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Aminobenzoic Acid (aminobenzoic + acid)
Selected AbstractsChemInform Abstract: Reactions of Aminobenzoic Acids with ,,,-Acetylenic ,-Hydroxy Nitriles: Synthesis of Functionalized Amino Acids and Unusually Facile Esterification and Acetylene Hydration.CHEMINFORM, Issue 29 2009Boris A. Trofimov Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 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] ChemInform Abstract: The Use of Formamidine Protection for the Derivatization of Aminobenzoic Acids.CHEMINFORM, Issue 15 2009Paul E. Zhichkin Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 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] A New Amperometric Biosensor Based on HRP/Nano-Au/L -Cysteine/Poly(o -Aminobenzoic acid)-Membrane-Modified Platinum Electrode for the Determination of Hydrogen PeroxideCHINESE JOURNAL OF CHEMISTRY, Issue 11 2006Ming-Yu Tang Abstract The third generation amperometric biosensor for the determination of hydrogen peroxide (H2O2) has been described. For the fabrication of biosensor, o -aminobenzoic acid (oABA) was first electropolymerized on the surface of platinum (Pt) electrode as an electrostatic repulsion layer to reject interferences. Horseradish peroxidase (HRP) absorbed by nano-scaled particulate gold (nano-Au) was immobilized on the electrode modified with polymerized o -aminobenzoic acid (poABA) with L -cysteine as a linker to prepare a biosensor for the detection of H2O2. Amperometric detection of H2O2 was realized at a potential of +20 mV versus SCE. The resulting biosensor exhibited fast response, excellent reproducibility and sensibility, expanded linear range and low interferences. Temperature and pH dependence and stability of the sensor were investigated. The optimal sensor gave a linear response in the range of 2.99×10,6 to 3.55×10,3 mol·L,1 to H2O2 with a sensibility of 0.0177 A·L,1·mol,1 and a detection limit (S/N=3) of 4.3×10,7 mol·L,1. The biosensor demonstrated a 95% response within less than 10 s. [source] Prediction of polymorphic N -acetylation of new drug candidates by correlation with human NAT1 and NAT2DRUG DEVELOPMENT RESEARCH, Issue 1 2002Katalin Jemnitz Abstract Due to interindividual variation in N -acetyltransferase 2 (NAT2) activity, pharmaceutical companies face the problem of polymorphic metabolism in drugs that are metabolized mainly or exclusively by this enzyme. An in vitro method has been developed to predict in vivo polymorphic N -acetylation at an early stage of drug development. Two new type 5H-2,3-benzodiazepine derivatives, Nerisopam (NER) with anxiolytic activity and GYKI47261 with antiepileptic activity, are metabolized mainly by N -acetylation in the rat and human. The selectivity of human N -acetyltransferases (NAT1,2) to form the acetylated metabolites has been investigated by correlation analysis. Twelve human liver samples were characterized for NAT1 and NAT2 phenotype based on their enzyme activity toward two selective NAT1 (p -aminobenzoic acid, PABA; p -aminosalicylic acid, PAS) and two selective NAT2 (sulfamethazine, SMZ; procainamide, PROC) substrates. Significant correlation was found between enzyme activities NAT1PABA/NAT1PAS and NAT2SMZ/NAT2PROC, respectively, and no correlation was observed comparing enzyme activities toward NAT1PABA/NAT2PROC. Enzyme activities using NER and GYKI 47261 as substrates were compared to activities obtained with NAT1 and NAT2 selective substrates, and the correlation coefficients were calculated. Good correlation was established between the rates of acetylation of the two drugs and that of the NAT2 selective substrate (NER/NAT2SMZ, r2=0.91, GYKI 47261/NAT2SMZ, r2=0.91). In contrast, no correlation was found between the rate of conjugation of the drugs and that of NAT1 selective substrate (NER/NAT1PABA, r2=0.022, GYKI 47261/NAT1PABA, r2=0.0004), suggesting polymorphic in vivo metabolism, since both drugs are acetylated preferably by NAT2. According to our results, correlation analysis based on in vitro acetylation activity may be used to predict in vivo polymorphic metabolism. Drug Dev. Res. 56:17,22, 2002. © 2002 Wiley-Liss, Inc. [source] Carboxydipeptidase activities of recombinant cysteine peptidasesFEBS JOURNAL, Issue 5 2004CPB of Leishmania mexicana, Cruzain of Trypanosoma cruzi The recombinant cysteine peptidases, cruzain from Trypanosoma cruzi and CPB2.8,CTE from Leishmania mexicana, are cathepsin L-like and characteristically endopeptidases. In this study, we characterized the carboxydipeptidase activities of these enzymes and compared them with those of human recombinant cathepsin B and cathepsin L. The analysis used the internally quenched fluorescent peptide Abz-FRFK*-OH and some of its analogues, where Abz is ortho -aminobenzoic acid and K* is (2,4-dinitrophenyl)-,-NH2 -lysine. These peptides were demonstrated to be very sensitive substrates, due to the strong quenching effect of K* on the fluorescence of the Abz group. The carboxydipeptidase activity of cruzain was shown to be very similar to that of cathepsin B, while that of CPB2.8,CTE is closer to the carboxydipeptidase activity of cathepsin L. The S2 subsite architecture of cruzain and the nature of the amino acid at the P2 position of the substrates determine its carboxydipeptidase activity and gives further and direct support to the notion that the carboxydipeptidase activity of the papain family cysteine peptidases rely on the S2,P2 interaction [Nägler D. K., Tam, W., Storer, A.C., Krupa, J.C., Mort, J.S. & Menard, R. (1999) Biochemistry38, 4868,4874]. Cruzain and CPB2.8,CTE presented a broad pH-range for both the endo- and exo-peptidase activities, although the later is approximately one order of magnitude lower. This feature, that is not common in related mammalian cysteine peptidases, is consistent with the enzymes being exposed to different environmental conditions and having different locations during parasite development. [source] Comparison of the specificity, stability and individual rate constants with respective activation parameters for the peptidase activity of cruzipain and its recombinant form, cruzain, from Trypanosoma cruziFEBS JOURNAL, Issue 24 2001Wagner A. S. Judice The Trypanosoma cruzi cysteine protease cruzipain contains a 130-amino-acid C-terminal extension, in addition to the catalytic domain. Natural cruzipain is a complex of isoforms, because of the simultaneous expression of several genes, and the presence of either high mannose-type, hybrid monoantennary-type or complex biantenary-type oligosacharide chains at Asn255 of the C-terminal extension. Cruzipain and its recombinant form without this extension (cruzain) were studied comparatively in this work. S2 to S2, subsite specificities of these enzymes were examined using four series of substrates derived from the internally quenched fluorescent peptide Abz-KLRFSKQ-EDDnp (Abz, ortho -aminobenzoic acid; EDDnp, N -(2,4-dinitrophenyl)-ethylenediamine). Large differences in the kinetic parameters were not observed between the enzymes; however, Km values were consistently lower for the hydrolysis of most of the substrates by cruzain. No difference in the pH,activity profile between the two enzymes was found, but in 1 m NaCl cruzipain presented a kcat value significantly higher than that of cruzain. The activation energy of denaturation for the enzymes did not differ significantly; however, a negative entropy value was observed for cruzipain denaturation whereas the value for cruzain was positive. We determined the individual rate constants (k1, substrate diffusion; k,1, substrate dissociation; k2, acylation; k3, deacylation) and the respective activation energies and entropies for hydrolysis of Abz-KLRFSKQ-EDDnp determining the temperature dependence of the Michaelis,Menten parameters kcat/Km and kcat as previously described [Ayala, Y.M. & Di Cera, E. (2000) Protein Sci.9, 1589,1593]. Differences between the two enzymes were clearly detected in the activation energies E1 and E,1, which are significantly higher for cruzipain. The corresponding ,S1 and ,S,1 were positive and significantly higher for cruzipain than for cruzain. These results indicate the presence of a larger energy barrier for cruzipain relating to substrate diffusion and dissociation, which could be related to the C-terminal extension and/or glycosylation state of cruzipain. [source] Amyloid-Like Fibrillogenesis through Supramolecular Helix-Mediated Self-Assembly of Tetrapeptides Containing Non-Coded , -Aminoisobutyric Acid (Aib) and 3-Aminobenzoic Acid (m -ABA)HELVETICA CHIMICA ACTA, Issue 6 2010Arpita Dutta Abstract Single-crystal X-ray diffraction studies of two terminally protected tetrapeptides Boc-Ile-Aib-Val- m -ABA-OMe (I) and Boc-Ile-Aib-Phe- m -ABA-OMe (II) (Aib=, -aminoisobutyric acid; m -ABA=meta -aminobenzoic acid) reveal that they form continuous H-bonded helices through the association of double-bend (type III and I) building blocks. NMR Studies support the existence of the double-bend (type III and I) structures of the peptides in solution also. Field emission scanning electron-microscopic (FE-SEM) and high-resolution transmission electron-microscopic (HR-TEM) images of the peptides exhibit amyloid-like fibrils in the solid state. The Congo red-stained fibrils of peptide I and II, observed between crossed polarizers, show green-gold birefringence, a characteristic of amyloid fibrils. [source] Influence of "Alternative" C-terminal amino acids on the formation of [b3 + 17 + Cat]+ products from metal cationized synthetic tetrapeptides,JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 5 2004V. Anbalagan Abstract The aim of this study was to investigate the dissociation patterns, and in particular the relative abundance of [b3 + 17 + Cat]+, for peptides with C-termini designed to allow transfer of the ,OH required to generate the product ion, but not necessarily as the most favored pathway. Working with the hypothesis that formation of a five-membered ring intermediate, including intramolecular nucleophilic attack by a carbonyl oxygen atom, is an important mechanistic step, several model peptides with general sequence AcFGGX were synthesized, metal cationized by electrospray ionization and subjected to collision-induced dissociation (CID). The amino acid at position X was one that either required a larger ring intermediate (,-alanine, ,-aminobutyric acid and ,-amino- n -caproic acid to generate six-, seven- or nine- membered rings, respectively) to transfer ,OH, lacked a structural element required for nucleophilic attack (aminoethanol) or prohibited cyclization because of the inclusion of a rigid ring (p - and m -aminobenzoic acid). For Ag+, Li+ and Na+ cationized peptides, our results show that amino acids requiring the adoption of larger ring intermediates suppressed the formation of [b3 + 17 + Cat]+, while amino acids that prohibit cyclization eliminated the reaction pathway completely. Formation of [b3 , 1 + Cat]+ from the alkali metal cationized versions was not a favorable process upon suppression or elimination of the [b3 + 17 + Cat]+ pathway: the loss of H2O to form [M , H2O + Cat]+ was instead the dominant dissociation reaction observed. Multiple-stage dissociation experiments suggest that [M , H2O + Cat]+ is not [b4 , 1 + Cat]+ arising from the loss of H2O from the C-terminus, but may instead be a species that forms via a mechanism involving the elimination of an oxygen atom from an amide group. Copyright © 2004 John Wiley & Sons, Ltd. [source] Sunscreens , what's important to knowJOURNAL OF THE EUROPEAN ACADEMY OF DERMATOLOGY & VENEREOLOGY, Issue 9 2008C Antoniou Abstract The popularity of sunscreens dramatically increased since ultraviolet irradiation was implicated in the pathogenesis of skin cancer and skin ageing. The absorption properties, safety, photostability of different organic and inorganic filters are reviewed: para -aminobenzoic acid, salicylates, cinnamates, benzophenones, butylmethoxydibenzoylmethane (Parsol 1789), drometrizole trisulphonic (Mexoryl XL), terephthalydene dicamphor sulphonic acid (Mexoryl SX), methylene bisbenzotriazol tetramethylbutylphenol (Tinasorb M), anisotriazine (Tinasorb S), titanium dioxide and zinc oxide. Furthermore, this review discusses the optimal methods for measuring the protection that a sunscreen offers, the role of sunscreen use in melanoma prevention and future trends in sunscreen filters development. [source] Tissue distribution of N -acetyltransferase 1 and 2 catalyzing the N -acetylation of 4-aminobiphenyl and O -acetylation of N -hydroxy-4-aminobiphenyl in the congenic rapid and slow acetylator Syrian hamsterMOLECULAR CARCINOGENESIS, Issue 4 2006David W. Hein Abstract N -acetyltransferase 1 (NAT1) and 2 (NAT2) enzymes catalyzing both deactivation (N -acetylation) and activation (O -acetylation) of arylamine carcinogens such as 4-aminobiphenyl (ABP) were investigated in a Syrian hamster model congenic at the NAT2 locus. NAT2 catalytic activities (measured with p -aminobenzoic acid) were significantly (P,<,0.001) higher in rapid than slow acetylators in all tissues (except heart and prostate where activity was undetectable in slow acetylators). NAT1 catalytic activities (measured with sulfamethazine) were low but detectable in most tissues tested and did not differ significantly between rapid and slow acetylators. ABP N -acetyltransferase activity was detected in all tissues of rapid acetylators but was below the limit of detection in all tissues of slow acetylators except liver where it was about 15-fold lower than rapid acetylators. ABP N -acetyltransferase activities correlated with NAT2 activities (r2,=,0.871; P,<,0.0001) but not with NAT1 activities (r2,=,0.132; P,>,0.05). Levels of N -hydroxy-ABP O -acetyltransferase activities were significantly (P,<,0.05) higher in rapid than slow acetylator cytosols for many but not all tissues. The N -hydroxy-ABP O -acetyltransferase activities correlated with ABP N -acetyltransferase activities (r2,=,0.695; P,<,0.0001) and NAT2 activities (r2,=,0.521, P,<,0.0001) but not with NAT1 activities (r2,=,0.115; P,>,0.05). The results suggest widespread tissue distribution of both NAT1 and NAT2, which catalyzes both N - and O -acetylation. These conclusions are important for interpretation of molecular epidemiological investigations into the role of N -acetyltransferase polymorphisms in various diseases including cancer. © 2006 Wiley-Liss, Inc. [source] Synthesis and characterization of aromatic/cycloaliphatic poly(amide- imide-imide)s from bis(4-amino- 3,5-dimethylphenyl) cycloalkane derivativesPOLYMER INTERNATIONAL, Issue 8 2007Bhuvana Sowrirajalu Abstract A series of novel aromatic diamines containing cycloaliphatic moieties was synthesized by the reaction of cycloalkanones like cyclohexanone and cycloheptanone with 2,6-dimethylaniline. The tetrimide diacid was synthesized using the prepared diamine with 3,3,,4,4,-benzophenonetetracarboxylic acid dianhydride/pyromellitic dianhydride and p -aminobenzoic acid. The polymers were prepared by treating the tetrimide diacid with different aromatic diamines. The structures of the monomers and polymers were identified using elemental analysis and Fourier transform infrared, 1H NMR and 13C NMR spectroscopy. The polymers show excellent solubility. The polymers are amorphous and have high optical transparency. They also show good thermal stability and their Tg value is found to be in the range 268,305 °C. Copyright © 2007 Society of Chemical Industry [source] Studies of waterborne emulsion of chemically modified epoxy resin,POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 1-2 2004Zhaoying Zhang Abstract The bisphenol-A type epoxy resin was modified by p -aminobenzoic acid. The modified resins were characterized using IR spectroscopy and differential scanning calorimetry (DSC). The progress of emulsification process was characterized by measuring the variations of conductivity and viscosity while dropping water into the modified resin solution. The factors influencing the emulsion particle size of the waterborne coating films of the modified resins were investigated. Copyright © 2004 John Wiley & Sons, Ltd. [source] Biocidal and catalytic efficiency of ruthenium(III) complexes with tridentate Schiff base ligandsAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 7 2010S. Arunachalam Abstract The reaction of the Schiff bases (obtained by condensing isatin with o -aminophenol/o -aminothiophenol/o -aminobenzoic acid) with [RuX3(EPh3)3] (where X = Cl/Br; E = P/As) in benzene afforded new, air-stable Ru(III) complexes of the general formula [Ru(L)X(EPh3)2] (L = dianion of tridentate Schiff bases). In all these reactions, the Schiff base ligand replaces one triphenylphosphine/triphenylarsine and two chlorides/bromides from the ruthenium precursors. The complexes were characterized by elemental analyses, spectral (FT,IR, UV,vis, 1H and 13C NMR for the ligands, and EPR) and electrochemical studies. All the metal complexes exhibit characteristic LMCT absorption bands in the visible region. The catalytic reactivity proved these complexes to be efficient catalysts in the oxidation of alcohols and CC coupling. All the complexes were screened for their biocidal efficiency against bacteria such as Staphylococcus epidermidis and Escherichia coli and fungi such as Botrytis cinerea and Aspergillus niger at 0.25, 0.50 and 1% concentrations. Copyright © 2010 John Wiley & Sons, Ltd. [source] Ortho-aminobenzoic acid-labeled bradykinins in interaction with lipid vesicles: Fluorescence studyBIOPOLYMERS, Issue 5 2002R. F. Turchiello Abstract The peptide hormone bradykinin (BK) (Arg1 -Pro2 -Pro3 -Gly4 -Phe5 -Ser6 -Pro7 -Phe8 -Arg9) and its shorter homolog BK1,5 (Arg1 -Pro2 -Pro3 -Gly4 -Phe5) were labeled with the extrinsic fluorescent probe ortho -aminobenzoic acid (Abz) bound to the N-terminal and amidated in the C-terminal carboxyl group (Abz-BK-NH2 and Abz-BK1,5 -NH2). The fragment des-Arg9 -BK was synthesized with the Abz fluorescent probe attached to the 3-amino group of 2,3-amino propionic acid (DAP), which positioned the Abz group at the C-terminal side of BK sequence, constituting the peptide des-Arg9 -BK-DAP(Abz)-NH2. The spectral characteristics of the probe were similar in the three peptides, and their fluorescent properties were monitored to study the interaction of the peptides with anionic vesicles of dimyristoylphosphatidylglycerol (DMPG). Time-resolved fluorescence experiments showed that the fluorescence decay of the peptides was best described by double-exponential kinetics, with mean lifetimes values around 8.0 ns in buffer pH 7.4 that increased about 10% in the presence of DMPG vesicles. About a 10-fold increase, compared with the values in aqueous solution, was observed in the steady-state anisotropy in the presence of vesicles. A similar increase was also observed for the rotational correlation times obtained from time-resolved anisotropy decay profiles, and related to the overall tumbling of the peptides. Equilibrium binding constants for the peptide,lipid interaction were examined monitoring anisotropy values in titration experiments and the electrostatic effects were evaluated through Gouy,Chapman potential calculations. Without corrections for electrostatic effects, the labeled fragment Abz-BK1,5 -NH2 presented the major affinity for DMPG vesicles. Corrections for the changes in peptide concentration due to electrostatic interactions suggested higher affinity of the BK fragments to the hydrophobic phase of the bilayer. © 2002 Wiley Periodicals, Inc. Biopolymers 65: 336,346, 2002 [source] Raman signatures of ligand binding and allosteric conformation change in hexameric insulinBIOPOLYMERS, Issue 5 2001Davide Ferrari Abstract Hexameric insulin is an allosteric protein that undergoes transitions between three conformational states (T6, T3R3, and R6). These allosteric states are stabilized by the binding of ligands to the phenolic pockets and by the coordination of anions to the His B10 metal sites. Raman difference (RD) spectroscopy is utilized to examine the binding of phenolic ligands and the binding of thiocyanate, p -aminobenzoic acid (PABA), or 4-hydroxy-3-nitrobenzoic acid (4H3N) to the allosteric sites of T3R3 and R6. The RD spectroscopic studies show changes in the amide I and III bands for the transition of residues B1,B8 from a meandering coil to an , helix in the T,R transitions and identify the Raman signatures of the structural differences among the T6, T3R3, and R6 states. Evidence of the altered environment caused by the ,30 Å displacement of phenylalanine (Phe) B1 is clearly seen from changes in the Raman bands of the Phe ring. Raman signatures arising from the coordination of PABA or 4H3N to the histidine (His) B10 Zn(II) sites show these carboxylates give distorted, asymmetric coordination to Zn(II). The RD spectra also reveal the importance of the position and the type of substituents for designing aromatic carboxylates with high affinity for the His B10 metal site. © 2001 John Wiley & Sons, Inc. Biopolymers (Biospectroscopy) 62: 249,260, 2001 [source] Photoallergic contact dermatitis is uncommonBRITISH JOURNAL OF DERMATOLOGY, Issue 4 2001A. Darvay Background Despite the enormous increase in sunscreen use, allergic contact (AC) and photoallergic (PA) reactions to ultraviolet (UV) filters are considered rare. Objectives To analyse the data from 2715 patients who underwent photopatch testing at St John's Institute of Dermatology during the period 1983,98. Methods A retrospective analysis of all positive photopatch test episodes was undertaken with the results retrieved from the environmental dermatology database and further verified with the original archived patch test documentation for each individual patient. Results In 111 patients with positive reactions (4·1%), there were 155 AC or PA reactions to allergens in the photopatch test series. Eighty PA reactions were observed in 62 (2·3%) patients (32 men and 30 women, age range 28,75 years), with UV filters accounting for 52 positive reactions (65%), drugs 16 (20%), musk ambrette 11 (14%) and the antiseptic trichlorocarbanilide one (1%). The most common UV filter photoallergen was benzophenone-3 with 14 positive results, followed by benzophenone-10 (n = 9), isopropyl dibenzoylmethane (n = 6), p -aminobenzoic acid (PABA) (n = 5), octyl dimethyl PABA (n = 5), butyl methoxydibenzoylmethane (n = 4), isoamyl methoxycinnamate (n = 2), ethyl methoxycinnamate (n = 2), octyl methoxycinnamate (n = 2), amyl dimethyl PABA (n = 2) and phenylbenzimidazole sulphonic acid (n = 1). A similar number of AC reactions to UV filters was detected in this study. Thus 49 patients (1·8%) had a total of 75 reactions: 51 due to UV filters and 24 as a result of exposure to fragrances and therapeutic agents. Benzophenone-10 accounted for 13 AC reactions and benzophenone-3 for eight reactions. Twenty-two patients had a PA reaction alone, whereas 19 patients had chronic actinic dermatitis and 15 patients polymorphic light eruption (PLE) in addition. Thus, 34 of the 62 patients (55%) had a preceding underlying photodermatosis. Conclusions These results show a low yield of positive photopatch tests. Thus, despite the large increase in the use of UV filters over the last decade, the development of PA reactions remains rare. Furthermore, most of the common UV filter photoallergens identified in this study, including PABA, amyl dimethyl PABA and benzophenone-10, are now rarely used in sunscreen manufacture, while isopropyl dibenzoylmethane was voluntarily removed from the market in 1993. Currently, benzophenone-3 is the commonest contact photoallergen still in widespread use. In contrast, the UVB filter octyl methoxycinnamate, used in a number of sunscreens, produced only two positive PA reactions in 12 years of testing. Nevertheless, although these reactions are extremely rare, patients with photodermatoses such as PLE and chronic actinic dermatitis do represent a group of patients at increased risk of developing photoallergy. Further photopatch test series should be regularly reviewed and updated, as the relevance of individual photoallergens changes over time. Currently, there is no evidence that PA reactions represent a common clinical problem. [source] Enantioselective [4+2]-Cycloaddition Reaction of a Photochemically Generated o -Quinodimethane: Mechanistic Details, Association Studies, and Pressure EffectsCHEMISTRY - A EUROPEAN JOURNAL, Issue 9 2004Benjamin Grosch Dipl. Abstract 1,2,3,4-Tetrahydro-2-oxoquinoline-5-aldehyde (2) was prepared from m -aminobenzoic acid and 3-ethoxyacryloyl chloride (4) in 19,% overall yield. Compound 2 underwent a photochemically induced [4+2]-cycloaddition reaction with various dienophiles upon irradiation in toluene solution. The exo product 10,a was obtained with acrylonitrile (9,a) as the dienophile, whereas methyl acrylate (9,b) and dimethyl fumarate (9,c) furnished the endo products 11,b and 11,c (69,77,% yield). The reactions proceeded at ,60,°C in the presence of the chiral complexing agent 1 (1.2 equiv) with excellent enantioselectivity (91,94,% ee). The enantiomeric excess increases in the course of the photocycloaddition as a result of the lower product association to 1. The intermediate (E)-dienol 8 was spectroscopically detected at ,196,°C in an EPA (diethyl ether/isopentane/ethanol) glass matrix. The association of the substrate 2 to the complexing agent 1 was studied by circular dichroism (CD) titration. The measured association constant (KA) was 589,M,1 at room temperature (25,°C) and normal pressure (0.1 MPa). An increase in pressure led to an increased association. At 400 MPa the measured value of KA was 703,M,1. Despite the stronger association the enantioselectivity of the reaction decreased with increasing pressure. At 25,°C the enantiomeric excess for the enantioselective reaction 2 + 9,a,10,a decreased from 68,% ee at 0.1 MPa to 58,% ee at 350 MPa. This surprising behavior is explained by different activation volumes for the diastereomeric transition states leading to 10,a and ent - 10,a. 1,2,3,4-Tetrahydro-2-oxochinolin-5-aldehyd (2) wurde ausgehend von m -Aminobenzoesäure und 3-Ethoxyacryloylchlorid (4) in fünf Schritten und einer Gesamtausbeute von 19,% hergestellt. Die Verbindung ließ sich in Toluol als Lösungsmittel mit verschiedenen Dienophilen in einer photochemisch induzierten [4+2]-Cycloaddition umsetzen (69,77,% Ausbeute), wobei als Hauptprodukt mit Acrylnitril (9,a) das exo -Produkt 10,a entstand. Methylacrylat (9,b) und Dimethylfumarat (9,c) lieferten die endo -Produkte 11,b and 11,c. In Gegenwart des chiralen Komplexierungsreagenz, 1 (1.2 Äquiv.) verliefen die Reaktionen mit exzellenter Enantioselektivität (91,94,% ee). Der Enantiomerenüberschuß nahm im Verlauf der photochemischen Umsetzung zu, was man auf die relativ zum Substrat 2 niedrigere Assoziation des Produkts zurückführen kann. Das intermediär gebildete (E)-Dienol 8 wurde spektroskopisch in einer EPA (Ether/i -Pentan/Ethanol) Glasmatrix bei ,196,°C nachgewiesen. Die Assoziation des Substrats 2 an das Komplexierungsreagenz 1 wurde durch CD-Titration genauer untersucht. Die Assoziationskonstante (KA) wurde bei Zimmertemperatur (25,°C) und Normaldruck (0.1 MPa) zu 589,M,1bestimmt. Bei höherem Druck beobachtete man eine verstärkte Assoziation und bei 400 MPa wurde eine Assoziationskonstante von KA=703,M,1bestimmt. Trotz der stärkeren Assoziaion nahm die Enantioselektivität mit wachsendem Druck ab. Bei 25,°C sank der Enantiomerenüberschuß der enantioselektiven Reation 2 + 9,a,10,a von 68,% ee bei 0.1 MPa auf 58,% ee bei 350 MPa. Dieses überraschende Verhalten läßt sich möglicherweise durch die unterschiedlichen Aktivierungsvolumina für die Übergangszustände erklären, die zu 10,a und ent - 10,a führen. [source] Antituberculosis Agents and an Inhibitor of the para -Aminobenzoic Acid Biosynthetic Pathway from Hydnocarpus anthelminthica SeedsCHEMISTRY & BIODIVERSITY, Issue 8 2010Jun-Feng Wang Abstract Investigation on the extracts of Hydnocarpus anthelminthica seeds led to the isolation of three new compounds, anthelminthicins A,C (1,3, resp.), and two known ones, namely chaulmoogric acid (4) and ethyl chaulmoograte (5). Their structures were determined mainly by using spectroscopic techniques. The absolute configuration at the cyclopentenyl moiety of compound 2 was rationalized by quantum calculations. Base hydrolysis, followed by optical-rotation comparison, allowed assignment of the configuration of chaulmoogric-acid moiety of compounds 3 and 5. Biological assays revealed that compounds 1,5 significantly inhibit Mycobacterium tuberculosis (MTB) growth with MIC values of 5.54, 16.70, 4.38, 9.82, and 16.80,,M, respectively. Compound 3 was found to inhibit the pathway between chorismate and para -aminobenzoic acid (pAba) with a MIC value of 11.3,,M, representing a new example of pAba inhibitor isolated from a natural source. All compounds were not toxic to Candida albicans SC5314 at a concentration up to 100,,M. [source] A New Amperometric Biosensor Based on HRP/Nano-Au/L -Cysteine/Poly(o -Aminobenzoic acid)-Membrane-Modified Platinum Electrode for the Determination of Hydrogen PeroxideCHINESE JOURNAL OF CHEMISTRY, Issue 11 2006Ming-Yu Tang Abstract The third generation amperometric biosensor for the determination of hydrogen peroxide (H2O2) has been described. For the fabrication of biosensor, o -aminobenzoic acid (oABA) was first electropolymerized on the surface of platinum (Pt) electrode as an electrostatic repulsion layer to reject interferences. Horseradish peroxidase (HRP) absorbed by nano-scaled particulate gold (nano-Au) was immobilized on the electrode modified with polymerized o -aminobenzoic acid (poABA) with L -cysteine as a linker to prepare a biosensor for the detection of H2O2. Amperometric detection of H2O2 was realized at a potential of +20 mV versus SCE. The resulting biosensor exhibited fast response, excellent reproducibility and sensibility, expanded linear range and low interferences. Temperature and pH dependence and stability of the sensor were investigated. The optimal sensor gave a linear response in the range of 2.99×10,6 to 3.55×10,3 mol·L,1 to H2O2 with a sensibility of 0.0177 A·L,1·mol,1 and a detection limit (S/N=3) of 4.3×10,7 mol·L,1. The biosensor demonstrated a 95% response within less than 10 s. [source] | |||||||||||||||||||||||||