116(P54) 抗潰瘍性天然物AI-77-Bのエナンチオ選択的合成(ポスター発表の部)
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AI-77-B (1), a gastroprotective substance isolated from Bacillus pumilus AI-77, gathers a considerable attention from synthetic chemists. In our own effort to synthesize AI-77-B (1) we already reported an enantioselective synthesis of the dihydroisocoumarin part A and the dihydroxyamino acid part B using D-ribose as a common chiral source. However, it still remains some problems particularly for the construction of the part A. In this paper we would like to report an alternative synthetic route to the part A which relies on a benzofuran strategy as a unique salicylic acid synthon and the successful synthesis of AI-77-B (1). 1. Synthesis of the dihydroisocoumarin part A The dihydroisocoumarin key intermediate 10 was prepared in an enantiomerically pure form as illustrated in Scheme 2. Thus, the coupling reaction of the Grignard reagent derived from 4-bromobenzofuran (3) with triflate 4 derived from D-ribose gave 5 in good yield. Ozonolysis of 5 followed by lactonization produced the desired dihydroisocoumarin derivative 7, which was further converted to 10 in good yields completely following our previously reported synthetic procedure. 2. Synthesis of the dihydroxyamino acid part B N-Boc lactam 13, which can be envisaged as a synthon of the dihydroxyamino acid part B, was efficiently constructed from D-ribose using stereoselective alkylation of 11 with allyltrimethylsilane as a key step. 3. Condensation of part A and part B Since our initial attempt to condense 10 and 13 using high-pressure technique was unsuccessful due to the unexpected isomerization of 10 to 17, we adopted a stepwise method. Thus, 13 was first hydrolyzed to 18 followed by condensation with 10 by the assistance of DCC provided 19. Oxidative cleavage of the terminal double bond in 19 gave 20, a fully protected form of AI-77-B (1). The final completion of this study is now underway.
- 天然有機化合物討論会の論文
- 1998-08-31
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