Halogenation Haloperoxidase

Heme-dependent haloperoxidases generate HOX as reactive species from H2O2 and X, which represents an X+ equivalent capable of undergoing electrophilic addition at electron-rich centers [270,271]. Aprototype biocatalyst of this group is the chloroperoxidase from Caldariomyces Jumago [272]. In many natural systems, such enzymes are responsible for the halogenation of electron-rich aromatic cores. 

In vanadium-dependent haloperoxidases, the metal center is coordinated to the imidazole system of a histidine residue, which is similarly responsible for creating hypochlorite or hypobromite as electrophilic halogenating species [274]. Remarkably, a representative of this enzyme class is capable of performing stereoselective incorporation of halides, as has been reported for the conversion of nerolidol to various snyderols. The overall reaction commences through a bromonium intermediate, which cyclizes in an intramolecular process the resulting carbocation can ultimately be trapped upon elimination to three snyderols (Scheme 9.37) [275]. 

Van Pee, K.-H., Dong, C., Flecks, S. etal. (2006) Biological halogenation has moved far beyond haloperoxidases. Advances in Applied Microbiology, 59, 127-157. 

Class and Ballschmitter (1988) suggested that 1,2-dibromoethane may be produced naturally in sea water from a dibromomethane precursor via a halogen exchange reaction. The dibromomethane is produced by brown algae via haloperoxidase enzymes and released to sea water. 

Haloperoxidases act as halide-transfer reagents in the presence of halide ions and hydrogen peroxide. In the first step, the halide ion is oxidized to a halonium-ion carrier, from which the positive halogen species is then transferred to the double bond. In an aqueous medium, the intermediary carbocation is trapped and racemic halohydrins are formed (Eq. 7). Selective examples of CPO-cata-lyzed formation of halohydrins are given in Table 9. In CPO-catalyzed reaction. 

Haloperoxidases are peroxidases capable of halogenating substrates in the presence of halide and hydrogen peroxide [14] or other reactions such as sulfoxidation, epoxidation and aromatic hydroxylation. Here, the halide ion is initially bound to the active site which may incorporate heme or vanadium or be metal free. The halide ion is incorporated into the substrate after electron transfer... 

Haloperoxidases. Many specialized peroxidases are active in halogenation reactions. Chloroperoxi-dases from fungi236 237 catalyze chlorination reactions like that of Eq. 16-11 using H202 and Cl as well as the usual peroxidase reaction. 

Latumus F, Mehrtens G, Gr0n C (1995) Haloperoxidase-Like Activity in Spruce Forest Soil - A Source of Volatile Halogenated Organic Compounds Chemosphere 31 3709... 

Franssen MCR (1994) Halogenation and Oxidation Reactions with Haloperoxidases. Biocatalysis 10 87... 

If the substrate for oxygen transfer step in the back-reaction of Compound I to the resting state is a halogen atom, the overall process is denoted haloperoxidase... 

The standard assay for haloperoxidase activity is the halogenation of monochloro-dimedone (mcd) (2-chloro-5,5-dimethyl-l,3-dimedone) using dihydrogen peroxide as the oxidant of the halide (Figure 4) [48],... 

Recently the amino acid sequence of vanadium chloroperoxidase was determined to have similar stretches with three families of acid phosphatases, which were previously considered unrelated [72], This sequence raises questions about the phosphatase activity of apo-V-ClPO and whether the acid phosphatases can coordinate vanadate and carry out peroxidative halogenation chemistry. In fact, apo-V-C1PO does have phosphatase activity, catalyzing the hydrolysis of/i-nitrophe-nol phosphate (p-NPP). In addition, /i-NPP displaces vanadate from V-CIPO. At this point, the haloperoxidase activity of the acid phosphatases containing coordinated vanadium(V) has not been reported. 

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