Synthesis of Indoloquinolines: An Intramolecular Cyclization Leading to Advanced Perophoramidine-Relevant Intermediates.

The bioactive natural product perophoramidine has proved a challenging synthetic target. An alternative route to its indolo[2,3-b]quinolone core structure involving a N-chlorosuccinimde-mediated intramolecular cyclization reaction is reported. Attempts to progress towards the natural product are also discussed with an unexpected deep-seated rearrangement of the core structure occurring during an attempted iodoetherification reaction. X-ray crystallographic analysis provides important analytical confirmation of assigned structures.

Halogenation Regulates Supramolecular Chirality at Hierarchical Levels of Self-Assembled N-Terminal Aromatic Amino Acids.

Halogenation brings about dramatic variations to the performance of self-assembled organic species, such as luminescence and crystallinity, but it has seldom been utilized for chirality control. Here we show the halogenation effect of self-assembling organic building units on supramolecular chirality and chiroptical responses. N-terminal aromatic amino acids with different substituted halogen atoms at p-phenylalanine residues self-assembled into one-dimensional fibrous structures. Halogenation induced the emergence of macroscopic chirality regardless of halogen properties like electronegativity, generating exclusive homochiral helical structures. Solid-state X-ray structures and time-dependent density functional theory were utilized for calculated electronic circular dichroism spectra, which evidenced the diverse driving forces to enable chiral molecular arrangements, including H-bonds and halogen bonds. Red-shifted luminescence was observed in brominated building units, giving rise to active circularly polarized luminescence. This work elucidates the multiple roles of halogen in chiral self-assembly systems, which provides insight into the rational control over supramolecular chirality and their chiroptical applications.

Engineered Enzymes Enable Selective N-Alkylation of Pyrazoles With Simple Haloalkanes.

Selective alkylation of pyrazoles could solve a challenge in chemistry and streamline synthesis of important molecules. Here we report catalyst-controlled pyrazole alkylation by a cyclic two-enzyme cascade. In this enzymatic system, a promiscuous enzyme uses haloalkanes as precursors to generate non-natural analogs of the common cosubstrate S-adenosyl-l-methionine. A second engineered enzyme transfers the alkyl group in highly selective C-N bond formations to the pyrazole substrate. The cosubstrate is recycled and only used in catalytic amounts. Key is a computational enzyme-library design tool that converted a promiscuous methyltransferase into a small enzyme family of pyrazole-alkylating enzymes in one round of mutagenesis and screening. With this enzymatic system, pyrazole alkylation (methylation, ethylation, propylation) was achieved with unprecedented regioselectivity (>99 %), regiodivergence, and in a first example on preparative scale.

Synthesis of novel halogenated triarylpyrazoles as selective COX-2 inhibitors: Anti-inflammatory activity, histopatholgical profile and in-silico studies.

A novel series of halogenated triarylpyrazoles 12a-l was designed and synthesized. All target compounds showed good in vitro COX-2 inhibitory activity (IC50 = 0.043-0.17 µM) over COX-1 (IC50 = 7.8 - 15.4 µM) relative to celecoxib (COX-1/IC50 = 9.87, COX-2/IC50 = 0.055), with acceptable selectivity index values (SI = 50.6-253.1). Also, they displayed moderate to potent in vivo anti-inflammatory activity (% edema inhibition = 16.9-87.9) comparable to celecoxib (% edema inhibition = 46.6-72.1) as standard drug. Three fluorinated pyrazoles 12a, 12g and 12j, exhibited superior anti-inflammatory activity at all time intervals (% edema inhibition = 42.1-87.9) with better gastric profile (UI = 1.25-2.5) than the traditional NSAID; indomethacin (UI = 14) and were close to the selective COX-2 inhibitor; celecoxib (UI = 1.75). In-silico docking and ADME studies of 12a, 12g and 12j supported the obtained biological data and pointed out their potential use for the development of bio-available, safe and potent anti-inflammatory drugs.

Halogenated Diazabutadiene Dyes: Synthesis, Structures, Supramolecular Features, and Theoretical Studies.

Novel halogenated aromatic dichlorodiazadienes were prepared via copper-mediated oxidative coupling between the corresponding hydrazones and CCl4. These rare azo-dyes were characterized using 1H and 13C NMR techniques and X-ray diffraction analysis for five halogenated dichlorodiazadienes. Multiple non-covalent halogen···halogen interactions were detected in the solid state and studied by DFT calculations and topological analysis of the electron density distribution within the framework of Bader's theory (QTAIM method). Theoretical studies demonstrated that non-covalent halogen···halogen interactions play crucial role in self-assembly of highly polarizable dichlorodiazadienes. Thus, halogen bonding can dictate a packing preference in the solid state for this class of dichloro-substituted heterodienes, which could be a convenient tool for a fine tuning of the properties of this novel class of dyes.

Selective Arylation of 2-Bromo-4-chlorophenyl-2-bromobutanoate via a Pd-Catalyzed Suzuki Cross-Coupling Reaction and Its Electronic and Non-Linear Optical (NLO) Properties via DFT Studies.

In the present study, 2-bromo-4-chlorophenyl-2-bromobutanoate (3) was synthesized via the reaction of 2-bromo-4-chlorophenol with 2-bromobutanoyl bromide in the presence of pyridine. A variety of 2-bromo-4-chlorophenyl-2-bromobutanoate derivatives (5a-f) were synthesized with moderate to good yields via a Pd-catalyzed Suzuki cross-coupling reaction. To find out the reactivity and electronic properties of the compounds, Frontier molecular orbital analysis, non-linear optical properties, and molecular electrostatic potential studies were performed.

Halogenated Flavones and Isoflavones: A State-of-Art on their Synthesis.

BACKGROUND: Flavonoid is a family of compounds present in the everyday consumption plants and fruits, contributing to a balanced diet and beneficial health effects. Being a scaffold for new drugs and presenting a wide range of applicability in the treatment of illnesses give them also an impact in medicine. Among the several types of flavonoids, flavone and isoflavone derivatives can be highlighted due to their prevalence in nature and biological activities already established. The standard synthetic route to obtain both halogenated flavones and isoflavones is through the use of already halogenated starting materials. Halogenation of the flavone and isoflavone core is less common because it is more complicated and involves some selectivity issues. OBJECTIVE: Considering the importance of these flavonoids, we aim to present the main and more recent synthetic approaches towards their halogenation. METHODS: The most prominent methodologies for the synthesis of halogenated flavones and isoflavones were reviewed. A careful survey of the reported data, using mainly the Scopus database and halogenation, flavones and isoflavones as keywords, was conducted. RESULTS: Herein, a review is provided on the latest and more efficient halogenation protocols of flavones and isoflavones. Selective halogenation and the greener methodologies, including enzymatic and microbial halogenations, were reported. Nevertheless, some interesting protocols that allowed the synthesis of halogenated flavone and isoflavone derivatives in specific positions using halogenated reagents are also summarized. CONCLUSION: Halogenated flavones and isoflavones have risen as noticeable structures; however, most of the time, the synthetic procedures involve toxic reagents and harsh reaction conditions. Therefore, the development of new synthetic routes with low environmental impact is desirable.

Increased Lipophilicity of Halogenated Ruthenium(II) Polypyridyl Complexes Leads to Decreased Phototoxicity in†vitro when Used as Photosensitizers for Photodynamic Therapy.

In the fight against cancer, photodynamic therapy is generating great interest thanks to its ability to selectively kill cancer cells without harming healthy tissues. In this field, ruthenium(II) polypyridyl complexes, and more specifically, complexes with dipyrido[3,2-a:2',3'-c]phenazine (dppz) as a ligand are of particular interest due to their DNA-binding and photocleaving properties. However, ruthenium(II) polypyridyl complexes can sometimes suffer from low lipophilicity, which hampers cellular internalisation through passive diffusion. In this study, four new [Ru(dppz-X2 )3 ]2+ complexes (X=H, F, Cl, Br, I) were synthesized and their lipophilicity (logP), cytotoxicity and phototoxicity on cancerous and noncancerous cell lines were assessed. This study shows that, counterintuitively, the phototoxicity of these complexes decreases as their lipophilicity increases; this could be due solely to the atomic radius of the halogen substituents.

Pd (II) Immobilized on Clinoptilolite as a Highly Active Heterogeneous Catalyst for Ullmann Coupling-type S-arylation of Thiols with Aryl Halides.

BACKGROUND: There are a number of protocols for Ullmann coupling-type S-arylation reactions, many of them suffer from the use of homogenous and often corrosive catalyst, cumbersome workup procedures, and long reaction times. Besides, many of these reagents are expensive and non-recoverable, leading to the generation of a large amount of toxic waste particularly when large-scale applications are considered. OBJECTIVE: The aim of this study was to prepare a new Pd catalyst bonded on the surface of zeolite as a heterogeneous catalyst. METHODS: A heterogeneous palladium catalyst has been prepared by immobilizing Pd ions on Clinoptilolite. This novel developed heterogeneous catalyst was thoroughly examined for Ullmann coupling-type S-arylation reaction using different bases, solvents and 0.003 mg of the catalyst. The structural and morphological characterizations of the catalyst were carried out using XRD, TGA, BET and TEM techniques. RESULTS: Highly efficient heterogeneous palladium catalyst has been developed by immobilizing Pd ions on Clinoptilolite, as one of the most abundant naturally occurring zeolites for Ullmann Sarylation. By using this method, we provide an efficient way to a wide variety of substituted thiolic compounds. Moreover, the catalyst is easily recovered using simple filtration and reused for 5 consecutive runs. CONCLUSION: In this effort, we developed a new Pd catalyst bonded on the surface of zeolite as a substrate to prepare the heterogeneous catalyst. We demonstrate that this novel catalyst offers reliable and convincing data that may offer a valuable application in further developing the science and technology of Ullmann reaction protocols and allied industries. Additionally, the catalyst was reusable and kept its high activities over a number of cycles.

A competition between hydrophobic and electrostatic interactions in protein-ligand systems. Binding of heterogeneously halogenated benzotriazoles by the catalytic subunit of human protein kinase CK2.

A series of chlorine-substituted benzotriazole derivatives, representing all possible substitution patterns of halogen atoms attached to the benzotriazole benzene ring, were synthetized as potential inhibitors of human protein kinase CK2. Basic ADME parameters for the free solutes (hydrophobicity, electronic properties) together with their binding affinity to the catalytic subunit of protein kinase CK2 were determined with reverse-phase HPLC, spectrophotometric titration, and Thermal Shift Assay Method, respectively. The analysis of position-dependent thermodynamic contribution of a chlorine atom attached to the benzotriazole ring confirmed the previous observation for brominated benzotriazoles, in which substitution at positions 5 and 6 with bromine was found crucial for ligand binding. In all tested halogenated benzotriazoles the replacement of Br with Cl decreases the hydrophobicity, while the electronic properties remain virtually unaffected. Supramolecular architecture identified in the just resolved crystal structures of three of the four possible dichloro-benzotriazoles shows how substitution distant from the triazole ring affects the pattern of intermolecular interactions. Summarizing, the benzotriazole benzene ring substitution pattern has been identified as the main driver of ligand binding, predominating the non-specific hydrophobic effect.

Efficient Biocatalytic Synthesis of Dihalogenated Purine Nucleoside Analogues Applying Thermodynamic Calculations.

The enzymatic synthesis of nucleoside analogues has been shown to be a sustainable and efficient alternative to chemical synthesis routes. In this study, dihalogenated nucleoside analogues were produced by thermostable nucleoside phosphorylases in transglycosylation reactions using uridine or thymidine as sugar donors. Prior to the enzymatic process, ideal maximum product yields were calculated after the determination of equilibrium constants through monitoring the equilibrium conversion in analytical-scale reactions. Equilibrium constants for dihalogenated nucleosides were comparable to known purine nucleosides, ranging between 0.071 and 0.081. To achieve 90% product yield in the enzymatic process, an approximately five-fold excess of sugar donor was needed. Nucleoside analogues were purified by semi-preparative HPLC, and yields of purified product were approximately 50% for all target compounds. To evaluate the impact of halogen atoms in positions 2 and 6 on the antiproliferative activity in leukemic cell lines, the cytotoxic potential of dihalogenated nucleoside analogues was studied in the leukemic cell line HL-60. Interestingly, the inhibition of HL-60 cells with dihalogenated nucleoside analogues was substantially lower than with monohalogenated cladribine, which is known to show high antiproliferative activity. Taken together, we demonstrate that thermodynamic calculations and small-scale experiments can be used to produce nucleoside analogues with high yields and purity on larger scales. The procedure can be used for the generation of new libraries of nucleoside analogues for screening experiments or to replace the chemical synthesis routes of marketed nucleoside drugs by enzymatic processes.

The Impact of Halogenated Phenylalanine Derivatives on NFGAIL Amyloid Formation.

The hexapeptide hIAPP22-27 (NFGAIL) is known as a crucial amyloid core sequence of the human islet amyloid polypeptide (hIAPP) whose aggregates can be used to better understand the wild-type hIAPP's toxicity to ß-cell death. In amyloid research, the role of hydrophobic and aromatic-aromatic interactions as potential driving forces during the aggregation process is controversially discussed not only in case of NFGAIL, but also for amyloidogenic peptides in general. We have used halogenation of the aromatic residue as a strategy to modulate hydrophobic and aromatic-aromatic interactions and prepared a library of NFGAIL variants containing fluorinated and iodinated phenylalanine analogues. We used thioflavin T staining, transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) to study the impact of side-chain halogenation on NFGAIL amyloid formation kinetics. Our data revealed a synergy between aggregation behavior and hydrophobicity of the phenylalanine residue. This study introduces systematic fluorination as a toolbox to further investigate the nature of the amyloid self-assembly process.

Ruthenium-Catalyzed C-H Arylation of 1-Naphthol with Aryl and Heteroaryl Halides.

While 8-aryl-1-napthols are promising dye molecules and useful intermediates in the synthesis of polycyclic aromatic hydrocarbons, they can be difficult to access. A new, ruthenium-catalyzed method for peri-C-H arylation of 1-naphthol with a variety of aryl and heteroaryl halides (iodides, bromides) is reported that overcomes the limitations of previous palladium-catalyzed approaches. Yields for the 21 examples range from 16 to 99%, with an average of 71%, and the reaction tolerates a variety of functional groups: pyridine, pyrimidine, primary aniline, aldehyde, and ester.

Synthesis of Alkyl Halides from Aldehydes via Deformylative Halogenation.

An unprecedented deformylative halogenation of aldehydes to alkyl halides is presented. Under oxidative conditions, 1,4-dihydropyridine (DHP), derived from an aldehyde, generated a C(sp3)- radical that coupled with a halogen radical that was generated from inexpensive and atom-economical halogen sources (NaBr, NaI, or HCl), to yield an alkyl halide. Because of the mild conditions, a wide range of functional groups were tolerated, and excellent site selectivity was achieved.

Development of DNA-Compatible Suzuki-Miyaura Reaction in Aqueous Media.

DNA-encoded chemical libraries (DELs) are a cost-effective technology for the discovery of novel chemical probes and drug candidates. A major limiting factor in assembling productive DELs is the availability of DNA-compatible chemical reactions in aqueous media. In an effort to increase the chemical accessibility and structural diversity of small molecules displayed by DELs, we developed a robust Suzuki-Miyaura reaction protocol that is compatible with the DNA structures. By employing a water-soluble Pd-precatalyst, we developed conditions that allow efficient coupling of DNA-linked aryl halides with a wide variety of boronic acids/esters including heteroaryl boronates.

Radical Hydroarylation of Functionalized Olefins and Mechanistic Investigation of Photocatalytic Pyridyl Radical Reactions.

We report the photoredox alkylation of halopyridines using functionalized alkene and alkyne building blocks. Selective single-electron reduction of the halogenated pyridines provides the corresponding heteroaryl radicals, which undergo anti-Markovnikov addition to the alkene substrates. The system is shown to be mild and tolerant of a variety of alkene and alkyne subtypes. A combination of computational and experimental studies support a mechanism involving proton-coupled electron transfer followed by medium-dependent alkene addition and rapid hydrogen atom transfer mediated by a polarity-reversal catalyst.

Small-molecule compounds targeting the STAT3 DNA-binding domain suppress survival of cisplatin-resistant human ovarian cancer cells by inducing apoptosis.

Constitutive activation of signal transducer and activator of transcription 3 (STAT3) plays important roles in oncogenic occurrence and transformation by regulating the expression of diverse downstream target genes important for tumor growth, metastasis, angiogenesis and immune evasion. Feasibility of targeting the DNA-binding domain (DBD) of STAT3 has been proven previously. With the aid of 3D shape- and electrostatic-based drug design, we identified a new STAT3 inhibitor, LC28, and its five analogs, based on the pharmacophore of a known STAT3 DBD inhibitor. Microscale thermophoresis assay shows that these compounds inhibits STAT3 binding to DNA with a Ki value of 0.74-8.87 µM. Furthermore, LC28 and its analogs suppress survival of cisplatin-resistant ovarian cancer cells by inhibiting STAT3 signaling and inducing apoptosis. Therefore, these compounds may serve as candidate compounds for further modification and development as anticancer therapeutics targeting the DBD of human STAT3 for treatment of cisplatin-resistant ovarian cancer.

Effects on tubulin polymerization and down-regulation of c-Myc, hTERT and VEGF genes by colchicine haloacetyl and haloaroyl derivatives.

Several colchicine analogues in which the N-acetyl residue has been replaced by haloacetyl, cyclohexylacetyl, phenylacetyl and various aroyl moieties have been synthesized. The cytotoxic activities of the synthesized compounds have been measured on three tumor cell lines (HT-29, MCF-7 and A549) and on one non-tumor cell line (HEK-293). These compounds exhibit high antiproliferative activities at the nanomolar level, in many cases with a higher potency than colchicine itself. Some of the compounds, particularly the haloacetyl derivatives, inhibit the polymerization of tubulin in a similar manner as colchicine. As regards the cell cycle, the most active compounds are the chlorobenzoyl and bromobenzoyl derivatives, which cause cell cycle arrest at the G2/M phase when tested at 20 nM, and the bromoacetyl derivative, which arrests the cell cycle at 15 nM. In addition, these colchicine derivatives have shown fairly active downregulating the expression of the c-Myc, hTERT and VEGF genes, as well as VEGF protein secretion, at very low concentrations.

Synthesis and antioxidant, antixanthine oxidase, and antielastase activities of novel N,S-substituted polyhalogenated nitrobutadiene derivatives.

In this study, three substituted polyhalogenated nitrobutadiene derivatives were synthesized. Compound 1-[(2,3-dibromopropyl)sulfanyl]-1,3,4,4-tetrachloro-2-nitrobuta-1,3-diene (4) was synthesized before by our group. Compounds 8-{[1-[(2,3-dibromopropyl)sulfany]-3,4,4-trichloro-2-nitrobuta-1,3-butadien-1-yl}-1,4-dioxa-8-azaspiro[4.5]decane (5) and 1-[(2,3-dibromopropyl)sulfanyl]-3,4,4-trichloro-N-(4-methylpiperazin-1-yl)-2-nitrobuta-1,3-diene-1-amine (6) were synthesized in this work as original compounds. Xanthine oxidase, elastase inhibition abilities, and antioxidant activities were investigated in this work for compounds 4, 5, and 6. In this study, compounds 4, 5, and 6 exhibited antixanthine oxidase, antielastase, and antioxidant activities. Among the compounds screened, compound 4 exhibited xanthine oxidase and elastase inhibitor effect similar to the standard compound. Among the three tested compounds, compound 6 showed potent DPPH radical scavenging and reducing power activities. Therefore, these three compounds (4, 5, and 6) may be useful as an antixanthine oxidase, antielastase, and antioxidant agent in pharmaceutical and cosmetic industry.

A carbon tetrachloride-free synthesis of N-phenyltrifluoroacetimidoyl chloride.

N-Phenyltrifluoroacetimidoyl chloride (PTFAI-Cl) is a reagent widely used for the preparation of glycosyl N-phenyltrifluoroacetimidates. However, the most commonly applied method requires carbon tetrachloride, a hepatotoxic reagent that has been phased out under the Montreal Protocol. We report a new synthesis of N-phenyltrifluoroacetimidoyl chloride (PTFAI-Cl) using dichlorotriphenylphosphane and triethylamine.