Tong et al. Bioresour. Bioprocess. (2019) 6:46 https://doi.org/10.1186/s40643-019-0280-6 REVIEW Open Access Enzyme-catalyzed C–F bond formation and cleavage Wei Tong1,2 , Qun Huang1,2, Min Li1,2 and Jian‑bo Wang1,2* Abstract Organofuorines are widely used in a variety of applications, ranging from pharmaceuticals to pesticides and advanced materials. The widespread use of organofuorines also leads to its accumulation in the environment, and two major questions arise: how to synthesize and how to degrade this type of compound efectively? In contrast to a considerable number of easy‑access chemical methods, milder and more efective enzymatic methods remain to be developed. In this review, we present recent progress on enzyme‑catalyzed C–F bond formation and cleav‑ age, focused on describing C–F bond formation enabled by fuorinase and C–F bond cleavage catalyzed by oxidase, reductase, deaminase, and dehalogenase. Keywords: Organofuorines, C–F bonds, Enzyme‑catalyzed, Degradation, Formation Introduction usually require harsh conditions and are not environ- Incorporation of fuorine into organic compounds usu- ment friendly (Dillert et al. 2007; Lin et al. 2012; Sulbaek ally endows organofuorines with unique chemical and Andersen et al. 2005). To solve these problems, devel- physical properties, a strategy that has been successfully opment of mild and green methods is urgently needed. applied in agrochemicals, materials science, and pharma- Biocatalysis has been playing an increasingly more ceutical chemistry (Phelps 2004; Müller et al. 2007; Shah important role in modern chemistry due to its high ef- and Westwell 2007; Hagmann 2008; Nenajdenko et al. ciency, specifc selectivity, and more environmentally 2015; Zhang et al. 2016; Lowe et al. 2017). Especially in friendly characteristics compared to chemical cataly- medicinal chemistry, the unique elemental properties sis. Tus, introducing biocatalytic methods into organic of fuorine have been proved to enhance metabolic sta- fuorine chemistry is a good choice to counter the def- bility and alter pharmacokinetic characteristics without ciencies of chemical catalysis (Kim et al. 2000; Liu and increasing the apparent spatial volume; thus, more than Avendaño 2013; Murphy 2016; Rotander et al. 2012). 20% of drugs are organofuorines (Zhou et al. 2016; Gillis Although biocatalysis has achieved signifcant progress in et al. 2015; Spooner et al. 2019). Te wide application of recent years, the feld of biocatalytic C–F bond formation organofuorines has motivated fast methodology devel- and cleavage is almost at an open stage. opment for fuorine incorporation (Purser et al. 2008; Since fuorine atoms are very small and strongly elec- Berger et al. 2011). In contrast to their synthesis, their tro-negative, when in an aqueous system fuoride ions degradation has also attracted signifcant attention due to are always tightly wrapped by the water molecules, and their increased use and the cumulative pollution result- thus, it is very difcult to form C–F bonds in an aqueous ing from their high stabilities. system (O’Hagan 2008; Ni and Hu 2016). Terefore, fuo- Chemists have developed versatile methods for the for- rine-containing natural products are very rare despite the mation and cleavage of C–F bonds, but these methods fact that elemental fuorine is the most fecund halogen in the Earth’s crust (O’Hagan and Deng 2014). To the best of *Correspondence: [email protected] our knowledge, only two diferent examples of enzyme- 1 Key Laboratory of Phytochemistry R&D of Hunan Province, College catalyzed C–F bond formation have been reported: one of Chemistry and Chemical Engineering, Hunan Normal University, is catalyzed by a mutant of glycosyltransferase, which Changsha 410081, People’s Republic of China Full list of author information is available at the end of the article catalyzes α-fuoroglycosides as transient intermediates © The Author(s) 2019. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creat iveco mmons .org/licen ses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Tong et al. Bioresour. Bioprocess. (2019) 6:46 Page 2 of 8 from DNP-activated sugars (Zechel et al. 2001), and the enzyme was characterized before 2005, it took approxi- other is the natural fuorinase, prompting the conversion mately 10 years to clarify the biosynthetic pathway of all of 5′-fuoro-5′-deoxyribose-1-phosphate (5′-FRP) from fuorinated products in Streptomyces cattleya, and their S-adenosyl-l-methionine (SAM) (Deng et al. 2004). In work proved that fuorinating enzyme that converts inor- this review, we focus on summarizing the recent progress ganic fuorine into organic fuorine (Deng et al. 2006; Zhu in mining and directed evolution of fuorinase and expect et al. 2007; Winkler et al. 2008; Dall’Angelo et al. 2013; to inspire the development of more unnatural fuorinases O’Hagan and Deng 2014; Wang et al. 2014; Carvalho and in the future. Oliveira 2017). However, attempts to identify enzymes Te C–F bond is the strongest σ bond, and thus, it is that biosynthesize nucleocidin 1 have failed for decades, difcult to cleave it under mild conditions (Goldman because the production of this molecule has been mys- 1969; Lemal 2004). When hydrogen is substituted by teriously silenced in the bacterium Streptomyces calvus fuorine, the metabolic stability of the compounds will be (Jenkins et al. 1976; Nashiru et al. 2001; Zechel et al. signifcantly improved; this property benefts the phar- 2003). In 2015, Zechel’s group reported that complemen- maceutical industry, but leads to the accumulation of tation of S. calvus ATCC13382 with a functional bldA- organofuorines in the environment (Wang et al. 2016). encoded Leu-tRNAUUA molecule restores the production Enzyme-catalyzed C–F bond cleavage has attracted of nucleocidin 1 and identifed the genes encoding the attention from researchers in environmental protec- biosynthesis of the 5′-O-sulfamate group of the nucleoci- tion, C–F bond activation, and enzymology, and several din 1 (Zhu et al. 2015). In the next year, O’Hagan’s group reviews have been published on the subject (Natara- provided the frst biosynthetic data on nucleocidin 1 jan et al. 2005). However, in recent years, reports in this assembly from isotope labeling studies (Bartholomé et al. area have been very rare. Herein, therefore, we present 2016; Feng et al. 2017). However, there was still no illumi- recently published examples of enzyme-catalyzed C–F nation for the mechanism of fuorination involved in this bond cleavage, dividing them into two types: hydrolytic biosynthetic pathway. In 2019, O’Hagan group disclosed defuorination, and oxireductive defuorination. Hope- two structures of novel fuorometabolites in S. calvus, fully, this review will attract increasing numbers of work- which belong to 3′-O-glucosylated, 4′-fuoro-riboad- ers to this important feld. enosines (6 and 7) (Scheme 1a). Tey are analogous of nucleocidin 1 and suspect to incorporate fuorine via a Enzyme‑catalyzed C–F bond formation same biocatalytic pathway (Feng et al. 2019). Te iden- Te frst natural organofuorine compound, identifed tifcation of these metabolites highly suggests that there in 1943, was fuoroacetate, a metabolite of the South- is a new type of fuorinase existing in S. calvus which ern African plant Dichapetalum cymosum (Marais 1943, deserves our attention. 1944). Te second one was isolated in 1956 from Strepto- Although the specifc activity of fuorinase has myces calvus; it is a nucleoside product named nucleoci- attracted considerable attention, its application is lim- din 1 which belongs to a new form of fuorine metabolites ited due to the drawbacks of narrow substrate scope and (Scheme 1a). Subsequently, the third structurally novel, low activity. To explore its utilization, it is necessary to fuorine-containing natural product 4-fuorothreonine mine new types of fuorinase or improve the activity of was isolated from the bacterium Streptomyces cattleya in known forms of fuorinase by directed evolution. Most 1986 (Sanada et al. 1986). Despite considerable interest research on fuorinase is focused on discovering new and a variety of speculative suggestions for uncovering forms of fuorinase through gene mining. To date, four the biochemical mechanism of fuorination, no spe- new fuorinases have been identifed, three of which have cifc details of fuorination’s biochemistry in any organ- been characterized (see Table 1) (Deng et al. 2014; Wang ism were provided until 2002. Tis milestone regarding et al. 2014; HimáTong 2014). Te frst was identifed from fuorinase was published in 2002 by O’Hagan’s group Streptomyces sp. MA37, a strain isolated in 2011 from (O’Hagan et al. 2002), who frst described an enzy- Ghana. Full genome sequences of the South American matic reaction occurring in the bacterium Streptomy- hospital pathogens, Nocardia brasiliensis (Deng et al. ces cattleya that catalyzes the conversion of fuoride 2014; Wang et al. 2014) and Actinoplanes sp. N902-109, ions and S-adenosylmethionine (SAM) to 5′-fuoro-5′- were deposited into the public domain in 2012 and 2013, deoxyfuoroadeno-sine (5′-FDA) (O’Hagan et al. 2002; respectively. Te draft genome of the marine bacterium see Scheme 1b). In the following year, O’Hagan’s team Streptomyces xinghaiensis NRRL B-24674 was depos- isolated and characterized fuorinase from Streptomyces ited in the public domain in 2011. More recently, a new cattleya (Schafrath et al. 2003), and the crystal structure fuorinase (FIA) gene has been identifed in the Strep- of fuorinase was resolved by the same group in 2004 tomyces xinghaiensis genome. Full genome sequencing (Dong et al. 2004; Deng et al. 2004). Although the basic of the organism revealed a gene encoding of a putative Tong et al. Bioresour. Bioprocess.