Quinolizidines. XIII. Syntheses of (.+-.)- and (-)-alangimarckines.
作者:TOZO FUJII、HIROSHI KOGEN、SHIGEYUKI YOSHIFUJI、MASASHI OHBA
DOI:10.1248/cpb.33.1946
日期:——
The first total synthesis of the Alangium alkaloid alangimarckine (8) has been accomplished in the form of a racemic modification by means of an initial coupling of the (±)-tricyclic amino acid 6 with tryptamine and succeeding steps proceeding through the intermediates (±)-7, (±)-10, and (±)-9. The 1'-epimers (±)-12 and (±)-11 were also produced in this reaction sequence. A parallel sequence of conversions starting with the (-)-tricyclic amino acid 6 yielded the chiral molecule (-)-8 via the intermediates (+)-7, (+)-10, and (+)-9, together with the 1'-epimer (-)-11 via (-)-12. The identity of the synthetic (-)-8 with natural alangimarckine unequivocally established the structure and absolute configuration of this alkaoid. The assignments of the configuration at C-1'of 8, 9, 11, and 12 were based on five criteria, namely, the ratio of products from the NaBH4 reduction of (±)-10, thin-layer chromatographic mobility, and proton and carbon-13 nuclear magnetic resonance and circular dichroism spectroscopic features.
通过(±)-三环氨基酸 6 与色胺的初始偶联,以及通过中间体(±)-7、(±)-10 和 (±)-9进行的后续步骤,首次以外消旋体修饰的形式完成了阿兰生物碱 alangimarckine (8) 的全合成。在此反应序列中还生成了 1'-epimers (±)-12 和 (±)-11。从(-)-三环氨基酸 6 开始的平行转化序列通过中间体(+)-7、(+)-10 和 (+)-9 生成了手性分子 (-)-8,并通过 (-)-12 生成了 1'-epimer (-)-11。合成的(-)-8 与天然金盏花碱的同一性明确地确定了这种烷烃的结构和绝对构型。8、9、11 和 12 的 C-1'构型的确定基于五个标准,即 (±)-10 的 NaBH4 还原产物的比例、薄层色谱流动性、质子和碳-13 核磁共振以及圆二色性光谱特征。