Acid-catalyzed and enzymatic hydrolysis of trans- and cis-2-methyl-3,4-epoxytetrahydropyran
作者:Giorgio Catelani、Ettore Mastrorilli
DOI:10.1039/p19830002717
日期:——
microsomal epoxide hydrolase is entirely regiospecific and involves in both cases exclusive attack at C-4. The racemic cis-epoxide reacts at a faster rate than the trans. The 2R,3R,4S-enantiomer of the latter epoxide reacts at a much faster rate than its antipode to yield the (–)-(2R,3R,4R)-diol which is isolated at least 98% optically pure up to almost 50% conversion when starting from the racemic substrate
鉴于反式-和顺式-3,4-环氧-2-甲基四氢吡喃的酸催化水解反应通过在C-4和C-3处同时打开(反式环氧化物中C-4的64%进攻)给出了相应的二醇,在顺式环氧化物中为86%),兔肝微粒体环氧化物水解酶催化的相同底物的水解完全是区域特异性的,在两种情况下都涉及C-4的排他性攻击。外消旋的顺式-环氧化物的反应速率比反式的快。后者的环氧化物的2 R,3 R,4 S-对映体的反应速率比其对映体快得多,从而产生(–)-(2 R,3 R当从外消旋底物开始时,分离出至少98%光学纯至几乎50%转化率的,4R)-二醇。由L-鼠李糖制备光学纯的(+)-(2 S,3 S,4 S)-二醇的参考样品。通过非对映异构MTPA酯的glc分析,也可以更精确地确定(-)-(2 R,3 R,4 R)-二醇的对映体过量。本结果证实了关于水解酶活性位点的拓扑结构的先前假设,并强调了环氧乙烷环附近亲脂性取代基的取向的首要重要性。