Flavin-dependent halogenases catalyze enantioselective olefin halocyclization

Abstract

Halocyclization of alkenes is a powerful bond-forming tool in synthetic organic chemistry and a key step in natural product biosynthesis, but catalyzing halocyclization with high enantioselectivity remains a challenging task. Identifying suitable enzymes that catalyze enantioselective halocyclization of simple olefins would therefore have significant synthetic value. Flavin-dependent halogenases (FDHs) catalyze halogenation of arene and enol(ate) substrates. Herein, we reveal that FDHs engineered to catalyze site-selective aromatic halogenation also catalyze non-native bromolactonization of olefins with high enantioselectivity and near-native catalytic proficiency. Highly selective halocyclization is achieved by characterizing and mitigating the release of HOBr from the FDH active site using a combination of reaction optimization and protein engineering. The structural origins of improvements imparted by mutations responsible for the emergence of halocyclase activity are discussed. This expansion of FDH catalytic activity presages the development of a wide range of biocatalytic halogenation reactions.

Atomic Chromium Coordinated Graphitic Carbon Nitride for Bioinspired Antibiofouling in Seawater

“…[ 11 , 18 , 19 ] Such natural enzyme can generate strong biocidal but environmentally friendly hypohalous acid (HOBr, HOCl) through catalytic oxidation of halide with environmental hydrogen peroxide (H 2 O 2 ). [ 20 , 21 , 22 ] Artificial vanadium and cerium oxide nanozymes have been developed for combating biofilm by mimicking naturally occurring defense mechanisms of vanadium haloperoxidases, showing superior advantage compared to conventional highly toxic heavy metal biocides. [ 23 , 24 ] Nevertheless, the low level of environmental H 2 O 2 (a typical concentration of ≈100 × 10 −9 m in seawater) [ 25 ] is the major bottleneck for haloperoxidase‐mimicking nanozyme to generate hypohalous acids sufficiently.…”

Directed Evolution of Flavin-Dependent Halogenases for Atroposelective Halogenation of 3-Aryl-4(3H)-quinazolinones via Kinetic or Dynamic Kinetic Resolution

“…While enantioselective catalysis using FDHs remains rare, the high selectivity obtained for halogenation of a range of structurally diverse quinazolinone substrates illustrates the utility of FDHs toward this end. This result, combined with the fact that engineered variants of RebH also catalyze enantioselective desymmetrization of meso-methylenedianilines 21 and halolactonization of olefins bearing pendant carboxylate nucleophiles 22 , highlights the diversity of substrate topologies and mechanisms for stereochemical induction that can be accommodated by these enzymes. Access to isolable quantities of single atropisomers of halogenated 3-(3-aminophenyl)-4(3H)quinazolinones is particularly useful given the biological activity of related structures 39 and the ease with which the bromide and amine substituents can be leveraged for subsequent synthetic elaboration.…”

“…Our group and others have established that flavin-dependent halogenases (FDHs) can be engineered to brominate a diverse range of substrates with high site selectivity. [15][16][17][18][19][20] We have also developed FDH variants that catalyze enantioselective chlorination of methylenedianilines 21 and halolactonization of olefins 22 . FDHs are believed to achieve this selectively by binding substrates such that only a single site is presented to HOX (X = Br, Cl) that is selectively bound and activated by a lysine residue within their active site.…”

Nothing lasts forever: understanding microbial biodegradation of polyfluorinated compounds and perfluorinated alkyl substances

“…2 ) (Gribble, 2012 , 2015 ; Dong et al ., 2020 ; Ludewig et al ., 2020 ), and brominated natural products are common in marine environments (Küpper and Carrano, 2019 ). Certain algae accumulate high levels of iodine (Mondal et al ., 2021 ), and iodine represents more than half the mass of the human hormone thyroxine (Thomas et al ., 2009 ). Indeed, many chlorinated, brominated and iodinated natural products contain four or more halogen substituents (Fig.…”