A new fluorescent fluoride chemosensor based on conformational restriction of a biaryl fluorophore

A new fluorescent anion sensor 1, based on a biaryl–thiourea system, exhibits a fluorescence emission enhancement via conformational restriction upon a hydrogen bond-mediated complexation of fluoride anions.     

Highly enantioselective deracemization of linear and vaulted biaryl ligands

[reaction: see text] A copper-mediated deracemization of the vaulted biaryl ligands VANOL and VAPOL can be readily achieved in the presence of (-)-spartiene. The optimal procedure involves the in situ generation of copper(II) and leads to the reproducible formation of (S)-VANOL and (S)-VAPOL in greater than 99% ee from the racemates. This method is superior to existing procedures for BINOL (92% ee).     

Polymeric membrane sodium-selective electrodes based on calix[4]arene ionophores

Six kinds of tetra alkylester type calix[4]arene derivatives, (R₁=R₂=CH₃1, C₂H₅2, C₃H₇3,n-C₄H₉4,t-C₄H₉5,n-C₁₀H₂₁6), a diethyl-didecyl mixed ester type (R₁=C₂H₅, R₂ =C₁₀H₂₁7), and three kinds of lower rim bridged types (R₁=C₂H₅, R₂–R₂=(CH₂)₁₀8, (CH₂)₁₂9, (CH₂)₂(OCH₂CH₂)₃10) were characterized by electrochemical measurement to elucidate the effect of the length of the alkyl group of alkoxycarbonyl substituents on Na⁺ selectivity. To obtain excellent Na⁺ selective ionophores, introduction of short chain alkyl groups rather than long chain ones, such as a decyl group, and maintenance of sufficient solubility of the calix[4]arene derivatives in the membrane solvent are required concurrently. Among the calix[4]arenes tested, 25,26,27,28-tetrakis[(ethoxycarbonyl)methoxy]-p-tert-butylcalix[4]arene2, and the diethyl-didecyl mixed ester type derivative7 are the best ionophores for a Na⁺ selective electrode. On the other hand, sodium selectivity of the bridged type derivative9 is comparable or even superior to that of the known bis(12-crown-4).This paper is dedicated to the commemorative issue on the 50th anniversary of calixarenes.     

A copper(II) ion-selective on-off-type fluoroionophore based on zinc porphyrin-dipyridylamino

A new copper(II) fluorescent sensor 5,10,15,20-tetra((p-N,N-bis(2-pyridyl)amino)phenyl)porphyrin zinc (1) has been designed and synthesized by the Ullmann-type condensation of bromoporphyrin zinc with 2,2'-dipyridylamine (dpa) under copper powder as a catalyst as well as with K2CO3 as the base in a DMF solution. It consists of two separately functional moieties: the zinc porphyrin performs as a fluorophore, and the dpa-linked-to-zinc porphyrin acts as a selected binding site for metal ions. It displays a high selectivity and antidisturbance for the Cu2+ ion among the metal ions examined (Na+, Mg2+, Cr3+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Ag+, Zn2+, Cd2+, Hg2+, and Fe3+) and exhibits fluorescence quenching upon the binding of the Cu2+ ion with an "on-off"-type fluoroionophoric switching property. The detection limit is found to be 3.3 x 10(-7) M (3s blank) for Cu2+ ion in methanol solution, and its fluorescence can be revived by the addition of EDTA disodium solution. The design strategy and remarkable photophysical properties of sensor 1 help to extend the development of fluorescent sensors for metal ions.     

Highly efficient energy transfer in the light harvesting system composed of three kinds of boron-dipyrromethene derivatives

A light-harvesting system containing three kinds of BODIPY fluorophores was synthesized. It exhibited very strong absorption in the region from 300 to 700 nm, and the energy transfer within it was highly efficient.     

Fluorescent probe for monosaccharides based on a functionalized boron-dipyrromethene with a boronic acid group

A new highly fluorescent probe based on a boron-dipyrromethene functionalized with a phenylboronic acid group was synthesized from 2,4-dimethylpyrrol and 4-formylphenylboronic acid. Spectral changes in both absorption and emission spectra were observed in the presence of sugars.     

Highly selective recognition of lead ion in water by a podand fluoroionophore/gamma-cyclodextrin complex sensor

We report herein a novel podand fluoroionophore/gamma-cyclodextrin (gamma-CyD) complex sensor that shows markedly high selectivity for lead (Pb2+) ion in water.     

Highly efficient synthesis of polysubstituted fluorene via iron-catalyzed intramolecular Friedel-Crafts alkylation of biaryl alcohols

An efficient and mild Fe(III)-catalyzed intramolecular Friedel-Crafts alkylation of biaryl methanol derivatives has been developed to achieve the substituted fluorene derivatives. The present reaction provides an excellent alternative to published methods because of its high yields, operational simplicity, mild conditions, and use of inexpensive and sustainable catalyst.     

Highly alpha- and beta-selective radical C-glycosylation reactions using a controlling anomeric effect based on the conformational restriction strategy. A study on the conformation-anomeric effect-stereoselectivity relationship in anomeric radical reactions.

We hypothesized that, because the stereoselectivity of anomeric radical reactions was significantly influenced by the anomeric effect, which can be controlled by restricting the conformation of the radical intermediate, the proper conformational restriction of the pyranose ring of the substrates would therefore make highly alpha- and beta-stereoselective anomeric radical reactions possible. Thus, the conformationally restricted 1-phenylseleno-D-xylose derivatives 9 and 10, restricted in a (4)C(1)-conformation, and 11 and 12, restricted in a (1)C(4)-conformation, were designed and synthesized by introducing the proper protecting groups on the hydroxyl groups on the pyranose ring as model substrates for the anomeric radical reactions. The radical deuterations with Bu(3)SnD and the C-glycosylation with Bu(3)SnCH(2)CH [double bond] CH(2) or CH(2) [double bond] CHCN, using the (4)C(1)-restricted substrates 9 and 10, afforded the corresponding alpha-products (alpha/beta = 97:3-85:15) highly stereoselectively, whereas the (1)C(4)-restricted substrates 11 and 12 selectively gave the beta-products (alpha/beta = 1:99-0:100). Thus, stereoselectivity was significantly increased by conformational restriction and was completely inverted by changing the substrate conformation from the (4)C(1)-form into the (1)C(4)-form. Ab initio calculations suggested that the radical intermediates produced from these substrates possessed the typical (4)C(1)- or (1)C(4)-conformation, which was similar to that of the substrates, and that the anomeric effect in these conformations would be the factor controlling the transition state of the reaction. Therefore, the highly alpha- and beta-selective reactions would occur because of the anomeric effect, which could be manipulated by conformational restriction of the substrates, as expected. This would be the first radical C-glycosylation reaction to provide both alpha- and beta-C-glycosides highly stereoselectively.     

Effect of obligatory replacement and conformational restriction on psychotropic activity of thyroliberin analogs

Easy lactamization of Gln(Asn)−Pro−NH₂ with the formation of cyclic dipeptides with the diketopiperazine structure (mimetics of the conformational fragments of linear tripeptides with the X−Protrans-bond) was observed in the synthesis of tripeptide Glp−Gln−Pro−NH₂ modified by the replacement of histidine with obligatory similar glutamine in thyroliberin (Glp−His−Pro−NH₂, TRH) and in the synthesis of its structural analog [Asn²]TRH. Ion peaks corresponding to the Glp and Pro amino acid residues were revealed in the mass spectra of the peptides synthesized. The biological properties of the compounds obtained were determined indicating that the obligatory replacement resulted in an increased physiological specificity of [Gln²]TRH. The enhanced activity of conformationally restricted cyclic peptides compared to linear ones suggests that the biologically active conformation responsible for the antidepressant activity of linear TRH analogs is the conformation with X−Protrans-bond. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2015–2020, October, 1998.     

Aziridines as a structural motif to conformational restriction of azasugars

In order to investigate the hypothesis that the glycosidase inhibitor isofagomine was bound to alpha- or beta-glucosidase in a 1,4B conformation, a number of bicyclic aziridines that adopt the 1,4B or B1,4 conformations were synthesised and investigated. (1R)-2-endo,3-exo-2,3-Dihydroxy-4-endo-4-hydroxymethyl-6- azabicyclo[3.1.0]hexane (5) and its N-methyl and N-benzyl analogues and (1S)-2-exo-3-endo-2,3-dihydroxy-4- endo-4-hydroxymethyl-6-azabicyclo-[3.1.0]hexane (6) were synthesised. The aziridines 5 and 6 were found to be weak or not inhibitors of alpha-glucosidase, beta-glucosidase and alpha-fucosidase.     

Efficient synthesis of β-C-glucosides via radical cyclization with a silicon tether based on the conformational restriction strategy

An efficient method for preparing β-C-glucosides using radical cyclization with a temporary connecting silicon tether was developed. In this reaction, conformational restriction of the substrates to the unusual ¹C₄-form is essential for the cyclization to occur.     

New Hg2+ and Cu2+ selective chromo- and fluoroionophore based on a bichromophoric azine

[graph: see text] A new probe, 1,4-bis(1-pyrenyl)-2,3-diaza-1,3-butadiene, selectively senses Hg2+ and Cu2+ through two different channels: the yellow-deep-pink color change and the enhancement of the fluorescence with the red shift of the excimer emission, which can visually be discernible by a green fluorescence in the presence of Hg2+ and an orange fluorescence in the presence of Cu2+.     

A new optical and electrochemical sensor for fluoride ion based on the functionalized boron-dipyrromethene dye with tetrathiafulvalene moiety

A new tetrathiafulvalene (TTF) derivative with the boron-dipyrromethene (BODIPY) moiety shows selectively optical and electrochemical sensing for fluoride ion. The mechanism of anion recognition has been investigated by ¹H NMR titration and DFT calculations. The results show that the receptor with redox active TTF moiety and fluorescent BODIPY subunits may be useful as sensors for detecting and sensing fluoride ion.     

Microcantilever biosensors based on conformational change of proteins

Microcantilevers (MCLs) hold a position as a cost-effective and highly sensitive sensor platform for medical diagnostics, environmental analysis and fast throughput analysis. MCLs are unique in that adsorption of analytes on the microcantilever (MCL) surface changes the surface characteristics of the MCL and results in bending of the MCL. Surface stress due to conformation change of proteins and other polymers has been a recent focus of MCL research. Since conformational changes in proteins can be produced through binding of anylates at specific receptor sites, MCLs that respond to conformational change induced surface stress are promising as transducers of chemical information and are ideal for developing microcantilever-based biosensors. The MCL can also potentially be used to investigate conformational change of proteins induced by non-binding events such as post-translational modification and changes in temperature or pH. This review will provide an overview of MCL biosensors based on conformational change of proteins bound to the MCL surface. The models include conformational change of proteins, proteins on membranes, enzymes, DNA and other polymers.     

Synthesis and characterization of phenol‐based biaryl proton conducting polymers

Biaryl hydroxy polymers with orthogonal disposition of proton transporting ? OH moieties have been synthesized via conventional free radical polymerization. The polymers are characterized for their thermal stability and proton conductivity, and the results are compared with the corresponding styrenic hydroxy polymers. The orthogonal disposition of ? OH moieties in biaryl polymers does result in lower E_a for proton transport. However, the lower E_a values in biaryl polymers did not translate into a net increase in proton conductivity. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

An efficient synthesis of beta-C-glycosides based on the conformational restriction strategy: Lewis acid promoted silane reduction of the anomeric position with complete stereoselectivity

[reaction: see text] The reduction of glyconolactols having an anomeric carbon substituent by Et(3)SiH/TMSOTf proceeded with complete stereoselectivity to produce the corresponding beta-C-glycosides when the substrates were conformationally restricted in the (4)C(1)-chair form by a 3,4-O-cyclic diketal or a 4,6-O-benzylidene protecting group. Thus, the efficient construction of beta-C-glycosides was achieved on the basis of the conformation restriction strategy.