(+)-Negamycin was prepared in 13 steps in an overall yield of 31% from commercially available ethyl (R)-(+)-4-chloro-3-hydroxybutanoate. The key step in the reaction sequence was a highly stereoselective asymmetric Michael addition of chiral amine (−)-21 [(1S,2R)-(−)-2-methoxybornyl-10-benzylamine] into the α,β-unsaturated carbonyl moiety of key intermediate 8, thus establishing the second chiral center
由(R)-(+)-4-
氯-
3-羟基丁酸乙酯,以13个步骤制备(+)-
游霉素,总产率为31%。反应顺序中的关键步骤是将手性胺(-)- 21 [(1 S,2 R)-(-)-2-甲氧基降
冰片基-10-苄基胺]高度立体选择性地不对称Michael加成到α,β-不饱和基团上关键中间体8的羰基部分,因此在(+)-新霉素中建立了第二个手性中心。还以类似方式制备了5-表位-霉素。