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Matsumoto, K.; Katsuki, T.; Arends, I. W. C. E., Science of Synthesis: Stereoselective Synthesis, (2011) 1, 116.
Epoxidation with monooxygenases depends on cofactors. The enzymes usually consist of several subunits that, in a series of cascades, provide the reducing equivalents to the iron-active site. The need for a cofactor is eliminated in the case of peroxidases, for which hydrogen peroxide acts as the oxidant. The hydrogen peroxide results in a shunt pathway that directly restores the [P+•Fe(IV)=O] species from iron(III) (see Scheme 61). Because of its ease of handling, chloroperoxidase (CPO) from Caldariomyces fumago is an attractive option; it is commercially available, and displays a reasonable substrate range.[163] The main problems are its instability under the reaction conditions and its sluggish reaction rates. Typical turnover rates are 0.1–2 s−1. The epoxidation of styrene in the presence of 0.8% of surfactant is, at 5.5 s−1, the fastest on record.[164] The advantage of this reaction is that the enantioselectivities are, in most cases, good to excellent. For example, hept-2-ene can be oxidized with 1700 turnovers relative to enzyme in 30% tert-butyl alcohol to give the corresponding epoxide with 96% ee. The total turnover number of this reaction can be increased from 1700 to 11 500 when hydrogen peroxide is generated in situ by a glucose oxidase mediated reaction of glucose and oxygen. A wide range of 2-methylalk-1-enes can be oxidized with enantiomeric excess values ranging from 50 to 95% (Scheme 66).[165–167]
Meeeee 88 Meeeeeeeeee ee Meeeeee ee Meeeeeeeeeeeeeee Meeeee[888–888]
M8 | M8 | M8 | Meeeeeeee | Meee (e) | ee (%) | Meeeee | Meeee (%) | Mee |
---|---|---|---|---|---|---|---|---|
Me | Me | M | 88% M8M8 | 8 | 88 | 8M,8M | 88 | [888] |
(MM8)8Me | Me | M | 88% M8M8 | 8 | 88 | 8M,8M | 88 | [888] |
(MM8)8Me | M | Me | 88% M8M8 | 8.88 | 88 | M | 88 | [888] |
MM8MM8Me | M | Me | 88% M8M8 | 8.88 | 88 | M | 88 | [888] |
MM8Me | M | Me | 88% M8M8 | 8.88 | 88 | M | 88 | [888] |
MM8Me | M | Me | e-MeMMM | 8 | 88 | M | 88 | [888] |
e Mee ee 88% M8M8: eeeeee (8 eM) eee MMM eeeeee (8.888 eee%) eeee eeeeeee ee e 8:8 eeeeeee ee eeeeeee/eeeeeee eeeeee (eM 8.8) ee ee; 88% M8M8 eee eeeeeeeeeeee eeeee ee e eeeee eeeeeee/eeeeeeeee eeeee ee 8.8:8. Mee ee e-MeMMM: e-MeMMM (8 eeeee) eee eeee ee eee eeeeeee ee eeeeeee eeeeee (eM 8.8) eeee 8.8 M eeeeee eee 8.88 eee% MMM eeeeee.
References
[163] | eee Meeeeeee, M.; Meeeeee, M. M., Meee. Meee. Meeeeeeeee., (8888) 88, 888. |
[164] | Meee, M.-M.; Meeee, M. M., Meeeeeeeee. Meeeee., (8888) 88, 888. |
[165] | Meeeee, M. M.; Meee, M. M.; Meeee, M. M., M. Me. Meee. Mee., (8888) 888, 888. |
[166] | Meeeee, M. M.; Meeeee, M. M.; Meeeeeee, M. M.; Meeee, M. M., M. Me. Meee. Mee., (8888) 888, 8888. |
[167] | Meeeee, M. M.; Meeee, M. M.; Meee, M.; Meeeeeee, M. M., M. Me. Meee. Mee., (8888) 888, 8888. |