Chemoenzymatic synthesis

Communications Chemistry is pleased to introduce a Collection of research works focused on recent developments within the interdisciplinary field of chemoenzymatic synthesis. Here, the Guest Editors highlight key themes and look towards the future of this research field.

The α-oxoamine synthases (AOSes) are a class of pyridoxal 5’-phosphate-dependent enzymes that catalyse Claisen-like condensation of amino acids with an acyl-CoA thioester to generate α-aminoketones, however, their application in chemoenzymatic synthesis remains limited due to the substrate specificity. Here, the authors report the structure-guided engineering of thermostable AOS from Thermus thermophilus to expand the range of amino acids and simplify N-acetylcysteamine acyl-thioester substrates.

Engineered heme proteins exhibit excellent sustainable catalytic carbene transfer reactivities enabling the transformation of olefins to cyclopropanes, however, exploiting unactivated and electron-deficient olefins in such reactions remains challenging. Here, the authors perform a quantum chemical mechanistic study to investigate the effects of olefin substituents, non-native amino acid axial ligands, and natural and non-natural macrocycles with the widely used ethyl diazoacetate, revealing the potential to design an efficient heme-inspired biocatalyst.

Modular polyketide synthases (PKSs) play a vital role in the biosynthesis of complex natural products with pharmaceutically relevant properties, and their modular architecture makes them an attractive target for engineering to produce platform chemicals and drugs. In this study, the authors demonstrate that the promiscuous malonyl/acetyl-transferase domain (MAT) from murine fatty acid synthase serves as a highly versatile tool for the production of polyketide analogs.

Enzymes play an important role in organic synthesis thanks to their high selectivity, however, such selectivity limits their substrate scope and hampers their wide application. Here, the authors report an approach to rationally select enzymes with proposed functionalities based on sequence analysis, exploring the substrate scope of 4-phenol oxidases by in silico sequence-function correlation analysis.

Asparaginyl ligases have been utilized as valuable tools for protein engineering, such as through site-specific bioconjugation or surface modification, however, their application is limited due to time-consuming preparation processes and unstable activities. Here, the authors develop a truncated protein ligase OaAEP1-C247A-aa55-351 from an OaAEP1-C247A mutant, which simplifies the preparation steps, tolerates a wider pH range, and enhances the catalytic activities by using efficient recognition and nucleophile motifs.

Norcoclaurine synthase from Thalictrum flavum (TfNCS) has been demonstrated to display high stereospecificity and yield in catalyzing the Pictet-Spengler reaction of dopamine with chiral aldehydes, however, the mechanism and factors related to this high stereospecificity remain unclear. Here, the authors conduct quantum chemical calculations and reveal the rate-limiting step and differential energy barriers for the reactions of two enantiomers of α-methylphenylacetaldehyde, as well as key residues related to stereospecificity.

Ipatasertib is a potent Akt (protein kinase B) inhibitor synthesized via a chemoenzymatic process. Here, the authors use mutational scanning and algorithm-aided enzyme engineering to optimize a ketoreductase from Sporidiobolus salmonicolor and generate a 10-amino acid substituted variant exhibiting a 64-fold higher k_cat and improved yield for the relevant alcohol intermediate, with ≥ 98% conversion and a diastereomeric excess of 99.7% (R,R-trans) from 100 g L^−1 ketone after 30 h.

Diterpene glycosyltransferase UGT76G1 is a key enzyme in the biosynthesis of rebaudioside A, a naturally sweet-tasting compound, however, its poor thermostability hinders its industrial application. Here, the authors use a computational design strategy to generate a mutant of UGT76G1 that exhibits improved thermostability and enzymatic activity.

β-Amino acid-containing macrolactams are a known natural product family exhibiting structural and functional diversity, however, the natural chemical space of this family remains underexplored. Here, the authors use a targeted β-amino acid-specific homology-based multi-query search to identify their potential microbial producers, explore the variation of their biosynthetic gene clusters, heterologously produce ciromicin A, and identify new macrotermycin derivatives.

D-Amino acids are widely present in nature and display diverse physiological functions, however, their large-scale synthesis remains challenging for specific amino acids. Here, the authors design hyper-thermostable ancestral L-amino acid oxidases (HTAncLAAO2), catalyzing the chemoenzymatic synthesis of D-tryptophan from L-tryptophan at a preparative scale.

Imine reductases can catalyze reductive amination reactions to produce chiral amines, however, transformation of bulky amines has been challenging. Here, by using an increasing-molecule-volume-screening method, the authors identify a group of imine reductases that can accept bulky amines and achieve an efficient gram-scale synthesis of an API sensipar analogue.

Flavin-based biocatalysis using flavin mononucleotide (FMN) cofactor attracts significant attention for its application in asymmetric alkene reduction and various other reactions, however, the scale-up of flavin-based biocatalysis in flow remains unexplored. Here, the authors develop a closed-loop flow platform for H₂-driven regeneration of cofactor FMNH₂ and ene-reduction using immobilized Old Yellow Enzyme, achieving >99% conversion of ketoisophorone to levodione.

Stereoselective production of trans-4-substituted cyclohexane-1-amines—including a key intermediate in the synthesis of antipsychotic drug cariprazine—remains challenging. Here, the authors develop a process catalyzed by a single transaminase to produce trans-4-substituted cyclohexane-1-amines from the corresponding cis/trans-diastereomeric mixtures via a cis-deamination approach in continuous-flow, to achieve a dynamic cis-to-trans isomerization.

Bicyclic peptides exhibit improved metabolic stabilities, membrane permeabilities, and target specificities over their linear and mono-cyclic counterparts, however, efficient bicyclization remains challenging. Here, the authors develop a one-pot tandem chemoenzymatic bicyclization by combination of penicillin-binding protein-type thioesterase-mediated head-to-tail macrolactamization and copper(I)-catalyzed azide–alkyne cycloaddition.

Lignin-derived phenolic acids can be upgraded to styrene derivatives through chemoenzymatic processes, however, the scale-up of such processes remains challenging. Here, the authors find that controlling the water activity during the decarboxylation of bio-based phenolic acids, including through the integration of a water reservoir, enables high conversions and efficient reaction times, that can be combined with a versatile acyl donor substrate scope.

Establishing biotechnological alternatives to chemical syntheses requires the rational design of biosynthetic pathways and degradation routes either as enzymatic cascades in vitro or as part of living organisms. Here, the authors use alanine dehydrogenase from Vibrio proteolyticus and the diaminopimelate dehydrogenase from Symbiobacterium thermophilum for the in vitro production of (R) and (S)-3-fluoroalanine, reaching >85% yield with complete enantiomeric excess.

Pyrroles are an important scaffold in medicinal chemistry with various bioactivities; however, the selective chemical halogenation of pyrroles remains challenging. Here, the authors develop an enzymatic site-selective chlorination of pyrrolic heterocycles by a flavin-dependent halogenase PrnC and apply it to the chemoenzymatic synthesis of a chlorinated analogue of the fungicide Fludioxonil.

The bio-hybrid fuel 4,5-dimethyl-1,3-dioxolane can be produced from glucose via 2,3-butanediol (2,3-BDO), however, the separation of microbially produced 2,3-BDO remains costly. Here, the authors develop an alternative process route to 4,5-dimethyl-1,3-dioxolane via the enzymatic production of 2,3-BDO.

Alcohol dehydrogenases (ADH) are known to be efficient and stereoselective biocatalysts for reducing prochiral carbonyl compounds to chiral alcohols; however, their catalytic performances remain limited for application. Here, the authors demonstrate the wide substrate scope of a L. kefir ADH variant with anti-Prelog specificity to generate (R)-alcohols.

The merger of chemical and biocatalysis can offer powerful new options to synthetic chemists. Here a combination of a nickel-catalyzed Suzuki-Miyaura reaction and an enzymatic stereoselective reduction provides enantiomerically-enriched alcohols from amides in a single reaction vessel, in water.

Combinatorial biosynthesis of natural products is a method to synthesize structurally diverse molecules with defined modifications. Here, the authors review the various approaches used for combinatorial biosynthesis of fungal natural products by engineering biosynthetic enzymes and pathways to generate novel molecules.

Sorbicillactone A is a nitrogen-containing sorbicillinoid that displays various bioactivities, identified from a sponge-derived Penicillium chrysogenum strain. The first and so far obly total synthesis of sorbicillactone A led to the racemate in 12 linear steps and a 0.13% overall yield. Here, the authors develop a chemoenzymatic stereoselective total synthesis of sorbicillactone A in 4 steps and 11% yield by using the enzyme SorbC for the enantioselective oxidative dearomatization of sorbillin to sorbicillinol followed by addition of an azlactone unit.

Gangliosides are composed of oligosaccharide chains attached to ceramides and are employed as targeted drugs and diagnostic biomarkers, however, their industrially-relevant synthesis remains challenging. Here, the authors develop a modular chemoenzymatic cascade assembly strategy for the customized and large-scale synthesis of ganglioside analogues with various glycan and ceramide epitopes.

Spirosorbicillinols A–C are fungal natural products that display various biological properties, but their total synthesis has yet to be accomplished. Here, the authors report the total synthesis of spirosorbicillinols A–C based on a chemo-enzymatic transformation of sorbicillin into sorbicillinol, which is fused to synthetically prepared scytolide and isomers by a Diels-Alder cycloaddition reaction.

Camptothecin derivatives are precursors of potent anticancer agents, but their biosynthesis remains largely unknown. Here two cytochrome P450 monooxygenases are shown to regiospecifically oxidize camptothecin, yielding 10- and 11- hydroxylated derivatives, which are subsequently used to produce a suite of known anticancer drugs and derivatives.