Synthesis of Novel 4-Acyloxy-2'-bromo-6'-chloropodophyllotoxin Derivatives Displaying Significant Insecticidal Activity against Mythimna separata

In order to explore novel natural product-based insecticidal agent, two important intermediates (2 and 3) and 4-acyloxy-2'-bromo-6'-chloropodophyllotoxin derivatives (4a-f and 5a-f) were designed and prepared, and their structures were confirmed by 1H NMR, 13C NMR, HRMS, ESI-MS, optical rotation and melting point (mp). The stereochemical configuration of compound 4b was unambiguously confirmed by single-crystal X-ray diffraction. Moreover, we evaluated the insecticidal activity of target compounds 4a-f and 5a-f against a serious agricultural pest of Mythimna separata by using the leaf-dipping method. Among all tested compounds, compounds 4d, 5d and 5f exhibited stronger insecticidal activity with a final mortality rate exceeding 60%. Especially compound 5d exhibited the best insecticidal activity, with a final mortality rate of 74.1%. It has been proven that introducing bromine or chlorine atoms at the C-2', C-2' and C-6' positions of the E ring of podophyllotoxin can produce more potent compounds. In addition, the configuration of the C-4 position is important for insecticidal activity, and 4β-configuration is optimal. This will pave the way for further design, structural modification, and development of derivatives of podophyllotoxin as insecticidal agents.

Efficient Synthesis and Structural Analysis of Chiral 4,4'-Biazulene

4,4'-Biazulene is a potentially attractive key component of an axially chiral biaryl compound, however, its structure and properties have not been clarified owing to the lack of its efficient synthesis. We report a breakthrough in the reliable synthesis of 4,4'-biazulene, which is achieved by the access to azulen-4-ylboronic acid pinacol ester and 4-iodoazulene as novel key synthetic intermediates for the Suzuki-Miyaura cross-coupling reaction. The X-ray crystallographic analysis of 4,4'-biazulene confirmed its axial chirality. The enantiomers of 4,4'-biazulene were successfully resolved by HPLC on the chiral stationary phase column. The kinetic experiments and DFT calculations indicate that the racemization energy barrier of 4,4'-biazulene is comparable to that of 1,1'-binaphthyl.

Macroalgal microbiomes unveil a valuable genetic resource for halogen metabolism

BACKGROUND

Macroalgae, especially reds (Rhodophyta Division) and browns (Phaeophyta Division), are known for producing various halogenated compounds. Yet, the reasons underlying their production and the fate of these metabolites remain largely unknown. Some theories suggest their potential antimicrobial activity and involvement in interactions between macroalgae and prokaryotes. However, detailed investigations are currently missing on how the genetic information of prokaryotic communities associated with macroalgae may influence the fate of organohalogenated molecules.

RESULTS

To address this challenge, we created a specialized dataset containing 161 enzymes, each with a complete enzyme commission number, known to be involved in halogen metabolism. This dataset served as a reference to annotate the corresponding genes encoded in both the metagenomic contigs and 98 metagenome-assembled genomes (MAGs) obtained from the microbiome of 2 red (Sphaerococcus coronopifolius and Asparagopsis taxiformis) and 1 brown (Halopteris scoparia) macroalgae. We detected many dehalogenation-related genes, particularly those with hydrolytic functions, suggesting their potential involvement in the degradation of a wide spectrum of halocarbons and haloaromatic molecules, including anthropogenic compounds. We uncovered an array of degradative gene functions within MAGs, spanning various bacterial orders such as Rhodobacterales, Rhizobiales, Caulobacterales, Geminicoccales, Sphingomonadales, Granulosicoccales, Microtrichales, and Pseudomonadales. Less abundant than degradative functions, we also uncovered genes associated with the biosynthesis of halogenated antimicrobial compounds and metabolites.

CONCLUSION

The functional data provided here contribute to understanding the still largely unexplored role of unknown prokaryotes. These findings support the hypothesis that macroalgae function as holobionts, where the metabolism of halogenated compounds might play a role in symbiogenesis and act as a possible defense mechanism against environmental chemical stressors. Furthermore, bacterial groups, previously never connected with organohalogen metabolism, e.g., Caulobacterales, Geminicoccales, Granulosicoccales, and Microtrichales, functionally characterized through MAGs reconstruction, revealed a biotechnologically relevant gene content, useful in synthetic biology, and bioprospecting applications. Video Abstract.

The Influence of Donor/Acceptor Interfaces on Organic Solar Cells Efficiency and Stability Revealed through Theoretical Calculations and Morphology Characterizations

End-groups halogenation strategies, generally refers to fluorination and chlorination, have been confirmed as simple and efficient methods to regulate the photoelectric performance of non-fullerene acceptors (NFAs), but a controversy over which one is better has existed for a long time. Here, two novel NFAs, C9N3-4F and C9N3-4Cl, featured with different end-groups were successfully synthesized and blended with two renowned donors, D18 and PM6, featured with different electron-withdrawing units. Detailed theoretical calculations and morphology characterizations of the interface structures indicate NFAs based on different end-groups possess different binding energy and miscibility with donors, which shows an obvious influence on phase-separation morphology, charge transport behavior and device performance. After verified by other three pairs of reported NFAs, a universal conclusion obtained as the devices based on D18 with fluorination-end-groups-based NFAs and PM6 with chlorination-end-groups-based NFAs generally show excellent efficiencies, high fill factors and stability. Finally, the devices based on D18: C9N3-4F and PM6: C9N3-4Cl yield outstanding efficiency of 18.53 % and 18.00 %, respectively. Suitably selecting donor and regulating donor/acceptor interface can accurately present the photoelectric conversion ability of a novel NFAs, which points out the way for further molecular design and selection for high-performance and stable organic solar cells.

Late-stage modification of bioactive compounds: Improving druggability through efficient molecular editing

Synthetic chemistry plays an indispensable role in drug discovery, contributing to hit compounds identification, lead compounds optimization, candidate drugs preparation, and so on. As Nobel Prize laureate James Black emphasized, "the most fruitful basis for the discovery of a new drug is to start with an old drug"1. Late-stage modification or functionalization of drugs, natural products and bioactive compounds have garnered significant interest due to its ability to introduce diverse elements into bioactive compounds promptly. Such modifications alter the chemical space and physiochemical properties of these compounds, ultimately influencing their potency and druggability. To enrich a toolbox of chemical modification methods for drug discovery, this review focuses on the incorporation of halogen, oxygen, and nitrogen-the ubiquitous elements in pharmacophore components of the marketed drugs-through late-stage modification in recent two decades, and discusses the state and challenges faced in these fields. We also emphasize that increasing cooperation between chemists and pharmacists may be conducive to the rapid discovery of new activities of the functionalized molecules. Ultimately, we hope this review would serve as a valuable resource, facilitating the application of late-stage modification in the construction of novel molecules and inspiring innovative concepts for designing and building new drugs.

Late-Stage Halogenation of Peptides, Drugs and (Hetero)aromatic Compounds with a Nucleophilic Hydrazide Catalyst

Unlike its other halogen atom siblings, chlorination of a bioactive compound can change its physiological characteristics, improve its pharmacological profile, and function as a point of diversification through cross-coupling reactions. As a result, it has been a crucial strategy for drug discovery and development. However, functional groups such as amines, amides, hydroxy groups, or carboxylic acids trap the Cl+ , severely limiting the reactivity and making direct chlorination far too difficult to be practical. Herein, we introduce a nucleophilic sulfonohydrazide catalyst for late-stage halogenation of peptides and drugs. This direct, mild and metal-free protocol shows high functional-group tolerance and is compatible with a range of structurally diverse peptides, drugs and aromatic compounds. Furthermore, DFT studies indicate that the reaction most likely proceeds via a cationic transition state. The gram-scale synthesis, high stability and efficiency of the catalyst provide a facile route for late-stage functionalization and intermediates for further derivatization.

A Porphyrin Iron(III) π-Dication Species and its Relevance in Catalyst Design for the Umpolung of Nucleophiles

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, 2 H 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.

Photoredox-Catalyzed Decarboxylative Bromination, Chlorination and Thiocyanation Using Inorganic Salts

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.

Heterogeneous Photocatalytic Recycling of FeX2/FeX3 for Efficient Halogenation of C-H Bonds Using NaX

Environmental-friendly halogenation of C-H bonds using abundant, non-toxic halogen salts is in high demand in various chemical industries, yet the efficiency and selectivity of laboratory available protocols are far behind the conventional photolytic halogenation process which uses hazardous halogen sources. Here we report an FeX2 (X = Br, Cl) coupled semiconductor system for efficient, selective, and continuous photocatalytic halogenation using NaX as halogen source under mild conditions. Herein, FeX2 catalyzes the reduction of molecular oxygen and the consumption of generated oxygen radicals, thus boosting the generation of halogen radicals and elemental halogen for direct halogenation and indirect halogenation via the formation of FeX3. Recycling of FeX2 and FeX3 during the photocatalytic process enables the halogenation of a wide range of hydrocarbons in a continuous flow, rendering it a promising method for applications.

An investigation of halogen induced improvement of β12 borophene for Na/Li storage by density functional theory

Pristine and halogen doped β12 borophene, as anode of lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), was considered by first-principles study based on density functional theory. Li and Na were adsorbed on β12 borophene with adsorption energies of -3.18 eV and -2.33 eV, respectively. The effect of halogen addition, X = F, Cl, Br, and I, to borophene sheet on adsorption and also diffusion pathways of Li and Na was studied. The adsorption energy calculations show that the halogen atoms improve Li/Na adsorption on borophene sheet. Also, the results indicate that Li/Na adsorption energies on Brominated borophene sheet are higher compared to other halogen types. Diffusion calculations show that Br addition induces an electron deficiency on BoBr surface which lowers the energy barrier of migration of Li and Na ions compared to the pristine borophene. According to density of states analysis, electron charge is transferred from Li and Na atoms toward halogenated borophene sheet. Also, it can be concluded that electron transfer from Li/Na to borophene host in BoX is higher compared to pristine borophene which is in agreement with adsorption energies. The fully lithiated/sodiated complexes of BoBr are Li_0.71BoBr and Na_0.50BoBr which is equivalent to theoretical specific capacities of 1401 and 981 mAh/g which are about 3.5 and 2.6 times higher than graphite for Li and Na adsorption, respectively. Higher specific capacity of Li compared to Na is mainly attributed to steric hindrance of Na regarding its greater size. Open circuit voltage values of 1.6 V and 1.4 V were obtained for Li and Na intercalation processes, respectively, into halogen added β₁₂ borophene indicating that this structure can be applied as anode for both LIB and SIB systems.

Directing Group-Free Regioselective meta-C-H Functionalization of Pyridines

The pyridine core is among the most common motifs found in pharmaceuticals and agrochemicals. Consequently, the C-H functionalization of pyridine is a prized reaction, as it can help access a broad spectrum of valuable chemicals. However, the intrinsic electronic properties of pyridines hinder their meta-C-H functionalization, requiring drastic conditions affecting functional group compatibility. A synthetic manoeuvre to overcome this challenge involves the temporary conversion of pyridines into electron-rich intermediates and subsequent regioselective electrophilic functionalization. This was recently accomplished by a ring-opening ring-closing sequence via Zincke imine intermediates by McNally and co-workers, and a dearomatization-rearomatization sequence via oxazino-pyridine intermediates by the Studer group. The mildness and simplicity of these protocols enable them to work with complex molecular setups for synthesizing natural products and bioactive molecules.

High cytotoxicity of a degraded TBBPA, dibromobisphenol A, through apoptotic and necrosis pathways

Halogenated flame retardants comprising bisphenol A (BPA) derivatives, such as tetrabromobisphenol A (TBBPA), have been studied their adverse effects on human health. However, despite the fact that these halogenated BPAs are easily degraded in the environment, the risks to living organisms due to these degraded products have mostly been overlooked. To evaluate the potential toxicity of degraded TBBPAs and related compounds, we examined the cytotoxicity of halogenated bisphenol A derivatives possessing one to four halogen atoms in vitro. The results indicated that the degraded TBBPA derivatives exhibited strong cytotoxicity against HeLa cells than TBBPA. Interestingly, the di-halogenated BPA derivatives possessing two halogen atoms exhibited the strongest cytotoxicity among tested compounds. In addition, a lactate dehydrogenase release assay, fluorescence spectroscopy and flow cytometry results indicated that dibromo-BPA and diiodo-BPA induced both apoptotic and necrotic cell death by damaging the cell membranes of HeLa cells. Moreover, Escherichia coli growth was inhibited in the presence of dehalogenated TBBPA and related compounds. These findings suggest that halogenated BPA derivatives that leak from various flame-retardant-containing products require strict monitoring, as not only TBBPA but also its degraded products in environment can exert adverse effects to human health.

Targeted Enzyme Modifications Enable Regioselective Biosynthesis of Fluorinated Polyketides

In attempts to enhance natural products as therapeutic agents, fluorination has emerged as a new tool for synthetic biologists and chemists. In recent articles published in Nature Chem. and Nature Chem. Bio., Grininger, Chang, and co-workers leveraged their expertise in engineering polyketide biosynthesis to incorporate fluorine into polyketide scaffolds.

TBAX/Oxone Mediated Halogenation of Pyrazoles and Other Heterocycles: An Entry to Important Cross Coupling Reactions

A facile, sustainable and eco-friendly protocol has been developed for the halogenation of various heterocycles using TBAX (TBAI/TBAB/TBACl) as halogenating agent, which afforded the products in 90-95% isolated yields. The reaction proceeds with low-cost TBAX and uses greener conditions like EtOH as a solvent and microwave as an alternative energy source for reaction. This protocol has been applied on pyrazoles and extended to different heterocycles like 7-azaindole, indazole, indole and 2-phenylimidazo[1,2-α]pyridines. The gram-scale iodination reaction has also been successfully performed by optimizing conventional heating conditions, which demonstrates its potential applicability in organic synthesis. Further these halogenated pyrazoles have been utilized for different coupling reactions including formation of arylated, alkynylated and sulfenated pyrazoles. However, TBAF mediated fluorination did not work.

Catalytic Asymmetric Halogenation/Semipinacol Rearrangement of 3-Hydroxyl-3-vinyl Oxindoles: A Stereodivergent Kinetic Resolution Process

A highly enantioselective halogenation/semipinacol rearrangement of isatin-derived allylic alcohols has been developed with a chiral N,N'-dioxide/Sc^III complex as catalyst. This strategy involved a pivotal stereodivergent kinetic resolution process and provided a facile and efficient entry to optically active halo-substituted quinolone derivatives and quinoline alkaloids with a quaternary stereocenter simultaneously under mild reaction conditions. Based on the control experiments together with kinetic studies and DFT calculations, a possible catalytic cycle was proposed to illustrate the reaction process and enantiocontrol.

Photocatalytic degradation of sulfamethoxazole using TiO2 in simulated seawater: Evidence for direct formation of reactive halogen species and halogenated by-products

Nowadays photoactivation mechanism of titanium dioxide nanoparticles (TiO₂ NPs) and reactive species involved in saline waters is not sufficiently established. In this study, TiO₂ photocatalytic process under simulated solar irradiation was evaluated in synthetic seawater and compared with deionized water, using sulfamethoxazole (SMX) as model organic compound. For a TiO₂ concentration of 100 mg L^-1, SMX degradation resulted two times slower in seawater than in deionized water by the determination of their pseudo-first order rate constants of 0.020 min^-1 and 0.041 min^-1, respectively. Selected scavenging experiments revealed no significant contribution of hydroxyl radicals (OH) on the degradation process in seawater, while these radicals contributed to circa 60% on the SMX depletion in deionized water. Instead, the involvement of reactive halogen species (RHS) as main contributors for the SMX degradation in seawater could be established. A mechanism for the RHS generation was proposed, whose initiation reactions involve halides with the TiO₂ photogenerated holes, yielding chlorine and bromine radicals (Cl and Br) that may later generate other RHS. Production of RHS was further confirmed by the identification of SMX transformation products (TPs) and their evolution over time, carried out by liquid chromatography-mass spectrometry (LC-MS). SMX transformation was conducted through halogenation, dimerization and oxidation pathways, involving mainly RHS. Most of the detected transformation products accumulated over time (up to 360 min of irradiation). These findings bring concerns about the viability of photocatalytic water treatments using TiO₂ NPs in saline waters, as RHS could be yielded resulting in the generation and accumulation of halogenated organic byproducts.

Structures, mechanisms and applications of flavin-dependent halogenases

Overall, this review highlights the structures, mechanisms and applications of flavin-dependent halogenases (FDHs) for future development of FDHs as potential biocatalysts. FDHs catalyze incorporation of halogen atoms into a broad range of substrates. The reactions involved in the production of various halogenated natural products which are important drugs. Typical substrates for FDHs include indole, pyrrole, phenolic and aliphatic compounds. In addition to organic substrates, all FDHs utilize reduced FAD (FADH^-), oxygen and halides as co-substrates. Structural studies reveal that FDHs all have similar FAD binding sites. However, FDHs have variations between the different isotypes including different recognition residues for substrate binding and some unique loop structures and conformations. These different structural differences suggest that variations in reaction catalysis exist. However, limited knowledge of the reaction mechanisms of FDHs is currently available. Various biocatalytic applications of FDHs have been explored. Further investigation of the catalytic reactions of FDHs is essential for improving enzyme engineering work to enable FDHs catalysis of challenging reactions.

Chlorination and bromination of 1,3-diphenylguanidine and 1,3-di-o-tolylguanidine: Kinetics, transformation products and toxicity assessment

This works investigates the chlorination and bromination of two rubber and polymer related chemicals, which have emerged as relevant water contaminants, i.e. 1,3-di-o-tolylguanidine (DTG) and 1,3-diphenylguanidine (DPG). Kinetic constants at different pH values were obtained and modelled, taking into account the pK_a values of DTG/DPG and HClO, showing that the maximum reaction rate (k_app > 10⁴ M^-1 s^-1) is obtained at pH values 8.8 for DPG and 9.1 for DTG. Bromination is also very fast, although unlike chlorination, deviation from the model was observed at neutral pH, which was attributed to formation of metastable transformation product (TP). A total of 35 TPs, corresponding to halogenation, hydroxylation, formation of monophenylguanidine derivatives and cyclization reactions, were tentatively identified. Furthermore it was found that chloroform can be formed up to a 25% molar yield, while dichloroacetonitrile was formed into less than a 3% yield. Several ecotoxicological endpoints were predicted by quantitative structure-activity relationship models (QSAR) for the TPs, some of which were predicted to be more toxic than DPG/DTG. Also a chlorinated solution investigated by a Vibrio Fisheri acute toxicity test, confirmed that toxicity increases with chlorination.

Synthesis and evaluation of antitumor activity of dibenzodiazepine derivatives

A series of dibenzodiazepine 2-position derivatives, bearing N-methylpiperazine at the C-11 position, were prepared by using a concise approach. Their inhibitory activities of tumor cell proliferation in vitro were tested in five cell lines, including breast cancer cell BCAP37, gastric cancer cell SGC7901, liver cancer cell HepG2, cervical cancer cell HeLa and acute promyelocytic leukemia cell HL-60. Several compounds showed efficient tumor activity with IC₅₀ values down to 0.30 μM. These compounds are expected to be a new class of potential anticancer lead compounds.

Oxidation byproducts from the degradation of dissolved organic matter by advanced oxidation processes - A critical review

Advanced oxidation processes (AOPs) have been increasingly used for the treatment of source waters and wastewaters. AOPs characteristically produce oxidation byproducts (OBPs) from the partial degradation of dissolved organic matter (DOM) and/or the transformation of inorganic ions (especially, halides) into highly toxic substances including bromate and halogenated organic OBPs (X-OBPs). However, despite the enormous health and environmental risks posed by X-OBPs, an integral understanding of the complex OBP formation mechanisms during AOPs is lacking, which limits the development of safe and effective AOP-based water treatment schemes. The present critical and comprehensive review was intended to fill in this important knowledge gap. The study shows, contrary to the hitherto prevailing opinion, that the direct incorporation of halide atoms (X^•) into DOM makes an insignificant contribution to the formation of organic X-OBPs. The principal halogenating agent is hypohalous acid/hypohalite (HOX/XO^-), whose control is, therefore, critical to the reduction of both organic and inorganic X-OBPs. Significant generation of X-OBPs has been observed during sulfate radical AOPs (SR-AOPs), which arises principally from the oxidizing effects of the unactivated oxidant and/or the applied catalytic activator rather than the sulfate radical as is commonly held. A high organic carbon/X^- molar ratio (>5), an effective non-catalytic activator such as UV or Fe²⁺, a low oxidant concentration, and short treatment time are suggested to limit the accumulation of HOX/XO^- and, thus, the generation of X-OBPs during SR-AOPs. At present, there are no established techniques to prevent the formation of X-OBPs during UV/chlor(am)ine AOPs because the maintenance of substantial amounts of active halogen is essential to these processes. The findings and conclusions reached in this review would advance the research and application of AOPs.

Synthesis of Nucleobase-Functionalized Morpholino Monomers

Morpholino antisense oligonucleotides are used as routine tools in developmental biology to investigate gene function during early embryogenesis. These chemically modified oligos contain morpholine ring connected with phosphorodiamidate linkages as backbone but carry unmodified nucleobases. In this chapter, we describe the methods to further modify the nucleobases using palladium-catalyzed cross-coupling reactions. The key reactions used are halogenations of the nucleobases in suitable position and subsequent Pd-catalyzed Sonogashira and Suzuki reactions. The sequential synthetic steps are described in detail in this chapter, and the examples are shown in tables.

Green pseudo-multicomponent synthesis of some new spirocyclopropane derivatives via electro-catalyzed reaction

Due to the diverse applications of cyclopropane analogs in bioorganic, medicinal, and pharmaceutical chemistry, a clean and efficient procedure was established to synthesize spirocyclopropane via an electrochemical reaction which involves a sequence of Michael addition, halogenation, and intramolecular ring-closing reaction. In this study, an environmentally benign synthesis of spirocyclopropane was carried out through the condensation of indan-1,3-dione by aromatic aldehydes or 2-benzylidenemalononitrile derivatives. Constant current electrosynthesis was applied to a mixture of propanol containing sodium bromide as an electrolyte and a brominating agent at room temperature, respectively.

The effect of halogenation on the antimicrobial activity, antibiofilm activity, cytotoxicity and proteolytic stability of the antimicrobial peptide Jelleine-I

Antimicrobial peptides (AMPs) are believed to be a promising class of antimicrobial agents against bacteria and fungi. To promote the clinical use of AMPs, their antimicrobial activity and susceptibility to protease degradation should be further improved. The antimicrobial peptide Jelleine-I was originally isolated from the royal jelly of honeybees (Apis mellifera) with a short sequence of PFKLSLHL-NH₂ (953.24 Da). Here, a series of halogenated derivatives of the antimicrobial peptide Jelleine-I were designed and synthesized. The results showed that the in vitro antimicrobial activity, antibiofilm activity and in vivo antimicrobial efficacy were enhanced 1-8-fold after halogenation. Additionally, the proteolytic stability of Jelleine-I was improved 10-100-fold by halogenation. Meanwhile, the halogenated derivatives retained negligible hemolytic activity and cytotoxicity. Among these derivatives, the antimicrobial activity and antibiofilm activity of chlorine-Jelleine-I (Cl-J-I), bromine-Jelleine-I (Br-J-I), and iodine-Jelleine-I (I-J-I) were better than those of fluorine-Jelleine-I (F-J-I). The stabilities of Br-J-I and I-J-I against the degradation of enzymes and the serum were better than those of F-J-I and Cl-J-I. In conclusion, this study may offer a useful strategy to enhance antimicrobial efficacy and proteolytic stability by halogenation. The halogenated derivatives Cl-J-I, Br-J-I and I-J-I may be considered as potential antimicrobial agents against microbial infection.

Halogenated trimethoprim derivatives as multidrug-resistant Staphylococcus aureus therapeutics

Incorporation of halogen atoms to drug molecule has been shown to improve its properties such as enhanced in membrane permeability and increased hydrophobic interactions to its target. To investigate the effect of halogen substitutions on the antibacterial activity of trimethoprim (TMP), we synthesized a series of halogen substituted TMP and tested for their antibacterial activities against global predominant methicillin resistant Staphylococcus aureus (MRSA) strains. Structure-activity relationship analysis suggested a trend in potency that correlated with the ability of the halogen atom to facilitate in hydrophobic interaction to saDHFR. The most potent derivative, iodinated trimethoprim (TMP-I), inhibited pathogenic bacterial growth with MIC as low as 1.25 μg/mL while the clinically used TMP derivative, diaveridine, showed resistance. Similar to TMP, synergistic studies indicated that TMP-I functioned synergistically with sulfamethoxazole. The simplicity in the synthesis from an inexpensive starting material, vanillin, highlighted the potential of TMP-I as antibacterial agent for MRSA infections.

Dihalohydration of Alkynols: A Versatile Approach to Diverse Halogenated Molecules

In this paper we outline how dihalohydration reactions of propargylic alcohols can be used to access a wide variety of useful halogenated building blocks. A novel procedure for dibromohydration of alkynes has been developed, and a selection of dichloro and dibromo diols and cyclic ethers were synthesized. The dihalohydration of homo-propargylic alcohols provides a useful route to 3-halofurans, which were shown to readily undergo cycloaddition reactions under mild conditions. Finally, a novel ring expansion of propargylic alcohols containing a cyclopropylalkyne provides access to halogenated alkenylcyclobutanes.

Expanding beyond canonical metabolism: Interfacing alternative elements, synthetic biology, and metabolic engineering

Metabolic engineering offers an exquisite capacity to produce new molecules in a renewable manner. However, most industrial applications have focused on only a small subset of elements from the periodic table, centered around carbon biochemistry. This review aims to illustrate the expanse of chemical elements that can currently (and potentially) be integrated into useful products using cellular systems. Specifically, we describe recent advances in expanding the cellular scope to include the halogens, selenium and the metalloids, and a variety of metal incorporations. These examples range from small molecules, heteroatom-linked uncommon elements, and natural products to biomining and nanotechnology applications. Collectively, this review covers the promise of an expanded range of elemental incorporations and the future impacts it may have on biotechnology.

Effects of halide ions on photodegradation of sulfonamide antibiotics: Formation of halogenated intermediates

The occurrence of sulfonamide antibiotics (SAs) in estuarine waters urges insights into their environmental fate for ecological risk assessment. Although many studies focused on the photochemical behavior of SAs, yet the effects of halide ions relevant to estuarine and marine environments on their photodegradation have been poorly understood. Here, we investigated the effects of halide ions on the photodegradation of SAs with sulfapyridine, sulfamethazine, and sulfamethoxazole as representative compounds. Results showed that halide ions did not significantly impact the photodegradation of sulfapyridine and sulfamethoxazole, while they significantly promoted the photodegradation of sulfamethazine. Further experiments found that ionic strength applied with NaClO4 significantly enhanced the photodegradation of the SAs, which was attributed to the decreased quenching rate constant of the triplet-excited SAs ((3)SA(∗)). Compared with ionic strength, specific Cl(-) effects retarded the photodegradation of the SAs. Our study found that triplet-excited sulfamethazine can oxidize halide ions to produce halogen radicals, subsequently leading to the halogenation of sulfamethazine, which was confirmed by the identification of both chlorinated and brominated intermediates. These results indicate that halide ions play an important role in the photochemical behavior of some SAs in estuarine waters and seawater. The occurrence of halogenation for certain organic pollutants can be predicted by comparing the oxidation potentials of triplet-excited contaminants with those of halogen radicals. Our findings are helpful in understanding the photochemical behavior and assessing the ecological risks of SAs and other organic pollutants in estuarine and marine environment.

Halogen-directed drug design for Alzheimer's disease: a combined density functional and molecular docking study

A series of halogen-directed donepezil drugs has been designed to inhibit acetyl cholinesterase (AChE). Density Functional theory (DFT) has been employed to optimize the chair as well as boat conformers of the parent drug and modified ligands at B3LYP/MidiX and B3LYP/6-311G + (d,p) level of theories. Charge distribution, dipole moment, enthalpy, free energy and molecular orbitals of these ligands are also investigated to understand how the halogen-directed modifications impact the ligand structure and govern the non-bonding interactions with the receptors. Molecular docking calculation has been performed to understand the similarities and differences between the binding modes of unmodified and halogenated chair-formed ligands. Molecular docking indicated donepezil and modified ligands had non-covalent interactions with hydrophobic gorges and anionic subsites of AChE. The -CF3-directed ligand possessed the most negative binding affinity. Non-covalent interactions within the ligand-receptor systems were found to be mostly hydrophobic and π- stacking type. F, Cl and -CF3 containing ligands emerge as effective and selective AChE inhibitors, which can strongly interact with the two active sites of AChE. In addition, we have also investigated selected pharmacokinetic parameters of the parent and modified ligands.

Complete reaction mechanisms of mercury oxidation on halogenated activated carbon

The reaction mechanisms of mercury (Hg) adsorption and oxidation on halogenated activated carbon (AC) have been completely studied for the first time using density functional theory (DFT) method. Two different halogenated AC models, namely X-AC and X-AC-X (X=Cl, Br, I), were adopted. The results revealed that HgX is found to be stable-state on the AC edge since its further desorption from the AC as HgX, or further oxidation to HgX2, are energetically unfavorable. Remarkably, the halide type does not significantly affect the Hg adsorption energy but it strongly affects the activation energy barrier of HgX formation, which obviously increases in the order HgI<HgBr<HgCl. This trend coincides with the experimental observations which reported the efficiency of halogen impregnated AC for Hg elimination significantly decreases as I-AC>Br-AC>Cl-AC. Thus, the study of the complete reaction mechanism is essential because the adsorption energy can not be used as a guideline for the rational material design in the halide impregnated AC systems. The activation energy is an important descriptor for the predictions of sorbent reactivity to the Hg oxidation process.

Synthesis, antiviral, cytotoxic and cytostatic evaluation of N 1-(phosphonoalkyl)uracil derivatives

Abstract

A series of N¹-(phosphonoalkyl)uracils was prepared in a two-step reaction sequence from ω-aminoalkylphosphonates and (E)-3-ethoxyacryloyl isocyanate followed by the uracil ring closure. Under standard conditions (NCS; NBS; I₂/CAN) all N¹-(phosphonoalkyl)uracils were transformed into the respective 5-halogeno derivatives to be later benzoylated at N3. All compounds were evaluated in vitro for activity against a broad variety of DNA and RNA viruses. One compound was slightly active against human cytomegalovirus in HEL cell cultures (EC₅₀ = 45 μM) while another showed weak activity against varicella-zoster virus (TK⁺ VZV strain OKA and TK⁻ VZV strain 07-1) with EC₅₀ = 43 and 53 µM, respectively. In addition, several compounds exhibited noticeable inhibitory effects on the proliferation of human cervical carcinoma cells (HeLa) at a concentration lower than 200 μM.

Graphical abstract

The Laurencia Paradox: An Endless Source of Chemodiversity

Nature, the most prolific source of biological and chemical diversity, has provided mankind with treatments for health problems since ancient times and continues to be the most promising reservoir of bioactive chemicals for the development of modern drugs. In addition to the terrestrial organisms that still remain a promising source of new bioactive metabolites, the marine environment, covering approximately 70% of the Earth's surface and containing a largely unexplored biodiversity, offers an enormous resource for the discovery of novel compounds. According to the MarinLit database, more than 27,000 metabolites from marine macro- and microorganisms have been isolated to date providing material and key structures for the development of new products in the pharmaceutical, food, cosmeceutical, chemical, and agrochemical sectors. Algae, which thrive in the euphotic zone, were among the first marine organisms that were investigated as sources of food, nutritional supplements, soil fertilizers, and bioactive metabolites.Red algae of the genus Laurencia are accepted unanimously as one of the richest sources of new secondary metabolites. Their cosmopolitan distribution, along with the chemical variation influenced to a significant degree by environmental and genetic factors, have resulted in an endless parade of metabolites, often featuring multiple halogenation sites.The present contribution, covering the literature until August 2015, offers a comprehensive view of the chemical wealth and the taxonomic problems currently impeding chemical and biological investigations of the genus Laurencia. Since mollusks feeding on Laurencia are, in many cases, bioaccumulating, and utilize algal metabolites as chemical weaponry against natural enemies, metabolites of postulated dietary origin of sea hares that feed on Laurencia species are also included in the present review. Altogether, 1047 secondary metabolites, often featuring new carbocyclic skeletons, have been included.The chapter addresses: (1) the "Laurencia complex", the botanical description and the growth and population dynamics of the genus, as well as its chemical diversity and ecological relations; (2) the secondary metabolites, which are organized according to their chemical structures and are classified into sesquiterpenes, diterpenes, triterpenes, acetogenins, indoles, aromatic compounds, steroids, and miscellaneous compounds, as well as their sources of isolation which are depicted in tabulated form, and (3) the biological activity organized according to the biological target and the ecological functions of Laurencia metabolites.

Crystal structure of halogenase PltA from the pyoluteorin biosynthetic pathway

Pyoluteorin is an antifungal agent composed of a 4,5-dichlorinated pyrrole group linked to a resorcinol moiety. The pyoluteorin biosynthetic gene cluster in Pseudomonas fluorescens Pf-5 encodes the halogenase PltA, which has been previously demonstrated to perform both chlorinations in vitro. PltA selectively accepts as a substrate a pyrrole moiety covalently tethered to a nonribosomal peptide thiolation domain PltL (pyrrolyl-S-PltL) for FAD-dependent di-chlorination, yielding 4,5-dichloropyrrolyl-S-PltL. We report a 2.75 Å-resolution crystal structure of PltA in complex with FAD and chloride. PltA is a dimeric enzyme, containing a flavin-binding fold conserved in flavin-dependent halogenases and monooxygenases, and an additional unique helical region at the C-terminus. This C-terminal region blocks a putative substrate-binding cleft, suggesting that a conformational change involving repositioning of this region is necessary to allow binding of the pyrrolyl-S-PltL substrate for its dichlorination by PltA.

Sieving properties of end group-halogenated Pluronic polymer matrix in DNA separation under nondenaturing CE analysis

CE-SSCP analysis is a well-established DNA separation method that is based on variations in mobility caused by sequence-induced differences in the conformation of single-stranded DNA. The resolution of CE-SSCP analysis was improved by using a Pluronic polymer matrix, and it has been successfully applied in various genetic analyses. Because the Pluronic polymer forms a micellar cubic structure in the capillary, it provides a stable internal structure for high-resolution CE-SSCP analysis. We hypothesized that formation of micellar cubic structure is influenced by the end hydroxyl group of the Pluronic polymer, which affords structural stability through hydrogen bonding. To test this hypothesis, the hydroxyl group was halogenated to eliminate the hydrogen bonding without disturbing the polarity of polymer matrix. CE-SSCP resolution of two DNA fragments with a single base difference was significantly worse in the halogenated polymer matrices due to band broadening. The viscoelastic properties of control (which has hydroxyl group), chlorinated, and brominated F108 solution upon heating were also investigated by rheological experiments, and we found that gelation was significantly associated with resolution. In this series of experiments, the effect of the hydroxyl group in Pluronic polymer matrix on separation resolution of CE-SSCP analysis was demonstrated.

Transition-Metal-Free ipso-Functionalization of Arylboronic Acids and Derivatives

Arylboronic acids and their derivatives have been widely exploited as important synthetic precursors in organic synthesis, materials science, and pharmaceutical development. In addition to numerous applications in transition-metal-mediated cross-coupling reactions, transition-metal-free transformations involving arylboronic acids and derivatives have recently received a surge of attention for converting the C-B bond to C-C, C-N, C-O, and many other C-X bonds. Consequently, a wide range of useful compounds, e.g., phenols, anilines, nitroarenes, and haloarenes, have been readily synthesized. Amongst these efforts, many versatile reagents have been developed and a lot of practical approaches demonstrated. The research in this promising field is summarized in the current review and organized on the basis of the type of bonds being formed.

Examination of disinfection by-product (DBP) formation in source waters: a study using log-transformed differential spectra

Formation of disinfection by-products (DBPs) in ten drinking source waters located in the United States was examined in this study. DBP generation was interpreted in the context of halogenation-induced changes of log-transformed absorbance spectra of dissolved organic matter (DOM) present in the waters. This approach allows probing the behavior of relatively minor structures that can be highly sensitive towards any process of interest, notably DOM halogenation. This concept was applied to examine effects of chlorination time on the kinetics of chlorine consumption and release of several DBP groups such as total trihalomethanes (THM4, including CHCl3, CHCl2Br, CHClBr2 and CHBr3), haloacetic acids (HAA9, including MCAA, MBAA, DCAA, TCAA, BCAA, DBAA, BDCAA, DBCAA and TBAA), haloacetonitriles (THAN4, including TCAN, DCAN, BCAN and DBAN), haloketones (HK2, including DCP and TCP), chloral hydrate (CH) and chloropicrin (CPN). Two alternative parameters, namely the differential logarithm of DOM absorbance at 350 nm (DLnA350) and change of the spectral slope in the range of wavelengths 325-375 nm (DSlope325-375) were introduced to quantify individual DBP species formed and Cl2 consumption. DLnA350 and DSlope325-375, especially DLnA350 were determined to be more reliable than differential absorbance at 272 nm that was utilized in prior applications of differential spectroscopy to characterize DBP formation. Strong linear relationships between DLnA350 values and concentrations of major groups of and individual DBP species (e.g. THM4, HAA9, HAN4 and CPN were found to exist (mostly, R(2) > 0.95) and the intercept of these correlations with the y-axis was near zero for the examined water sources. Correlations between DLnA350 values and concentrations of CH and HK2 were also strong but they were nonlinear. The slope of the correlations between the concentrations of major groups of DBP species vs -DLnA350 were also well correlated with SUVA254 and LnA350 for all the examined source waters. It indicates that log-transformations of the absorbance spectra of surface water and parameters based on such transformations (e.g., DLnA350 and DSlope325-375) have a potential to provide an alternative reliable approach to monitor the halogenation of DOM and attendant formation of individual DBP species.

Effects of halogenated aromatics/aliphatics and nitrogen(N)-heterocyclic aromatics on estimating the persistence of future pharmaceutical compounds using a modified QSAR model

The effects of halogenated aromatics/aliphatics and nitrogen(N)-heterocyclic aromatics on estimating the persistence of future pharmaceutical compounds were investigated using a modified half life equation. The potential future pharmaceutical compounds investigated were approximately 2000 pharmaceutical drugs currently undergoing the United States Food and Drug Administration (US FDA) testing. EPI Suite (BIOWIN) model estimates the fates of compounds based on the biodegradability under aerobic conditions. While BIOWIN considered the biodegradability of a compound only, the half life equation used in this study was modified by biodegradability, sorption and cometabolic oxidation. It was possible that the potential future pharmaceutical compounds were more accurately estimated using the modified half life equation. The modified half life equation considered sorption and cometabolic oxidation of halogenated aromatic/aliphatics and nitrogen(N)-heterocyclic aromatics in the sub-surface, while EPI Suite (BIOWIN) did not. Halogenated aliphatics in chemicals were more persistent than halogenated aromatics in the sub-surface. In addition, in the sub-surface environment, the fates of organic chemicals were much more affected by halogenation in chemicals than by nitrogen(N)-heterocyclic aromatics.

The carbonate analogues of 5'-halogenated resiniferatoxin as TRPV1 ligands

A series of carbonate analogues of 5'-halogenated RTX have been investigated in order to examine the effect of the carbonate group as a linker and the role of halogens in the reversal of activity from agonism to antagonism for rat and human TRPV1 heterologously expressed in Chinese hamster ovary cells. The carbonate analogues showed similar activities to the corresponding RTX derivatives in rat TRPV1 but lower potency in human TRPV1. 5-Halogenation converted the agonists to partial agonists or full antagonists and the extent of antagonism reflected the order of I>Br>Cl>F, with a somewhat greater extent of antagonism for the derivatives of the 4-amino RTX surrogates compared to the corresponding derivatives of RTX itself. The carbonate analogues of I-RTX (60) and 5-bromo-4-amino-RTX (66) were potent and full antagonists with Ki(ant)=2.23 and 2.46 nM, respectively, for rat TRPV1, which were ca. 5-fold more potent than I-RTX (2) under our conditions. The conformational analysis of the I-RTX-carbonate (60) indicated that its bent conformation was similar to that of I-RTX, consistent with compound 60 and I-RTX showing comparable potent antagonism.