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Herein, an operationally simple temperature-dependant regioselective halogenation of phenols and anilines in water using readily accessible and highly stable Lewis base adducts (LBAs) is reported. These newly discovered LBAs [DBUBr]+Br− and [DBUI]+I− are compatible with a wide range of substrates for regioselective brominations and iodinations with excellent yields (up to 95%), and the products were directly isolated just by filtration and characterized without column chromatographic purification. The organobase DBU was recovered and reused for making corresponding LBAs without a substantial loss of activity. Further halogenations are chemoselective and nucleoselective and proceeded with a very good E-factor. Complimentary regioselectivity (ortho over para) of both aniline and phenol for monohalogenation is a unique feature of the methodology. [ABSTRACT FROM AUTHOR]

In this work, the combined effects of anion substitution (with Br− and I−) and SiO2 addition on the Li-ion conductivity in LiBH4 have been investigated. Hexagonal solid solutions with different compositions, h-Li(BH4)1−α(X)α (X = Br, I), were prepared by ball milling and fully characterized. The most conductive composition for each system was then mixed with different amounts of SiO2 nanoparticles. If the amount of added complex hydride fully fills the original pore volume of the added silica, in both LiBH4-LiBr/SiO2 and LiBH4-LiI/SiO2 systems, the Li-ion conductivity was further increased compared to the h-Li(BH4)1−α(X)α solid solutions alone. The use of LiBH4-LiX instead of LiBH4 in composites with SiO2 enabled the development of an optimal conductive pathway for the Li ions, since the h-Li(BH4)1−α(X)α possesses a higher conductivity than LiBH4. In fact, the Li conductivity of the silica containing h-Li(BH4)1−α(X)α is higher than the maximum reached in LiBH4-SiO2 alone. Therefore, a synergetic effect of combining halogenation and interface engineering is demonstrated in this work. [ABSTRACT FROM AUTHOR]

Halogenation of aromatic aldoximes with N-chlorosuccinimide under mild conditions produced a variety of highly functionalized compounds, including the corresponding hydroximoyl chlorides and furazan N-oxides. In some cases, the reaction was accompanied by chlorination of the aromatic ring. The initial aldoximes were prepared from substituted benzaldehydes and hydroxylamine hydrochloride. The structure of some of the synthesized compounds was determined by X-ray analysis. [ABSTRACT FROM AUTHOR]

Machine learning (ML) has quickly emerged in synthetic organic chemistry to predict reaction outcomes such as yields and stereoselectivities. Notably, recent applications of the ML approach showed powerful performance in solving various chemical problems. However, the requirement of numerous descriptors and large datasets hampers the general use by non‐specialists. In this study, simple ML models were developed by utilizing easily available 13C‐NMR chemical shifts of the substrates as familiar descriptors to predict the site‐selectivity of geminal chlorofluorination of unsymmetrical 1,2‐dicarbonyl compounds. We identified that the feed‐forward neural network (FNN) model provides higher accuracy compared to other algorithms. Then, better prediction performance was acquired through streamlined models using minimal, only empirically relevant descriptors. [ABSTRACT FROM AUTHOR]

Flavin-dependent monooxygenases (FDMOs) are known for their remarkable versatility and for their crucial roles in various biological processes and applications. Extensive research has been conducted to explore the structural and functional relationships of FDMOs. The majority of reported FDMOs utilize C4a-(hydro)peroxyflavin as a reactive intermediate to incorporate an oxygen atom into a wide range of compounds. This review discusses and analyzes recent advancements in our understanding of the structural and mechanistic features governing the enzyme functions. State-of-the-art discoveries related to common and distinct structural properties governing the catalytic versatility of the C4a-(hydro)peroxyflavin intermediate in selected FDMOs are discussed. Specifically, mechanisms of hydroxylation, dehalogenation, halogenation, and light-emitting reactions by FDMOs are highlighted. We also provide new analysis based on the structural and mechanistic features of these enzymes to gain insights into how the same intermediate can be harnessed to perform a wide variety of reactions. Challenging questions to obtain further breakthroughs in the understanding of FDMOs are also proposed. [ABSTRACT FROM AUTHOR]

This document is a research article that focuses on the total synthesis of ajudazol A, a natural product. The authors, researchers from the University of Bonn, provide detailed information about the experimental procedures and characterization data. The document is technical in nature and provides information relevant to organic chemistry and natural product synthesis. [Extracted from the article]

Functionalized triptycene derivatives have attracted significant research interest because of their potential applications in many research fields. Although the conventional Diels‐Alder reaction of anthracenes with benzynes has been a versatile synthetic tool for functionalized triptycenes, it is hardly possible to control the product regioselectivity. In this report, we demonstrate the selective synthesis of 1,8,13‐trisubstituted triptycenes by Pd‐catalyzed α‐bromination. As for the directing group, SMe group was the most effective to facilitate the halogenation of the proximal three benzene rings. The obtained product was further derivatized through allylation and Rh‐catalyzed hydroboration reactions. [ABSTRACT FROM AUTHOR]

Healthy development of the gut microbiome provides long-term health benefits. Children raised in countries with high infectious disease burdens are frequently exposed to diarrhoeal pathogens and antibiotics, which perturb gut microbiome assembly. A recent cluster-randomized trial leveraging >4,000 child observations in Dhaka, Bangladesh, found that automated water chlorination of shared taps effectively reduced child diarrhoea and antibiotic use. In this substudy, we leveraged stool samples collected from 130 children 1 year after chlorine doser installation to examine differences between treatment and control children's gut microbiota. Water chlorination was associated with increased abundance of several bacterial genera previously linked to improved gut health; however, we observed no effects on the overall richness or diversity of taxa. Several clinically relevant antibiotic resistance genes were relatively more abundant in the gut microbiome of treatment children, possibly due to increases in Enterobacteriaceae. While further studies on the long-term health impacts of drinking chlorinated water would be valuable, we conclude that access to chlorinated water did not substantially impact child gut microbiome development in this setting, supporting the use of chlorination to increase global access to safe drinking water.

[Display omitted] The present study explores the synthesis of new potential Cereblon ligands, 2-amino derivatives of (thio)morpholine-3,5-diones. The resulting compounds demonstrate notable cytotoxic effects in tests conducted in vitro on myeloma cell lines, highlighting the potential of these compounds as molecular glues. [ABSTRACT FROM AUTHOR]

We report the synthesis of two novel halogenated nitro-arylhimachalene derivatives: 2-bromo-3,5,5,9-tetramethyl-1-nitro-6,7,8,9-tetrahydro-5H-benzo[7]annulene (bromo-nitro-arylhimachalene) and 2-chloro-3,5,5,9-tetramethyl-1,4-dinitro-6,7,8,9-tetrahydro-5H-benzo[7]annulene (chloro-dinitro-arylhimachalene). These compounds were derived from arylhimachalene, an important sesquiterpene component of Atlas cedar essential oil, via a two-step halogenation and nitration process. Characterization was performed using 1H and 13C NMR spectrometry, complemented by X-ray structural analysis. Quantum chemical calculations employing density functional theory (DFT) with the Becke3-Lee-Yang-parr (B3LYP) functional and a 6-31++G(d,p) basis set were conducted. The optimized geometries of the synthesized compounds were consistent with X-ray structure data. Frontier molecular orbitals and molecular electrostatic potential (MEP) profiles were identified and discussed. DFT reactivity indices provided insights into the compounds’ behaviors. Moreover, Hirshfeld surface and 2D fingerprint analyses revealed significant intermolecular interactions within the crystal structures, predominantly H–H and H–O contacts. Molecular docking studies demonstrate strong binding affinities of the synthesized compounds to the active site of protein 7B2W, suggesting potential therapeutic applications against various isolated smooth muscles and neurotransmitters.

Covering: Up to December 2020Enzymatic halogenation reactions are essential for the production of thousands of halogenated natural products. However, in recent years, scientists discovered several halogenases that transiently incorporate halogen atoms in intermediate biosynthetic molecules to activate them for further chemical reactions such as cyclopropanation, terminal alkyne formation, C-/O-alkylation, biaryl coupling, and C-C rearrangements. In each case, the halogen atom is lost in the course of biosynthesis to the final product and is hence termed "cryptic". In this review, we provide an overview of our current knowledge of cryptic halogenation reactions in natural product biosynthesis.

Aim. To synthesize new fluoro-containing building blocks for medicinal chemistry purposes using electrophilic reactions of 7-(trifluoromethyl)-2,3-dihydro-1H-pyrrolizine. Results and discussion. Synthetic approaches to 5-halogeno- and 5-acyl-7-(trifluoromethyl)-2,3-dihydro-1H-pyrrolizines have been developed. The obtained new trifluoromethyl-containing pyrrolyzines are promising building blocks for medicinal chemistry. Experimental part. The synthesis of the target compounds began with known 7-(trifluoromethyl)-2,3-dihydro-1H-pyrrolizine and included halogenation and acylation reactions using N-halogen succinimides and acylating reagents. Conclusions. New synthetic approaches to a number of 7-(trifluoromethyl)-2,3-dihydro-1H-pyrrolizines with various substituents, such as halogen atoms or acyl groups, at the position 5 of the pyrrole ring have been developed. This opens the door to the use of such promising trifluoromethyl-containing building blocks for medicinal chemistry needs.

Abstract Unstrained C─C bond activation is attained in homopolymers through mechanochemical bond scission followed by functionalization to yield mostly semi‐telechelic polymer chains. Ball milling poly(ethylene oxide) (PEO) in the presence of 1‐(bromoacetyl)pyrene (BAPy) yields the pyrene terminated PEO. Similarly, milling with 2,4′‐dibromoacetophenone followed by Suzuki coupling allows the introduction of various aryl end groups. PEOs with a molecular weight below 20 kDa show no functionalization, supporting a mechanochemical mechanism. The protocol is also tested with doxorubicin, yielding the drug‐polymer conjugate. PEO halogenation is also demonstrated by milling PEO with iodine, N‐bromosuccinimide, or N‐iodosuccinimide, which can then be reacted with an amine substituted anthracene. Grinding additional carbon polymers with BAPy indicates that this functionalization method is general for different polymer chemistries.

Isoporphyrins have recently been identified as remarkable species capable of turning the nucleophile attached to the porphyrin ring into an electrophile, thereby providing umpolung of reactivity (Inorg. Chem. 2022, 61, 8105–8111). They are generated by nucleophilic attack on an iron(III) π‐dication, a class of species that has received scant attention. Here, we explore the effect of the porphyrin meso‐substituent and report a iron(III) π‐dication bearing the meso‐tetraphenylporphyrin (TPP) ligand. We provide an extensive study of the species by UV/Vis absorption, 2H NMR, EPR, applied field Mössbauer, and resonance Raman spectroscopy. We further explore the system's highly dynamic and tunable properties and address the nature of the axial ligands as well as the conformation of the porphyrin ring. The insights presented are essential for the rational design of catalysts for the umpolung of nucleophiles. Such catalytic avenues could for example provide a novel method for electrophilic chlorinations. We further examine the importance of electronic tuning of the porphyrin by nature of the meso‐substituent as a factor in catalyst design. [ABSTRACT FROM AUTHOR]

A general catalytic protocol for the halodecarboxylation of aliphatic carboxylic acids via ligand-to-metal charge transfer (LMCT) is presented. This conversion is capable of transforming primary, secondary, and tertiary alkyl acids into the corresponding bromo-, iodo- and chloroalkanes using water as a solvent under an air atmosphere. The broad range of substrate scope, the use of a green solvent, and the ability to derivatize drug molecules and natural products offer a new prospect for decarboxylative halogenation reactions. [ABSTRACT FROM AUTHOR]

By means of the Hurd–Mori reaction, 2-(1,2,3-thiadiazol-4-yl)-5-methyl-thiophene was synthesized. Its bromination with N-bromosuccinimide under conditions of radical initiation leads to a labile 2-bromomethyl derivative which, in the presence of proton donors or when heated, rearranges to 2-(1,2,3-thiadiazol-4-yl)-4-bromo-5-methylthiophene. The possibility of rearrangement was confirmed by quantum chemical calculations. Chlorination of 2-(1,2,3-thiadiazol-4-yl)-5-methylthiophene with sulfuryl chloride both in the presence of AIBN and without it leads to 2-(1,2,3-thiadiazol-4-yl)-3,4-dichloro-5-methylthiophene. Intermediate products that form in the course of both processes are established and schemes of their formation are offered. Bromination of 2-(1,2,3-thiadiazol-4-yl)-4-bromo- and -3,4-dichloro-5-methylthiophenes with N-bromosuccinimide proceeds at the methyl group. Obtained bromomethyl derivatives undergo nucleophilic substitution reactions in the usual manner. [ABSTRACT FROM AUTHOR]

β-halogenated enol esters and ethers are versatile building blocks in organic synthesis, which has attracted increasing attention. In this study, we report the facile trans-oxyiodination and oxychlorination of alkynes, leading to the direct construction of versatile halogenated enol esters and ethers. This transformation features an easy operation, optimal atomic economy, a strong functional group tolerance, broad substrate scope, and excellent trans-selectivity. Employing highly electrophilic bifunctional N–X (halogen) reagents was the key to achieving broad reaction generality. To our knowledge, this transformation represents the first oxyhalogenation system employing N–X (halogen) reagents as both oxylation and halogenation sources. [ABSTRACT FROM AUTHOR]

Rapid industrialization and urbanization are the two significant issues causing environmental pollution. The polluted water from various industries contains refractory organic materials such as dyes. Heterogeneous photocatalysis using semiconductor metal oxides is an effective remediation technique for wastewater treatment. In this research, we used a co-precipitation-assisted hydrothermal method to synthesize a novel I-FeWO4/GO sunlight-active nanocomposite. Introducing dopant reductive iodine species improved the catalytic activity of FeWO4/GO. I− ions improved the catalytic performance of H2O2 by doping into FeWO4/GO composite. Due to I− doping and the introduction of graphene as a support medium, enhanced charge separation and transfer were observed, which is crucial for efficient heterogeneous surface reactions. Various techniques, like FTIR, SEM-EDX, XRD, and UV–Vis spectroscopy, were used to characterize composites. The Tauc plot method was used to calculate pristine and iodine-doped FeWO4/GO bandgap. Iodine doping reduced the bandgap from 2.8 eV to 2.6 eV. The degradation of methylene blue (MB) was evaluated by optimizing various parameters like catalyst concentration, oxidant dose, pH, and time. The optimum conditions for photocatalysts where maximum degradation occurred were pH = 7 for both FeWO4/GO and I-FeWO4/GO; oxidant dose = 9 mM and 7 mM for FeWO4/GO and I-FeWO4/GO; and catalyst concentration = 30 mg and 35 mg/100 mL for FeWO4/GO and I-FeWO4/GO; the optimum time was 120 min. Under these optimum conditions, FeWO4/GO and I-FeWO4/GO showed 92.0% and 97.0% degradation of MB dye. [ABSTRACT FROM AUTHOR]

Traditional butyl rubber halogenation technology involves the halogenation of IIR using molecular chlorine or bromine in a solution. However, this method is technologically complex. This study investigated a novel method for the halogenation of butyl rubber to enhance its stability and resistance to thermal oxidation and aggressive media. The butyl rubber was modified through mechanochemical modification, induced by solvent swelling in a polychlorinated n-alkane solution. During the modification, samples were obtained with chlorine content ranging from 3 to 15%. After extraction, the halogen content was quantitatively determined with the oxygen flask combustion method and X-ray photoelectron spectroscopy. It was shown that for samples with total chlorine content of up to 6%, there was almost no leaching of chlorine from the samples. The chemical structure of the extracted rubbers was ascertained using FT-IR and 1H NMR spectroscopy, and it was demonstrated that all samples showed absorption peaks and signals typical for chlorobutyl rubbers. It was observed that modification with polychlorinated n-alkanes improved the thermal and oxidative stability (the oxygen absorption rate decreased by 40%) and chemical resistance, estimated by the degree of swelling, which decreased with the increase in the chlorine content. This technology allows the production of a chlorinated rubber solution that can be directly used by rubber goods manufacturers and suppliers. [ABSTRACT FROM AUTHOR]

In a tris(pentafluorophenyl)borane [B(C6F5)3]‐catalyzed reaction of alkenes with cyanogen halides (XCN), BrCN proceeds in a cyanation/bromination manner, in which a cationic CN character is realized. The reaction using ICN switched the mode to iodination/cyanation for enamide substrates and electron‐enriched styrenes. The origin of the iodination/cyanation is the B(C6F5)3‐enhanced σ‐hole generated on ICN. [ABSTRACT FROM AUTHOR]

Herein, we have devised a metal‐free stereoselective protocol mediated by selectfluor for the dibromination of sugar enol‐ethers and monobromination of heterocyclic compounds. The dibromination of glycals was achieved within 5 minutes at room temperature with excellent yields. The tolerance of various protecting groups such as acetyl, benzyl, and silyl in sugars was checked. When the same reagent system was applied to substituted indoles and chromones 3‐brominated products were obtained but at elevated temperatures. The synthetic utility of the methodology was demonstrated by using the brominated indoles and chromones to synthesize the 3‐aryl indoles and isoflavones respectively via Suzuki‐Miyura cross‐coupling reactions. [ABSTRACT FROM AUTHOR]

2 Iron(III)-Catalyzed Halogenation of Arenes When we began this program of research, we were aware of other transition-metal-catalyzed methods for arene iodination that used NIS. Keywords: iron and copper catalysis; halogenation; thioarylation; -Ullmann coupling; heterocycle synthesis EN iron and copper catalysis halogenation thioarylation -Ullmann coupling heterocycle synthesis 1852 1865 14 09/15/23 20231004 NES 231004 Graph 1 Introduction Traditionally, the most common method for the radioiodination of aromatic compounds to generate single photon emission computed tomography (SPECT) tracers for medical imaging involves oxidative iodination of aryl stannanes (Scheme 1a). [36] As a Lewis acid catalyst for general iodination of arenes, silver(I) triflimide allowed fast and high-yielding reactions under similar conditions and in comparable yields to the corresponding iron(III)-catalyzed reaction. While the initial focus of this program was the development of halogenation reactions and in particular, a new procedure for radioiodination of aromatic compounds, we realized that both the synthetic utility of aryl halides and the mild nature of these transformations meant they could be combined with other reactions for the one-pot, multistep synthesis of functionalized arenes and benzannulated heterocycles. [Extracted from the article]

The utilization of DMSO or Ph2SO/(COBr)2 or (COCl)2 for the bromination or chlorination of arenes has been explored. Notably, monobromination of activated arenes can be achieved with high regioselectivity using the combination of dimethyl sulfoxide and oxalyl bromide. Bromodimethylsulfonium bromide generated in situ was proposed to be the active species for bromination. In contrast, the practicality of chlorination of arenes with DMSO or Ph2SO/(COCl)2 is limited due to production of the formation of by-products such as aryldimethylsulfonium chlorides or dichlorinated arenes. [ABSTRACT FROM AUTHOR]

A series of halogenated systems for pyrazolo[1,5-a]pyrimidines have been developed. Selective transformations of pyrazolo[1,5-a]pyrimidines by mono- and di-iodination were achieved by varying the ratio of pyrazolo[1,5-a]pyrimidines to NIS. In addition, the reaction of pyrazolo[1,5-a]pyrimidines with NBS or NCS uniquely gave dibrominated or dichlorinated products. The wide range of substrates, good functional group tolerance and gram-scale synthesis further demonstrate the application potential of this reaction. This work provides an efficient method for the construction of structurally diverse halogenated pyrazolo[1,5-a]pyrimidine derivatives. [ABSTRACT FROM AUTHOR]

Oxyhalide glasses are utilized in the process of immobilizing nuclear waste and function as scintillating agents for the purpose of radiation detection. The objective of this study is to examine the enhanced mechanical and radiation attenuation characteristics of newly developed oxyhalide glasses by incorporating zinc-iodide. This study investigates the synthesis process, mechanical properties, and experimental gamma-neutron radiation transmission properties. A halogen-free base glass, consisting of an oxide mixture of P 2 O 5 , TeO 2 , and ZnO, was synthesized. Following that, the initial glass composition was further strengthened by the addition of zinc bromide (ZnBr 2), zinc chloride (ZnCl 2), zinc fluoride (ZnF 2), and zinc iodide (ZnI 2) in a successive manner. The experimental configuration entailed positioning circular glass samples between a 133Ba radioisotope and a Canberra High Purity Germanium (HPGe) detector. The determination of attenuation coefficients is achieved through the measurement of individual attenuation properties. Afterwards, theoretical approaches are utilized to determine the mechanical characteristics of halogenated glasses, including Young's modulus (Y), Bulk modulus (K), Shear modulus (G), Longitudinal modulus (L), and Poisson's modulus (v). The results of the study suggest that the implementation of the halogenation process on the P 2 O 5 –TeO 2 –ZnO base composition led to a significant enhancement in the examined properties. The incorporation of zinc-iodide in the halogenation process resulted in a significant improvement in the gamma absorption properties. The utilization of zinc in the halogenation process demonstrates multifunctional capabilities, which involve the potential to enhance various glass properties, including durability and gamma-ray absorption properties. It can be concluded that zinc-iodide demonstrates enhanced halogenation capabilities in comparison to zinc bromide, zinc chloride, and zinc fluoride. [ABSTRACT FROM AUTHOR]

Decarboxylative halogenation reactions of alkyl carboxylic acids are highly valuable reactions for the synthesis of structurally diverse alkyl halides. However, many reported protocols rely on stoichiometric strong oxidants or highly electrophilic halogenating agents. Herein, we describe visible‐light photoredox‐catalyzed decarboxylative halogenation reactions of N‐hydroxyphthalimide‐activated carboxylic acids that avoid stoichiometric oxidants and use inexpensive inorganic halide salts as the halogenating agents. Bromination with lithium bromide proceeds under simple, transition‐metal‐free conditions using an organic photoredox catalyst and no other additives, whereas dual photoredox‐copper catalysis is required for chlorination with lithium chloride. The mild conditions display excellent functional‐group tolerance, which is demonstrated through the transformation of a diverse range of structurally complex carboxylic acid containing natural products into the corresponding alkyl bromides and chlorides. In addition, we show the generality of the dual photoredox‐copper‐catalyzed decarboxylative functionalization with inorganic salts by extension to thiocyanation with potassium thiocyanide, which was applied to the synthesis of complex alkyl thiocyanates. [ABSTRACT FROM AUTHOR]

We developed the remote selective C−H bromination for the synthesis of C4′‐brominated biarylphosphine oxides using FeBr3 as a brominating reagent. C3′‐Brominated products were obtained in reactions with substrates bearing a 2,4,6‐triisopropyl substituent on the bottom ring. Moreover, direct access to C5‐chlorinated peri‐substituted(1‐naphthalenyl)phosphines is developed using FeCl3 as a chlorinating reagent. These halogenated compounds can be utilized for cross‐coupling reactions to construct functionalized phosphine oxides. [ABSTRACT FROM AUTHOR]

In this study, we present a straightforward and environmentally friendly electrochemical approach for achieving selective halogenation of N‐heteroarenes, including indoles, diazoles, pyrroles, quinolinone, and naphthols. Our method utilizes commercially available and affordable ammonium halides as halogen source. A library of valuable halogenated N‐heteroarenes can be synthesized in moderate to excellent yields under mild conditions (transition‐metal‐free, oxidant‐free, ethanol as solvent, atmospheric environment). The approach demonstrates a broad substrate scope, excellent tolerance towards various functional groups, and scalability. [ABSTRACT FROM AUTHOR]

Single C−F transformations of aromatic trifluoromethyl compounds are challenging issues due to the strong C−F bond. We have recently developed selective methods for single C−F transformations such as allylation of o‐hydrosilyl‐substituted benzotrifluorides through the hydride abstraction with trityl cations. Single C−F thiolation and azidation of o‐(hydrosilyl)benzotrifluorides were achieved using trityl sulfides and trityl azide catalyzed by Yb(OTf)3. Treatment of o‐(hydrosilyl)benzotrifluorides with trityl chloride resulted in single C−F chlorination. The resulting fluorosilyl group served in further transformations including protonation, halogenation, and Hiyama cross‐coupling with C−Si cleavage. We also synthesized benzyl fluorides by LiAlH4‐reduction of the resulting fluorosilanes and further C−F transformations. These methods enabled us to prepare a broad range of organofluorines from simple benzotrifluorides through C−F and C−Si transformations. [ABSTRACT FROM AUTHOR]

Depsides and depsidones have attracted attention for biosynthetic studies due to their broad biological activities and structural diversity. Previous structure‒activity relationships indicated that triple halogenated depsidones display the best anti-pathogenic activity. However, the gene cluster and the tailoring steps responsible for halogenated depsidone nornidulin (3) remain enigmatic. In this study, we disclosed the complete biosynthetic pathway of the halogenated depsidone through in vivo gene disruption, heterologous expression and in vitro biochemical experiments. We demonstrated an unusual depside skeleton biosynthesis process mediated by both highly-reducing polyketide synthase and non-reducing polyketide synthase, which is distinct from the common depside skeleton biosynthesis. This skeleton was subsequently modified by two in-cluster enzymes DepG and DepF for the ether bond formation and decarboxylation, respectively. In addition, the decarboxylase DepF exhibited substrate promiscuity for different scaffold substrates. Finally, and interestingly, we discovered a halogenase encoded remotely from the biosynthetic gene cluster, which catalyzes triple-halogenation to produce the active end product nornidulin (3). These discoveries provide new insights for further understanding the biosynthesis of depsidones and their derivatives. A new and concise biosynthetic pathway of nornidulin (3) was elucidated. The depside skeleton 2 is synthesized by a collaborating hrPKS and nrPKS pair, followed by etherification, decarboxylation and halogenation. [Display omitted] [ABSTRACT FROM AUTHOR]

Recycling of all-trans-retinal to 11-cis-retinal through the visual cycle is a fundamental metabolic pathway in the eye. A potent retinoid isomerase (RPE65) inhibitor, (R)-emixustat, has been developed and tested in several clinical trials; however, it has not received regulatory approval for use in any specific retinopathy. Rapid clearance of this drug presents challenges to maintaining concentrations in eyes within a therapeutic window. To address this pharmacokinetic inadequacy, we rationally designed and synthesized a series of emixustat derivatives with strategically placed fluorine and deuterium atoms to slow down the key metabolic transformations known for emixustat. Crystal structures and quantum chemical analysis of RPE65 in complex with the most potent emixustat derivatives revealed the structural and electronic bases for how fluoro substituents can be favorably accommodated within the active site pocket of RPE65. We found a close (∼3.0 Å) F-π interaction that is predicted to contribute ∼2.4 kcal/mol to the overall binding energy.

C(sp3 )-Cl bonds are present in numerous biologically active small molecules, and an ideal route for their preparation is by the chlorination of a C(sp3 )-H bond. However, most current methods for the chlorination of C(sp3 )-H bonds are insufficiently site selective and tolerant of functional groups to be applicable to the late-stage functionalization of complex molecules. We report a method for the highly selective chlorination of tertiary and benzylic C(sp3 )-H bonds to produce the corresponding chlorides, generally in high yields. The reaction occurs with a mixture of an azidoiodinane, which generates a selective H-atom abstractor under mild conditions, and a readily-accessible and inexpensive copper(II) chloride complex, which efficiently transfers a chlorine atom. The reaction's exceptional functional group tolerance is demonstrated by the chlorination of >30 diversely functionalized substrates and the late-stage chlorination of a dozen derivatives of natural products and active pharmaceutical ingredients.

Density functional calculations have provided evidence that a Ag(I)-mediated deconstructive fluorination of N-benzoylated cyclic amines (LH) with Selectfluor [(F-TEDA)(BF4)2] begins with an association of the reactants to form a singlet state adduct {[(LH)-Ag]-[F-TEDA]2+}. The subsequent formation of an iminium ion intermediate, [L+-Ag]-HF-[TEDA]+, is, formally, a Ag(I)-mediated hydride abstraction event that occurs in two steps: (a) a formal oxidative addition (OA) of [F-TEDA]2+ to the Ag(I) center that is attended by an electron transfer (ET) from the substrate (LH) to the Ag center (i.e., OA + ET, this process can also be referred to as a F-atom coupled electron transfer), followed by (b) H-atom abstraction from LH by the Ag-coordinated F atom. The overall process involves lower-lying singlet and triplet electronic states of several intermediates. Therefore, we formally refer to this reaction as a two-state reactivity (TSR) event. The C-C bond cleavage/fluorination of the resulting hemiaminal intermediate via a ring-opening pathway has also been determined to be a TSR event. A competing deformylative fluorination initiated by hemiaminal to aldehyde equilibration involving formyl H-atom abstraction by a TEDA2+ radical dication, decarbonylation, and fluorination of the resulting alkyl radical by another equivalent of Selectfluor may also be operative in the latter step.

Halogenated natural products number in the thousands, but only in rare cases are the evolutionary advantages conferred by the halogens understood. We set out to investigate the lissoclimide family of cytotoxins, which includes several chlorinated members, because of our long-standing interest in the synthesis of chlorinated secondary metabolites.Our initial success in this endeavor was a semisynthesis of chlorolissoclimide (CL) from the commercially available sesquiterpenoid sclareolide. Featuring a highly selective and efficient-and plausibly biomimetic-C-H chlorination, we were able to access enough CL for collaborative studies, including X-ray cocrystallography with the eukaryotic ribosome. Through this experiment, we learned that CL's chlorine atom engages in a novel halogen-π dispersion interaction with a neighboring nucleobase in the ribosome E-site.Owing to the limitations of our semisynthesis approach, we established an analogue-oriented approach to access numerous lissoclimide compounds to both improve our understanding of structure-activity relationships and to learn more about the halogen-π interaction. In the course of these studies, we made over a dozen lissoclimide-like compounds, the most interesting of which contained chlorine-bearing carbons with unnatural configurations. Rationalizing the retained potency of these compounds that appeared to be a poor fit for the lissoclimide binding pocket, we came to realize that the chlorine atoms would engage in these same halogen-π interactions even at the expense of a chair to twist-boat conformational change, which also permitted the compounds to fit in the binding site.Finally, because neither of the first two approaches could easily access the most potent natural lissoclimides, we designed a synthesis that took advantage of rarely used terminal epoxides to initiate polyene cyclizations. In this case, the chlorine atom was incorporated early and helped control the stereochemical outcome of the key step.Over the course of this project, three different synthesis approaches were designed and executed, and our ability to access numerous lissoclimides fueled a range of collaborative biological studies. Further, chlorine played impactful roles throughout various aspects of both synthesis and biology. We remain inspired to learn more about the mechanism of action of these compounds and to deeply investigate the potentially valuable halogen-π dispersion interaction in the context of small molecule/nucleic acid binding. In that context, our work offers an instance wherein we might have gained a rudimentary understanding of the evolutionary importance of the halogen in a halogenated natural product.

The article shares insight on whether the combination of para-Fluorofentanyl (pFF) and fentanyl is coincidental or intentional. It refers to illicitly manufactured fentanyls as a primary contributor to opioid overdose deaths worldwide. It cites conflicting reports regarding the potency of pFF compared to fentanyl and hypothesizes that the inclusion of pFF is an intentional addition by illicit laboratories to prolong the effects of fentanyl.

In aquifers, acetylene (C2H2) is a product of abiotic degradation of trichloroethene (TCE) catalyzed by in situ minerals. C2H2 can, in turn, inhibit multiple microbial processes including TCE dechlorination and metabolisms that commonly support dechlorination, in addition to supporting the growth of acetylenotrophic microorganisms. Previously, C2H2 was shown to support TCE reductive dechlorination in synthetic, laboratory-constructed cocultures containing the acetylenotroph Pelobacter sp. strain SFB93 and Dehalococcoides mccartyi strain 195 or strain BAV1. In this study, we demonstrate TCE and perchloroethene (PCE) reductive dechlorination by a microbial community enriched from contaminated groundwater and amended with C2H2 as the sole electron donor and organic carbon source. The metagenome of the stable, enriched community was analyzed to elucidate putative community functions. A novel anaerobic acetylenotroph in the phylum Actinobacteria was identified using metagenomic analysis. These results demonstrate that the coupling of acetylenotrophy and reductive dechlorination can occur in the environment with native bacteria and broaden our understanding of biotransformation at contaminated sites containing both TCE and C2H2IMPORTANCE Understanding the complex metabolisms of microbial communities in contaminated groundwaters is a challenge. PCE and TCE are among the most common groundwater contaminants in the United States that, when exposed to certain minerals, exhibit a unique abiotic degradation pathway in which C2H2 is a product. C2H2 can act as both an inhibitor of TCE dechlorination and of supporting metabolisms and an energy source for acetylenotrophic bacteria. Here, we combine laboratory microcosm studies with computational approaches to enrich and characterize an environmental microbial community that couples two uncommon metabolisms, demonstrating unique metabolic interactions only yet reported in synthetic, laboratory-constructed settings. Using this comprehensive approach, we have identified the first reported anaerobic acetylenotroph in the phylum Actinobacteria, demonstrating the yet-undescribed diversity of this metabolism that is widely considered to be uncommon.

Today, the chemistry of quaternary ammonium compounds is rapidly developing field owing, among other things, to the need to combat periodic outbreaks of various infectious diseases, which in some cases assume pandemic proportions. This review summarizes the most recent studies, published mainly over the past 10 years, devoted to advances in the synthesis of bisquaternary ammonium compounds for various purposes. The synthetic methods include monoalkyl halogenation of diamines, dialkyl halogenation of amines, methyltrifluoromethanesulfonation reactions, and anion exchange reactions. [ABSTRACT FROM AUTHOR]

Penta-iodination of the B2–6 positions of the {CB11} monocarborane cluster is reported. Products of the structure [2,3,4,5,6-I5-CB11H6-12-X]− (X = H, Me, Et, Ph, Br, I) were obtained and fully characterized. X-ray crystal structures of three new compounds confirm this particular substitution pattern. The synthetic method relies on palladium catalysis/B–H activation, assisted by the C1-COOH directing group. The one-pot procedure enables penta-iodination and subsequent decarboxylation under convenient conditions. The B2–6 regioselectivity is complementary to the commonly observed reactivity of {CB11} clusters, which follows the trend B12 > B7–11 > B2–6 for electrophilic substitution. Thus, for the first time upper-belt halogenation is achieved without prior modification of the lower-belt positions. [ABSTRACT FROM AUTHOR]

Two metallofullerene frameworks (MFFs) constructed from a penta‐shell Keplerate cuprofullerene chloride, C60@Cu24@Cl44@Cu12@Cl12, have been successfully prepared via a C60‐templated symmetry‐driven strategy. The icosahedral cuprofullerene chloride is assembled on a C60 molecule through [η2‐(C=C)]−CuI and CuI−Cl coordination bonds, resulting in the penta‐shell Keplerate with the C60 core canopied by 24 Cu, 44 Cl, 12 Cu and 12 Cl atoms that fulfill the tic@rco@oae@ico@ico penta‐shell polyhedral configuration. By sharing the outmost‐shell Cl atoms, the cuprofullerene chlorides are connected into 2D or 3D (snf net) frameworks. TD‐DFT calculations reveal that the charge transfer from the outmost CuI and Cl to C60 core is responsible for their light absorption expansion to near‐infrared region, implying anionic halogenation may be an effective strategy to tune the light absorption properties of metallofullerene materials. [ABSTRACT FROM AUTHOR]

Motivated by the excellent electronic and optoelectronic properties of two-dimensional (2D) Ga-monochalcogenides, we systematically investigated the effect of halogenation on physical properties of monolayer GaX (X = S, Se) by the first-principles calculations. Crystal lattices of GaX were decomposed with the halogen atom being absorbed on top of the Ga atom. Unexpectedly, a series of monolayer GaXY (X = S, Se; Y = F, Cl, Br, I) was formed. Except for GaXF, other monolayer GaXY has good structural stability at room temperature. With the broken mirror symmetry, monolayer GaXY has superior flexibility, a direct bandgap in the range of 0.78–4.43 eV, the intrinsic vertical polarization, and larger in-plane as well as out-of-plane piezoelectric coefficients than Ga-monochalcogenides. Moreover, by comparing the structural stability and side-dependent electronic band alignment, we concluded that monolayer GaXY (X = S, Se; Y = Cl, Br) is suitable for photocatalytic water-splitting applications. [ABSTRACT FROM AUTHOR]

The catalyst‐free electrochemical halogenation and trifluoromethylation of 4H‐pyrido[1,2‐a]pyrimidin‐4‐ones was realized under external‐oxidant‐free conditions. This strategy provides an easy and green access to functionalized new 4H‐pyrido[1,2‐a]pyrimidin‐4‐one derivatives with broad scope, good functional group tolerance and high regioselectivity. [ABSTRACT FROM AUTHOR]

This paper describes the Pd(II)‐catalyzed, picolinamide‐directing‐group‐aided C(sp2)−H (ortho) functionalization of racemic and enantiopure β‐phenylalanines and 3‐amino‐3‐phenylpropanols (1,3‐amino alcohols). The C(sp2)−H (ortho) functionalizations including arylation, bromination, iodination, and alkoxylation were attempted. The C(sp2)−H (ortho) arylation reactions gave biaryl or terphenyl‐type β‐phenylalanine scaffolds, halogenation and methoxylation reactions gave ortho C−H halogenated or methoxylated β‐phenylalanines. Additionally, the C−H arylation of an ortho‐methyl substituted β‐phenylalanine containing both C(sp2)−H and remote C(sp3)−H bonds was investigated. β‐Phenylalanine is an arylated β‐amino acid motif present in various natural products, bioactive molecules, and β‐peptides and it is a precursor to medicinally active compounds. Accordingly, this work contributes to the expansion of the library of unnatural β‐phenylalanine (β‐amino acid) derivatives through site‐selective C−H functionalization. [ABSTRACT FROM AUTHOR]

In nature, flavin‐dependent halogenases (FDHs) catalyze site‐selective chlorination and bromination of aromatic natural products. This ability has led to extensive efforts to engineer FDHs for selective chlorination, bromination, and iodination of electron rich aromatic compounds. On the other hand, FDHs are unique among halogenases and haloperoxidases that exhibit catalyst‐controlled site selectivity in that no examples of enantioselective FDH catalysis in natural product biosynthesis have been characterized. Over the past several years, our group has established that FDHs can catalyze enantioselective reactions involving desymmetrization, atroposelective halogenation, and halocyclization. Achieving high activity and selectivity for these reactions has required extensive mutagenesis and mitigation of problems resulting from hypohalous acid generated during FDH catalysis. The single‐component flavin reductase/FDH AetF is unique among the wild type enzyme we have studied in that it provides high activity and selectivity toward several asymmetric transformations. These results highlight the ability of FDH active sites to tolerate different substrate topologies and suggest that they could be useful for a broad range of oxidative halogenations. [ABSTRACT FROM AUTHOR]

Various approaches to the synthesis of 3-halopyrazolo[1,5-a]pyrimidines were studied. It is shown that the most effective strategy consists in the construction of the azoloazine core followed by halogenation with N-iodo- or N-bromosuccinimide. A series of 3-halopyrazolo[1,5-a]pyrimidines, which are bioisosteric analogs of natural purine nucleic bases and the drug Triazavirin®, were synthesized using this strategy. The obtained compounds are interesting as precursors of novel C-nucleosides, which can be synthesized by C-C-coupling with (pseudo)ribosides containing a keto group. [ABSTRACT FROM AUTHOR]

Introduction: The antimicrobial pyrrolnitrin from Pseudomonas strains is formed in four steps from tryptophan and comprises two flavin-dependent halogenases. Both PrnC and PrnA can carry out regioselective chlorination and bromination and are carrier protein-independent. Whilst the tryptophan halogenase PrnA has been studied in detail in the past, this study focuses on the pyrrole halogenating enzyme PrnC. Methods: The halogenating enzyme PrnC, as well as the essential electron suppliers, the flavin reductases, have been produced soluble in E. coli. Furthermore, a screening of a rational compound library revealed that the pyrrole is essential for substrate recognition; however, the substitution pattern of the benzene ring is not limiting the catalysis. Results and discussion: This renders PrnC to be a synthetically valuable enzyme for the synthesis of pyrrolnitrin congeners. For its natural substrate monodechloroaminopyrrolnitrin (MDA), the KM value was determined as 14.4 ± 1.2 µM and a kcat of 1.66 ± 0.02 min-1, which is comparable to other halogenases. [ABSTRACT FROM AUTHOR]