Alkyl Substituents (alkyl + substituent)

Distribution by Scientific Domains
Distribution within Chemistry

Selected Abstracts

A Novel Synthetic Approach to Benzo[d]isothiazole 1,1-Diones Having a Secondary Alkyl Substituent at the 3-Position.

CHEMINFORM, Issue 30 2004
Zhaopeng Liu
Abstract For Abstract see ChemInform Abstract in Full Text. [source]

ChemInform Abstract: Reactions of Acetylenes, Possessing Bulky Alkyl Substituents, with S2Cl2.

CHEMINFORM, Issue 4 2001
-Oxothioketones, 2-Dithietes., Thiirene 1-Oxides, Unexpected Formation of
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

Synthesis and Dynamic Features of (Chloro)zirconocene Cations Stabilised by Pendant (Diarylphosphanyl)alkyl and (Dimethylamino)alkyl Substituents at Their Cyclopentadienyl Ring Systems

Steve Dring
Abstract Treatment of the substituted (diarylphosphanyl)methyl group-4 metallocene complexes [(C5H4,CR1R2,PAr2)2ZrCl2] (2: R1/R2 = CH3/CH3, H/CH3, H/aryl) with Li[B(C6F5)4] in dichloromethane solution results in chloride ligand abstraction (with LiCl precipitation) to yield the complexes [(C5H4,CR1R2,PAr2)2Zr,Cl+] (5), with both phosphanyl groups internally coordinated to the metal centre. Three possible diastereoisomers are observed in the case of 5c (R1 = H; R2 = CH3), while bulkier R2 substituents give higher selectivities. The thermally induced (reversible) cleavage of the Zr,phosphane linkage results in dynamic NMR behaviour. Gibbs activation energies of ,G,(298 K) = 14.8 0.5 and 14.5 0.5 kcal/mol were obtained for these intramolecular equilibration processes in the complexes trans - 5d (R1 = H; R2 = Ph) and trans - 5e (R1 = H; R2 = ferrocenyl), respectively. Treatment of the substituted (dimethylamino)methyl metallocene complexes [(C5H4,CR1R2,NMe2)2ZrCl2] (6a, 6b) with Li[B(C6F5)4] proceeds analogously to yield the cation systems [{C5H4,C(CH3)2,NMe2}2ZrCl+] (12a) and [{C5H4,CH(CH3),NMe2}2ZrCl+] (12b, three possible diastereoisomers). Both complexes have their pairs of amino groups coordinated to the metal centre. The complexes exhibit dynamic NMR spectra. Selective equilibration of the diastereotopic N(CH3)A(CH3)B resonances of complex 12a is observed [,G,(233 K) = 11.5 0.2 kcal/mol], whereas the adjacent C(CH3)A(CH3)B methyl groups remain diastereotopic. The dynamic equilibration of the latter was observed at a markedly higher temperature [,G,(333 K) = 17.3 0.2 kcal/mol]. Treatment of [{C5H4,C(CH3)2,NMe2}CpZrCl2] (10) with Li[B(C6F5)4] resulted in the formation of complex [{C5H4,C(CH3)2,NMe2}CpZr,Cl+] (11), which shows the internal ,N(CH3)A(CH)B equilibration proceeding with a markedly higher activation barrier [,G,(333 K) = 17.6 0.2 kcal/mol] than in 12a, and a stereochemical memory effect indicative of solvent coordination to the metal centre of the resulting highly electrophilic chlorozirconocene cation intermediate. Complex 11 was characterised by an X-ray crystal structure analysis, which shows the internal Zr,amine coordination. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

Synthesis of Chiral Imidazole Derivatives as Purine Precursors

Jerzy Suwi
Abstract From commercially available chiral building blocks, we have developed methods for the syntheses of imidazole derivatives that contain a chiral alkyl substituent at ring atom. These compounds are suitable for further transformation into Nalkyl purine derivatives. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

Structure,Activity Relationship in the Domain of Odorants Having Marine Notes

Jean-Marc Gaudin
Abstract We synthesized or re-synthesized a large series of 2H -1,5-benzodioxepin-3(4H)-ones 9 (Scheme,1), 4,5-dihydro-1-benzoxepin-3(2H)-ones 10 (Schemes 3 and 4) and 5,6,8,9-tetrahydro-7H -benzocyclohepten-7-ones 11 (Schemes 5 and 6), since the lead compound for the olfactory note of perfumes based on marine accords is a well-known benzodioxepinone named Calone 1951 (9b). We meticulously described the odor profile of each synthesized compound and discussed relevant structure,odor relationships (Tables,1,3). In particular, we revealed a correlation between the conformation of the seven-membered ring and the activities of these compounds (Table,4 and Fig.,3). We also clarified the effect of the position and the size of the alkyl substituent at the aromatic ring. [source]

Enders' SAMP-Hydrazone as Traceless Auxiliary in the Asymmetric 1,4-Addition of Cuprates to Enones

Karsten Sammet
Abstract Conjugate additions of Gilman cyanocuprates to (S)- N -amino-2-(methoxymethyl)pyrrolidine (SAMP)-hydrazones 4, 5 derived from cyclic and acyclic ,,,-unsaturated ketones were investigated. A protocol utilizing copper(II) sulfate/ammonium chloride was evolved, which allowed cleavage of SAMP (S)- 1 under the hydrolysis and work-up conditions, followed by recovery of the auxiliary with ethylenediaminetetraacetic acid (EDTA). The enantioselectivity of cuprate additions was dominated for cyclic SAMP-hydrazones 4 by the cuprate alkyl substituent and the ring size, in the case of acyclic arylidene SAMP-hydrazones 5, however, by the nature of the aryl substituent. Electron-donating substituents gave poor enantiomeric excesses, whereas electron-withdrawing groups provided excellent ee values of 98,99%. The configuration of the new stereocenter was determined to be (R). Moreover, a reaction sequence was developed which integrates a tandem 1,4-addition/methylation and traceless hydrolytic cleavage of the auxiliary (S)- 1 in a one-pot reaction, resulting in enantiomerically pure methyl ketones 11,13, each of them with>99% ee. [source]

Fluorene-based liquid crystalline networks with linearly polarized blue emission

Marta Millaruelo
Abstract A series of fluorene-based luminophores containing methacrylic end groups have been prepared and incorporated into uniaxially oriented liquid crystalline films by in situ photopolymerization. Various structural modifications on the 2-(4-cyanophenyl)fluorene core, which include alkyl chains at the 9-position and elongation of the rigid core with one additional phenyl ring, have been investigated to generate emitters with adjusted liquid crystal compatibility, improved luminescence and dichroic properties. Polarized blue-emitting films were produced that had an acceptable photostability, and it was found that the polarization emission was better for samples with low (5%) cross-linker contents. Polarization of the luminescence was favored by the liquid crystalline properties of the luminophore. In addition, the detrimental effect of the alkyl substituent at the fluorene core on the mesomorphism and on the emission polarization can be overcome by lengthening the ,-system. 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4804,4817, 2007 [source]

Synthesis and characterization of alkylated N -vinylformamide monomers and their polymers

Lianjun Shi
Abstract N -alkyl- N -vinylformamide monomers (alkyl: n -butyl, hexyl, decyl, and dodecyl) are synthesized in two steps: first, preparation of N -vinylformamide potassium salt by the reaction of N -vinylformamide (NVF) with potassium t -butoxide, then reaction with alkyl bromide. All four monomers are liquid and are characterized by IR, 1H NMR, 13C NMR, and mass spectra. They exist as rotomers in solution and a 2D NOE experiment on the N -hexyl containing polymer shows the E isomer to be favored. The polymerizability of the four monomers is from good to fair, depending upon the length of alkyl chain on the N -atom--the longer the chain length, the lower lower the polymerizability of monomer. The hydrolysis of poly(N -hexyl- N -vinylformamide) and poly(N -dodecyl- N -vinylformamide) under acidic and basic conditions was examined. Studies show that hydrolytic cleavage of formyl groups of poly (N -alkylated- N -vinylformamide) depends on the hydrophobicity of the alkyl substituent on the N -atom under acidic conditions; both polymers were hydrolyzed to only a minor extent under alkaline conditions. The N -alkylated monomers can copolymerize with NVF and demonstrate amphiphilic properties. The copolymers demonstrate a critical aggregation concentration above which they can solubilize a water insoluble dye; the N -hexyl containing copolymer stabilizes a castor oil-in-water emulsion. 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4994,5004, 2004 [source]

Antibacterial and Hemolytic Activities of Quaternary Pyridinium Functionalized Polynorbornenes

Tarik Eren
Abstract In this study, amphiphilic polyoxanorbornene with different quaternary alkyl pyridinium side chains were synthesized. The biological efficiencies of these polymers, with various alkyl substituents, were determined by bacterial growth inhibition assays and hemolytic activity (HC50) against human red blood cells (RBCs) to provide selectivity of these polymers for bacterial over mammalian cells. A series of polymers with different alkyl substituents (ethyl, butyl, hexyl, octyl, decyl and phenylethyl) and two different molecular weights (3 and 10 kDa) were prepared. The impact of alkyl chain length divided the biological activity into two different cases: those with an alkyl substituent containing four or fewer carbons had a minimum inhibitory concentration (MIC) of 200 g,,mL,1 and a HC50 greater than 1,650 g,,mL,1, while those with six or more carbons had lower MICs,,,12.5 g,,mL,1 and HC50,,,250 g,,mL,1. Using MSI-78, the potent Magainin derivative which has an MIC,=,12.0 g,,mL,1 and HC50,=,120 g,,mL,1, as a comparison, the polymers with alkyl substituents ,C4 (four carbons) were not very potent, but did show selectivity values greater than or equal to MSI-78. In contrast, those with alkyl substituents ,C6 were as potent, or more potent, than MSI-78 and in three specific cases demonstrated selectivity values similar to, or better than, MSI-78. To understand if these polymers were membrane active, polymer induced lipid membrane disruption activities were evaluated by dye leakage experiments. Lipid composition and polymer hydrophobicity were found to be important factors for dye release. [source]

Herbicidal action of 2-hydroxy-3-alkyl-1,4-naphthoquinones

Philip J Jewess
Abstract The main mode of herbicidal activity of 2-hydroxy-3-alkyl-1,4-naphthoquinones is shown to be inhibition of photosystem II (PSII). The herbicidal and in vitro activities have been measured and correlated with their (Log)octanol/water partition coefficients (Log Ko/w). The length of the 3- n -alkyl substituent for optimal activity differed between herbicidal and in vitro activity. The maximum in vitro activity was given by the nonyl to dodecyl homologues (Log Ko/w between 6.54 and 8.12), whereas herbicidal activity peaked with the n -hexyl compound (Log Ko/w,=,4.95). The effect of chain branching was also investigated using isomeric pentyl analogues substituted at position 3. All exhibited similar levels of in vitro activities but herbicidal activities differed, albeit moderately, with the exception of one analogue that was much less phytotoxic. Other modes of action were also investigated using two representative compounds. They did not show any activity on photosystem I or mitochondrial complex I, or generate toxic oxygen radicals by redox cycling reactions. Only moderate activity was found against mitochondrial complex III from plants, in contrast to much higher corresponding activity using an insect enzyme. 2002 Society of Chemical Industry [source]

The participation of the anion and alkyl substituent of diaryliodonium salts in photo-initiated cationic polymerization reactions

Chul Ho Park
Abstract The photo-initiated cationic polymerization (PCP) of epoxides using diaryliodonium salt photoacid generators (PAGs) bearing alkyl groups and anions was investigated. The properties and reactivities of a series of iodonium salts containing various cations and anions were compared in the context of a PCP reaction. The products from the decomposition of the cations of these salts were analyzed using gas chromatography-mass spectrometry (GC-MS) spectra. The relationship between the molecular structure of the salts and their reaction mechanism in the PCP reaction was investigated. Based on the results of the investigation, it was concluded that the structures of the cations and anions of theiodonium salts affect the PCP reaction rate, which was controlled by the products from the diaryliodonium salts. As part of an additional investigation, the diaryliodonium salts-epoxide materials were applied to 254,nm-photo-patterning. Copyright 2006 John Wiley & Sons, Ltd. [source]

Nitric Oxide Synthase Inhibition by Pentacycloundecane Conjugates of Aminoguanidine and Tryptamine

Dennis K. Wilkes
Abstract This paper describes the synthesis and in-vitro activity of pentacycloundecane-conjugated aminoguanidine and tryptamine analogues on nitric oxide synthase (NOS) using rat brain homogenate. Both aminoguanidine and tryptamine-derived NOS inhibitors show selectivity towards the inducible and neuronal isoforms of the NOS enzyme, but are weak inhibitors and complete inhibition of the enzyme occurs only at high millimolar concentrations. In view of the increased NOS inactivation observed with alkyl substitution of these structures, the present study aimed to evaluate the effect of the pentacycloundecane cage moiety as an alkyl substituent on the in vitro NOS inhibition of aminoguanidine and tryptamine compounds. Comparison of the IC50 values of aminoguanidine (IC50 = 2.30610,3 M) and 8-imino- N -guanidino-pentacyclo-undecane 2 (IC50 = 8.80310,5 M) revealed a more than 26-fold increase in potency. The ability of tryptamine to inhibit NOS activity was also markedly improved by the various pentacycloundecane substituents. The compounds, 3-hydroxy-4-[3-(2-aminoethyl)indole]-azahexacyclo[,6.03,10.05,9.08,11]dodecane 4 and 8-[3-(2-aminoethyl) indole]-pentacyclo[5.4.02,6.03,10.05,9]undecane 7 showed the best activity of the tryptamine analogues with a more than 3-fold increase in nitric oxide synthase inhibition. The results confirmed that the pentacycloundecane structure substantially enhanced the NOS inhibitory potency as observed for the six new NOS inhibitors. [source]

Anticonvulsant activity, teratogenicity and pharmacokinetics of novel valproyltaurinamide derivatives in mice

Nina Isoherranen
The purpose of this study was to synthesize novel valproyltaurine (VTA) derivatives including valproyltaurinamide (VTD), N -methyl-valproyltaurinamide (M-VTD), N,N -dimethyl-valproyltaurinamide (DM-VTD) and N -isopropyl-valproyltaurinamide (I-VTD) and evaluate their structure,pharmacokinetic,pharmacodynamic relationships with respect to anticonvulsant activity and teratogenic potential. However, their hepatotoxic potential could not be evaluated. The metabolism and pharmacokinetics of these derivatives in mice were also studied. VTA lacked anticonvulsant activity, but VTD, DM-VTD and I-VTD possessed anticonvulsant activity in the Frings audiogenic seizure susceptible mice (ED50 values of 52, 134 and 126 mg kg,1, respectively). VTA did not have any adverse effect on the reproductive outcome in the Swiss Vancouver/Fnn mice following a single i.p. injection of 600 mg kg,1 on gestational day (GD) 8.5. VTD (600 mg kg,1 at GD 8.5) produced an increase in embryolethality, but unlike valproic acid, it did not induce congenital malformations. DM-VTD and I-VTD (600 mg kg,1 at GD 8.5) produced a significant increase in the incidence of gross malformations. The incidence of birth defects increased when the length of the alkyl substituent or the degree of N -alkylation increased. In mice, N-alkylated VTDs underwent metabolic N-dealkylation to VTD. DM-VTD was first biotransformed to M-VTD and subsequently to VTD. I-VTD's fraction metabolized to VTD was 29%. The observed metabolic pathways suggest that active metabolites may contribute to the anticonvulsant activity of the N-alkylated VTDs and reactive intermediates may be formed during their metabolism. In mice, VTD had five to 10 times lower clearance (CL), and three times longer half-life than I-VTD and DM-VTD, making it a more attractive compound than DM-VTD and I-VTD for further development. VTD's extent of brain penetration was only half that observed for the N-alkylated taurinamides suggesting that it has a higher intrinsic activity that DM-VTD and I-VTD. In conclusion, from this series of compounds, although VTD caused embryolethality, this compound emerged as the most promising new antiepileptic drug, having a preclinical spectrum characterized by the highest anticonvulsant potential, lowest potential for teratogenicity and favorable pharmacokinetics. British Journal of Pharmacology (2003) 139, 755,764. doi:10.1038/sj.bjp.0705301 [source]

In the Quest for a Virtual Pseudo Receptor for Sandalwood-Like Odorants.


Based on similarities between naturally occurring (,)-(Z)- , - or (+)-(Z)- , -santalol ((,)- 1 or (+)- 2, resp.) and the reversed (E)-configured synthetic derivatives from campholenal (7a), a simple model A was developed. Besides reconciliation of this stereochemical aspect, this initial model also tentatively explained the enantiodiscriminations as well as the large spectra of distances separating the OH function from the lipophilic quaternary center(s) reported for different classes of substrates. Evolution, modifications, and refinement of this imperfect model allied with the research for alternative possibilities are illustrated, along with a historical guideline, in the light of olfactively challenging synthetic seco-substructures as well as literature reports. Despite evolution of the inadequate model A and a plausible interpretation of the lipophilic part, the topological positions of the OH function and its vicinal alkyl substituent could nevertheless not be fully ascertained by this approach. This apparently inconclusive empirical concept prompted us to turn our attention towards a computerized methodology, which will constitute the second and third part of this study. [source]

Chiral discrimination of 2-arylalkanoic acids by (1S,2S)-1-aminoindan-2-ol and (1S,2S)-2-aminoindan-1-ol: Correlation of the relative configuration of the amino and hydroxy groups with the pattern of a supramolecular hydrogen-bond network in the less-soluble diastereomeric salt

CHIRALITY, Issue 6 2003
Kazushi Kinbara
Abstract The diastereomeric resolution of 2-arylalkanoic acids with enantiopure trans -1-aminoindan-2-ol and trans -2-aminoindan-1-ol were studied. Enantiopure trans -1-aminoindan-2-ol had a moderate resolving ability for 2-arylalkanoic acids having a naphthyl group as an aryl substituent at the ,-position, while enantiopure trans -2-aminoindan-1-ol had a moderate-to-high resolving ability for a wide variety of the acids having a methyl group as an alkyl substituent at the ,-position. The crystal structures of the corresponding less-soluble salts revealed that a reinforced columnar hydrogen-bond network was formed in the less-soluble salts with trans -1-aminoindan-2-ol, while a rather stable hydrogen-bond sheet was generated with the assistance of water molecules in the less-soluble salts with trans -2-aminoindan-1-ol. These results suggest that not only the relative configuration but also the position of the hydrogen-bonding groups in resolving agents have a considerable effect on the structure of the less-soluble salts. The difference in favorable hydrogen-bond structure determined the adaptivity to the structural feature of target racemic 2-arylalkanoic acids in the resolution by trans -1-aminoindan-2-ol and trans -1-aminoindan-2-ol, respectively. Chirality 15:564,570, 2003. 2003 Wiley-Liss, Inc. [source]

Novel Anion Exchangers for Electrodes with Improved Selectivity to Divalent Anions

Vladimir Egorov
Abstract It has been found that replacing of several long-chain alkyl substituents at the nitrogen atom of lipophilic quaternary ammonium salts (QAS) by methyls results in a dramatic increase of the potentiometric selectivity of ion-selective electrodes (ISE) with QAS-based plasticized PVC membranes to some divalent anions against the monovalent ones. The discussed effect of QAS cation nature on the potentiometric selectivity is also partly retained for ISE with neutral carrier-based membranes doped with QAS to provide anion permselectivity. This opens up new possibilities to control the potentiometric selectivity of ISE for divalent anions by the appropriate selection of the anion exchanger. [source]

Synthesis, Characterization, and Protonation Reactions of Ar-BIAN and Ar-BICAT Diimine Platinum Diphenyl Complexes

Jerome Parmene
Abstract PtII diphenyl complexes (N,N)PtPh2 [N,N = diimines Ar,N=C(An)C=N,Ar with Ar = substituted aryl groups] have been prepared and characterized by 1H, 13C, and 195Pt NMR spectroscopy. The 195Pt NMR spectroscopic data establish the electronic influence exerted by substituents at the backbone of the diimine ligand system to the metal center. When compared to diimines Ar,N=CMe,CMe=N,Ar, the electron-withdrawing ability of the Ar-BIAN ligand and the electron-donating ability of the O,O-heterocyclic Ar-BICAT systems are demonstrated. Trends in 195Pt NMR chemical shifts suggest that electronic tuning of the metal center is better achieved through variations of the diimine backbone substituents rather than variation of the substituents at the N-Aryl groups. Protonation of (N,N)PtPh2 in dichloromethane/acetonitrile at ,78 C furnishes the corresponding PtIV hydrides (N,N)PtPh2H(NCMe)+. The PtIV hydrides liberate benzene with the formation of (N,N)PtPh(NCMe)+ when the temperature is raised. A second protonation and rapid benzene elimination produces the dicationic PtII species (N,N)Pt(NCMe)22+ at approximately 50 C. Protonation of (N,N)PtPh2 in the absence of acetonitrile results in the clean formation of (N,N)PtPh(,2 -C6H6)+ at temperatures that depend on the steric hindrance provided by the alkyl substituents at the diimine N-aryl groups. These findings support the notion that the metal is the kinetically preferred site of protonation. The results qualitatively agree with a recent mechanistic study of protonation-induced reactions of (diimine)PtPh2 complexes that bear simple methyl substituents at the diimine backbone. Several compounds have been crystallographically characterized. All complexes have the expected square planar environment at the metal. Modest variations in the metric parameters suggest that the Ar-BICAT system has a weaker trans influence than the Ar-BIAN and Ar-DAB systems. [source]

Symmetrical and Nonsymmetrical Liquid Crystalline Oligothiophenes: Convenient Synthesis and Transition-Temperature Engineering

Julie Leroy
Abstract Two approaches to transition-temperature engineering in liquid crystalline oligothiophenes are described: (i) substitution at the aromatic core with two identical branched alkyl chains and (ii) desymmetrization of the molecule with two alkyl substituents of different length or structure. Key steps in the synthesis of symmetrical and nonsymmetrical terthiophenes and quaterthiophenes involve Suzuki coupling and carbanion alkylation. A well-adjusted balance between the ,,, stacking of the aromatic core and the disorder caused by the peripheral alkyl chains is demonstrated to be important for the control of the thermotropic behavior of oligothiophene mesogens. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

Synthesis and Characterization of Pyrazolyl-Functionalized Imidazolium-Based Ionic Liquids and Hemilabile (Carbene)palladium(II) Complex Catalyzed Heck Reaction

Ruihu Wang
Abstract Neat reactions of 1-(pyrazolylmethyl)imidazole with an excess of alkyl or polyfluoroalkyl halides at 100 C followed by subsequent metathetical reactions with LiN(SO2CF3)2 or KPF6 at 25 C gave rise to a series of monoquaternary salts 3a,3k. These salts can be also prepared through treatment of 1-alkylimidazole with 1-(chloromethyl)pyrazole hydrochloride in the presence of base, followed by anion exchange with LiN(SO2CF3)2 or KPF6. Their phase-transition temperature, thermal stability, density and solubility in common solvents have been investigated. Most of the bis(trifluoromethanesulfon)amide salts are room-temperature ionic liquids. The effect of anions and of alkyl substituents bonded to the imidazolium cation on the physicochemical properties was examined. Using 3-butyl-1-(pyrazolylmethyl)imidazolium chloride (2d), the precursor of 3-butyl-1-(pyrazolylmethyl)imidazolium bis(trifluoromethanesulfon)amide (3d), as a reactant, a hemilabile (N-heterocyclic carbene)palladium(II) complex 4 was synthesized through a (carbene)silver(I) transfer reagent. It was characterized by single-crystal X-ray diffraction analysis. The catalytic activity and recyclability of 4 in 3d were preliminarily evaluated by consecutive Heck reactions using different substrates. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

Synthesis, Structural Diversity, and Ligand-Transfer Potential of (Carbene)copper(I) Complexes

Galmari Venkatachalam
Abstract Copper(I) complexes comprising different N-heterocyclic carbene ligands were prepared via in situ deprotonation and metallation. Depending on the wingtip groups on the carbene ligand (alkyl vs. aryl, chelating or monodentate), a variety of different structural motifs were identified, such as a trigonal planar geometry (alkyl wingtips) and an unprecedented see-saw-type structure (pyridinyl wingtip groups). While aryl wingtip groups increase the stability of the complexes, alkyl substituents induce rapid demetallation in the presence of moisture. The reactivity of these complexes was used to establish a carbene-transfer protocol, which is illustrated by the formation of new cyclic thiourea compounds (transfer to sulfur) and new (carbene)ruthenium(II) complexes (transfer to ruthenium). This suggests that (carbene)copper(I) complexes could become valuable alternatives to (carbene)silver(I) complexes for synthesizing (carbene)metal systems via transmetallation. [source]

Polystannanes: Polymers of a Molecular, Jacketed Metal,Wire Structure,

Fabien Choffat
Abstract Organometallic polymers comprising a backbone of covalently connected metal atoms can be regarded as molecular metal wires surrounded by a jacket of organic matter. Such polymers are rare and their materials properties are largely unexplored. Here, we report on polystannanes, (SnR2)n, that is, polymers with a backbone of tin atoms, which are synthesized by dehydropolymerization of dialkylstannanes (H2SnR2) with the catalyst [RhCl(PPh3)3]. The polystannanes feature reversible phase transitions into liquid-crystalline states, remarkably, even below room temperature, and, interestingly, oriented either parallel or perpendicular to external driving forces, depending on the length of the alkyl substituents. [source]

Gold Catalysis: Efficient 1,3-Induction with Diastereotopic Homopropargyl Alcohols in the Phenol Synthesis

A. Stephen
Abstract Furans with diastereotopic alkynyl groups were prepared and then converted to anellated phenols in gold-catalyzed reactions. In all cases a highly diastereoselective reaction was observed. The stereochemical outcome of the 1,3-induction could be assigned by two independent crystal structure analyses, showing a cis -arrangement of the two alkyl substituents on the benzoanellated cyclohexene ring. [source]

Bile acid sequestrants based on cationic dextran hydrogel microspheres.


Abstract Cationic dextran hydrogel microspheres with pendant quaternary ammonium groups having alkyl substituents (C2,C12) at quaternary nitrogen were synthesized. The in vitro sorption of sodium salts of four bile acids (glycocholic, cholic, taurocholic, and deoxycholic acids) with these hydrogels was studied as a function of substituent alkyl chain length and bile acid hydrophobicity. Sorption experiments were performed in phosphate buffer solutions (pH 7.4) containing one bile salt (individual sorption) or mixtures of several bile salts (competitive sorption). Parameters for individual sorption were calculated taking into consideration the stoichiometric and cooperative binding of bile salts to oppositely charged polymer hydrogels. The results show that the increase in the length of the alkyl chain of the substituent leads to an increase in both ionization constant K0 and overall stability constant of binding K, but decreases the cooperativity parameter u. The competitive sorption studies indicate that the hydrogels display a good affinity for both dihydroxylic and trihydroxylic bile salts. The molar ratio of maximum amounts bound for the two types of bile acid is 2 to 1, which is much lower than those reported for other cationic polymers recommended as bile acid sequestrants. The binding constants for the sorption of bile salts by some dextran hydrogels are 20,30 times higher than those obtained for cholestyramine under similar sorption conditions. 2001 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:681,689, 2001 [source]

Mechanism and structure,reactivity correlation in the homogeneous, unimolecular elimination kinetics of 2-substituted ethyl methylcarbonates in the gas phase

Gabriel Chuchani
Abstract The gas-phase elimination kinetics of 2-substituted ethyl methylcarbonates were determined in a static reaction system over the temperature range of 323,435C and pressure range 28.5,242 Torr. The reactions are homogeneous, unimolecular and follow a first-order rate law. The kinetic and thermodynamic parameters are reported. The 2-substituents of the ethyl methylcarbonate (CH3OCOOCH2CH2Z, Z=substituent) give an approximate linear correlation when using the Taft,Topsom method, log(kZ/kH)=,(0.570.19),,+(1.340.49),R, (r=0.9256; SD=0.16) at 400C. This result implies the elimination process to be sensitive to steric factors, while the electronic effect is unimportant. However, the resonance factor has the greatest influence for a favorable abstraction of the ,-hydrogen of the C,,H bond by the oxygen carbonyl. Because ,, is significant, a good correlation of the alkyl substituents of carbonates with Hancock's steric parameters was obtained: log(kR/kH) versus ESC for CH3OCOOCH2CH2R at 400C, R=alkyl, ,=,0.17 (r=0.9993, SD=0.01). An approximate straight line was obtained on plotting these data with the reported Hancock's correlation of 2-alkyl ethylacetates. This result leads to evidence for the ,-hydrogen abstraction by the oxygen carbonyl and not by the alkoxy oxygen at the opposite side of the carbonate. The carbonate decompostion is best described in terms of a concerted six-membered cyclic transition state type of mechanism. Copyright 2003 John Wiley & Sons, Ltd. [source]

Antibacterial and Hemolytic Activities of Quaternary Pyridinium Functionalized Polynorbornenes

Tarik Eren
Abstract In this study, amphiphilic polyoxanorbornene with different quaternary alkyl pyridinium side chains were synthesized. The biological efficiencies of these polymers, with various alkyl substituents, were determined by bacterial growth inhibition assays and hemolytic activity (HC50) against human red blood cells (RBCs) to provide selectivity of these polymers for bacterial over mammalian cells. A series of polymers with different alkyl substituents (ethyl, butyl, hexyl, octyl, decyl and phenylethyl) and two different molecular weights (3 and 10 kDa) were prepared. The impact of alkyl chain length divided the biological activity into two different cases: those with an alkyl substituent containing four or fewer carbons had a minimum inhibitory concentration (MIC) of 200 g,,mL,1 and a HC50 greater than 1,650 g,,mL,1, while those with six or more carbons had lower MICs,,,12.5 g,,mL,1 and HC50,,,250 g,,mL,1. Using MSI-78, the potent Magainin derivative which has an MIC,=,12.0 g,,mL,1 and HC50,=,120 g,,mL,1, as a comparison, the polymers with alkyl substituents ,C4 (four carbons) were not very potent, but did show selectivity values greater than or equal to MSI-78. In contrast, those with alkyl substituents ,C6 were as potent, or more potent, than MSI-78 and in three specific cases demonstrated selectivity values similar to, or better than, MSI-78. To understand if these polymers were membrane active, polymer induced lipid membrane disruption activities were evaluated by dye leakage experiments. Lipid composition and polymer hydrophobicity were found to be important factors for dye release. [source]

Computational chemistry study of the environmentally important acid-catalyzed hydrolysis of atrazine and related 2-chloro- s -triazines

Phillip Sawunyama
Abstract Many chlorine-containing pesticides, for example 2-chloro- s -triazines, are of great concern both environmentally and toxicologically. As a result, ascertaining or predicting the fate and transport of these compounds in soils and water is of current interest. Transformation pathways for 2-chloro- s -triazines in the environment include dealkylation, dechlorination (hydrolysis), and ring cleavage. This study explored the feasibility of using computational chemistry, specifically the hybrid density functional theory method, B3LYP, to predict hydrolysis trends of atrazine (2-chloro- N4 -ethyl- N6 -isopropyl-1,3,5-triazine-2,4-diamine) and related 2-chloro- s -triazines to the corresponding 2-hydroxy- s -triazines. Gas-phase energetics are described on the basis of calculations performed at the B3LYP/6-311++G(d,p)//B3LYP/6-31G* level of theory. Calculated free energies of hydrolysis (,hG298) are nearly the same for simazine (2-chloro- N4,N6 -diethyl-1,3,5-triazine-2,4-diamine), atrazine, and propazine (2-chloro- N4,N6 -di-isopropyl-1,3,5-triazine-2,4-diamine), suggesting that hydrolysis is not significantly affected by the side-chain amine-nitrogen alkyl substituents. High-energy barriers also suggest that the reactions are not likely to be observed in the gas phase. Aqueous solvation effects were examined by means of self-consistent reaction field methods (SCRF). Molecular structures were optimized at the B3LYP/6-31G* level using the Onsager model, and solvation energies were calculated at the B3LYP/6-311++G(d,p) level using the isodensity surface polarizable continuum model (IPCM). Although the extent of solvent stabilization was greater for cationic species than neutral ones, the full extent of solvation is underestimated, especially for the transition state structures. As a consequence, the calculated hydrolysis barrier for protonated atrazine is exaggerated compared with the experimentally determined one. Overall, the hydrolysis reactions follow a concerted nucleophilic aromatic substitution (SNAr) pathway. Published in 2002 for SCI by John Wiley & Sons, Ltd [source]

Atomic study of molecular wires composed of thiophene oligomers

P. Bai
Abstract In this paper, we study the electron conductance of thiophene oligomers based molecular wires through atomic structures using the first principles method based on density functional theory and nonequilibrium Green's function. The molecular wires are built by sandwiching various thiophene oligomers between two metal electrodes via terminal groups at atomic levels. The effects of alkyl substituents on the thiophene oligomers are modelled by varying inter-ring angles of the oligomers. Thiophene dimers, tetramers and hexamers are used to studied thiophene size effects. The projected orbitals, energy gaps, transmission functions and current,voltage characteristics of the molecular wires are calculated and analyzed. Results show that the molecular wires with the planar structures of thiophene oligomers have larger electron transmission functions, hence better electronic conductance than those with twist structures. The conductance of molecular wires decreases when the chain length of the thiophene oligomer increases. The results can provide guidance for design of thiophene molecular electronic wires and other devices. ( 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Structures of alkyl-substituted Trger's base derivatives illustrate the importance of Z, for packing in the absence of strong crystal synthons

Christophe M. L. Vande Velde
Crystal structures of Trger's base (5,11-methano-2,8-dimethyl-5,6,11,12-tetrahydrodibenzo[b,f][1,5]diazocine) analogues with the methyl groups replaced by ethyl, iso -propyl and tert -butyl groups were studied. The incidence of Z, > 1 structures increases to rather conspicuous levels. The reasons behind this trend are expanded upon, and a possible explanation is given in the flexibility of the alkyl substituents and van der Waals stabilization. In combination these effects allow for an additional stabilization of the packing by small changes in the molecular conformations, thus expanding the size of the asymmetric unit. [source]

Amino-substituted O6 -benzyl-5-nitrosopyrimidines: interplay of molecular, molecular-electronic and supramolecular structures

Antonio Quesada
The structures of eight 2,4,6-trisubstituted-5-nitrosopyrimidines (one of which crystallizes in two polymorphs) have been determined, including seven O6 -benzyl derivatives which are potential, or proven, in vitro inhibitors of the human DNA-repair protein O6 -alkylguanine-DNA-transferase. In the derivatives having an amino substituent at the 4-position, an intramolecular N,H,O hydrogen bond with the nitroso O as an acceptor leads to an overall molecular shape similar to that of substituted purines. There is a marked propensity for these nitroso compounds to crystallize with Z, = 2. The structure of an analogue with no nitroso group is also reported for comparative purposes. Compounds containing the N -alkyl substituents ,NHCH2COOEt, ,NHCH2CH2COOEt and ,NHCH(CH2Ph)COOEt, derived from amino acid esters, exhibit a rich variety of conformational behaviour, and in all of the nitroso compounds the bond lengths provide strong evidence for a highly polarized electronic structure. Associated with this polarization is extensive charge-assisted hydrogen bonding between the molecules, leading to supramolecular aggregation in the form of finite (zero-dimensional) aggregates, chains, molecular ladders, sheets and frameworks. [source]

Dualistic actions of cromakalim and new potent 2H -1,4-benzoxazine derivatives on the native skeletal muscle KATP channel

Domenico Tricarico
New 2H -1,4-benzoxazine derivatives were synthesized and tested for their agonist properties on the ATP-sensitive K+ channels (KATP) of native rat skeletal muscle fibres by using the patch-clamp technique. The novel modifications involved the introduction at position 2 of the benzoxazine ring of alkyl substituents such as methyl (,CH3), ethyl (,C2H5) or propyl (,C3H7) groups, while maintaining pharmacophore groups critical for conferring agonist properties. The effects of these molecules were compared with those of cromakalim in the presence or absence of internal ATP (10,4M). In the presence of internal ATP, all the compounds increased the macropatch KATP currents. The order of potency of the molecules as agonists was ,C3H7 (DE50=1.63 10,8M) >,C2H5 (DE50=1.11 10,7M)>,CH3 (DE50=2.81 10,7M)>cromak-slim (DE50= 1.42 10,5M). Bell-shaped dose,response curves were observed for these compounds and cromakalim indicating a downturn in response when a certain dose was exceeded. In contrast, in the absence of internal ATP, all molecules including cromakalim inhibited the KATP currents. The order of increasing potency as antagonists was cromakalim (IC50=1.15 10,8M),CH3 (IC50=2.6 10,8M)>,C2H5 (IC50=4.4 10,8M)>,C3H7 (IC50=1.68 10,7M) derivatives. These results suggest that the newly synthesized molecules and cromakalim act on muscle KATP channel by binding on two receptor sites that have opposite actions. Alternatively, a more simple explanation is to consider the existence of a single site for potassium channel openers regulated by ATP which favours the transduction of the channel opening. The alkyl chains at position 2 of the 2H -1,4-benzoxazine nucleus is pivotal in determining the potency of benzoxazine derivatives as agonists or antagonists. British Journal of Pharmacology (2003) 139, 255,262. doi:10.1038/sj.bjp.0705233 [source]