The biosynthesis of picromycin using 13C enriched precursors.

Sir: Using 13C enriched precursors it has been elucidated recently1) that the aglycone of the leucomycins was derived from five acetates, one propionate, one butyrate and an unknown C2-unit corresponding to carbons-3 and -4. In the case of magnamycin which is C-9 oxidation product of leucomycin, previous studies using 14C labeled precursors2) suggested an acetate origin for carbons-3 and -4. Another biosynthetic investigation on the 16-membered macrolide antibiotic tylosin3) afforded evidence that carbons-3, -4 and -18 of this compound were originating from a propionate unit. Taking an interest in whether the aglycone of a 14-membered macrolide has such biogenetically unknown carbons, an investigation with picromycin as an example was undertaken. In the biosynthesis of erythromycin, it has been well established that 27 carbons of its aglycone are derived from seven propionates.41 Although propionate and acetate have been estimated in many articles to be precursors for aglycone of picromycin,4~6) there is not enough evidence to support this speculation. In this paper we report the incorporation pattern of [1-13C]-acetate and [1-13C] propionate into picromycin. Streptomyces flavochromogenes, a picromycin-producing strain, was inoculated into a seed medium containing 2 % glucose, 0.5% meat extract, 0.5 % peptone, 0.1 % yeast extract, 0.5 % NaCl and 0.3 % CaCO3 and cultivated on a reciprocal shaking machine at 27°C. A 48-hour culture was transferred into a picromycin-producing medium containing 1 % starch, 1 % yeast extract, 1 % casamino acids and 0.5 % CaCO3, and it was fermented at 27°C. After 8 hours, each of 13C-labeled precursors was added and the fermentation was continued for an additional 26~30 hours. The culture filtrates (500 ml) were then extracted with chloroform at pH 8.0 and the extracts were concentrated to dryness. The crude materials containing picromycin were chromatographed over silica gel thin-layer