Synthesis of new aryl(hetaryl)-substituted tandospirone analogues with potential anxiolytic activity via reductive Heck type hydroarylations

Tandospirone (I), developed as an anxiolytic drug, is an aryl-piperazine compound that binds to both 5-HT_1A and dopamine D4 receptors. Palladium-catalysed hydroarylation reactions of tandospirone analogues containing an oxygen bridge and 3-(trifluoromethyl)phenyl or 2,3-dichlorophenyl groups were studied in order to find a new stereoselective access to a series of new exo-aryl(hetaryl)-substituted derivatives with potential biological activity.     

Comparative electrochemical properties of fluorinated endoperoxides related to the G-factor series

Fluorinated analogues of natural product G3-factor were synthesized and evaluated for their antiplasmodium activity. Electrochemical studies allowed us to measure the reduction potential E_p of the new compounds and to compare the effect of fluorine atoms on peroxo bridge stability.     

New pentacyclic triterpene saponins with strong anti-leishmanial activity from the leaves of Maesa balansae

Six new triterpene saponins bearing an oxygen bridge between C-13 and C-28 and with pronounced anti-leishmanial activity were isolated from the methanolic extract of leaves of the Vietnamese medicinal plant Maesa balansae. The structure was established on the basis of detailed NMR (COSY, NOESY, HMQC, HMBC, TOCSY and DEPT) and FAB-MS studies along with chemical degradation. All saponins identified contained the same pentaglycosidic side chain, but a different esterification pattern on the triterpenoid part. Biological evaluation of the individual compounds against visceral leishmaniasis (Leishmania infantum amastigotes) revealed a much better activity in vitro compared to the reference compound Pentostam^®, which is currently used as first-line treatment for leishmaniasis.     

Antimicrobial Peptide Brevivin-1RL1 from Frog Skin Secretion Induces Apoptosis and Necrosis of Tumor Cells

Cancer has always been one of the most common malignant diseases in the world. Therefore, there is an urgent need to find potent agents with selective antitumor activity against cancer cells. It has been reported that antimicrobial peptides (AMPs) can selectively target tumor cells. In this study, we focused on the anti-tumor activity and mechanism of Brevivin-1RL1, a cationic α-helical AMP isolated from frog Rana limnocharis skin secretions. We found that Brevivin-1RL1 preferentially inhibits tumor cells rather than non-tumor cells with slight hemolytic activity. Cell viability assay demonstrated the intermolecular disulfide bridge contributes to the inhibitory activity of the peptide as the antitumor activity was abolished when the disulfide bridge reduced. Further mechanism studies revealed that both necrosis and apoptosis are involved in Brevivin-1RL1 mediated tumor cells death. Moreover, Brevivin-1RL1 induced extrinsic and mitochondria intrinsic apoptosis is caspases dependent, as the pan-caspase inhibitor z-VAD-FMK rescued Brevinin-1RL1 induced tumor cell proliferative inhibition. Immunohistology staining showed Brevivin-1RL1 mainly aggregated on the surface of the tumor cells. These results together suggested that Brevivin-1RL1 preferentially converges on the cancer cells to trigger necrosis and caspase-dependent apoptosis and Brevivin-1RL1 could be considered as a pharmacological candidate for further development as anti-cancer agent.     

Synthesis, structure and some reactions of a multi-bridged unsaturated cyclooctadecane derivative formally having two cycloheptatrienes

Double annulation of 1,6-bis(bromomethyl)-1,3,5-cycloheptatriene with diethyl acetonedicarboxylate under basic conditions provided the title cyclooctadecane derivative having formally two 1,3,5-cycloheptatriene moieties. An NMR study of the compound suggested that one moiety stays as a cycloheptatriene form and the other as a norcaradiene form. X-ray crystallographic analysis revealed that two methano bridges have syn- and anti-configurations to the central carbonyl bridge and also showed that one of the moieties having the syn-methano bridge stays a CHT form and the other having the anti-methano bridge stays an NCD form.     

Bromelain Enzyme from Pineapple: In Vitro Activity Study under Different Micropropagation Conditions

The aim of this work was to evaluate the activity of bromelain in pineapple plants (Ananas comosus var. Comosus), Pérola cultivar, produced in vitro in different culture conditions. This enzyme, besides its pharmacological effects, is also employed in food industries, such as breweries and meat processing. In this work, the enzymatic activity was evaluated in the tissues of leaves and stems of plants grown in culture medium without plant growth regulator. The most significant levels of bromelain were observed in leaf tissue after 4?months of culture in vitro in medium with a filter paper bridge, followed by medium gelled by the agar. The results of this study, regarding the different structures of the pineapple (leaves and stems) in vitro showed that the activity of bromelain varied depending on the culture conditions, the time and structure of which was quantified, ensuring a viable strategy in the production of seedlings with high levels of bromelain in subsequent phases of micropropagation.     

Synthesis of novel carbohydrate-based valine-derived formamide organocatalysts by CuAAC click chemistry and their application in asymmetric reduction of imines with trichlorosilane

Novel organocatalysts combining carbohydrate and N-formyl-l-valine derivatives were prepared by Cu^II-catalyzed diazo transfer and Cu^I-catalyzed azide–alkyne 1,3-dipolar cycloaddition CuAAC click chemistry. It was found that the carbohydrate-based valine-derived formamide organocatalyst had high catalytic activity for the asymmetric reduction of imines with trichlorosilane. The reduction can proceed at room temperature in toluene in high yield (up to 98%) and with excellent enantioselectivity (up to 94%). ‘CuAAC’ click chemistry is a bridge to link N-formyl-l-valine derived organocatalysts with carbohydrates.     

Non-C2-Symmetric Bis-Benzimidazolium Salt Applied in the Synthesis of Sterically Hindered Biaryls

A novel non-C₂-symmetric bis-benzimidazolium salt derived from (±)-valinol has been prepared by a simple and straightforward process in good yield. The structure of bis-benzimidazolium salt provided a bulky steric group on the ethylene bridge; which facilitates the catalytic efficacy in the C(sp²)–C(sp²) formation. Its catalytic activity in Suzuki–Miyaura cross-coupling reaction of unactivated aryl chlorides has been found to have high efficacy in 1 mol% Pd loading. This protocol demonstrated the potential on the synthesis of sterically hindered biaryls.     

The Influence of Bridge Type on the Activity of Supported Metallocene Catalysts in Ethylene Polymerization简

Ethylene polymerization was carried out by immobilization of rac-ethylenebis(1-indenyl)zirconium dichloride(Et(Ind)2 ZrCl2) and rac-dimethylsilylbis(1-indenyl)zirconium dichloride(Me2 Si(Ind)2 ZrCl2) preactivated with methylaluminoxane(MAO) on calcinated silica at different temperatures. Polymerizations of ethylene were conducted at different temperatures to find the optimized polymerization temperature for maximum activity of the catalyst. The Me2 Si bridge catalyst showed higher activity at the lower polymerization temperature compared to the Et bridge catalyst. The highest catalytic activities were obtained at temperatures about 50 °C and 70 °C for Me2 Si(Ind)2 ZrCl2 /MAO and Et(Ind)2 ZrCl2 /MAO catalysts systems, respectively. Inductively coupled plasma-atomic emission spectroscopy results and polymerization activity results confirmed that the best temperature for calcinating silica was about 450 °C for both catalysts systems. The melting points of the produced polyethylene were about 130 °C, which could be attributed to the linear structure of HDPE.     

Design and synthesis of a Mn(III)-porphyrin steroid conjugate used as a new cleavable affinity label: on the road to semi-synthetic catalytic antibodies

We here report the synthesis of a novel porphyrin-steroid conjugate which was designed for the site-specific incorporation of a non-natural heme cofactor at the binding site of an anti-estradiol antibody, in order to get a semi-synthetic catalytic antibody with a monooxygenase-like activity. The general strategy involved a coupling reaction between a testosterone modified by an arm bearing a cleavable disulfide bridge and a meso-tetraarylporphyrin bearing two successive meso-ortho-substituted-phenyl rings, α,α-5,10-bis-[{o-(2-carboxyethyl)carboxamido}phenyl]-15,20-diphenyl-porphyrin. The final porphyrin-steroid conjugate was successfully purified and fully characterized, and was subsequently metalated with manganese acetate. The metalloporphyrin moiety will be used to be coupled with the antibody to generate a new biocatalyst with monooxygenase-like activities.     

Studies on the liquid junction potential corrections of electrolytes at aqueous + mixed solvent boundaries

Liquid junction potentials (E_J) generated at the boundaries of various salt bridge/mixed aqueous + organic solutions, have been determined by comparing the measured emf of silver cells with the calculated emf using literature values of transfer activity coefficients γ_t (Ag⁺) and γ_t (Cl⁻) based on the tetraphenylarsonium-tetraphenylborate (TATB) assumption.The E_J values have been analyzed in terms of the ion-solvent interaction, determined by ionic transfer Gibbs energies, and the so-called solvent-solvent interaction. The effect of varying the cation, anion, and concentration of bridge electrolyte, is assessed in aqueous acetonitrile (AN), ethanol (EtOH), and dimethylsulfoxide (DMSO). It is concluded that the previously reported solvent-solvent contribution to E_J is merely a correction factor to the ion-solvent interaction contribution due to solvent mixing at the boundary. Four salt bridges (sat. K₂SO₄ 3.5 M KCl, 3.5 M NaClO₄, and 0.1 M Et₄N-picrate) are compared on the basis of E_J.The recommended salt bridge for use with mixed aqueous + organic solutions is 3.5 M NaClO₄ in water. Appropriate E_J correction factors are presented for emf measurements in mixtures of AN + H₂O, EtOH + H₂O, and DMSO + H₂O.     

Lewis acid catalysed rearrangements of unsaturated bicyclic [2.2.n] endoperoxides in the presence of vinyl silanes; access to novel Fenozan BO-7 analogues

Reactions of a series of unsaturated bicyclic [2.2.n] endoperoxides with allyltrimethylsilane in the presence TMSOTf or SnCl₄ provides the cis-configured endoperoxides 9a-12. It is proposed that this novel reaction proceeds via attack of the allylsilane on the carbocation derived from heterolytic cleavage of the endoperoxide bridge. The reaction proceeds with a high degree of diastereoselectivity and we propose that the bulky -CH₂SiMe₃ substituent adopts an equatorial position in a product-like transition state. In contrast to Fenozan B0-7, these compounds displayed poor antimalarial activity versus chloroquine-resistant parasites in vitro.     

Tripodal Ru(II) complexes with conjugated and non-conjugated rigid-rod bridges for semiconductor nanoparticles sensitization

Three tripodal Ru(II)-polypyridyl complexes have been synthesized as models to study long-range electron transfer in TiO₂ semiconductor nanoparticles thin films, in particular to study the effect of the conjugation of the bridge containing the Ru complex and for distance dependence studies. The tripodal sensitizers, which are 1,3,5,7-tetraphenyladamantane derivatives having three COOMe anchoring groups and one rigid-rod bridge substituted with a Ru(II) complex, are the longest prepared to date (Ru-to-footprint distance ∼24 Å). Two have a rigid-rod bridge made of two p-ethynylphenylene units (Ph-E)₂ capped with a 4-2,2′-bipyridyl (bpy) ligand or a 5-1,10-phenanthrolinyl (phen) ligand for the Ru complex. The third tripod, which contains a bpy ligand for the Ru complex, has one bicyclo[2.2.2]octylene (Bco) unit in place of a p-phenylene (Ph) unit and is the first example of a tripodal sensitizer with a non-conjugated bridge.     

Structural constraints for the formation of macrocyclic rhombimines

Rhombimines, macrocyclic tetraimines, have been obtained by the condensation of enantiomerically pure trans-1,2-diaminocyclohexane with aromatic dialdehydes connected by a one-atom bridge. The efficiency of the cyclocondensation is dependent upon the nature of the dialdehyde bridge atom: low selectivity was observed and rationalized by computational analysis for sp² hybridized bridge atoms. Unusual triple-split exciton Cotton effects were measured and calculated for highly symmetrical, tetrachromophoric rhombimines.     

Electrical network of nanofluidic diodes in electrolyte solutions: Connectivity and coupling to electronic elements

We consider a nanopore network with simple connectivity, demonstrating a two-dimensional circuit (full-wave rectifier) with ensembles of conical pores acting as nanofluidic diodes. When the bridge nanopore network is fed with an input potential signal of fluctuating polarity, a fixed output polarity is obtained. The full-wave rectification characteristics are demonstrated with square, sinusoidal, and white noise input waveforms. The charging of a load capacitor located between the two legs of the bridge demonstrates that the nanofluidic network is effectively coupled to this electronic element. These results can be relevant for energy transduction and storage procedures with nanopores immersed in electrolyte solutions. Because the individual nanofluidic resistances can be modulated by chemical, electrical, and optical signals, the balanced bridge circuit can also be useful to miniaturize nanopore-based sensing devices.     

Physalinol A,a 1,10-seco-physalin with an epidioxy from Physalis alkekengi L. var. franchetii (Mast.) Makino

Physalinol A (1), a novel 1, 10-seco-physalin with a peroxy bridge, was isolated from the organic extracts of Physalis alkekengi L. var. franchetii (Mast.) Makino. The structure was determined on the basis of 1D and 2D NMR spectra and HR-ESI-MS data. The absolute configuration of 1 was evidenced by X-ray diffraction data and further confirmed by ECD calculations. The isolated compound 1 has no cytotoxicity against HCT-116 and PC-3 cancer cell lines and a weak antimicrobial activity against Escherichia coil. In addition, compound 1 also exhibited a weak anti-inflammatory action in lipopolysacaride (LPS)-induced RAW 264.7 macrophages with an IC₅₀ value of 57.3?±?1.03?μM.     

Long-range electron and excitation energy transfer in donor–bridge–acceptor systems

Donor–bridge–acceptor (D-B-A) systems, either as supermolecules or on surfaces, have been extensively studied with respect to long-range electron (ET) and excitation energy (EET) transfer. In more recent years, the main research objective has been to develop knowledge on how to construct molecular-based devices, with predetermined electron transfer properties, intended for application in electronics and photovoltaics. At present, such construction is in general hampered for several reasons. Most importantly, the property of a D-B-A system is not a simple linear combination of properties of the individual components, but depends on the specific building blocks and how they are assembled. An important example is the ability of the bridge to support the intended transfer process. The mediation of the transfer is characterized by an attenuation factor, β, often viewed as a bridge specific constant but which also depends on the donor and the acceptor, i.e. the same bridge can either be poorly or strongly conducting depending on the donor and acceptor. This review gives an account of the experimental exploration of the attenuation factor β in a series of bis(porphyrin) systems covalently linked by bridges of the oligo(phenyleneethynylene) (OPE) type. Attenuation factors for ET as well as for both singlet and triplet EET are discussed. A report is also given on the dependence of the transfer efficiency on the energy-gap between the donor and bridge states relevant for the specific transfer process. The experimental variation of β with varying donor and acceptor components is shown for a range of conjugated bridges by representative examples from the literature. The theoretical rationalization for the observed variation is briefly discussed. Based on the Gamow tunneling model, the observed variations in β-values with varying donors and acceptors for the same bridges is simulated successfully simultaneously as the observed energy-gap dependence is modelled.     

Synthesis and characterization of chiral, bridged resorcinarenes as templates for asymmetric catalysis

A full study of the synthesis of chiral, bridged resorcinarenes (3a-3l, 13a, 13b) is presented using Mannich condensation of C_2v-tetraprotected resorcinarenes with chiral 1,n-diamines bearing homochiral α-methylbenzyl auxiliaries at each terminal nitrogen. The study has revealed the methodology to be applicable to preparing a broad range of bridged structures with varying lengths of bridge, different functionality in the bridge and various protecting groups on the upper rim. Reproducible and satisfactory yields in the reaction were only obtained with the pendant R group as methyl. The bridged adducts have been fully characterized by a range of spectroscopic techniques, and NMR has revealed varying trends in the way the various bridges protrude into the cavity. Low temperature NMR as well as X-ray structures of tetramesylate 15 and tetratoluate 3g has revealed hydrogen bonding to the amine nitrogens in the bridge to be an important control element for positioning the bridge relative to the cavity of the bowl. The derivatives provide chiral templates for asymmetric catalysis studies using cooperative effects in the bowl.     

Mise en évidence de l'entité Sb2F4O dans un composé d'addition moléculaire avec l'urée étude structurale de [(NH2)2CO]2,Sb2F4O

The X-ray structure determination of [NH₂)₂CO]₂ · Sb₂F₄O shows the existence of linked units urea-Sb₂F₄O which show the Sb₂F₄O entity, not yet known. Crystal structure was solved with a singlecrystal X-ray diffraction study (the final R value is 0.046). The Sb₂F₄O unit is composed of a symmetric and short SbOSb bridge, and of four fluorine atoms, two being bonded to each antimony atom and situated in trans position relative to the SbOSb bridge. The bridge bond strength is assigned to a pπdπ overlap.     

Differential 3ω calorimeter

We have developed a new dynamic calorimeter using the differential 3ω detection method. The differential 3ω calorimeter is capable of measuring dynamic heat capacity of liquid samples. The new calorimeter consists of a Wheatstone bridge made of two identical heater/sensors, and is based on the sensitive null detection method. The balancing is done automatically at all frequencies and is independent of temperature; once a sample is placed on one heater/sensor, a third harmonic signal is produced due to the difference in the two arms of the bridge. The differential 3ω calorimeter provides enhancements over traditional dynamic methods in dynamic range (up to 30 kHz), resolution, and ease of operation.