Diastereoselective Microbial Hydroxylation of Milbemycin Derivatives(Microbiology & Fermentation Industry)

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The diastereoselective hydroxylation of milbemycin A_4 (1) at the13β-position (→2) was performed by cultures of Streptomyces violascens (ATCC 31560). 14,15-epoxymilbemycin A_4 (3) was formed via a parallel reaction as a byproduct. The conversion and the product ratio, 2/3, were improved by the addition of organic solvents. The best results, i.e., 91% conversion with 92% 2 and 8% 3, were obtained by adding 2.5% DMSO to the culture broth. Oxime 7 was also hydroxylated at the 13β-position by S. violascens under similar conditions. In the case of milbemycin A_3 (9) and D (10), the main products after treatment with S. violascens were the corresponding 14,15-epoxides, 13 and 14, respectively.
1989-06-23