Quinolizidines. XVI. Chiral syntheses of 9-demethylcephaeline and 10-demethylcephaeline.
作者:TOZO FUJII、MASASHI OHBA
DOI:10.1248/cpb.33.5264
日期:——
In order to establish the structure of the Alangium alkaloid demethylcephaeline, chiral syntheses of the two possible alternative structures, (-)-9-demethylcephaeline (1) and (-)-10-demethylcephaeline (2), have been accomplished through a "cincholoipon-incorporating route." The synthesis of (-)-2 started with an initial condensation of the tricyclic acid (-)-12b, prepared from the ester (-)-11b by alkaline hydrolysis, with 3-benzyloxy-4-methoxyphenethylamine and proceeded through the intermediates (-)-13b, (+)-15b, and (-)-14b. The 1'-epimers (-)-18b and (-)-17 were also produced in this reaction sequence. A parallel sequence of conversions starting with (+)-15a afforded (-)-1 via the intermediate (-)-14a, together with the 1'-epimer (-)-16 via (-)-18a. Unfortunately, however, lack of a sufficient amount of natural (-)-demethylcephaeline for a detailed and direct comparison precluded identification of either (-)-1 or (-)-2 with this alkaloid, leaving its chemistry incomplete.
为了确定八角豆生物碱去甲基头孢碱的结构,通过“cincholoipon”完成了两种可能的替代结构((-)-9-去甲基头孢碱 (1) 和 (-)-10-去甲基头孢碱 (2))的手性合成。 -合并路线。” (-)-2 的合成始于三环酸 (-)-12b(由酯 (-)-11b 通过碱性水解制备)与 3-苄氧基-4-甲氧基苯乙胺的初步缩合,并通过中间体 ( -)-13b、(+)-15b和(-)-14b。 1'-差向异构体 (-)-18b 和 (-)-17 也在该反应序列中产生。从 (+)-15a 开始的平行转化序列通过中间体 (-)-14a 提供 (-)-1,并通过 (-)-18a 提供 1'-差向异构体 (-)-16。然而不幸的是,由于缺乏足够量的天然 (-)-去甲基头孢碱来进行详细和直接的比较,因此无法用这种生物碱鉴定 (-)-1 或 (-)-2,从而使其化学成分不完整。