Desaturation reactions catalyzed by soluble methane monooxygenase

Abstract

Soluble methane monooxygenase (MMO) is shown to be capable of catalyzing desaturation reactions in addition to the usual hydroxylation and epoxidation reactions. Dehydrogenated products are generated from MMO-catalyzed oxidation of certain substrates including ethylbenzene and cyclohexadienes. In the reaction of ethylbenzene, desaturation of ethyl C-H occurred along with the conventional hydroxvlations of ethyl and phenyl C-Hs. As a result, styrene is formed together with ethylphenols and phenylethanols. Similarly, when 1,3- and 1,4-cyclohexadienes were used as substrates, benzene was detected as a product in addition to the corresponding alcohols and epoxides. In all cases, reaction conditions were found to significantly affect the distribution among the different products. This new activity of MMO is postulated to be associated with the chemical properties of the substrates rather than fundamental changes in the nature of the oxygen and C-H activation chemistries. The formation of the desaturated products is rationalized by formation of a substrate cationic intermediate, possibly via a radical precursor. The cationic species is then proposed to partition between recombination (alcohol formation) and elimination (alkene production) pathways. This novel function of MMO indicates close mechanistic kinship between the hydroxylation and desaturation reactions catalyzed by the nonheme diiron clusters.

A growing family of O2 activating dinuclear iron enzymes with key catalytic diiron(III)-peroxo intermediates: Biological systems and chemical models

“…Despite numerous similarities between toluene monooxygenases and sMMO, it is worth noting that these two enzymes also present differences regarding their reactivity toward hydrogen peroxide. For example, whereas toluene monooxygenases catalyze the hydroxylation of aromatic compounds by hydrogen peroxide, sMMO has been shown to catalyze the desaturation reaction of aromatic compounds, such as ethylbenzene, in the presence of H2O2 [61].…”

Catalytic Promiscuity in Biocatalysis: Using Old Enzymes to Form New Bonds and Follow New Pathways

“…[46] Methane monooxygenase, another non-heme diiron enzyme, catalyzes methane hydroxylation as well as a wide range of other oxidations including epoxidation, N-oxide formation, dehalogenation, and desaturation of benzylic substrates. [47] Degradation enzymes, such as cytochrome P450 enzymes, which contain a heme iron, also catalyze a wide range of oxidations.…”

Microbial Desaturation of Bis(1‐chloro‐2‐propyl) Ether into a Dichloro Vinyl Ether

“…strain ATCC 58400 occurs by a cytochrome P450-mediated hydroxylation of the carbon atom adjacent to the ether bridge, which leads to the formation of a hemiacetal. [6] However, ether-cleaving methane monooxygenase (MMO) is known to catalyze hydroxylation but also desaturation reactions, [7] which after hydration will also result in a hemiacetal structure with ether as substrate.…”