Hydrogen atom transfer methodology for the synthesis of C-22, C-23, and C-25 stereoisomers of cephalostatin north 1 side chain from spirostan sapogenins
作者:Carmen Betancor、Raimundo Freire、Inés Pérez-Martín、Thierry Prangé、Ernesto Suárez
DOI:10.1016/j.tet.2005.01.077
日期:2005.3
A simple synthesis of all eight C-22, C-23, and C-25 diastereoisomers of the cephalostatin north 1 side chain has been accomplished from (25R)-5α-spirostan-3β-ol (tigogenin). The synthesis involves selective hydroxylations at C-23 and C-25 and reductive opening of the 1,6-dioxaspiro[4.5]decane spirostan system to give a conveniently protected 5α-furostan-3β,23,25,26-tetrol. The construction of the
从(25 R)-5α-spirostan-3β-ol(tigogenin)已完成了cephalostatin北1侧链的所有8个C-22,C-23和C-25非对映异构体的简单合成。合成过程涉及在C-23和C-25处进行选择性羟基化作用,以及1,6-二氧杂螺环[4.5]癸烷螺环烷体系的还原性开放,从而得到方便地保护的5α-呋喃斯坦3β,23,25,26-四醇。所需的1,6-二氧杂螺[4.4]壬烷体系的构建需要通过C-25烷氧基进行的分子内氢提取反应为关键步骤。螺环酮单元的酸催化异构化表明22 R异构体是热力学产物,而22 S异构体是热力学产物。异构体是动力学控制的结果。还研究了1,6-二氧杂螺[4.4]壬烷和1,6-二氧杂螺[4.5]癸烷体系之间的酸催化平衡。在1,6-二氧杂螺[4.4]壬烷单元中,观察到的3 J 23,24耦合常数表明,五元折叠的F环在从22 S变为22 R异构体时会发生构象变化。