Regioselective and Stereoselective Epoxidation of n-3 and n-6 Fatty Acids by Fungal Peroxygenases.

Epoxide metabolites from n-3 and n-6 polyunsaturated fatty acids arouse interest thanks to their physiological and pharmacological activities. Their chemical synthesis has significant drawbacks, and enzymes emerge as an alternative with potentially higher selectivity and greener nature. Conversion of eleven eicosanoid, docosanoid, and other n-3/n-6 fatty acids into mono-epoxides by fungal unspecific peroxygenases (UPOs) is investigated, with emphasis on the Agrocybe aegerita ( Aae UPO) and Collariella virescens (r Cvi UPO) enzymes. GC-MS revealed the strict regioselectivity of the n-3 and n-6 reactions with Aae UPO and r Cvi UPO, respectively, yielding 91%-quantitative conversion into mono-epoxides at the last double bond. Then, six of these mono-epoxides were obtained at mg-scale, purified and further structurally characterized by 1 H, 13 C and HMBC NMR. Moreover, chiral HPLC showed that the n-3 epoxides were also formed (by Aae UPO) with total S/R enantioselectivity ( ee > 99%) while the n-6 epoxides (from r Cvi UPO reactions) were formed in nearly racemic mixtures. The high regio- and enantioselectivity of several of these reactions unveils the synthetic utility of fungal peroxygenases in fatty acid epoxidation.