Radical Monofluoroalkylative Alkynylation of Olefins by a Docking-Migration Strategy.

A radical-mediated monofluoroalkylative alkynylation of alkenes is disclosed for the first time. The reaction demonstrates a remarkably broad substrate scope in which both activated and unactivated alkenes are suitable starting materials. The concurrent addition of an alkynyl and a monofluoroalkyl group onto an alkene proceeds through a docking-migration sequence, affording a vast array of valuable fluoroalkyl-substituted alkynes. Many complex natural products and drug derivatives are readily functionalized, demonstrating that this method can be used for late-stage alkynylation.

One-Pot NBS-Promoted Synthesis of Imidazoles and Thiazoles from Ethylarenes in Water.

A facile and eco-friendly method has been developed for the synthesis of imidazoles and thiazoles from ethylarenes in water. The reaction proceeds via in situ formation of α-bromoketone using NBS as a bromine source as well as an oxidant, followed by trapping with suitable nucleophiles to provide the corresponding products in good yields under metal-free conditions.

Carbon dots-involved chemiluminescence: Recent advances and developments.

In recent years, more and more nanomaterials-based chemiluminescence (CL) systems have appeared to improve the sensitivity and expand the scope of the analytical applications with the explosive growth and development of nanomaterials and technology. As a fascinating class of luminescent carbon nanomaterials, carbon dots (CDs) are now substantially studied in fabricating CL based assays due to their unique optical and mechanical properties. Herein, we summarize and highlight the current developments of CDs-involved weak or ultraweak CL systems, as well as the corresponding mechanisms and proper applications in some fields. CDs can take part in the CL reactions as oxidants, emitting species directly involved in redox oxidation, energy acceptors of CL energy transfer, or even catalysts involving other luminophores. In fact, they always have more than one role in many cases, owing to the formation of various excited species with short life in CL systems. Therefore, in this review article, the most recent progress of the different CDs-assisted CL systems including the mechanisms and applications are presented. Finally, the conclusions and future prospects of this field are also discussed. The significant features of the CDs-based CL systems may open up new prospects and challenges in a wider range of fields.

Esterification of Aryl/Alkyl Acids Catalysed by N-bromosuccinimide under Mild Reaction Conditions.

N-halosuccinimides (NXSs) are well-known to be convenient, easily manipulable and low-priced halogenation reagents in organic synthesis. In the present work, N-bromosuccinimide (NBS) has been promoted as the most efficient and selective catalyst among the NXSs in the reaction of direct esterification of aryl and alkyl carboxylic acids. Comprehensive esterification of substituted benzoic acids, mono-, di- and tri-carboxy alkyl derivatives has been performed under neat reaction conditions. The method is metal-free, air- and moisture-tolerant, allowing for a simple synthetic and isolation procedure as well as the large-scale synthesis of aromatic and alkyl esters with yields up to 100%. Protocol for the recycling of the catalyst has been proposed.

Characterization of an acidic α-galactosidase from hemp (Cannabis sativa L.) seeds and its application in removal of raffinose family oligosaccharides (RFOs).

An acidic α-galactosidase designated as hemp seed α-galactosidase (HSG) was purified from hemp (Cannabis sativa L.) seeds. By means of chromatographic procedures which involved chromatography on the cation-exchangers CM-cellulose and SP-Sepharose, chromatography on the anion-exchangers DEAE-cellulose and Q-Sepharose, and gel filtration on Superdex 75 using fast protein liquid chromatography, HSG was purified to electrophoretic homogeneity. Results of SDS-PAGE and gel filtration on FPLC Superdex 75 revealed that the enzyme was a monomeric protein with a molecular weight of 38 kDa. Sequences of the inner peptides of the α-galactosidase obtained by MALDI-TOF-MS showed that HSG was a novel α-galactosidase since there was a little similarity to the majority of α-galactosidases recorded in the literature. A pH of 3.0 and a temperature of 50°C were optimal for the activity of the enzyme. The activity of HSG was inhibited by the chemical modification with N-bromosuccinimide (NBS) reagent. HSG contained 16 tryptophan residues and two tryptophan residues on the surface, which were crucial to the α-galactosidase activity. The heavy metal ions Cd2+, Cu2+, Hg2+ and Zn2+ inhibited its activity. The Km and Vmax for the hydrolysis of pNPGal (4-nitrophenyl α-D-galactopyranoside) were respectively 0.008 mM and 68 µM min-1 mg-1. HSG also catalyzed the hydrolysis of raffinose and other natural substrates. Hence the α-galactosidase possesses a tremendous potential for food and feed industries in the elimination of indigestible oligosaccharides from leguminous products.

Selective and Efficient Generation of ortho-Brominated para-Substituted Phenols in ACS-Grade Methanol.

The mono ortho-bromination of phenolic building blocks by NBS has been achieved in short reaction times (15-20 min) using ACS-grade methanol as a solvent. The reactions can be conducted on phenol, naphthol and biphenol substrates, giving yields of >86% on gram scale. Excellent selectivity for the desired mono ortho-brominated products is achieved in the presence of 10 mol % para-TsOH, and the reaction is shown to be tolerant of a range of substituents, including CH3, F, and NHBoc.

Regioselective Oxo-Amination of Alkenes and Enol Ethers with N-Bromosuccinimide-Dimethyl Sulfoxide Combination: A Facile Synthesis of α-Amino-Ketones and Esters.

An unprecedented conversion of alkenes and enol ethers to the corresponding α-imido carbonyl compounds with excellent regioselectivity and yields has been developed. This oxo-amination process employs readily available N-bromosuccinimide (NBS) and secondary amines as N-sources and dimethyl sulfoxide (DMSO) as the oxidant and also leads to the production of amino alcohols in a single step on reduction, thus broadening the scope of this operationally simple reaction. For the first time, the formation of reactive Me2S(+)-O-Br species generated by the interaction of NBS with DMSO has been proven.

Preparation and characterization of a novel variant of human tumor necrosis factor-related apoptosis-inducing ligand from the rhesus monkey, Macaca mulatta.

Human tumor necrosis factor-related apoptosis-inducing ligand (hTRAIL) and its variants are attractive antitumor drug candidates. The predicted amino acid sequence of the functional extracellular domain of Macaca mulatta TRAIL (mmTRAIL) was found to differ from that of hTRAIL at four positions. In this study, the gene encoding mmTRAIL was cloned and recombinantly expressed in Escherichia coli at a yield of approximately 20-30 mg/L, which was two times higher than that of hTRAIL. SDS-PAGE showed that denatured mmTRAIL and hTRAIL had similar molecular weights. However, size-exclusion chromatography and dynamic light scattering (DLS) analysis demonstrated that the molecular size of native mmTRAIL was smaller than that of native hTRAIL. Cooling solutions of these proteins from room temperature to 0 °C induced considerable precipitation of hTRAIL but not of mmTRAIL, indicating that mmTRAIL was more soluble than hTRAIL at low temperatures. Additionally, mmTRAIL was more resistant than hTRAIL to N-bromosuccinimide (NBS)-induced precipitation. Although mmTRAIL and hTRAIL showed comparable nanomolar affinities for human death receptors, the dissociation rate of the mmTRAIL-receptor complex was slower than that of the hTRAIL-receptor complex, suggesting that the mmTRAIL-receptor complex was more stable. Moreover, mmTRAIL induced caspase-dependent apoptosis in human tumor cells with an IC50 that was two to three times lower than that of hTRAIL. However, in vivo evaluation demonstrated that mmTRAIL or hTRAIL led to a similar level of tumor suppression in mice bearing COLO205 xenografts. Nevertheless, the advantage of its better solubility should promote the production and further use of mmTRAIL in cancer biotherapy.

N-Bromosuccinimide promoted and base switchable one pot synthesis of α-imido and α-amino ketones from styrenes.

An N-Bromosuccinimide (NBS) promoted one pot strategy for the synthesis of α-amino functionalized aryl ketones starting from commercially available styrenes has been developed. NBS participates in multiple tasks, such as bromonium ion formation, oxidation of bromohydrin and providing a nucleophilic nitrogen source. The reaction can easily be switched between α-imido and α-amino ketones by the choice of base. This one pot strategy was successfully applied for the synthesis of psychoactive drug candidates, amfepramone, mephedrone and 4-MEC.

Luffa acutangula agglutinin: Primary structure determination and identification of a tryptophan residue involved in its carbohydrate-binding activity using mass spectrometry.

A lectin from phloem exudates of Luffa acutangula (ridge gourd) was purified on chitin affinity chromatography and characterized for its amino acid sequence and to study the role of tryptophan in its activity. The purified lectin was subjected to various proteolytic digestions, and the resulting peptides were analyzed by liquid chromatography coupled electrospray ionization ion trap mass spectrometer. The peptide precursor ions were fragmented by collision-induced dissociation or electron transfer dissociation experiments, and a manual interpretation of MS/MS was performed to deduce amino acid sequence. This gave rise to almost complete sequence coverage of the lectin which showed high-sequence similarity with deduced sequences of phloem lectins present in the database. Chemical modification of lysine, tyrosine, histidine, arginine, aspartic acid, and glutamic acid residues did not inhibit the hemagglutinating activity. However, the modification of tryptophan residues using N-bromosuccinimide showed the loss of hemagglutinating activity. Additionally, the mapping of tryptophan residues was performed to determine the extent and number of residues modified, which revealed that six residues per molecule were oxidized suggesting their accessibility. The retention of the lectin activity was seen when the modifications were performed in the presence of chitooligosaccharides due to protection of a tryptophan residue (W102) in the protein. These studies taken together have led to the identification of a particular tryptophan residue (W102) in the activity of the lectin.

Mono- and di-bromo platinum(IV) prodrugs via oxidative bromination: synthesis, characterization, and cytotoxicity.

Platinum(IV)-based anticancer prodrugs have attracted much attention due to their relative inertness under physiological conditions, being activated inside cells, and their capacity for functionalization with a variety of small-molecule or macromolecule moieties. Novel asymmetric platinum(IV) compounds synthesized through expedient and unique methods are desired. Here we utilize N-bromosuccinimide (NBS) and carry out oxidative bromination on platinum(II) drugs, namely cisplatin, carboplatin, and oxaliplatin, to obtain asymmetric and mono-bromo platinum(IV) prodrugs. Different solvents are used to obtain various compounds, and the compounds are further functionalized. Di-bromo compounds are also obtained through NBS-directed oxidative bromination in ethanol. The crystal structures of representative compounds are discussed, and the reduction potentials of some compounds are examined. A cytotoxicity test shows that the mono- and di-bromo platinum(IV) compounds are active against human ovarian cancer cells. Our study enriches the family of asymmetric platinum(IV) prodrugs and provides with a convenient strategy to obtain brominated platinum(IV) complexes.

Synthesis of Breitfussin B by Late-Stage Bromination.

The breitfussins are halogenated natural products whose structures were determined with the assistance of atomic-force microscopy. The site selectivity of N-bromosuccinimide-mediated bromination of a model breitfussin core was found to be strongly dependent on solvent selection; use of acetone led to oxazole bromination, and use of a pyridine-containing mixture led to pyrrole bromination. This tunable site-selective bromination was used in a protecting-group-free synthesis of breitfussin B that proceeded in 9.2% yield over 12 reactions and five chromatographic separations. A bromooxazole analogue of breitfussin A was also prepared by late-stage bromination but isomerized on silica gel to form breitfussin B. This isomerization appeared to proceed through a unimolecular pathway.

Halogenative difluorohomologation of ketones.

A method for the difluorohomologation of ketones accompanied by halogenation of a C-H bond is described. The reaction involves silylation, difluorocarbene addition using Me3SiCF2Br activated by a bromide ion, and halogenation of intermediate cyclopropanes with N-bromo- or N-iodosuccinimide. The whole process is performed without isolation of intermediates. The resulting α,α-difluoro-ß-halo-substituted ketones can be readily converted into fluorine containing pyrazole derivatives and oxetanes.

Stereoselective Syntheses of the Conjugation-Ready, Downstream Disaccharide and Phosphorylated Upstream, Branched Trisaccharide Fragments of the O-PS of Vibrio cholerae O139.

N-Bromosuccinimide-mediated 4,6-O-benzylidene ring opening in 8-azido-3,6-dioxaoctyl 4,6-O-benzylidene-2-deoxy-2-trichloroacetamido-ß-D-glucopyranoside afforded the corresponding 4-O-benzoyl-6-bromo-6-deoxy analogue, which was coupled with 3,4,6-tri-O-acetyl-2-O-benzyl-α-D-galactopyranosyl chloride to give the 1,2-cis α-linked disaccharide as the major product. Conventional hydroxyl group manipulation in the latter and products of further conversions gave the desired, functionalized disaccharide α-D-GalpA-(1→3)-ß-D-QuipNAc. The rare, foregoing sequence forms the downstream end in the O-specific polysaccharide of both Vibrio cholerae O22 and O139. Halide-assisted glycosylation at 4(I)-OH in 8-azido-3,6-dioxaoctyl 6-O-benzyl-2-deoxy-3-O-(2,3,4,6-tetra-O-acetyl-ß-D-galactopyranosyl)-2-trichloroacetamido-ß-D-glucopyranoside, obtained by regioselective reductive opening of the acetal ring in the parent 4(I),6(I)-O-benzylidene derivative, with 2,4-di-O-benzyl-α-colitosyl bromide, gave exclusively the α-linked trisaccharide. The latter was sequentially deacetylated and selectively benzylated to give 8-azido-3,6-dioxaoctyl 2,4-di-O-benzyl-3,6-dideoxy-α-L-xylo-hexopyranosyl-(1→4)-[3-O-benzyl-ß-D-galactopyranosyl-(1→3)]-6-O-benzyl-2-deoxy-2-trichloroacetamido-ß-D-glucopyranoside. Subsequent selective phosphorylation of the triol, thus obtained, with 2,2,2-trichloroethyl phosphorodichloridate afforded isomeric (R,S)-(P)-4(II),6(II)-cyclic phosphates, which were both obtained in crystalline form and fully characterized. Each of the latter was globally deprotected by catalytic (Pd/C) hydrogenation/hydrogenolysis to give the desired, amino-functionalized, spacer-equipped, phosphorylated upstream trisaccharide fragment of the O-PS of V. cholerae O139.

A novel transition metal free [bis-(trifluoroacetoxy)iodo]benzene (PIFA) mediated oxidative ipso nitration of organoboronic acids.

A mild, convenient and transition metal free methodology for oxidative ipso nitration of diversely functionalized organoboronic acids, including heteroaryl- and alkylboronic acids, has been developed at ambient temperature using a combination of [bis-(trifluoroacetoxy)]iodobenzene (PIFA) - N-bromosuccinimide (NBS) and sodium nitrite as the nitro source. It is anticipated that the reaction proceeds through in situ generation of NO2 and O-centred organoboronic acid radicals followed by the formation of an O-N bond via combination of the said radicals. Finally transfer of the NO2 group to the aryl moiety occurs through 1,3-aryl migration to provide the nitroarenes.

Four-component reaction leading to highly functionalized sulfoalkoxy carbonyl compounds.

A facile regio- and diastereoselective four-component protocol has been developed involving an α,ß-unsaturated carbonyl compound, a cyclic ether, a sulfonic acid and a halogen reagent to access highly anti-α-bromo-ß-sulfoalkoxyl carbonyl derivatives. Some of these products have high toxicity against human chronic myeloid leukemia cells.

Enantioselective bromocyclization of allylic amides catalyzed by BINAP derivatives.

A highly enantioselective bromocyclization of allylic amides with N-bromosuccinimide (NBS) was developed with DTBM-BINAP as a catalyst, affording chiral oxazolines with a tetrasubstituted carbon center in high yield with up to 99% ee. By utilizing the bromo substituent as a handle, the obtained compounds were converted to synthetically useful chiral building blocks.

A versatile and one-pot strategy to synthesize α-amino ketones from benzylic secondary alcohols using N-bromosuccinimide.

A metal-free one-pot strategy has been developed for the first time to synthesize pharmaceutically important α-amino ketones from readily available benzylic secondary alcohols and amines using N-bromosuccinimide. This new reaction proceeds via three consecutive steps involving oxidation of alcohols, α-bromination of ketones, and nucleophilic substitution of α-bromo ketones to give α-amino ketones. Importantly, this novel one-pot greener reaction avoids direct usage of toxic and corrosive bromine. This methodology has been employed efficiently to synthesize pharmaceutically important amfepramone and pyrovalerone in a single step.

An unexpected 2,3-dihydrofuran derivative ring opening initiated by electrophilic bromination: scope and mechanistic study.

An unexpected 2,3-dihydrofuran ring opening process at the C(4)-C(5) bond has been developed. N-Bromosuccinimide and DABCO were used as the electrophilic halogen source and the catalyst, respectively. Mechanistic study indicates that moisture in the solvent might contribute to the reaction. The resulting brominated product could be further oxidized to yield a synthetically valuable 1,2-diketo building block.

The reaction of 2-amino-4H-pyrans with N-bromosuccinimide.

The reaction of racemic 2-amino-4H-pyrans, such as 3-amino-1-aryl-1H-benzo[f]chromene-2-carbonitriles, with N-bromosuccinimide (NBS), in CH2Cl2, at room temperature, is a very quick, regio, stereoselective, and high yielding process, affording major racemic (1S, 2S)-2-bromo-3-imino-benzo[f]chromene or racemic (1S, 2S)-2-bromo-3-(bromoimino)-benzo[f]chromene derivatives, when using 1.0 or 2.2 equivalents of NBS, respectively. This reaction, extended to isomeric 2-amino-4-aryl-4H-benzo[h]chromene-3-carbonitriles, showed an unexpected reactivity, affording racemic (3S,4S)-3-bromo-2-(bromoimino)-benzo[h]chromene-3-carbonitriles or 2-oxo-2H-benzo[h]chromene-3-carbonitriles, when using 2.2 or 1.0 equivalents of NBS, respectively. The reaction of alkyl 6-amino-5-cyano-2-methyl-4H-pyran-3-carboxylates has yielded unstable racemic (3S,4S)-alkyl 3-bromo-2-(bromoimino)-3-cyano-6-methyl-3,4-dihydro-2H-pyran-5-carboxylates. The mechanism of these reactions has been investigated by computational methods.