culture. The fermentation was further continued for 72 hours and harvested. The harvested broth was adjusted to pH 8.5 and extracted twice with ethyl acetate. The ethyl acetate extract was washed with 5 acetic acid. The aqueous layer was removed, its pH adjusted to 8.5 and then extracted with toluene. The toluene extract contained a mixture of enriched AR-5 antibiotics, AR-5 #1 (mycinamicin I) and AR-5 #2 (mycinamicin II). For 13C NMR studies , further purification, on a silicagel column using the solvent system toluene methylene chloride methanol conc. ammonia (16: 4: 2: 0.1), was carried out to separate AR-5 #1 (mycinamicin I) and AR-5 #2 (mycinamicin II). 13C NMR of the cold and the enriched antibio-