16 ポリケチドラクトンを経るオレアンドライド類の立体選択的合成(口頭発表の部)

概要

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Here will be described the enantioselective synthesis of oleandolides (7 and 9) from the polyketide lactone 8 derived from oleandomycin (1) as a chemical simulation of path B. The aglycone 7 was obtained in 75% yield from 5 in 3 steps through removal of the amino sugar moiety by treatment of the N-oxide with trimethylsilyl iodide. Exhaustive oxidation of the four hydroxyl groups in 7 was realized by exposure to RuO_4 in CCl_4 to give the polyketide lactone 8 (M^+ 366). The reduction of 8 was achieved by Zn(BH_4)_2 in the presence of MgBr_2 to provide stereo-selectively the tetraol 9 as cubes in 80% yield. The absolute structure of the macrolide was defined by the X-ray crystallographic analysis to be (5R, 8R, 9R)-9-dihydro-8-methyl-epi-oleandolide (9) as depicted in Fig. 1. The stereochemistry of the macrolide 9 was incompatible with that of the natural macrolide 2 only at the C-5. The reduction of 8, however, without MgBr_2 gave a 1: 1 mixture of 7 and 9. On the other hand, the C-9 ketone 14, which was obtained from 7 by selective benzylidenation and oxidation, was led to the biosynthetic precursor 2 by catalytic hydrogenation.
天然有機化合物討論会の論文
1987-07-25