| abstract |
A process of separating a desired (-) stereoisomer which is selected from (-) menthol or an equivalent (-) compound where the isopropyl group is replaced with an isopropanol or an isopropylene group, from a starting material comprising: 40 to 100 m/m % of a mixture of (-)-menthol and (+)-menthol; up to 30 m/m % of a mixture of (-)-isomenthol and (+)-isomenthol; up to 20 m/m % of a mixture of (-)-neomenthol and (+)-neomenthol; and up to 10 m/m % of a mixture of (-)-neoisomenthol and (+)-neoisomenthol or an equivalent (±) mixture where the isopropyl group is replaced with an isopropanol or an isopropylene group, includes the steps of: contacting the starting material with an esterifying agent and a stereospecific enzyme which is a Pseudomonas lipase enzyme which stereoselectively esterifies the -OH group of the desired (-) steroisomer, for a time sufficient to convert a desired percentage of the desired (-) stereoisomer to a desired (-) esterified compound where the -OH group is converted to a group -O-C(O)-R4, wherein R4 is an alkyl or an aryl group, to give a first reaction product including the desired (-) esterified compound, the organic solvent, the unconverted stereoisomers, excess esterifying agent and by-products of the reaction; and separating the desired (-) esterified compound from the first reaction product. The process is of particular application for the production of (-)-menthol. |