The addition of HCN to 4-alkylcyclohexanones 1 to give cyanohydrins 2 is strongly catalyzed by hydroxy-ni trile lyases (HNLs). With PaHNL, from bitter almond, trans-addition occurs almost exclusively, yielding trans-2. With MeHNL, from cassava, cis-addition is preferred to give cis-2. cis-Selectivity is nearly quantitative, especially for cyclohexanones with larger 4-substituents. Comparable results with respect to the stereoselectivity were observed in the HNL-catalyzed addition of HCN to 4-alkoxycyclohexanones 3ag. In contrast, the stereoselectivity in the HNL-catalyzed addition to 4-alkanoyloxycyclohexanones 3hk is very poor. The transformation of cis-4-propylcyclohexanone cyanohydrin (2c) into the corresponding cis-spirotetronic acid 7 occurs without any isomerization.Key words: enzyme, hydroxynitrile lyase, cyclohexanones, cyanohydrins, cis/trans-stereoselectivity. 
在4-烷基
环己酮1中加入HCN生成腈醇2,这个反应会受到羟基腈酰酶(HNLs)的强烈催化。使用来自苦杏仁的PaHNL,反应主要发生顺式加成,生成顺-2。使用来自木薯的MeHNL,顺式加成优先生成顺-2。对于4-取代基较大的
环己酮,顺式选择性几乎是定量的。在HNL催化下,HCN加成到4-烷氧基
环己酮3a-g中时,立体选择性的结果与前者相当。相反,在HNL催化下,HCN加成到4-烷酰氧基
环己酮3h-k中时,立体选择性非常差。将顺-4-丙基
环己酮腈醇(2c)转化为相应的顺-螺四氢酸7时,不会发生任何异构化。关键词:酶、羟基腈酰酶、
环己酮、腈醇、顺/反-立体选择性。