Lipase-mediated epoxidation of the cyclic monoterpene limonene to limonene oxide and limonene dioxide

Limonene is an industrially interesting monoterpene that accumulates in bulk quantities as by-product of the fruit juice industry. The corresponding epoxides are versatile synthetic intermediates and additives for the chemical industry. Due to a number of disadvantages of classical chemical epoxidation including serious safety issues and unwanted side-reactions, we here used a mild lipase-catalyzed chemo-enzymatic epoxidation system, with either free or different immobilized forms of Candida antarctica lipase B. Full limonene conversion (> 98%) was easily achieved at 40 degrees C within less than 24 h. The enzymatic activities in the formation of limonene monoxide significantly varied from either 1-3.4 U/mg(biocatalyst) at r. t. or from 1.7-4.9 U/mg(biocatalyst) at 40 degrees C. For the first time we showed that it is possible to generate high amounts of limonene dioxide (similar to 30% with CalB on carrier 350 at 40 degrees C) using this mild lipase-mediated epoxidation method. Enzyme activities and limonene dioxide yields strongly depend on the nature of the selected enzyme carrier, the immobilization method and the reaction temperature