Single-electron oxidation and nucleophilicity of aminomethylated calix[4]resorcinarenes

The electrochemical oxidation of a number of aminomethylated calix[4]resorcinarenes (AMC) with different substituents at the nitrogen atom and the kinetics of nucleophilic substitution reactions of these compounds with p-nitrophenyl bis(chloromethyl)phosphinate were studied. The reactivity of the ionic associates of AMC in the nucleophilic substitution and the behavior of AMC in electrooxidation are determined by the same factors, namely, the amino-group basicity and the nature of the substituents at the nitrogen atom. These factors influence the ratio of the zwitter-ionic and anionic forms of AMC.     

Protolytic properties and reactivity of aminomethylated calix[4]resorcarenes in reactions with esters of phosphorus acids

The acid-base properties and the kinetics of reactions of aminomethylated calix[4]resorcarenes (AMC) withp-nitrophenyl esters of phosphorus acids in aqueous solutions of propan-2-ol (80 vol.% PrⁱOH) were studied by potentiometry, UV spectrophotometry, and³¹P NMR spectroscopy. The effect of the length of the hydrocarbon radical and substituents at the nitrogen atom on the protolytic properties and reactivity of AMC was studied. The reactions studied occur in two stages. At the first stage, phosphorylated AMC are formed, which are hydrolyzed to the corresponding acids at the second stage. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 456–461, March, 1999.     

Oxidation of 2-dialkylaminomethyl-4,6-di-tert-butylphenols

Oxidative transformations of 2-dialkylaminomethyl-4,6-di-tert-butylphenols depend on the nature of the oxidant, the character of the substituents at the nitrogen atom, and the medium. A mechanism of the oxidation of these compounds is suggested. The molecular structure of the compound obtained as a result of oxidative trimerization of 2-dimethylaminomethyl-4,6-di-tert-butylphenol was established by X-ray structural analysis. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1328–1335, July, 1997.     

Photochromic dihetarylethenes. 19. Synthesis of 1,2-dihetarylethenes on the basis of thieno[3,2-b]pyrroles linked by a maleimide bridge

New photochromic 1,2-dihetarylethenes containing maleimide-bridged thieno[3,2-b]pyrrole fragments with aliphatic and aromatic substituents at the nitrogen atom were synthesized.     

Synthesis and kinetic investigation of the selective acidolysis of para-substituted N-benzyl- or N-phenyl-N-phenylacetyl-α,α-dialkylglycine cyclohexylamides

Several derivatives of N-phenylacetyl-N-benzyl-α,α-dimethylglycine cyclohexylamide and their α,α-dibenzylglycine analogues were synthesised by a Ugi-Passerini reaction. In addition, a few analogues of the former but having an N-phenyl instead of a benzyl group at the nitrogen atom were synthesised. The compounds in each of these three sets differed from each other at position 4 of the N-benzyl (and N-phenyl) group. These adducts were submitted to acidolysis with TFA to obtain the corresponding free acids, the reactions being monitored by HPLC and data collected for kinetic purposes. The kinetic data were submitted to Hammett uni- and biparametric relationships and the results were analysed in terms of structure-reactivity in connection with the sensitivity of the reaction rates to the electronic contributions of the various substituents at position 4 of the aromatic rings. The results allowed comparison with information obtained in previous investigations and rationalise the contribution of the substituent at the nitrogen atom to the lability of the C-terminal amide bond.     

Molecular Polarizability of Organic Compounds and Their Complexes: XLVII. Conformations of Some 2,4,6-Triarylpyridines, 2-Aryl-4-phenyl-6-tert-butylpyridines,and the Corresponding Pyridinium Cations in Solutions,as Determined from the Cotton-Mouton Effect

The conformations of some 2,4,6-triarylpyridines, 2-aryl-4-phenyl-6-tert-butylpyridines, and the corresponding pyridinium cations in dioxane and acetonitrile solutions were determined from the Cotton-Mouton effect. These systems are nonplanar; the angles by which the aryl substituents at positions 2 and 6 of the heteroring are turned relative to the heteroring plane are close to those observed in biphenyl and its p-substituted derivatives; these angles depend on substituents in the rings and, in the case of cations, at the pyridinium nitrogen atom.     

New strategies for the synthesis of N-alkylated indoles (Review)

New data, mostly published in the last five years, on methods for the synthesis of N-alkylated indoles both as a result of direct introduction of the alkyl substituent at the nitrogen atom and by construction of the indole heterocyclic system are reviewed. Only examples of indole derivatives containing branched, sterically hindered, and chiral alkyl substituents at the nitrogen atom are discussed.     

Me‐BIPAM for the Synthesis of Optically Active 3‐Aryl‐3‐hydroxy‐2‐oxindoles by Ruthenium‐catalyzed Addition of Arylboronic Acids to Isatins

A chiral O‐linked C₂‐symmetric bidentate phosphoramidite (Me‐BIPAM) was found to be efficient for the ruthenium‐catalyzed addition of arylboronic acids to isatins. Asymmetric synthesis of 3‐aryl‐3‐hydroxy‐2‐oxindoles by 1,2‐addition of arylboronic acids to isatins was carried out in the presence of [RuCl₂(PPh₃)₃]/(R,R)‐Me‐BIPAM and KF, resulting in an enantioselectivity as high as 90 % ee. It was found that the reaction with N‐protected isatins proceeds with high yields and good enantioselectivities. The best protective groups on the nitrogen atom were different depending on the substituents on the aromatic ring. The use of a N‐benzyl group resulted in excellent enantioselectivities in many substrates compared with other groups.     

Highly Efficient Cyclic Dinucleotide Based Artificial Metalloribozymes for Enantioselective Friedel–Crafts Reactions in Water

The diverse secondary structures of nucleic acids are emerging as attractive chiral scaffolds to construct artificial metalloenzymes (ArMs) for enantioselective catalysis. DNA‐based ArMs containing duplex and G‐quadruplex scaffolds have been widely investigated, yet RNA‐based ArMs are scarce. Here we report that a cyclic dinucleotide of c‐di‐AMP and Cu²⁺ ions assemble into an artificial metalloribozyme (c‐di‐AMP?Cu²⁺) that enables catalysis of enantioselective Friedel–Crafts reactions in aqueous media with high reactivity and excellent enantioselectivity of up to 97 % ee. The assembly of c‐di‐AMP?Cu²⁺ gives rise to a 20‐fold rate acceleration compared to Cu²⁺ ions. Based on various biophysical techniques and density function theory (DFT) calculations, a fine coordination structure of c‐di‐AMP?Cu²⁺ metalloribozyme is suggested in which two c‐di‐AMP form a dimer scaffold and the Cu²⁺ ion is located in the center of an adenine‐adenine plane through binding to two N7 nitrogen atoms and one phosphate oxygen atom.     

N-丙烯酰吗啉在可聚合叔胺-过硫酸钾水溶性引发体系引发下的水溶液聚合

本文报道了以甲基丙烯酸－N，N－甲氨基乙酯（DMAEMA）与过硫酸盐体系以引发的丙烯酰吗啉（AMP）的水溶液聚合，得到下列方程：Rp［K2S2O8］0．46［DMAEMA］0．49［AMP］1．09；Ea＝30．21KJ／mol。试用四氯乙烯（TCNE）处理的丙烯酸吗啉聚合物P（AMP）的紫外光谱分析，发现DMAEMA不仅参与引发AMP聚合，而且还进入P（AMP）分子链中。P（AMP）分子量比聚丙烯酰腹P（AAm）的小，而且随AMP（DMAEMA或温度）增加而增加（降低）。P（AMP）及其轻度交联的水凝胶表现出热敏性。     

Reactions of N- and C-Alkenylanilines: II. Halocyclization of 2-(2-Cycloalkenyl)anilines

The reaction of 2-(2-cyclopentenyl)anilines with I₂ in the presence of NaHCO₃ results in formation of 3-iodocyclopenta[b]indoles in high yields. Under similar conditions 2-(2-cyclohexenyl)anilines give rise to cyclization products whose structure depends on the solvent and substituents in the aromatic ring and on the nitrogen atom.     

The mutual influence of the imine substituents of terephthal-bis-imines concerning their reactivity towards Fe2(CO)9

The reaction of terephthal-bis-imines with Fe₂(CO)₉ proceeds via a C---H activation reaction in the ortho position with respect to one of the imine functions. The corresponding hydrogen atom is shifted towards the former imine carbon atom producing a methylene group instead. The dinuclear iron complexes formed by this reaction sequence and showing no coordination of the second imine group were isolated from reactions of bis-imines with both phenyl and cyclohexyl substituents at the imine nitrogen atoms. In addition, we observed three different reaction pathways of the second imine substituent of the starting material which is obviously thus influenced by the fact that the first one is coordinating an Fe₂(CO)₆ moiety. If the organic substituent at the imine nitrogen atoms is a phenyl group the formation of a trinuclear complex is achieved in which an additional Fe(CO)₃ group is coordinating the CN double bond and one of the carbon---carbon bonds of the central phenyl ring in an η⁴-fashion. The same reaction leads to the isolation of a tetranuclear iron---carbonyl compound in which both imine substituents were transformed via the pathway described above, each building up dinuclear subunits. In contrast to this the reaction of a bis-imine with cyclohexyl groups at the imine nitrogen and thus an enhanced nucleophilicity leads to the formation of a tetranuclear complex in which only one imine group reacts under C---H activation with subsequent hydrogen migration towards the former imine carbon atom. The second imine substituent also shows a C---H activation reaction in the ortho position with respect to the imine group but the corresponding hydrogen atom is transferred to one of the aromatic carbon atom of the central phenyl ring of the ligand. The C=N double bond remains unreacted and only coordinates the second Fe₂(CO)₆ moiety via the nitrogen lone pair.     

Reaction of 2-aminobenzoxazoles with compounds with activated multiple bonds

The reaction of 2-aminobenzoxazoles with activated alkenes of the acrylic acid type and its derivatives and methyl vinyl ketone proceeds in the presence of basic catalysts to give products of mono- and diaddition at the exocyclic nitrogen atom. The reaction of 5(6)-substituted 2-aminobenzoxazoles with esters of propyl and acetylenedicarboxylic acids in the absence of catalysts leads to the production of condensed 2-oxopyrimidines. The effect of substituents and the reaction conditions on the course of the process was investigated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1467–1471, November, 1984.     

The influence of structural changes of the N‐substituent on liquid crystalline behaviour of ester imides

Several new ester imide derivatives with different N‐substituents in the imide ring were synthesized and their mesogenic properties investigated by thermal analysis, optical microscopy and X‐ray diffraction. All the esters of N‐4‐[(4′‐decyloxybiphenyl‐4‐yl)oxycarbonyl]phthalimideacetic acid and aliphatic alcohols exhibited monolayer SmA and SmC phases. In addition, for the ethyl and propyl esters a monotropic hexatic (F or I) phase was observed. The introduction of additional substituents at the carbon atom in the methylenemethoxycarbonyl group (in the vicinity of the nitrogen atom) substantially influenced liquid crystalline properties: the compounds with a flexible chain exhibited monotropic SmA–SmB dimorphism, but liquid crystalline properties vanished for the substituent containing the more rigid phenyl ring.     

Protonenresonanzuntersuchungen an Aminoboranen—II: Einflüsse von para-Phenylsubstituenten auf die Rotationsbarriere um die N?B-Bindung

The electronic influence of substituents on the free enthalpy of rotation around the N? B bond in aminoboranes was investigated in two series of compounds: (a) (CH₃)₂N?BCl (phenyl-p-X), containing the para-phenyl substituent at the boron atom, and (b) (p-X-phenyl)CH₃N?B(CH₃)₂, containing the para-phenyl substituent at the nitrogen atom of the N? B linkage (X = ? NR₂, ? OCH₃, ? C(CH₃)₃, ? Si(CH₃)₃, ? H, ? F, ? Cl, ? Br, ? I, ? CF₃ and ? NO₂). By comparing the rotational barriers in corresponding compounds of both series, a reverse effect of the substituents could be observed. Electron-withdrawing substituents in the para position of the phenyl ring increase the ΔG_c^≠ if the phenyl group is attached to the boron atom; on the other hand, a lower ΔG_c^≠ is observed if the phenyl ring is bonded to the nitrogen atom of the N? B system. Substitution of the phenyl ring with electron-donating substituents in the paraposition exerts the opposite effect. Within each series of compounds, the differences of ΔG_c^≠ values [δ(ΔG_c^≠) = ΔG_c^≠ (X) ? ΔG_c^≠ (X = H)] between substituted and unsubstituted compounds can be explained in terms of inductive and mesomeric effects of the ring substituents and can be correlated with the Hammett σ constant of each substituent. A comparison of the slopes of the plotted lines shows that the influence of the ring substituents is more pronounced in compounds with N-phenyl-p-X than in those with B-phenyl-p-X.     

Spectroscopic studies of interactions in poly(N‐acryloyl‐N′‐methylpiperazine)/acidic polymer complexes

Poly(N‐acryloyl‐N′‐methylpiperazine) (PAMP) forms complexes with four strong acidic polymers, namely, poly(styrenesulfonic acid), poly(vinylphosphonic acid), poly(acrylic acid) and poly(methacrylic acid) in ethanol/water (1:1) solution. The nature of interpolymer interactions in various complexes was studied by Fourier transform infrared (FTIR) spectroscopy and X‐ray photoelectron spectroscopy (XPS). Both the carbonyl oxygen and the amide nitrogen of PAMP are involved in hydrogen‐bonding interactions. Some of the amine nitrogens of PAMP are protonated and therefore PAMP also interacts with the acidic polymers through ionic interactions. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 501–508, 2000     

Application of the addition of triorganozincates to N-(tert-butanesulfinyl)imines to the enantioselective synthesis of α-amino acids

Highly enantiomerically enriched N-protected α-amino acids can be easily prepared from optically pure N-(tert-butanesulfinyl)imines by a four-step sequence involving: diastereoselective addition of a triorganozincate to the imine, removal of the sulfinyl group, benzoylation of the nitrogen atom of the obtained primary amine and oxidation of one of the substituents on the carbon atom α to the nitrogen. Using the same configuration in the sulfinyl chiral auxiliary, amino acids with the (R) or the (S) configuration can be prepared by choosing the proper combination of imine and organozincate. α,α-Disubstituted α-amino esters with high optical purity can also be prepared by the diastereoselective addition of trialkylzincates to α-imino esters.     

Nickel complexes with cyclic ligands containing P and N atoms as coordination sites: novel biomimetic catalysts for hydrogen oxidation

Nickel complexes with new cyclic ligands containing phosphorus and nitrogen atoms as coordination sites are novel efficient catalysts for hydrogen oxidation. A systematic study of their electrochemical properties made it possible to classify the nickel systems in question into four groups according to the sequence of electron transfer processes in the reduction (M^II-M^I-M⁰) and to the nature of solvents and counterions. Regularities of catalytic transformations involving nickel complexes with P,N-cyclic ligands in the H₂ oxidation reaction in the coordination sphere of the catalyst and a correlation between the structure of the complex and its redox properties were established. The most efficient catalysts contain phenyl and 2-pyridyl substituents at the phosphorus atom and benzyl or 2-pyridyl substituents at the nitrogen atom.     

Asymmetric synthesis of α- and β-amino acids by diastereoselective addition of triorganozincates to N-(tert-butanesulfinyl)imines

The diastereoselective addition of triorganozincates to (R)-N-(tert-butanesulfinyl)imines has been used as a key step to achieve the synthesis of highly enantiomerically enriched N-protected α- and β-amino acids. Desulfinylation of the addition products followed by benzoylation of the nitrogen atom of the obtained primary amines and oxidation of one of the substituents on the carbon atom connected to the nitrogen complete the sequence. Using the same configuration in the sulfinyl chiral auxiliary, α-amino acids with the (R) or the (S) configuration can be prepared by choosing the proper combination of imine and organozincate. α,α-Disubstituted α-amino esters with high enantiomeric purity can also be prepared when α-imino esters are the starting substrates.     

Structure–Activity Studies on the Fluorescent Indicator in a Displacement Assay for the Screening of Small Molecules Binding to RNA

A series of xanthone and thioxanthone derivatives with aminoalkoxy substituents were synthesized as fluorescent indicators for a displacement assay in the study of small‐molecule–RNA interactions. The RNA‐binding properties of these molecules were investigated in terms of the improved binding selectivity to the loop region in the RNA secondary structure relative to 2,7‐bis(2‐aminoethoxy)xanthone (X2S) by fluorimetric titration and displacement assay. An 11‐mer double‐stranded RNA and a hairpin RNA mimicking the stem loop IIB of Rev response element (RRE) RNA of HIV‐1 mRNA were used. The X2S derivatives with longer aminoalkyl substituents showed a higher affinity to the double‐stranded RNA than the parent molecule. Introduction of a methyl group on the aminoethoxy moiety of X2S effectively modulated the selectivity to the RNA secondary structure. Methyl group substitution at the C1′ position suppressed the binding to the loop regions. Substitution with two methyl groups on the amino nitrogen atom resulted in reducing the affinity to the double‐stranded region by a factor of 40 %. The effect of methyl substitution on the amino nitrogen atom was also observed for a thioxanthone derivative. Titration experiments, however, suggested that thioxanthone derivatives showed a more prominent tendency of multiple binding to RNA than xanthone derivatives. The selectivity index calculated from the affinity to the double‐stranded and loop regions suggested that the N,N‐dimethyl derivative of X2S would be suitable for the screening of small molecules binding to RRE.