Asymmetric Synthesis of Epicylindrospermopsin via Intramolecular Nitrone Cycloaddition. Assignment of Absolute Configuration
作者:James D. White、Joshua D. Hansen
DOI:10.1021/ja012709r
日期:2002.5.1
establishes its absolute configuration and corroborates the corrected structural assignment previously made to this toxin by Weinreb et al. The hydroxylamine 3, prepared from 4-bromobenzyloxyacetaldehyde, was condensed with aldehyde 4, obtained in nine steps from (R)-methionine, to give nitrone 16. Intramolecular cycloaddition of 16 proceeded stereoselectively to yield the oxazabicyclo[2.2.1]heptane 17, which
完成了 (-)-epicylindrospermopsin (2) 的合成,确定了其绝对构型并证实了 Weinreb 等人先前对该毒素进行的校正结构分配。由 4-溴苄氧基乙醛制备的羟胺 3 与醛 4 缩合,醛 4 在九个步骤中由 (R)-甲硫氨酸得到,得到硝酮 16。 16 的分子内环加成立体选择性地进行,得到氧氮杂双环 [2.2.1] 庚烷 17,还原和脱保护后得到哌啶 18。后者通过环脲 19 转化为转化的 C12 醇 20,衍生的叠氮化物 22 环化产生 25 的胍部分。 C12 羟基的最终硫酸化提供 (-) -2.