Stereoselective synthesis of β,ε-dihydroxy-α-amino acids by ring opening of 4,5-dihydroisoxazolyl derivatives
作者:Giuseppe Cremonesi、Piero Dalla Croce、Francesco Fontana、Claudio Fiorelli、Concetta La Rosa
DOI:10.1016/j.tetasy.2008.11.034
日期:2008.12
Enantiomerically pure β-(4,5-dihydroisoxazol-3-yl)-substituted β-hydroxy-α-amino acids were synthesised stereoselectively by means of an addition reaction between (5,5-disubstituted-4,5-dihydroisoxazol-3-yl)-carbaldehydes and (R)-(+)-2,5-dihydro-3,6-dimethoxy-2-isopropylpyrazine (Schöllkopf’s reagent) as a chiral auxiliary. The addition gave mixtures of only two adducts with high diastereoselectivity. The
通过(5,5-二取代-4,5-二氢异恶唑-3-之间的加成反应)立体选择性地合成对映体纯的β-(4,5-二氢异恶唑-3-基)-取代的β-羟基-α-氨基酸。 yl)-甲醛和(R)-(+)-2,5-二氢-3,6-二甲氧基-2-异丙基吡嗪(Schöllkopf试剂)作为手性助剂。该加成仅产生具有高非对映选择性的两种加合物的混合物。主要的非对映异构体的空间构型是根据光谱数据和公认的Schöllkopf醛醇缩合模型确定的的试剂。吡嗪环随后的酸催化水解产生β-(4,5-二氢异恶唑-3-基)-β-羟基-α-氨基甲基酯的混合物以及两种部分水解的二肽的混合物。这些化合物的4,5-二氢异恶唑环的最终还原裂解使得获得β,ε-二羟基-γ-氧代-ε,ε-二取代的α-氨基酸衍生物的甲酯成为可能。