ISOFLAVONOIDS FROM STREPTOMYCETES - ORIGINS OF GENISTEIN, 8-CHLOROGENISTEIN, AND 6,8-DICHLOROGENISTEIN

Fermentations conducted with aureolic-acid producing and non-producing Streptomyces griseus strains in soybean-meal-containing medium yielded phenolic metabolites which were chomatographically and spectrally unrelated to either aureolic acid or its aglycone, chomomycinone. The yellow, phenolic compounds were isolated and characterized by H-1 nmr, C-13 nmr, and ms as the isoflavonoids genistein (5,7,4'-trihydroxyisoflavone) [1], 8-chlorogenistein [2], and 6,8-dichlorogenistein [3]. The presence of 1 in the soybean meal used in these fermentations was confirmed by extraction, isolation, and spectral identification. S. griseus grown in medium without soybean meal produced no isoflavonoids. Biotransformation of 1 yielded both chlorinated metabolites 2 and 3, demonstrating that these isoflavonoids are products of microbial halogenation. Labelled isoflavonoids were not obtained when S. griseus was incubated with radiolabelled acetate or phenylalanine. These results demonstrate that isoflavonoids isolated from streptomycetes cultivated in media containing plant-derived nutrients such as soybean meal or cotton seed meat likely originate from the medium components and are not of microbial biosynthetic origin.