Heteroatoms In Ring Research Articles

Specificity and Selectivity in Photoluminescent Properties of π-Conjugated Benzheterazole Molecules

Benzheterazole derivatives with ethylene and phenyl linkers have been studied as model compounds to understand the role of (i) aromatic and heteroaromatic rings on the photophysical properties, (ii) extended π-structure and the proximity of heteroatoms in the aromatic rings, and (iii) substitutional effect of benzheterazoles at the 1,2-position of the ethylene and 1,2- and 1,4-position of the phenyl linkers. In this study we highlight the crucial parameters that govern selective white light emission against the other spectral colors emitted by the benzheterazole derivatives. Distinguishably, benzothiazoles substituted at 1,2-positions in both ethylene and phenyl linkers show pronounced broad-band emission against several other molecules which show a dominant blue or green or red emission. The electroluminescent properties of the model molecules 1,2-bis(benzothiazolyl)ethylene (1,2-BBE—sample 1a) and 1,2-bis(benzothiazolyl)benzene (1,2-BBB—sample 2a), showing white light emission, are demonstrated. The device configuration involving sample 1a is ITO/PEDOT:PSS/PFO:1,2-BBE (100 nm)/Al(200 nm), which shows a white light emission with peak maxima at 525 nm, at an onset voltage of 8 V and fwhm ∼ 170 nm consisting of all the components of blue, green, and red emission. For sample 2a, the device configuration is ITO/PEDOT:PSS/NPB(40 nm)/1,2-BBB(60 nm)/BCP(8 nm)/LiF(0.6 nm)/Al(200 nm) with peak maxima at 505 nm and fwhm ∼ 150 nm at an onset voltage of 8 V.

Effect of the matrix on proton conductivity in electrolyte membranes containing deoxyribonucleic acids

Organic–inorganic hybrid electrolyte membranes were prepared with a sol–gel reaction of 3-glycidoxypropyltrimethoxysilane (GPTMS) and tetraethoxysilane (TEOS) in the presence of different amounts of deoxyribonucleic acid (DNA), and compared with DNA/poly(ethylene imine) (PEI) and DNA/poly(ethylene oxide) (PEO) blend membranes with the aim of understanding the matrix effect on the electrolyte membrane properties. DNA, comprising of phosphates along a rod-like polymer of heteroatomic rings, was used as a facilitate proton transport channel in electrolyte membranes under low humidity conditions and was dispersed inside of the inorganic matrix created with the TEOS/GPTMS solution, which produced an amorphous electrolyte membrane. The proton conductivity of the DNA/TEOS/GPTMS electrolyte membranes increased with DNA loading and temperature. The proton conductivity of 30 wt% of DNA in an amorphous inorganic matrix at 120 °C under an N 2 environment was measured at 4.9 × 10 −4 S/cm, which is an order of magnitude higher than that of DNA in a crystalline PEO matrix and is lower than that in a more basic PEI matrix. This result implies that the main requirements for high proton transport under low humidity are the homogeneity of the membrane along with the dissociation of the proton from its ionic sites in the matrix.

Geminal interaction and “anomeric effect”

Quantum-chemical calculations by the methods of RHF/6-31G(d) and MP2/6-31+G(d) show equal ratio of the lengths of axial and equatorial bonds and electron density on the atoms forming them in cyclohexane and its mono derivatives and in six-membered heterocyclic molecules as well. This feature is due to the interaction of atoms in the chair form of these molecules regardless of the presence in them of a heteroatom. Introducing heteroatom to a cyclohexane ring leads only to increase in the difference between axial and equatorial bonds. This equation excludes the possibility to ascribe the elongation of axial bonds and increase in the electron density on atoms forming them in the heterocyclic molecules to the p,σ*-conjugation of the lone electron pair of the ring heteroatom with the antibonding orbital of the axial bond. Features of molecular geometry defined by the mutual influence of atoms in them, including inductive and non-inductive interaction of geminal atoms in triatomic groups Y-Z-M, result in energetic preference of gauche conformations of these molecules and “anomeric effect” in them.

Characterization of deoxyribonucleic acid/poly(ethylene oxide) proton-conducting membranes

DNA, comprising phosphate ions along a rod-like polymer of heteroatomic rings, was used as the proton transport channel in polymer electrolyte membranes under conditions of high temperature and low humidity. Cast DNA/poly(ethylene oxide) (PEO) blend membranes containing different amounts of DNA were prepared and characterized. Two different molecular weights of PEO were used to provide mechanical strength. The proton conductivity of DNA/PEO membranes increased with the DNA loading and the temperature. The crystallinity of PEO decreased with increasing amounts of DNA, which would improve interaction between the basic oxygen of PEO and the acidic hydrogen of DNA. This would enhance the dissociation of hydrogen from DNA phosphate groups, resulting in increased proton conductivity. The DNA/PEO complexes were investigated in terms of their complexation energy using density functional theory and the effect of hydrogen dissociation from phosphate was studied.

Synthesis and Spectral Properties of Near-Infrared Aminophenyl-, Hydroxyphenyl-, and Phenyl-Substituted Heptamethine Cyanines

Diverse meso-aminophenyl-, hydroxyphenyl-, and phenyl-substituted heptamethine cyanine dyes were prepared by a modified Suzuki--Miyaura method in good yields. In addition, direct Suzuki coupling of Vilsmeier--Haack reagent extends the procedure to the synthesis of otherwise difficult cyanine dyes containing multiple heteroatoms in the indolium ring. The new compounds possess excellent spectral properties and can be used to label bioactive molecules and nanoparticles. The one-pot synthesis procedure eliminates the cumbersome steps of protecting/deprotecting amino or hydroxy groups.

The influence of exocyclic phosphorous substituents on the intrinsic stability of four-membered heterophosphetes: a theoretical study

Four-membered heterophosphetes such as oxaphosphetes, thiaphosphetes, and azaphosphetes have long been considered desirable target molecules for organic chemists because of their interesting structural features. In spite of extensive investigation, only one azaphosphete and one thiaphosphete have been synthesized to date. In this paper, two possible conformers of these four-membered rings, as well as their open-ring phosphorane forms with a set of exocyclic substituents and a few ring heteroatoms were studied by molecular computations. The results suggested that the relative stability of these compounds is strongly dependent on the electronic effect of the exocyclic P-substituents. Three different types of exocyclic substituents X were recognized. However, only the strong electron-withdrawing substituents (X=F, CN, OCN, SCN) were able to stabilize the ring forms, providing the possibility to design stable heterophosphetes on the basis of the present computational results.

Synthesis and glycosidase inhibitory activities of chain-modified analogues of the glycosidase inhibitors salacinol and blintol

The synthesis of chain-modified analogues of the naturally-occurring glycosidase inhibitor, salacinol, and its selenium analogue, blintol is described. The modification consists of a frame shift of the sulfate moiety by one carbon atom in the zwitterionic structures as well as an extension of the acyclic chain to five carbons. The target molecules were synthesized by alkylation of 1,4-anhydro-2,3,5-tri-O-p-methoxybenzyl-4-thio (or seleno)-d-arabinitol at the ring heteroatom by 2,3,5-tri-O-p-methoxybenzyl d- or l-xylitol-1,4-cyclic sulfate, followed by deprotection with trifluoroacetic acid. Two of the four compounds inhibit recombinant human maltase glucoamylase, one of the key intestinal enzymes involved in the breakdown of glucose oligosaccharides in the small intestine, with Ki values of 20±4 and 53±5μM.

Two-photon Absorption Properties of Heteroatomic Ring Molecules

The nonlinear optical properties of three benzothiazolyl-derivatives newly synthesized were calculated using few-state model and DFT method. The results showed that a red-shift of the maximum absorption took place when the delocalization of the ?仔 electrons in the organic molecules increases. When the conjugate chain had a longer size, the contribution of the increasing size of the conjugate chain on the increasing cross section was much more important than that of changing of electron drawing group. This kind of molecule had a better TPA (two-photon absorption) characteristic.

4-[(4-Ethoxyphenyl)aminoacetyl]-6,7-dimethyl-1,2,3,4-tetrahydroquinoxalin-2-one

All the inter­atomic distances in the title compound, C22H25N3O4, are normal. The heteroatom ring of the quinoxalinone system shows a half-chair conformation, slightly distorted towards a sofa. In the crystal structure, the mol­ecules dimerize via a pair of N—H⋯O hydrogen bonds. The dimers are linked by C—H⋯O and possible C—H—π inter­actions into a three-dimensional network.

4-(2-Benzylaminoacetyl)-1,2,3,4-tetrahydroquinoxalin-2-one

All inter­atomic distances of the title compound, C17H17N3O2, are normal. The phenyl ring of the benzyl­amino­methyl substituent is disordered over two positions. The heteroatom ring of the quinoxolinone system shows a half-chair conformation. The mol­ecules are held together by inter­molecular N—H⋯O hydrogen bonds resulting in a chain along the crystallographic c axis. The chains are linked via weak inter­molecular C—H⋯O and C—H⋯N hydrogen bonds into a three-dimensional hydrogen-bonded network.

Design of TTF-Based Phosphazenes Combining a Good Electron-Donor Capacity and Possible Inclusion Adduct Formation

The physical properties of porous material can be modulated by intercalation of small molecules, whose size, in the case of tris-o-phenylenedioxy)cyclotriphosphazene (TPP)-based materials, vary with the different side groups. Starting from the TPP structure, a series of new derivatives were constructed through the core ring [(NP)(3)] substitution by [(CNH)(3)], [(CO)(3)], and [(CS)(3)] or/and the side group substitution by tetrathiafulvalene and a series of related fragments including bis(ethylenedithio)tetrathiafulvalene, 2-methylene-1, 3-dithiole, and 2-methylene-5,6-dihydro[1,3]dithiolo[4,5-b][1,4]dithiine. In the side fragment, such a substitution corresponds to the replacement of a ring heteroatom, an addition of substituents, or both. With use of theoretical methodologies based on DFT-B3LYP/6-31G* and HF/6-31G*//B3LYP/6-31G* approaches, molecular geometries and electronic properties including the LUMO and HOMO energies, the HOMO-LUMO gap, as well as the ionization potential (IP) were calculated. In comparison with the commonly used organic superconductors, most of the molecules investigated were predicted to show comparable or better electron-donor strength. Interestingly, a number of cyclophosphazene [(NP)(3)]-containing compounds were predicted to show the "paddle wheel" shape responsible for inclusion adducts formation, making these compounds to be potential candidates for organic superconductors with the ease of modulating their conducting properties by intercalation of suitable acceptors.

A New Class of Glucosidase Inhibitor: Analogues of the Naturally Occurring Glucosidase Inhibitor Salacinol with Different Ring Heteroatom Substituents and Acyclic Chain Extension

Six chain-extended analogues of the naturally occurring glycosidase inhibitor salacinol, with ring-heteroatom variation, were synthesized for structure-activity studies with different glycosidase enzymes. The syntheses involved the reaction of PMB-protected D- and L- seleno-, thio-, and iminoarabinitol with a benzylidene- and isopropylidene-protected 1,3-cyclic sulfate, derived from commercially available D-sorbitol, in 1,1,1,3,3,3-hexafluoro-2-propanol containing potassium carbonate. Deprotection of the products afforded the novel selenonium, sulfonium, and iminium analogues of salacinol containing polyhydroxylated, monosulfated, extended acyclic chains of 6-carbons, differing in stereochemistry at the stereogenic centers and ring-heteroatom constitution. Four of these compounds inhibit recombinant human maltase glucoamylase, one of the key intestinal enzymes involved in the breakdown of glucose oligosaccharides in the small intestine, with Ki values in the micromolar range, thus providing lead candidates for the treatment of Type 2 diabetes.

Synthesis and Conformational Analysis of 2‘-Fluoro-5-methyl-4‘-thioarabinouridine (4‘S-FMAU)

An improved synthesis of 2'-deoxy-2'-fluoro-5-methyl-4'-thioarabinouridine (4'S-FMAU) is described. Participation of the 3'-O-benzoyl protecting group in the thiosugar precursor influenced the stereochemistry of the N-glycosylation reaction in nonpolar solvents, permitting a higher beta/alpha ratio than previously observed for similar Lewis acid catalyzed glycosylations. Conformational analysis of the nucleoside using 3JHH and 3JHF NMR coupling constants together with the PSEUROT program showed that it adopted a predominantly northern conformation in contrast to 2'-deoxy-2'-fluoro-5-methylarabinouridine (FMAU), whose PSEUROT conformational analysis is presented here for the first time, which showed a dominantly southeast conformation. The sharp conformational switch attained by replacing the ring heteroatom is attributed to a decrease in relevant steric and stereoelectronic effects.

Electron ionization mass spectra of phosphorus‐containing heterocycles. I. 1,4,4a,5,6,7,8,8a‐octahydro‐2H‐3,1,2‐benzoxazaphosphinine 2‐oxides

The electron ionization mass spectra of 27 cis- and trans-annelated 1,4,4a,5,6,7,8,8a-octahydro-2H-3,1,2-benzoxazaphosphinine 2-oxides were recorded to clarify the effects of the ring heteroatom (O or N), ring annelation, the P configuration and the substituents attached to the ring or to the N and P atoms. For compounds 1-12 different alkyl radical and alkene losses and the cleavage of the P-heteroatom bonds, instead of the P-C bonds, were representative and dependent mainly on the substitution on the N and P atoms. The replacement of Ph and OPh by N(CH2CH2Cl)2 on the P atom had a dramatic influence on the fragmentation process: new fragment ions were obtained and very little M+ (1-3%) was formed. Only slight differences were found between some of the corresponding isomers, but interestingly the compounds formed clear groups on the basis of the differences in their fragmentation, depending on the ring-N and ring-P substituents.

A Mild Pummerer-Like Reaction of Carbohydrate-Based Selenoethers and Thioethers Involving Linear Ozonide Acetates as Putative Intermediates

Pummerer-like rearrangements of carbohydrate-based heterocycles containing selenium and sulfur were investigated. To the best of our knowledge, this is the first report on the Pummerer rearrangement in selenoheterocycles. Ozonization of 1,4-anhydro-D-galactitol or 1,5-anhydroxylitol derivatives containing sulfur or selenium as the ring heteroatom gave unstable intermediates that were attributed to ozonides. These intermediates decomposed upon warming to give selenoxides or sulfoxides. Significantly, addition of acetic anhydride at low temperature to the ozonization reaction mixtures gave Pummerer-rearrangement products after warming to ambient temperature. However, when the isolated selenoxides or sulfoxides were treated with acetic anhydride, Pummerer rearrangement occurred but the sulfoxides required much higher reaction temperatures. The latter results are at variance with the former and are interpreted in terms of the rearrangement of the ozonide acetate intermediates in the former cases. To probe whether the rearrangement proceeded heterolytically via extrusion of singlet oxygen or homolytically via the generation of radical species, trapping experiments with rubrene and electron paramagnetic resonance (EPR) studies with the radical trap DMPO were performed. The results of these experiments are consistent with the intermediacy of radical species and suggest a new and milder synthetic method to generate Pummerer-type products.

Synthesis and Biological Activity of Prostaglandin Analogs Containing Heteroatoms in the Cyclopentane Ring

Synthesis and Biological Activity of Prostaglandin Analogs Containing Heteroatoms in the Cyclopentane Ring

Convenient methods for the synthesis of d4, d2 and d6 isotopomers of 4-(4-fluorobenzyl)piperidine

Pure 4-(4-fluoro-[2,3,5,6-2H4]benzyl)piperidine was prepared via the Grignard reaction of 4-fluoro-[2,3,5,6-2H4]bromobenzene and pyridine-4-aldehyde followed by consecutive deoxygenation and heteroatomic ring saturation in the presence of palladium on carbon catalyst. An improved method for the catalytic H/D exchange in benzylic positions of 4-(4-fluorobenzyl)piperidine and its d4 derivative has also been described. Copyright © 2005 John Wiley & Sons, Ltd.

Syntheses and properties of mixed dinuclear copper(II) complexes with heterocyclic dithiocarbamates and a cyclic octadentate tertiary amine

Five new CuII complexes of general formula [Cu2(Rdtc)tpmc](ClO4)3, (1)–(5), where tpmc and Rdtc− refer to N,N′,N′′,N′′′-tetrakis(2-pyridylmethyl)-1,4,8,11-teraazacyclotetradecane and piperidine- (Pipdtc), 4-morpholine- (Morphdtc), 4-thiomorpholine- (Timdtc), piperazine- (Pzdtc) or N-methylpiperazine- (N-Mepzdtc) dithiocarbamates, respectively, have been prepared. Elemental analyses, conductometric and magnetic measurements, u.v./vis, i.r., e.p.r. and mass spectroscopy have been employed to characterize them. The complexes adopt an exo coordination of CuII ions and tpmc. The dithiocarbamate ion joins both the sulphur and the copper atoms acting as a bridging ligand The presence of different heteroatoms in the piperidine ring influences the ν(C=N) and ν(C=S) vibrations which decrease in the order of the complexes: Pipdtc > N-Mepipdtc > Pzdtc > Morphdtc > Timdtc ligands. Attention has been paid to the detailed mechanism of the mass spectral fragmentation of the complexes. The geff factors of the complexes have been also estimated by e.p.r. spectra. Finally, the complexes obtained demonstrate microbiologycal activity against some bacteria.

Assessment of the metabolic stability of the methyl groups in heterocyclic compounds using CH bond dissociation energies: Effects of diverse aromatic groups on the stability of methyl radicals

AbstractThe CH bond dissociation energies (BDEs) of the methyl groups attached to a large number of heterocyclic compounds are calculated using a carefully calibrated B3LYP method. These CH bond dissociation energies are important for evaluating the metabolic stability of the methyl groups in heterocyclic compounds that may be used as drug candidates. It is found that the CH BDEs of the methyl groups attached to diverse heterocycles can dramatically vary from ca 80 to ca 100 kcal mol−1 (1 kcal = 4.184 kJ). Therefore, the benzylic positions of different heterocycles may have remarkably different metabolic stabilities varying by ∼1012‐fold. The heteroatoms in the aromatic rings vary the benzylic BDEs either by delocalizing the spin or by changing the charge carried by the radical center. N‐Methyl groups have systematically higher CH BDEs than C‐methyl groups. NH, O and S groups have similar effects on the benzylic CH BDEs. A methyl group at the α‐position relative to the NH, O and S groups usually has a lower BDE than that at the β‐position. On the other hand, the N group has a different effect on the benzylic CH BDEs. A methyl group at the β‐position relative to N has a lower CH BDE than that at the α‐position. There is a special aromatization effect associated with 1‐methyl‐2H‐isoindole, 1‐methylisobenzofuran, 1‐methylbenzo[c]thiophene and related compounds. This aromatization effect dramatically decreases the benzylic CH BDEs. Finally, an interesting QSAR model has been developed. This model not only can successfully predict the benzylic CH BDEs of diverse heterocyclic compounds, but also can clearly and quantitatively reveal the mechanisms for the variation of the CH BDEs. Copyright © 2004 John Wiley & Sons, Ltd.

Studies of Novel Heterocyclic Insensitive High Explosive Compounds: Pyridines, Pyrimidines, Pyrazines and Their Bicyclic Analogues

AbstractThe rationale behind using heterocyclic compounds [1], particularly nitrogen heterocycles, as higher energy insensitive high explosives is discussed, including the potential advantages compared with carbocyclic compounds. The types of functional groups used to impart energy to heterocyclic nuclei, whilst maintaining insensitivity, and methodologies for their introduction, are covered. The latter include nitration (by conventional and clean synthetic methods), amination, and oxidation (on ring heteroatoms and of exocyclic amino groups). Strategies for maximising the energetic content of a given heterocyclic nucleus are also examined. The syntheses of specific examples at QinetiQ are described, based on the following nuclei: pyridine, pyrimidine, pyrazine, quinoxaline, quinazoline, pteridine and purine. Strategies for obtaining the desired amino‐nitro derivatives and their heterocyclic N‐oxides are outlined. Optimisation of the synthetic routes for several candidates is discussed. The physical, explosive and thermal properties of the more successful candidates are described, with suggestions for their potential application in military stores.