Abstract
Monooxygenases are promising catalysts because they in principle enable the organic chemist to perform highly selective oxyfunctionalisation reactions that are otherwise difficult to achieve. For this, monooxygenases require reducing equivalents, to allow reductive activation of molecular oxygen at the enzymes' active sites. However, these reducing equivalents are often delivered to O2 either directly or via a reduced intermediate (uncoupling), yielding hazardous reactive oxygen species and wasting valuable reducing equivalents. The oxygen dilemma arises from monooxygenases' dependency on O2 and the undesired uncoupling reaction. With this contribution we hope to generate a general awareness of the oxygen dilemma and to discuss its nature and some promising solutions.
Highlights
Following in the path of the well-established hydrolases,[2] the number of industrial[1a,3] and pre-industrial examples[4] of biocatalytic redox reactions is increasing rapidly.[1c,5] From a synthetic point of view monooxygenases are of particular interest for the organic chemist because they succeed in balancing high reactivity and selectivity
The oxygen dilemma is a reality that has to be faced in biocatalytic oxyfunctionalisation chemistry
The high reactivity of molecular oxygen with the most common natural and man-made redox mediators interferes in most electron-transport chains delivering electrons to monooxygenases
Summary
Oxidoreductases appear set to become practical catalysts for organic synthesis.[1]. Following in the path of the well-established hydrolases,[2] the number of industrial[1a,3] and pre-industrial examples[4] of biocatalytic redox reactions is increasing rapidly.[1c,5] From a synthetic point of view monooxygenases are of particular interest for the organic chemist because they succeed in balancing high reactivity (needed to activate inert CÀH bonds) and selectivity (by confining the reactive oxygenating species in a well-defined protein scaffold). Monooxygenases in principle give access to selective hydroxylations, epoxidations, Baeyer–Villiger oxidations and even halogenations (Scheme 1). In comparison with their chemical counterparts, monooxygenases often excel in terms of selectivity and catalyst performance [turnover numbers (TNs) and turnover frequencies (TOFs)].[6]. There is, still a range of issues to be solved to make monooxygenases truly practical catalysts Amongst these there is the oxygen dilemma, which we briefly outline in this contribution. The protein scaffold controls the interaction between these reactive oxygen transfer species [e.g., Fe·oxo complexes or (hydro)peroxyflavins] and the substrates, leading to highly selective oxyfunctionalisation reactions.[1c].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: Chembiochem : a European journal of chemical biology
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
