Preparation Of L-menthol By Biocatalyzed Diastereoselective Resolution

L-menthol has a great value of industrial use because of its cooling effect. It is widely used in production of sugar, cigar, medicine, cosmetics and so on. The output of 1-menthol extracted from natural plants is quite unstable due to the climate change. So we tried to develop a new chemical-biological method of producing L-menthol by asymmetric hydrolysis and asymmetric transesterification of the racemic menthyl substrate.First, we have found a very effective lipase ASL to catalyze the asymmetric transesterification of racemic menthol and got a very good stereoselectivity towards 1-menthol, the dep>95%。Then immobilization technology was applied to improve the performance of ASL. Diatomite and macro-porous resin were used as the carrier of the ASL by adsorption. The performance of these two immobilized ASL were studied and results showed that the specific activity of the enzyme protein have been greatly improved as well as stability. Compared to the free ASL, the specific activity of diatomite immobilized ASL have improved by 3.8 times and that of macro-porous resin have improved by 9.8 times. The operating stability of NKA macro-porous resin immobilized ASL have improved to 1.5 times and the stability against heat has improved by 3.6 times.The ectoenzyme from the strain we screened was applied as the catalyst of the asymmetric hydrolysis of racemic menthyl esters and a good stereoselectivity was observed, dep>98%. Racemic Menthyl propionate was used as the substrate for the first time and the dep have reached 99% with the effective conversion at 22%.