Stereospecific Epoxidation of Limonene Catalyzed by Peroxygenase from Oat Seeds.

Limonene is one of the most abundant naturally occurring cyclic monoterpenes and has recently emerged as a sustainable alternative to petroleum-based solvents as well as a chemical platform for the production of value-added compounds. The biocatalytic epoxidation of both enantiomers of limonene was carried out in the presence of a peroxygenase-containing preparation from oat () flour. Different reaction profiles were observed depending on the starting enantiomer of limonene, but in both cases the 1,2-monoepoxide was obtained as the main product with excellent diastereoselectivity. -1,2-monoepoxide and -1,2-monoepoxide were isolated from the reaction of ()-limonene and ()-limonene, respectively, and the reactions were scaled-up to 0.17 M substrate concentration. The process is valuable for operational simplicity, lack of toxic metal catalysts, and cost-effectiveness of the enzymatic source. Pure stereoisomers of 1,2-monoepoxides of limonene constitute a useful starting material for biorenewable polymers, but can be also converted into other chiral derivatives by epoxide ring opening with nucleophiles. As a proof of concept, a tandem protocol for the preparation of enantiopure (1,2,4)-1,2-diol from ()-limonene and (1,2,4)-1,2-diol from ()-limonene was developed.