engleski

Catalytic Activity of Halohydrin Dehalogenases Towards Spiroepoxides

Halohydrin dehalogenases catalyse ring-closure of halohydrins, as well as the ring-opening of epoxides with both halide and non-natural nucleophiles, such as cyanide, azide and nitrite.1 What makes this enzyme attractive for synthetic purposes is the fact that ring opening reactions are irreversible and highly b-regioselective. Moreover, reactions can proceed with high enantioselectivity with a wide variety of synthetic substrates.2 Aromatic and aliphatic mono- and disubstituted terminal epoxides are known to be accepted by halohydrin dehalogenses. However, spiroepoxides as substrates have not been studied till now.In our present studies we have discovered that halohydrin dehalogenase from Arthrobacter sp. (HheA) and Agrobacterium radiobacter (HheC) display activity towards chiral spiroepoxides. The enzymatic resolution of series of methyl- substituted 1-oxaspiro[2, 5]octanes were performed in the presence of HheA and HheC by using azide as a nucleophile. Both enzymes were overexpressed in E. coli and purified by ion- exchange chromatography. In general, activity, enantioselectivity and stereopreference were enzyme dependent. HheC displayed higher enantioselectivity (E up to 200) compared to HheA (E = 3). Substituents on different positions of the cyclohexane ring were found to have large effect on the enzyme activity. Methyl substituent situated closer to the epoxide moiety caused decrease in the reaction rate but at the same time increase in enantioselectivity of the HheC catalysed reactions.

halohydrin dehalogenase ; spiroepoxides ; azides

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