Remarkable Regio Research Articles

Recent Developments and Applications of Biocatalytic and Chemoenzymatic Synthesis for the Generation of Diverse Classes of Drugs.

Biocatalytic and chemoenzymatic biosynthesis are powerful methods of organic chemistry that use enzymes to execute selective reactions and allow the efficient production of organic compounds. The advantages of these approaches include high selectivity, mild reaction conditions, and the ability to work with complex substrates. The utilization of chemoenzymatic techniques for the synthesis of complicated compounds has lately increased dramatically in the area of organic chemistry. Biocatalytic technologies and modern synthetic methods are utilized synergistically in a multi-step approach to a target molecule under this paradigm. Chemoenzymatic techniques are promising for simplifying access to essential bioactive compounds because of the remarkable regio- and stereoselectivity of enzymatic transformations and the reaction diversity of modern organic chemistry. Enzyme kits may include ready-to-use, reproducible biocatalysts. Its use opens up new avenues for the synthesis of active therapeutic compounds and aids in drug development by synthesizing active components to construct scaffolds in a targeted and preparative manner. This study summarizes current breakthroughs as well as notable instances of biocatalytic and chemoenzymatic synthesis. To assist organic chemists in the use of enzymes for synthetic applications, it also provides some basic guidelines for selecting the most appropriate enzyme for a targeted reaction while keeping aspects like cofactor requirement, solvent tolerance, use of whole cell or isolated enzymes, and commercial availability in mind.

Direct, Stereodivergent, and Catalytic Michael Additions of Thioimides to α,β-Unsaturated Aldehydes - Total Synthesis of Tapentadol.

Direct and stereodivergent Michael additions of N-acyl 1,3-thiazinane-2-thiones to α,β-unsaturated aldehydes catalyzed by chiral nickel(II) complexes are reported. The reactions proceed with a remarkable regio-, diastereo-, and enantioselectivity, so access to any of the four potential Michael stereoisomers is granted through the appropriate choice of the chiral ligand of the nickel(II) complex. Simple removal of the heterocyclic scaffold furnishes a wide array of either syn or anti enantiomerically pure derivatives, which can be exploited for the asymmetric synthesis of biologically active compounds, as demonstrated in a new approach to tapentadol. In turn, a mechanism, based on theoretical calculations, is proposed to account for the stereochemical outcome of these transformations.

Direct, Stereodivergent, and Catalytic Michael Additions of Thioimides to α,β‐Unsaturated Aldehydes – Total Synthesis of Tapentadol

AbstractDirect and stereodivergent Michael additions of N‐acyl 1,3‐thiazinane‐2‐thiones to α,β‐unsaturated aldehydes catalyzed by chiral nickel(II) complexes are reported. The reactions proceed with a remarkable regio‐, diastereo‐, and enantioselectivity, so access to any of the four potential Michael stereoisomers is granted through the appropriate choice of the chiral ligand of the nickel(II) complex. Simple removal of the heterocyclic scaffold furnishes a wide array of either syn or anti enantiomerically pure derivatives, which can be exploited for the asymmetric synthesis of biologically active compounds, as demonstrated in a new approach to tapentadol. In turn, a mechanism, based on theoretical calculations, is proposed to account for the stereochemical outcome of these transformations.

Recent Applications of Flavin-Dependent Monooxygenases in Biosynthesis, Pharmaceutical Development, and Environmental Science

Flavin-dependent monooxygenases (FMOs) have raised substantial interest as catalysts in monooxygenation reactions, impacting diverse fields such as drug metabolism, environmental studies, and natural product synthesis. Their application in biocatalysis boasts several advantages over conventional chemical catalysis, such as heightened selectivity, safety, sustainability, and eco-friendliness. In the realm of biomedicine, FMOs are pivotal in antibiotic research, significantly influencing the behavior of natural products, antimicrobial agents, and the pathways critical to drug synthesis They are also underscored as potential pharmaceutical targets, pivotal in opposing disease progression and viable for therapeutic intervention. Additionally, FMOs play a substantial role in environmental science, especially in pesticide processing and in preserving plant vitality. Their involvement in the biosynthesis of compounds like polyethers, tropolones, and ω-hydroxy fatty acids, with remarkable regio- and stereoselectivity, renders them indispensable in drug discovery and development. As our comprehension of FMOs’ catalytic mechanisms and structures advances, through the use of cutting-edge biotechnologies like computational design and directed evolution, FMOs are poised to occupy an increasingly significant role in both scientific exploration and industrial applications.

Green and rapid acid-catalyzed ynamide skeletal rearrangement and stereospecific functionalization with anisole derivatives

Environmentally friendly acid-catalyzed 2-alkynyl-ynamides (N–Csp) bond cleavage, alkyne migration and stereospecific functionalization with anisole derivatives for the synthesis of challenging indole scaffolds in 5–10 minutes.

Cytochrome P450 monooxygenase-mediated tailoring of triterpenoids and steroids in plants.

The cytochrome P450 monooxygenase (CYP) superfamily comprises hemethiolate enzymes that perform remarkable regio- and stereospecific oxidative chemistry. As such, CYPs are key agents for the structural and functional tailoring of triterpenoids, one of the largest classes of plant natural products with widespread applications in pharmaceuticals, food, cosmetics, and agricultural industries. In this review, we provide a full overview of 149 functionally characterised CYPs involved in the biosynthesis of triterpenoids and steroids in primary as well as in specialised metabolism. We describe the phylogenetic distribution of triterpenoid- and steroid-modifying CYPs across the plant CYPome, present a structure-based summary of their reactions, and highlight recent examples of particular interest to the field. Our review therefore provides a comprehensive up-to-date picture of CYPs involved in the biosynthesis of triterpenoids and steroids in plants as a starting point for future research.

Synthesis and Reactivity of 3‐Halo‐4,5‐dihydroisoxazoles: An Overview

AbstractThe 3‐halo‐4,5‐dihydroisoxazole moiety is an interesting emerging feature in medicinal and organic chemistry fields. The properties of this nucleus are intimately correlated with the nature of the halogen substituent, ranging from inertness to instability. In between, the 3‐bromo‐Δ2‐isoxazoline scaffold stands out as a handleable and easily affordable electrophilic warhead, able to react with nucleophilic active sites of different enzymes, determining inhibitory effects. However, the importance of 3‐bromo‐Δ2‐isoxazolines does not rely only upon their biological activity. In fact, they are valuable synthetic intermediates, presenting a peculiar reactivity spectrum that allows access to useful chemical functions, ranging from variously decorated dihydroisoxazoles to β‐hydroxynitriles, β‐hydroxyesters, and γ‐hydroxyamines. The synthesis of 3‐bromo‐Δ2‐isoxazolines is predominantly based on the 1,3‐dipolar cycloaddition, a pericyclic reaction accompanied by a remarkable regio‐ and stereo‐selectivity. Thus, this intermediate lends itself especially well to the production of complex molecules with regio‐ and stereo‐chemical requirements.

Selective Double C–H Functionalization: A 4-Component Catellani Reaction

Achieving high selectivity through multiple C–H functionalization is a challenging task. In this issue of <i>Chem</i>, Lumb, Luan, and co-workers disclose a clever strategy taking advantage of steric remote effects for the synthesis of poly-substituted arenes through a 4-component Catellani reaction with remarkable regio- and chemoselectivity by using readily available reagents.

Methods for the detection and analysis of dioxygenase catalyzed dihydroxylation in mutant derived libraries.

Rieske non-heme iron dioxygenases (ROs) are promising candidates to perform dihydroxylation reactions, since they are capable to incorporate both atoms of molecular oxygen into vicinal non-activated CH bonds, endowing valuable products for pharmaceutical and chemical applications. ROs harbor attractive features such as, striking activity in combination with remarkable regio- and stereo-selectivity, wide reaction spectrum, and broad substrate scope. In order to identify, characterize, and enhance targeted features of dioxygenases and related oxygen dependent enzymes via enzyme engineering and evolution approaches, proper screening and analytical methods are essential to detect and to analyze the expected dihydroxylation activity. This chapter presents different methodologies suitable for the study of dihydroxylation reactions. Detailed descriptions of our established analytical protocols for both gas and liquid chromatography, as well as a colorimetric assay to detect dioxygenase activity are provided. In addition, a novel and reliable system for real-time detection of oxygen consumption, in vivo, is reported.

Directed Copper-Catalyzed Intermolecular Aminative Difunctionalization of Unactivated Alkenes.

A diverse collection of copper-catalyzed intermolecular aminative difunctionalizations of unactivated alkenes with N-halodialkylamines as the terminal dialkylamino source is reported. A bidentate auxiliary tethered on the alkene substrates is crucial, which can promote the migratory insertion of nonactivated alkenes into the aminyl radical-metal complex and stabilize the resultant high-valent copper intermediate to allow for further transformations. By employing this strategy, the intermolecular aminohalogenation reactions and a three-component aminoazidation reaction of unactivated alkenes with dialkylamino source were successively achieved in a remarkable regio- and stereoselective manner. These reactions were performed under neutral conditions and maintained excellent functional group tolerance toward a wide range of N-halodialkylamines and unactivated alkenes. Further mechanistic studies and DFT calculations supported a concerted migratory insertion of the C-C double bond into the aminyl radical-metal complex to form a Cu(III) intermediate.

Microbial Transformation of Flavonoids by Isaria fumosorosea ACCC 37814.

Glycosylation is an efficient strategy to modulate the solubility, stability, bioavailability and bioactivity of drug-like natural products. Biological methods, such as whole-cell biocatalyst, promise a simple but highly effective approach to glycosylate biologically active small molecules with remarkable regio- and stereo-selectivity. Herein, we use the entomopathogenic filamentous fungus Isaria fumosorosea ACCC 37814 to biotransform a panel of phenolic natural products, including flavonoids and anthraquinone, into their glycosides. Six new flavonoid (4-O-methyl)glucopyranosides are obtained and structurally characterized using high resolution mass and nuclear magnetic resonance spectroscopic techniques. These compounds further expand the structural diversity of flavonoid glycosides and may be used in biological study.

Methylglucosylation of aromatic amino and phenolic moieties of drug-like biosynthons by combinatorial biosynthesis

Glycosylation is a prominent strategy to optimize the pharmacokinetic and pharmacodynamic properties of drug-like small-molecule scaffolds by modulating their solubility, stability, bioavailability, and bioactivity. Glycosyltransferases applicable for "sugarcoating" various small-molecule acceptors have been isolated and characterized from plants and bacteria, but remained cryptic from filamentous fungi until recently, despite the frequent use of some fungi for whole-cell biocatalytic glycosylations. Here, we use bioinformatic and genomic tools combined with heterologous expression to identify a glycosyltransferase-methyltransferase (GT-MT) gene pair that encodes a methylglucosylation functional module in the ascomycetous fungus Beauveria bassiana The GT is the founding member of a family nonorthologous to characterized fungal enzymes. Using combinatorial biosynthetic and biocatalytic platforms, we reveal that this GT is a promiscuous enzyme that efficiently modifies a broad range of drug-like substrates, including polyketides, anthraquinones, flavonoids, and naphthalenes. It yields both O- and N-glucosides with remarkable regio- and stereospecificity, a spectrum not demonstrated for other characterized fungal enzymes. These glucosides are faithfully processed by the dedicated MT to afford 4-O-methylglucosides. The resulting "unnatural products" show increased solubility, while representative polyketide methylglucosides also display increased stability against glycoside hydrolysis. Upon methylglucosidation, specific polyketides were found to attain cancer cell line-specific antiproliferative or matrix attachment inhibitory activities. These findings will guide genome mining for fungal GTs with novel substrate and product specificities, and empower the efficient combinatorial biosynthesis of a broad range of natural and unnatural glycosides in total biosynthetic or biocatalytic formats.

Copper-Catalyzed Alkene Aminoazidation as a Rapid Entry to 1,2-Diamines and Installation of an Azide Reporter onto Azahetereocycles.

A copper-catalyzed aminoazidation of unactivated alkenes is achieved for the synthesis of versatile unsymmetrical 1,2-diamine derivatives. This transformation offers an effective approach to installing an amide and an azide from two diffenent amino precursors onto both terminal and internal alkenes, with remarkable regio- and stereoselectivity. Mechanistic studies show that this diamination reaction proceeds via a nucleophilic amino cyclization followed by an intermolecular C-N bond formation using electrophilic azidoiodinane. This pathway differs from previous azidoiodinane-initiated alkene functionalization, suggesting new reactivity of azidoiodinane. Furthermore, this aminoazidation reaction provides an efficient strategy to introduce azide, one of the most useful chemical reporters, onto a broad range of bioactive azaheterocycles, offering new opportunities in bioorthogonal chemistry and biological studies. Rapid syntheses of 5-HT2C agonist, (-)-enduracididine and azido-cholesterol derivatives demonstrate broad applications of this method in organic synthesis, medicinal chemistry, and chemical biology.

Carbonylation of Aziridines as a Powerful Tool for the Synthesis of Functionalized β‐Lactams

Within heterocyclic chemistry, β‐lactams comprise an extraordinary class of strained compounds, recognized for their biological importance as potent antibiotics and their chemical value as flexible building blocks for the construction of diverse nitrogen‐containing structures. Among the synthetic routes available to access this interesting scaffold, the carbonylation of aziridines, in which carbon monoxide is inserted into one of the ring carbon–nitrogen bonds, is praised for its efficiency and remarkable regio‐ and stereoselectivity. This review provides a comprehensive overview of aziridine‐to‐azetidin‐2‐one carbonylation studies. The protocols are categorized according to the different transition metals (i.e. rhodium, palladium, nickel, iron, and cobalt) that have been employed (in a catalytic or stoichiometric amount) to effect this transformation.

Use of chemical auxiliaries to control p450 enzymes for predictable oxidations at unactivated C-h bonds of substrates.

Cytochrome P450 enzymes (P450s) have the ability to oxidize unactivated C-H bonds of substrates with remarkable regio- and stereoselectivity. Comparable selectivity for chemical oxidizing agents is typically difficult to achieve. Hence, there is an interest in exploiting P450s as potential biocatalysts. Despite their impressive attributes, the current use of P450s as biocatalysts is limited. While bacterial P450 enzymes typically show higher activity, they tend to be highly selective for one or a few substrates. On the other hand, mammalian P450s, especially the drug-metabolizing enzymes, display astonishing substrate promiscuity. However, product prediction continues to be challenging. This review discusses the use of small molecules for controlling P450 substrate specificity and product selectivity. The focus will be on two approaches in the area: (1) the use of decoy molecules, and (2) the application of substrate engineering to control oxidation by the enzyme.

ChemInform Abstract: Our Recent Progress on the Intramolecular Diels—Alder Reaction Approach in Natural Products Synthesis: Synthetic Studies of the Octahydronaphthalene Substructure of Versipelostatins and the A/B/C‐Tricyclic Substructure of GKK1032s

AbstractReview: [66 refs.

Mechanistic insights into the Pd-catalyzed intermolecular asymmetric allylic dearomatization of multisubstituted pyrroles: understanding the remarkable regio- and enantioselectivity.

In this article we report a comprehensive density functional theory study on the Pd-catalyzed intermolecular asymmetric allylic dearomatization reactions of multisubstituted pyrroles. The calculated results are in line with the previous experimental observations (J. Am. Chem. Soc. 2014, 136, 6590), and the remarkable regio- and enantioselectivity are well explained. Of all the potential nucleophilic sites around the multisubstituted pyrrole ring, the reaction always occurs at the position where the HOMO of the molecule distributes most significantly. In contrast to the common view on the enantioselectivity of the Pd-catalyzed asymmetric allylic substitution reactions, we find that the steric interaction between the nucleophile and the chiral ligand does not have the dominating effect on the enantioselectivity of the reaction. Instead, the interaction between the allyl moiety and the incoming nucleophile plays an important role in the enantioselectivity-determining process.

Our recent progress on the intramolecular Diels-Alder reaction approach in natural products synthesis: synthetic studies of the octahydronaphthalene substructure of versipelostatins and the A/B/C-tricyclic substructure of GKK1032s.

During this decade, the enantio- and stereoselective synthesis of natural products has been actively explored in the author's laboratory. In this account, the author outlines practical syntheses of the polycyclic substructures of two novel structurally formidable antibiotics, namely, the trans-fused octahydronaphthalene moiety of versipelostatins and the A/B/C-tricyclic decahydrofluorene moiety of GKK1032s. Both syntheses have been achieved with remarkable regio- and stereoselectivity via intramolecular Diels-Alder reactions using well-designed enantiomeric substrates.

High-cell-density cultivation of recombinant Escherichia coli, purification and characterization of a self-sufficient biosynthetic octane ω-hydroxylase

We have recently described the biocatalytic characterization of a self-sufficent biosynthetic alkane hydroxylase based on CYP153A13a from Alcanivorax borkumensis SK2 (thereafter A13-Red). Despite remarkable regio- and chemo-selectivity, A13-Red suffers of a difficult-to-reproduce expression and moderate operational stability. In this study, we focused our efforts on the production of A13-Red using high-cell-density cultivation (HCDC) of recombinant Escherichia coli. We achieved 455 mg (5,000 nmol) of functional enzyme per liter of culture. Tight control of cultivation parameters rendered the whole process highly reproducible compared with flask cultivations. We optimized the purification of the biocatalyst that can be performed in either two or three steps depending on the application needed to afford A13-Red up to 95 % homogeneous. We investigated different reaction conditions and found that the total turnover numbers of A13-Red during the in vitro hydroxylation of n-octane could reach up to 3,250 to produce 1-octanol (1.6 mM) over a period of 78 h.

ChemInform Abstract: Ligand‐Controlled Remarkable Regio‐ and Stereodivergence in Intermolecular Hydrosilylation of Internal Alkynes: Experimental and Theoretical Studies.

AbstractBy a simple variation of the ligands in the ruthenium catalysts an unprecedented switching of product regio‐ and stereoselectivity is observed.