Study On The Enzyme-catalyzed Synthesis Of Chiral α-cyanohydrin And α-cyanamide

Chiral cyanohydrins and their esters, as an important class of chiral intermediates, its chiral synthesis methods have drawn attention of academia and industry circles. Primary discussions about purification methods of S-Hydroxynitrile lyase from Cassava and applications in asymmetric cyanohydrination are led by Zheng Zubiao of our group. On such basis, the second chapter reports the optimized method of extraction and purification of crude enzyme of S-Hydroxynitrile lyase in cassava leaves, which can then be used to catalyze asymmetric hydrocyanation of aromatic aldehydes, hetero-aromatic aldehydes, aliphatic aldehydes. The result shows that when the substituent group on benzene ring is electron donating group, the reaction is selective preferably, with an ee value of 91%～93%; When the substituent group on benzene ring is electron-withdrawing group, the reaction exerts a larger effect on its selectivity, with ee value reducing to 62%～76%. When a large substituent group is on the benzene ring, due to steric hindrance of enzyme on the catalytic activity, thus ee value of 3-phenoxybenzaldehyde is only 20%. When the substrate is heteroaromatic aldehydes, the reaction ee value is 86% to 96%, but if there is substituent group on the heterocyclic ring, the yield show declination. This paper use S- Hydroxynitrile lyase which is got via one-step precipitation to catalyze asymmetric synthesis of S-cyanohydrin. Due to the multi-sourced cassava, the simple extraction method and its good selectivity, the method in this paper is of high application value.Chiral a-cyanamide is an important intermediate compound which is of applicable value to the synthesis of pharmaceuticals, new materials.Lee and Ahn have reported PaHNL (Hydroxynitrile lyase in almond) catalyzed asymmetric hydrocyanation reaction of chiral imines. Although the de value of the reaction product was not high, only 42%～62%, that paper is the only report about biocatalytic synthesis of chiral cyanamide. But according to our research, the results of the paper are wrong. In the absence of the enzyme, the reaction selectivity can also achieve the same level. It is believed that the result is induced by the chiral centre of chiral imine rather than the effect of enzyme catalysis. On this basis, this paper explores the chiral induction influence of chiral imines with different substituent groups. All of these are summarized in the third chapter of this thesis.The fourth chapter discusses the feasibility that Hydroxynitrile lyase catalyzes asymmetric Strecker reaction under different acid-base environments. Secondly, it explores the asymmetric acetylation reaction of racemic cyanamide with industrialized FLV lipase under various conditions. The results show that FLV lipase has high sensibility to the steric hindrance when it catalyzes reaction. It does not catalyze high sterically hindered cyanamide.