Diastereoselective Microbial Hydroxylation of Milbemycin Derivatives
作者:Gerardo M. Ramos Tombo、Oreste Gmsalba、Hans-Peter Schär、Bruno Frei、Peter Maienfisch、Anthony C. O’Sullivan
DOI:10.1080/00021369.1989.10869540
日期:1989.6
The diastereoselective hydroxylation of milbemycin A4 (1) at the 13/f-position (-*2) was performed by cultures of Streptomyces violascens (ATCC 31560). 14,15-epoxymilbemycin A4 (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 A3 (9) and D (10), the main products after treatment with S. violascens were the corresponding 14,15-epoxides, 13 and 14, respectively.
Synthesis and Configuration of Some Hydroxymilbemycin Derivatives Including 22,23-Dihydroavermectin B1b Aglycone
作者:Bruno Frei、Philip Huxley、Peter Maienfisch、Hari Babu Mereyala、G�nther Rist、Anthony C. O'Sullivan
DOI:10.1002/hlca.19900730713
日期:1990.10.31
of several configurationally defined hydroxymilbemycin derivatives is described. One of these allylic alcohols is the known 5-O-[(tert-butyl)dimethylsilyl]-13α-hydroxymilbemycin D (= 5-O-[(tert-butyl)-dimethylsilyl]-22,23-dihydroavermectin B1b, aglycone; 15D), the synthesis of which represents LI conversion of the milbemycin to the avermectin series of natural products. The configurations at C(13),
Milbemycin derivatives: Epoxidation of milbemycins.
作者:SATORU NAITO、AKIO SAITO、YOUJI FURUKAWA、TADASHI HATA、YASUO NAKADA、SHIGEKI MURAMATSU、JUNYA IDE
DOI:10.7164/antibiotics.47.812
日期:——
Epoxidation reactions (MCPBA epoxidation and Sharpless epoxidation) were examined as a means of chemically modifying milbemycins as part of our program for discovering anthelmintics. 8, 9-Epoxy-, 14, 15-epoxy-, 8, 9-14, 15-diepoxy-, and 3, 4-8, 9-14, 15-triepoxymilbemycin A4 were se-lectively obtained from milbemycin A4 and its derivatives, in which either the C-5 and C-7 hydroxyl groups or C-5 alone were protected as appropriate by a silyl ether (in the former case) or a carbonyl group. Further silylation or epoxidation on these epoxidized compounds indicated that the configuration of each epoxide moiety of the mono- and diepoxides is in accord with that of the corresponding epoxide moiety of the triepoxide. Furthermore, in order to confirm the absolute configurations of these epoxide functionalities, an X-ray analysis of a carbamate derivative from the triepoxymilbemycin was conducted.