Nitrite-mediated synthesis of chiral epichlorohydrin using halohydrin dehalogenase from Agrobacterium radiobacter AD1.

In the current study, the haloalcohol dehalogenase HheC gene from Agrobacterium radiobacter AD1 was synthesized and expressed in Escherichia coli. After purification using Ni-nitrilotriacetic acid affinity chromatography, HheC was used in the synthesis of chiral epichlorohydrin in the presence of NO₂⁻. The optimal pH, temperature, and NO₂⁻ concentration for enantioselectivity are 5.0, 37°C, and 60 mM, respectively. The maximum velocity and Michaelis constant values for (S)-epichlorohydrin are 714.3 µmol min⁻¹ mg⁻¹ and 17.2 mM, respectively, whereas those for (R)-epichlorohydrin are 166.8 µmol min⁻¹ mg⁻¹ and 29.0 mM, respectively. Under optimal conditions, (R)-epichlorohydrin with 99% enantiomeric excess was obtained after an 18 Min reaction; the yield reached 41%, which is the highest amount obtained for chiral epichlorohydrin synthesis using haloalcohol dehalogenase. In addition, (R)-epichlorohydrin with 99% enantiomeric excess was successfully obtained from 1,3-dichloro-2-propanol by the ring opening of racemic epichlorohydrin in the presence of NO₂⁻ after the ring closure of 1,3-dichloro-2-propanol with HheC. To the best of our knowledge, the current study is the first report on the kinetic resolution of epichlorohydrin with NO₂⁻ and synthesis of chiral epichlorohydrin with 99% enantiomeric excess from 1,3-dichloro-2-propanol by combining ring closure of 1,3-dichloro-2-propanol and ring opening of racemic epichlorohydrin.