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The efficient, specific incorporation of isotope from [carb0xy-~~C]-3-amin0-5-hydroxybenzoic acid into the C-6 methyl group of porfiromycin by Streptomyces verticillatus establishes this amino-acid as the biogenetic precursor of the methylbenzoquinone nucleus of the mitomycin antibiotics.

Cultures of Nocardia mediterranea utilise atmospheric oxygen to form the C-1 oxygen function and C-29 vinyl ether group of the ansamycin antibiotics rifamycin B, 0, and S, while the C-8 phenolic hydroxy group and C-8 carbon atom are both derived from the carboxy group of 3-amino-5-hydroxybenzoic acid; these results exclude 8-deoxyansamycins as possible biosynthetic intermediates.

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Absolute Configurations of Macrolide Antibiotics of the Bafilomycin and Leucanicidin Groups.-The absolute configuration of bafilomycin B 1 (Ia), C 1 , D, and leucanicidin (Ib) is established by conversion of these compounds into bafilomycin A 1 , whose skeleton has the absolute configuration shown in the scheme.-(O'SHEA, M. G.; RICKARDS, R. W.; ROTH-SCHILD, J. M.; LACEY, E.; J.