Recent approaches for clickable poly(2-oxazoline)-based functional stimuli-responsive polymers and related applications

Abstract

Poly(2-oxazoline)s (POxs) are well-known thermo-responsive polymers that exhibit reversible hydrophilic–hydrophobic phase transitions at the lower critical solution temperature (LCST). Using living cationic ring-opening polymerisation, various functional groups can be introduced into POxs. Several clickable POxs with propargyl or azide end groups have been designed and subsequently reacted with various functional groups to prepare multifunctional POxs that respond to stimuli such as temperature, pH, chemicals and light. In this article, we briefly review recent approaches for clickable POx-based functional stimuli-responsive polymers and related applications.     

PHOSPHORORGANISCHE VERBINDUNGEN 1171, EINE NEUE METHODE ZUM NACHWEIS DER FUNKTIONELLEN GRUPPEN: OH,NH2 UND SH DURCH AUSLOSUNG VON FLUORESZENZ

Abstract

Covalently with a fluorescence support linked nitroarylester groups quench the fluorescence. The substitution of the fragment with the quenching group by an other functional group initiates fluorescence. If this substitution reaction is chemoselective, a reagent for the selective detection of a special functional group is available.

The non fluorescent compounds 1a and 1b are OH-(resp. F^(-)) selective; the compounds 5 and 7 are NH-selective and the compounds 8 and 9 are SH-selective. Dansyl-nitroimidazolide 7a discriminates between neutral and basic α-amino acids.     

A DFT study on a calix[5]crown-based heteroditopic receptor

The structures and binding energies of complexes formed between tris-ureido-calix[5]crown 1 and n- and 2-phenylethylammonium chloride have been determined by density functional calculations. Density functional theory analysis shows that the heteroditopic receptor 1 binds organic salt species with positive cooperativity.     

Synthesis of 5- and 6-Acyl-1-cyano and -1-ethoxycarbonyl Cycloalkenes

Abstract

Conjugated addition of primary nitroalkanes to the functional acetates 3 and 4 in basic medium, leads to the cyclic nitroesters 5 and nitronitriles 6. These derivatives are easily converted via the Nef reaction to the corresponding γ-ketoestesrs 7 and γ-ketonitriles 8 in good yields.     

PYRAZOLONES AS VERSATILE PRECURSORS FOR THE SYNTHESIS OF FUSED AND BINARY HETEROCYCLES

The reaction of pyrazolone bearing a β-ketoester moiety with aliphatic dibasic functional reagents in ethanol afforded the binary ring heterocycles 2, 6, and 10. Whereas, when using an excess of the dibasic reagent, the dipyrazolo [3,4-c: 3′, 4′-f] [1,2]diazepine derivative 5 was, obtained. On the other hand, when compound 1 reacted with hydrazine hydrate in acetic acid, it furnished the pyrazolo[3,4-b]pyridine derivative 7 in which the hydrazine hydrate acts as a monofunctional reagent. Also, the reaction of 1 with m-anisidine according to Knorr synthesis gave the α,β-unsaturated ketone derivative 9 in lieu of the anticipated quinolone derivative 8. Furthermore, treatment of compound 1 with aromatic dibasic functional reagents afforded 11 and 13. Eventually, compound 11 was annelated through its reaction with ammonium carbonate to give pyrazolo[3,4-b]pyrido[6,5-b]benzodiazepin 12.     

Semantically predicting protein functions based on protein functional connectivity

BackgroundThe current availability of public protein–protein interaction (PPI) databases which are usually modelled as PPI networks has led to the rapid development of protein function prediction approaches. The existing network-based prediction approaches mainly focus on the topological similarities between immediately interacting proteins, neglecting the protein functional connectivity which is the functional tightness between proteins. In this paper, we attempt to predict the functions of unannotated proteins based on PPI networks by incorporating the protein functional connectivity, as well as the similarity of protein functions, into the prediction procedure.ResultsAn approach named Semantic protein function Prediction based on protein Functional Connectivity (SPFC) is proposed to achieve a higher accuracy in predicting functions of unannotated protein. We define the functional connectivity and function addition for each protein, and incorporate them into the prediction. We evaluated the SPFC on real PPI datasets and the experiment results show that the SPFC method is more effective in function prediction than other network-based approaches.ConclusionIncorporating the functional connectivity of each protein into the function prediction can significantly improve the accuracy of protein prediction.     

Convenient Synthesis of 2,4-Disubstituted Tetrahydrothiophenes from Mannich's Adducts

Ammonium salts of β-functionalized allylic amines 1 were successfully employed as electrophilic agents with functional thiols. The obtained intermediate 2 underwent intramolecular cyclization in the presence of potassium tert-butoxide to afford 2,4-disubstituted tetrahydrothiophenes 3.     

Kinetic Resolution of Piperazine-2-Carboxamide by Leucine Aminopeptidase. An Application in the Synthesis of the Nucleoside Transport Blocker (-) Draflazine

The resolution of N-t-Boc-piperazine carboxamide 5 proceeded smoothly in the presence of leucine aminopeptidase to produce acid (S)-1 and amide (R)-5 with good optical purity. Sequential alkylation and functional group manipulation of carboxamide (S)-5 provided the known nucleoside transport blocker draflazine (-) 2.     

C-Phosphorylation of Compounds with the Electron-Rich Double Carbon-Nitrogen Bond

Abstract

C-phosphorylation of N,N-dimethylhydrazones and N,N-dimethyl-N′-arylamidines by phosphorus tribromide was first accomplished. It directs to the formation of novel types of functional P(III) derivatives (1–3)     

Cholesterol-based simple supramolecular gelators: an approach to selective sensing of CN− ion with application in dye adsorption

Cholesterol-linked simple supramolecular gelators 1–3 with functional diversity have been designed on 4-hydroxybenzaldehyde backbone for anion sensing through gel-to-sol methodology. Change in functional group in the gelators of common structural feature has significant impact on gelation, gel properties, morphology and anion sensing behavior. The dicyanovinyl derivative 3 has been established as superior gelator among the three as it forms gel from varieties of solvents with lowest concentration. All the three gels are applied in anion recognition. The gel state of 1 remains virtually intact in presence of all the anions tested. The oxime derivative 2 interacts with basic anions like CN^?, F^? and AcO^? and displays no selectivity in gel phase anion sensing. On contrary, the dicyanovinylated analogue 3 shows gel-to-sol transition selectively in presence of CN^? and validates its visual sensing. Additionally, the gel of 3 as explored in dye adsorption works well in rapid removal of crystal violet, a cationic dye from waste water.     

Evaluation of <Superscript>13</Superscript>C NMR spectra of cyclopropenyl and cyclopropyl acetylenes by theoretical calculations

A convenient methodology was developed for a very accurate calculation of ¹³C NMR chemical shifts of the title compounds. GIAO calculations with density functional methods (B3LYP, B3PW91, PBE1PBE) and 6-311+G(2d,p) basis set predict experimental chemical shifts of 3-ethynylcyclopropene (1), 1-ethynylcyclopropane (2) and 1,1-diethynylcyclopropane (3) with high accuracy of 1–2 ppm. The present article describes in detail the effect of geometry choice, density functional method, basis set and effect of solvent on the accuracy of GIAO calculations of ¹³C NMR chemical shifts. In addition, the particular dependencies of ¹³C chemical shifts on the geometry of cyclopropane ring were investigated.     

The Alkylidenphthalan–1-Alkylisobenzofuran Equilibrium: A Computational Study

Semiempirical (AM1, PM3) and density functional theoretical studies (B3LYP/6-31G*) are reported for the tautomerism of 2-methylidene-2,5-dihydrofurans (3a–e) and the corresponding 2-methylfurans (4a–e) and of benzannulated derivatives (5a–e, 6a–e, 7–14).     

A CONVENIENT SYNTHESIS OF 3-BROMOFLAVONES

ABSTRACT

The reaction of flavones with 2,4,4,6-tetrabromo-2,5-cyclohexadienone(1) gave the corresponding 3-bromoflavones under the mild reaction condition. Flavones containing easily oxidizable functional groups were also brominated without deleterious oxidation products.     

Ultrasound-assisted one pot synthesis of polysubstituted meta-terphenyls using ring transformation strategy

An ultrasound-assisted rapid synthesis of meta-terphenyls 9 by the carbanion-induced ring transformation reaction of 6-aryl-5-methyl-2H-pyran-2-ones 7 with functionalized ketones 8 under basic conditions at room temperature has been delineated. The present method gives an easy access to functionally crowded m-terphenyls 9 with notable features including mild reaction condition, remarkable functional groups tolerance, shorter reaction time and high product yields.     

Synthesis,crystal structure,and BSA interaction with a new Co(II) complex based on 5-(trifluoromethyl)pyridine-2-carboxylic acid

Abstract

A new complex, Co(Htpc)₂(H₂O)₂ (1) (Htpc = 5-(trifluoromethyl)pyridine-2-carboxylic acid), has been synthesized and characterized by X-ray single-crystal diffraction, elemental analysis, infrared spectral analysis, and thermogravimetric analysis. Meanwhile, the optimized geometric structure of the ligand was determined using the M06-2X functional of density functional theory (DFT) with the 6-311?+?G(d, p) basis set. The gap energies ΔE between the frontier molecular orbitals were computed in different solvent media (water, methanol and ethanol) using the time dependent density functional theory (TD-DFT)/M06-2X by applying the Polarizable Continuum Model (PCM). The coordination sphere around Co(II) is distorted octahedral with two chelating tpc^- ligands and two coordinated water molecules. Bovine serum albumin (BSA) binding properties of the ligand, CoCl₂·6H₂O and 1 were investigated by fluorescence and UV–Vis absorption spectroscopy, revealing 1 exhibits higher binding affinity with BSA than free ligand and CoCl₂·6H₂O. ΔG, ΔH and ΔS at 298 and 308?K manifested that van der Waals interactions and hydrogen bonds were the main forces in the binding process.     

Reduction of silver cation in the cavity of diaza-18-crown-6: A theoretical study

The structure and stability of diaza-18-crown-6 (1) complex with silver cation was studied by the density functional method with the PBE functional. The reduction of the cation in the macrocycle cavity was simulated and possible stability of the resulting van der Waals complex of the crown ether 1 with silver atom was analyzed. It is shown that, after electron capture, two equilibrium conformers of Ag⁺·1 give two structures locally stable with respect to the dissociation into the silver atom and the crown ether in its nearest equilibrium conformation. One of the neutral structures, that of the C _s symmetry, corresponds to a global minimum on the potential energy surface of the Ag⁰—1 system. It ensures the thermodynamic stability of the reduced complex with respect to dissociation. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 395–399, March, 2007.     

Quantitative <Superscript>2</Superscript>H NMR spectroscopy

The selectivity of deuterium distribution between the nonequivalent positions in 3-carene (1), 4-α-acetyl-2-carene (2), and 4-(1-hydroxyethyl)-2-carene (3) has been measured by ²H-{¹H} NMR spectroscopy at the natural abundance of deuterium. These “H/D-isotope portraits” were shown to be typical of terpenes and terpenoids produced in plants via the biosynthetic DXP pathway. The mechanism of acylation of 1 was studied by the density functional theory method (PBE functional, TZ2p basis set). The six-membered ring in compound 1 is planar. However, the endo attack of electrophiles on this ring is more favorable both kinetically and thermodynamically. It was shown both experimentally and theoretically that the elimination of a hydrogen atom in the second reaction step proceeds stereoselectively at the C(2) atom from the anti position with respect to the three-membered ring and occurs with pronounced nucleophilic assistance from the carbonyl group. For Part 2, see Ref. 1. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1657–1664, August, 2008.     

Efficient Synthesis of New Nucleoside Analogues with a Methylenecyclobutane Unit

Synthesis of eight nucleoside analogues 4–11 with a methylenecyclobutane unit is described. Wittig reaction with 2‐hydroxymethylcyclobutanone 12 gave a mixture of Z (13) and E (14) derivatives, which was separated before functional modifications. The heterocyclic moieties were introduced via a Mitsunobu reaction either on the saturated chain or on the unsaturated chain. When adenine was used in this reaction, only the N‐9 substitution products were obtained. Removal of the protecting groups provided the target products.     

Theoretical design of a fluorescence sensor with configuration-transformed metal ion recognition of aza-18-crown-6

A novel configuration-transformed metal-ion-recognizing fluorescent molecular sensor was designed. The ground state geometries of the free ligand L(L₁, L₂)and their metal ion complex L/Mⁿ⁺ have been investigated theoretically by density functional theory (DFT). The interaction of L and a series of alkaline earth metal ions have been carried out by the natural bond orbital (NBO) and mayer bond order. The calculated results reveal that the metal ion Sr²⁺ has strong interaction with the free ligand L. The excited states, absorption spectra and fluorescence emission spectra of the free ligands L₁, L₂ and their complexes L/Mⁿ⁺ were performed by the time-density functional theory (TD-DFT). The UV-vis results show that the absorption peak of L₂/Sr²⁺ has an obvious change compared with that of L₂, which indicates that the free ligand L₂ can specifically identify the metal ion Sr²⁺. Furthermore, L₂/Sr²⁺ is superior fluorescent molecular sensor compared with other molecules.     

Microwave-Promoted Syntheses of Pyridine Carboxamides and tert-Carboximides from Novel 6-Acetylpyridine-2-carboxylic Acid

A novel 6-acetylpyridine-2-carboxylic acid (4) was obtained occasionally during the synthesis of asymmetric ethyl 6-acetylpyridine-2-carboxylate (3) from 2,6-dipiclinic acid (1). Compounds 3 and 4 could transform mutually under some specific conditions. Two reactions of distinctive types occurred when they reacted with the aromatic amines as precursors, due to different functional groups on the 2-position of pyridine in the molecules of 3 and 4: one was Schiff base condensation and the other was an amidation reaction. From the latter reaction, two series of new compounds, pyridine carboxamides (5a–d) and pyridine tert-carboximides (6a–h), resulted. The relevant reaction mechanism is discussed in detail.