Block and graft copolymers based on cationic ring-opening polymerizations

The highly living character of a number of cationic polymerizations has been used to synthesize new, well defined, segmented copolymers. This has been achieved by sequential monomer additions, by grafting reactions, by macromonomer copolymerizations as well as by transfer to polymer. In the present report, a number of examples of such polymers will be presented. The new materials are based on tetrahydrofurane (THF), alkyloxazolines (ROx), cyclic amines, cyclic acetals and cyclic sulfides.     

Characteristic monomials with chirality fittingness for combinatorial enumeration of isomers with chiral and achiral ligands

A new method of combinatorial enumeration based on characteristic monomials with chirality fittingness (CM-CFs) has been proposed in order to enumerate isomers with chiral ligands as well as with achiral ones. The CM-CFs have been defined as monomials that consist of three kinds of dummy variables in light of the subduction of the Q-conjugacy representations for chiral and achiral cyclic groups. A procedure of calculating CM-CFs for cyclic groups and finite groups has been discribed so as to tabulate them as CM-CF tables. Then the CM-CF method has been applied to the enumeration of isomers with achiral ligands as well as chiral ones.     

A Versatile Strategy for Screening Custom-Designed Warhead-Armed Cyclic Peptide Inhibitors

Demand for peptide-based pharmaceuticals has been steadily increasing, but only limited success has been achieved to date. To expedite peptide-based drug discovery, we developed a general scheme for cell-based screening of cyclic peptide inhibitors armed with a user-designed warhead. We combined unnatural amino acid incorporation and split intein-mediated peptide cyclization techniques and integrated a yeast-based colorimetric screening assay to generate a new scheme that we call the custom-designed warhead-armed cyclic peptide screening platform (CWCPS). This strategy successfully discovered a potent inhibitor, CY5-6Q, that targets human histone deacetylase 8 (HDAC8) with a K_D value of 15 nM. This approach can be a versatile and general platform for discovering cyclic peptide inhibitors.     

Study of the secretion from a scale insect (Ceroplastes ceriferus) diterpenoids and sesterterpenoids

Structures of four new minor sesterterpenoids 1–3,18 and three new diterpenoids 12–14 isolated from the secretion of Ceroplastes ceriferus are described. All four sesterterpenoids are 14-membered monocyclic compounds; one of them has been chemically correlated with cericeroic acid¹ of proven absolute stereochemistry. The “cyclic wax” was a complex mixture of esters consisting of fatty acids (C₁₀-C₃₂) and unusual cyclic alcohols (diterpenoids and sesterterpenoids)     

Development of the method of polystyrene chloromethylation using the synthesis in gel approach

Russian Chemical Bulletin - A new method for the preparation of poly(chloromethylstyrene) by synthesis in a gel via treating of linear polystyrene with cyclic formals in thionyl chloride has been...     

Stereoselective synthesis of orthogonally protected alpha-methylnorlanthionine

[reaction: see text] As the unusual amino acid norlanthionine (nor-Lan) has previously been incorporated into cyclic peptide analogues of the ring C of lantibiotic nisin, we report here the stereoselective synthesis of the new (S,R)- and (R,R)-alpha-methylnorlanthionines (alpha-Me-nor-Lan). The orthogonally protected derivatives of these compounds have also been prepared. The key step in the synthesis of these bisamino acids was the S(N)2 opening reaction of the corresponding cyclic sulfamidates with the SH group of appropriately protected l-cysteine derivatives.     

3.5次微分循环示波计时电位法的研究

将半积分半微分技术应用于循环示波计时电位曲线的处理,可大大抑制充电电流的影响,提高示波测定的灵敏度和分辨率.据此,本文提出了3.5次微分循环示波计时电位法,研究了该方法的特点并将其用于HAc-NaoH-铜铁试剂(HCup)体系中铅示波特性的研究和微量铅的测定.     

Poly(phenylene oxide); electropolymerization on mild steel and anticorrosive properties of the layer: A new corrosion test

The electropolymerization of phenyl salicylate by cyclic potential sweeps over mild steel gives rise to the formation of a poly(phenylene oxide) (PPO) film. In order to study the anticorrosive properties of PPO a new rapid corrosion test has been devised.     

Copper(I)‐Mediated Denitrogenative Macrocyclization for the Synthesis of Cyclic α3β‐Tetrapeptide Analogues

A copper(I)‐mediated denitrogenative reaction has been successfully developed for the preparation of cyclic tetrapeptides. The key reactive intermediate, ketenimine, triggers intramolecular cyclization through attack of the terminal amine group to generate an internal β‐amino acid with an amidine linkage. The chemistry developed herein provides a new synthetic route for the preparation of cyclic α₃β‐tetrapeptide analogues that contain important biological properties and results in rich structural information being obtained for conformational studies. With the success of this copper(I)‐catalyzed macrocyclization, two histone deacetylase inhibitor analogues consisting of the cyclic α₃β‐tetrapeptide framework have been successfully synthesized.     

High-throughput sequence determination of cyclic peptide library members by partial Edman degradation/mass spectrometry

Cyclic peptides provide attractive lead compounds for drug discovery and excellent molecular probes in biomedical research. Large combinatorial libraries of cyclic peptides can now be routinely synthesized by the split-and-pool method and screened against biological targets. However, post-screening sequence determination of hit peptides has been problematic. In this report, a high-throughput method for the sequence determination of cyclic peptide library members has been developed. TentaGel microbeads (90 mum) were spatially segregated into outer and inner layers; cyclic peptides were displayed on the bead surface, whereas the inner core of each bead contained the corresponding linear peptide as the encoding sequence. After screening of the cyclic peptide library against a macromolecular target, the identity of hit peptides was determined by sequencing the linear encoding peptides inside the bead using a partial Edman degradation/mass spectrometry method. On-bead screening of an octapeptide library (theoretical diversity of 160 000) identified cyclic peptides that bind to streptavidin. A 400-member library of tyrocidine A analogues was synthesized on TentaGel macrobeads and solution-phase screening of the library directly against bacterial cells identified a tyrocidine analogue of improved antibacterial activity. Our results demonstrate that the new method for cyclic peptide sequence determination is reliable, operationally simple, rapid, and inexpensive and should greatly expand the utility of cyclic peptides in biomedical research.     

A new electrochemical method based on transfer at a liquid/liquid interface: Determination of barium and strontium

A new kind of polyoxyethylene ionophore is introduced to facilitate metal ion transfer across a liquid/liquid interface. The transfer of Ba(2+) and Sr(2+), facilitated by polyethylene glycol 400 across the interfaces of water/nitrobenzene and water/1,2-dichloroethane, has been studied in detail by cyclic voltammetry, and a new method for the determination of barium and strontium established. Both metals can be determined by cyclic voltammetry with good selectivity and reproducibility.     

Ketene acetal monomers: Synthesis and characterization

A new, facile, and high-yield synthesis of ketene acetals derived from readily available and inexpensive starting materials has been developed. For example, an α,β-unsaturated aldehyde can be condensed with an alkane diol to afford a 2-vinyl substituted cyclic acetal. This latter compound can be converted to the desired cyclic ketene acetal by isomerization of the double bond in the presence of tris(triphenylphosphine)ruthenium(II) dichloride. Good to excellent yields of cyclic ketene acetals were obtained employing this method. The novel monomers were fully characterized by IR, NMR, and by elemental analysis. © 1996 John Wiley & Sons, Inc.     

A test procedure for separating viscous recovery and accumulated unrecoverable deformation of polymer under cyclic loading

After uniaxial tension and creep tests, asymmetric stress cycle tests have been performed on two polycarbonate (PC) materials with different molecular weights at room temperature. The effects of stress level (mean stress and stress amplitude) and time-dependent factors (stress rate and peak hold time) on ratcheting were studied. To separate the contributions of viscous recovery and accumulated unrecoverable deformation, a new test procedure has been proposed and performed on polycarbonate. The results demonstrate that the proposed test procedure is suitable for separating the viscous recovery and accumulated unrecoverable deformation. The study clearly shows that, for PC, both the viscous recovery and the accumulated unrecoverable deformation cannot be neglected for cyclic loading; previous viscous deformation has significant influence on the following cyclic accumulated deformation.     

A simple and efficient synthesis of functionalized cyclic carbonate monomers using a versatile pentafluorophenyl ester intermediate

An improved two-step synthetic route to functionalized cyclic carbonate monomers that features a novel cyclic carbonate intermediate with an active pentafluorophenyl ester group (MTC-OPhF(5)) has been developed. The versatile pentafluorophenyl ester intermediate can be synthesized on the gram to kilogram scale in one high-yielding step and is easy to store and handle on the benchtop. The active pentafluorophenyl ester of MTC-OPhF(5) is amenable to further substitution with suitable nucleophiles such as alcohols and amines to generate functionalized cyclic carbonates in high yields. The substitution reaction is tolerant of a wide variety of functionalities, including various hydrophobic and hydrophilic groups, reactive functionalities (via thiol-ene click chemistry or alkyl halides), and protected acids, alcohols, thiols, and amines. In view of the ever-increasing need for biodegradable and biocompatible polymers, this new methodology provides a simple and versatile platform for the synthesis of new and innovative materials.     

Catalytic epoxidation of cyclic vinylsilanes by ruthenium(II) complexes under aerobic conditions

A new methodology has been developed for the catalytic epoxidation of cyclic vinylsilanes using a ruthenium(II) bisoxazoline complex 2 with molecular oxygen. An attempt has been made to understand the role of -SiMe₃ group on the rate of epoxidation process.     

Selective Reactions with Organoaluminum Compounds

With the aid of selected examples an overview is given of the development trends in highly discriminative reactions using organoaluminum compounds. (1) Isomerization of substituted oxiranes into allyl alcohols has been effected both stereo- and regioselectively by means of a new organoaluminum reagent, diethylaluminum 2,2,6,6-tetramethylpiperidide (DATMP); this reaction which provides a new route for the regiospecific transformation of allyl alcohols into 1,3-dienes. (2) A novel nonenzymic heterolysis of allylic phosphates of terpenoids has been effected by organoaluminum compounds and has enabled development of a new method for the selective synthesis of cyclic terpenes. (3) The reductive condensation of α-haloketones with carbonyl compounds in the presence of diethylaluminum chloride and zinc affords β-hydroxy-carbonyl derivatives in good yields with exclusion of undesired self-condensations products.     

Study of the Electrostatic Interaction of Lysine Monolayer on Glassy Carbon Electrodes Using the Electrochemical Method

A covalent modified glassy carbon electrode (GCE) with Lysine (Lys) has been fabricated via an electrochemical oxidation procedure. The electrostatic interaction of the monolayer has been investigated by cyclic voltammetry (CV) with Fe(CN)₆^3? redox probe in different concentrations of protons and different charged cations, respectively. The electrochemical method can be a new feasible method for the study of electrostatic interaction of the monolayer.     

Cyclic PNA-based compound directed against HIV-1 TAR RNA: modelling, liquid-phase synthesis and TAR binding

A cyclic molecule including a hexameric PNA sequence has been designed and synthesized in order to target the TAR RNA loop of HIV-1 through the formation of a "kissing complex". For comparison, its linear analogue has also been investigated. The synthesis of the cyclic and linear PNA has been accomplished following a liquid-phase strategy using mixed PNA and fully N-protected (aminoethylglycinamide) fragments. The interactions of this cyclic PNA and its linear analogue with TAR RNA have been studied and the results indicate clearly that no interaction occurs between the cyclic antisense PNA and TAR RNA, whereas a tenuous interaction has been detected with its linear PNA analogue.     

Synthesis of s-substituted derivatives of cyclic thionamides

A new preparative method for synthesizing S-substituted derivatives of cyclic thionamides by the cleavage of salts of thionamides with five-, six-, and seven-membered rings has been developed. It has been shown that the onium salts of the N-substituted derivatives of cyclic thionamides undergo cleavage at the C-S bond under the action of water or a weak base with the formation of N-substituted lactams and mercaptans.     

Cysteine cyclic pyrrole-imidazole polyamide for sequence-specific recognition in the DNA minor groove

Pyrrole-imidazole (PI) polyamides are small DNA-binding molecules that can recognize predetermined DNA sequences with high affinity and specificity. Hairpin PI polyamides have been studied intensively; however, cyclic PI polyamides have received less attention, mainly because of difficulties with their synthesis. Here, we describe a novel cyclization method for producing PI polyamides using cysteine and a chloroacetyl residue. The cyclization reaction is complete within 1 h and has a high conversion efficiency. The method can be used to produce long cyclic PI polyamides that can recognize 7 bp DNA sequences. A cyclic PI polyamide containing two β-alanine molecules had higher affinity and specificity than the corresponding hairpin PI polyamide, demonstrating that the cyclic PI polyamides can be used as a new type of DNA-binding molecule.