Showing papers in "Journal of The Chemical Society-perkin Transactions 1 in 1998"
450 citations
TL;DR: In this paper, the tuning of donor reactivity during coupling reactions, such that we may avoid the lengthy protecting-group manipulations of classical carbohydrate synthesis, affords a strategy for the rapid assembly of large sugar systems.
Abstract: The concise preparation of complex oligosaccharides remains a significant challenge for synthetic organic chemistry. The tuning of donor reactivity during coupling reactions, such that we may avoid the lengthy protecting-group manipulations of classical carbohydrate synthesis, affords a strategy for the rapid assembly of large sugar systems. Competition reactions have been used to quantify the influence of protecting groups, monosaccharide type, and anomeric leaving groups on the reactivity of various glycosyl donors.
233 citations
TL;DR: In this paper, the authors present a review of the literature from 1999 to February 2001, focusing on the use of the Perkin Transformer algorithm in the context of cancer diagnosis.
Abstract: Covering March 1999 to February 2001. Previous review: J. Chem. Soc., Perkin Trans. 1, 1999, 2849
230 citations
198 citations
TL;DR: Chiral bicyclic 1,2,4-triazolium salts having a defined face of the heterocyclic ring hindered have been synthesized and they catalyse the benzoin condensation in good yield as mentioned in this paper.
Abstract: Chiral bicyclic 1,2,4-triazolium salts having a defined face of the heterocyclic ring hindered have been synthesised and they catalyse the benzoin condensation in good yield; the enantiomeric excesses obtained (up to 80%) are much better than with closely related thiazolium salts and the opposite enantiomer of benzoin predominates.
171 citations
TL;DR: The metal-based luminescence of the Eu and Tb complexes of the octadentate ligands L1 and L2a/2b is a function of pH in aqueous solution.
Abstract: The metal-based luminescence of the Eu and Tb complexes of the octadentate ligands L1 and L2a/2b is a function of pH in aqueous solution: in [EuL1], the red-emission is switched on following N-protonation of the sensitising phenanthridine group (pKa = 4.2, pKS1 = 4.4) with a luminescence enhancement of over 500 for λexc 370 nm. With the Tb complex, the green luminescence switches off following protonation (pKT1 = 5.7) because back-energy transfer occurs rapidly to the low-lying triplet state only in the protonated complex (ET = 21 300 cm–1) and not in the unprotonated (ET = 22 000 cm–1) form. In the corresponding N-methylated complexes, the metal-based emission is quenched by halide ions (e.g.Ksv
–1 = 40 mmol dm–3 for Cl– in [MeEuL1]+) and, for the terbium complexes only, by molecular oxygen (Ksv–1 = 45 Torr for [MeTbL1]+).
162 citations
TL;DR: In this article, the authors showed that long-range migration of 4-hydroxybenzaldehyde molecules on its (010)-face into contacting crystals of p-toluidine or p-anisidine occurs along two different cleavage planes.
Abstract: Twenty preparatively useful azomethines have been quantitatively (100% yield at 100% conversion) obtained as hydrates by grinding together solid anilines with solid benzaldehydes without passing through liquid phases. Unlike (acid catalyzed) azomethine syntheses in solution, the solid–solid condensations proceed ‘waste-free’. The solid-state mechanisms have been elucidated by atomic force microscopy (AFM) and in part by scanning near-field optical microscopy (SNOM) in three cases. The results indicate long distance migration of the aldehydes into the lattice of the aniline derivatives. Stumpy protrusions are formed at the direct points of contact but also close distance sublimation (100 nm range) is successful in the case of p-chlorobenzaldehyde and p-nitroaniline. Long-range flow of 4-hydroxybenzaldehyde molecules on its (010)-face into contacting crystals of p-toluidine or p-anisidine occurs along two different cleavage planes. Steep hills and valleys are left behind. The molecular migrations through the sites of contact are interpreted in terms of crystal packing. The ease of these solid–solid condensation reactions relies on the crystal packing.
149 citations
TL;DR: In this paper, a complete reaction mechanism is proposed, wherein the free-radical oxidation obeys Kochi's mechanism, and the heterolytic dehydrogenation is based on either a high-valent CuIVO species or a [Cu(OH)Cl]2 species.
Abstract: Allylic and benzylic alcohols were oxidized in good yields to the respective ketones by tert-butyl hydroperoxide (TBHP) in the presence of copper salts under phase-transfer catalysis conditions. This dehydrogenation was found to proceed via a heterolytic mechanism. CuCl2, CuCl, and even copper powder were equally facile as catalysts, as they were all transformed in situ to Cu(OH)Cl which was extracted into the organic phase by the phase-transfer catalyst (PTC). Deuterium labeling experiments evidenced the scission of the benzylic C–H bond in the rate-determining step. Nonproductive TBHP decomposition was not observed in the presence of the alcohol substrates. Conversely, the oxygenation of π-activated methylene groups in the same medium was found to be a free radical process, and the major products were the appropriate tert-butyl peroxides. Catalyst deactivation, solvent effects, and extraction effects are discussed. By applying Minisci’s postulations concerning the relative reactivity of TBHP molecules towards tert-butoxyl radicals in protic and nonprotic environments, the coexistence of the homolytic and the heterolytic pathways can be explained. A complete reaction mechanism is proposed, wherein the free-radical oxidation obeys Kochi’s mechanism, and the heterolytic dehydrogenation is based on either a high-valent CuIVO species or a [Cu(OH)Cl]2 species.
129 citations
TL;DR: In this article, the luminescence properties of several 11 lanthanide ion (Sm3+, Tb3+, Dy3+, Pr3+, Nd3+, Ho3+, Tm3+ and Yb3+) complexes based on the m-terphenyl-containing ligands 1−3 have been studied in methanol solutions.
Abstract: The luminescence properties of several 11 lanthanide ion (Sm3+, Tb3+, Dy3+, Pr3+, Nd3+, Ho3+, Tm3+ and Yb3+) complexes based on the m-terphenyl-containing ligands 1–3 have been studied in methanol solutions. The organic complexes show their typical luminescence in the visible (Sm3+, Tb3+, Dy3+ and Pr3+) and in the near-infrared (Nd3+, Er3+ and Yb3+) region of the electromagnetic spectrum. The degree of shielding of the lanthanide ions from high-energy quenching modes of the solvent by the acyclic ligand 3 is less than the shielding by the macrocyclic ligands 1 and 2.Not only the high-energy vibrational modes of the solvent quench the luminescent state, but also the C–H modes of the organic ligand, and even O–D and C–D modes can contribute significantly to the quenching. In general, the high-energy vibrational O–H and C–H modes are most efficient in luminescence quenching, but the quenching is strongly dependent on the magnitude of the energy gap between the lowest luminescent state and a lower-lying state. Luminescence at longer wavelengths can be quenched relatively easily because of the smaller energy gaps, rendering all quenching pathways, especially quenching by the remaining C–H modes in the partially deuterated ligand, efficient. When the energy gap is resonant with (an overtone of) a vibrational mode, i.e. O–H, C–H, O–D or C–D, the luminescence is very efficiently quenched by these modes and can even be extinguished. For instance: Ho3+ luminescence was not observed because the 5S25F5 transition is resonant with the C–H vibrational mode, deuteration is less effective than expected for Pr3+ because the energy gap is resonant with the first overtone of the C–D vibration, and Nd3+ is efficiently quenched by the deuterated solvent because the energy gap is resonant with the first overtone of the O–D vibration.
126 citations
TL;DR: In this paper, the size of the cavities provided by the (ethoxycarbonyl)methoxy groups arranged on the periphery of the thiacalix[4]arene skeleton was determined to be 1∶1 with the stability constant of 102.85 mol-1 dm3 in 50 (v/v)% CDCl3-CD3OD.
Abstract: 5,11,17,23-Tetra-tert-butyl-2,8,14,20-tetrathiacalix[4]arene-25,26,27,28-tetrol (TCA) underwent facile tetra-O-alkylation by treatment with ethyl bromoacetate in the presence of an alkali carbonate as base catalyst in DMF or acetone to provide a mixture of conformational isomers (cone, partial cone, and 1,3-alternate) of 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis[(ethoxycarbonyl)methoxy]-2,8,14,20-tetrathiacalix[4]arene (1), the stereochemistries of which were unambiguously assigned by 1H NMR and X-ray analysis. The isomer distribution depended significantly on the base used, thus providing a facile route for the preparation of a particular conformer; Na2CO3, K2CO3, and Cs2CO3 gave cone- (77% yield), partial-cone- (58% yield), and 1,3-alternate-1 (78% yield) in acetone, respectively. Cone- and partial-cone-1, in turn, showed preference for Na+ and K+, respectively, in an ion-pair extraction study, while 1,3-alternate-1 preferred most Rb+ ion, followed by K+ and then Cs+. These results imply that the size of the cavities provided by the (ethoxycarbonyl)methoxy groups arranged on the periphery of the thiacalix[4]arene skeleton is in the order cone- < partial-cone- < 1,3-alternate-1. The ion selectivity of cone-1 was rather better than that of the methylene-bridged counterpart, 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis[(ethoxycarbonyl)methoxy]calix[4]arene (2). The stoichiometry of the complex of cone-1 with Na+ ion was determined to be 1∶1 with the stability constant of 102.85 mol–1 dm3 in 50 (v/v)% CDCl3–CD3OD.
123 citations
TL;DR: In this article, a review of Contemp. Org. Synth., 1997, 4, 281 is presented, with a focus on the authorship of the authors and the authors.
Abstract: Covering: 1 November 1996 to 31 October 1997Previous review: Contemp. Org. Synth., 1997, 4, 281
TL;DR: In this paper, the ortho-substituted aryl fluorides can be selectively produced from unsymmetrical diaryliodonium salts using a cyclotron generated [18F]fluoride ion.
Abstract: Diaryliodonium salts have been shown to react with fluoride ion at 80 °C in acetonitrile to generate aryl fluorides. The regioselectivity is controlled electronically and by the bulk of the ortho-substituents on the rings, with the latter the dominant factor such that electron-rich rings can be fluorinated. ortho-Substituted aryl fluorides can be selectively produced from unsymmetrical diaryliodonium salts. The process has been used to synthesise [18F] labelled aromatics by the use of cyclotron generated [18F]fluoride ion.
TL;DR: The photomerocyanines resulting from the UV irradiation of closed colourless 3,3-diphenyl-3H-naphtho[2,1-b]pyran and its 3, 3-bis(4-fluorophenyl) derivative have been studied by UV-VIS and NMR spectroscopy as discussed by the authors.
Abstract: The photomerocyanines resulting from the UV irradiation of closed colourless 3,3-diphenyl-3H-naphtho[2,1-b]pyran and its 3,3-bis(4-fluorophenyl) derivative have been studied by UV–VIS and NMR spectroscopy.Kinetic bleaching studies have been carried out on a UV–VIS spectrometer at the photostationary state in acetonitrile solution. A thermal biexponential back-isomerization is observed. These two different kinetics can be attributed to two different isomers of the photomerocyanine.NMR spectroscopy allows us to obtain a 1H, 13C and 19F (where present) structural identification of these two forms: complete assignment for the predominant isomer (trans–cis) and partial assignment for the second one (trans–trans). The presence of a third form (which quickly decays) is also observed. Each open form follows a mono-exponential decay, with very different bleaching rate coefficients. This is the first time that 19F NMR has been used to identify the number and structure of isomers produced by irradiation, illustrating the advantages of this technique.
TL;DR: Both biocatalytic electrodes, Au/PQQ–FAD/GOx and Au/MP-11, were assembled into a biofuel cell using glucose and H2O2 as the fuel substrate and the oxidizer, respectively.
Abstract: Apoglucose oxidase was reconstituted onto a pyrroloquinoline quinone and flavin adenine dinucleotide phosphate, PQQ–FAD, monolayer associated with a rough Au electrode to yield a bioelectrocatalytically active glucose oxidase, GOx. Electrically contacted PQQ–FAD/GOx monolayer was applied to the biocatalytic oxidation of glucose. A microperoxidase-11, MP-11, monolayer was assembled onto a rough Au electrode and used for the biocatalytic reduction of H2O2. Both biocatalytic electrodes, Au/PQQ–FAD/GOx and Au/MP-11, were assembled into a biofuel cell using glucose and H2O2 as the fuel substrate and the oxidizer, respectively. The biofuel cell generates an open-circuit voltage, Voc, of ca. 310 mV and a short-circuit current density, isc, of ca. 114 µA cm–2. The maximum electrical power, Pmax, extracted from the cell is 32 µW at an external optimal load of 3 kΩ. The fill factor of the biofuel cell, f = PmaxIsc–1Voc–1, is ca. 25%.
TL;DR: A review of the literature published during the period from October 1996 to October 1997, with an emphasis placed upon solid-phase small molecule synthesis, linkers and cleavage strategies is given in this article.
Abstract: This review covers the literature published during the period from October 1996 to October 1997, with an emphasis placed upon solid-phase small molecule synthesis, linkers and cleavage strategies.
TL;DR: In this article, N-alkyl-substituted prop-2-yn-1-amines and N-tri-, tetra-and penta-alkyl or cycloalkyl chains of appropriate length are present in the guanidines and the reaction readily occurs under heterogenous conditions without solvent.
Abstract: N-alkyl-substituted prop-2-yn-1-amines and N-tri-, tetra- and penta-alkyl-substituted guanidines or other strong organic bases assemble under the action of carbon dioxide to afford carbamates, from which methyleneoxazolidinones 2 are formed by ring closure. If alkyl or cycloalkyl chains of appropriate length are present in the guanidines the reaction readily occurs under heterogenous conditions without solvent.
TL;DR: In this paper, a synergistic antioxidation mechanism involving the recycling of α-tocopherol by the green tea polyphenol is proposed, which significantly increases the inhibition period and protects the latter from depletion.
Abstract: Peroxidation of linoleic acid was initiated by a water soluble azo initiator 2,2′-azo(2-amidinopropane)dihydrochloride (AAPH) in tert-butyl alcohol–water solution and inhibited by α-tocopherol and polyphenols extracted from green tea, i.e. (–)-epicatechin (EC), (–)-epigallocatechin (EGC), (–)-epicatechin gallate (ECG), (–)-epigallocatechin gallate (EGCG) and gallic acid (GA), either alone or in combination. The reaction kinetics were followed by oxygen uptake, formation of linoleic acid hydroperoxides and consumption of the antioxidants. It was found that the tea polyphenols could slow the rate of peroxidation with an activity sequence of EGCG > EGC ≈ ECG > EC ≈ GA, but no definite inhibition period was observed. On the other hand, the tea polyphenols could significantly increase the inhibition period of α-tocopherol and protect the latter from depletion with an activity sequence of EGCG ECG ≈ EGC > GA > EC when they were used in combination. A synergistic antioxidation mechanism involving the recycling of α-tocopherol by the tea polyphenol is proposed.
TL;DR: EPR spin trapping together with UV-VIS spectroscopy has been employed to examine the reaction of HOCl with amino acids and some small peptides in the presence of free amine groups on both amino acid side chains and at the N-terminus as discussed by the authors.
Abstract: EPR spin trapping together with UV–VIS spectroscopy has been employed to examine the reaction of HOCl with amino acids and some small peptides. Evidence has been obtained for the formation and subsequent decomposition of short-lived chloramine derivatives from free amine groups present on both amino acid side-chains and at the N-terminus. Radical formation, detected by EPR spin trapping, occurs concurrently with chloramine decomposition. This process is enhanced by, but does not require, the presence of added Fe2+. With some substrates nitrogen-centred (aminyl, RNH˙ or RNH2˙+) radicals, formed from cleavage of the N–Cl bond of the chloramine, can be detected. These initial aminyl radicals undergo a variety of hydrogen atom abstraction, rearrangement and fragmentation reactions to give carbon-centred species. Evidence has been obtained for both inter- and intra-molecular (1,2- and 1,5-) hydrogen atom abstraction reactions, decarboxylation and β-scission processes. The last of these only occurs to a significant extent where the resulting radical is highly stabilised, for example, by aromatic substituents, and results in loss of the amino acid side-chain. Studies with N-acetyl derivatives and peptides are consistent with reaction of HOCl at amide (peptide) bonds to give transient chloramides which rapidly decompose to give (undetected) amidyl [˙N(R)C(O)R′] radicals. These species undergo rapid 1,2-hydrogen atom shift reactions to give (stabilised) α-carbon radicals with most peptides. Evidence has also been obtained for the occurrence of hydrogen atom abstraction and decarboxylation reactions with these substrates.
TL;DR: In this article, the authors present a review of the work of this article on the Perkin Transformer Transformer and its application in the area of bioengineering, including the following:
Abstract: Covering: 1 April 1998 to 30 June 1999. Previous review: J. Chem. Soc., Perkin Trans. 1, 1998, 4175.
TL;DR: The solution conformation of the synthetic octapeptide Boc-Leu-Val-Val, D-Pro-Gly Type II′ β-turns was investigated in organic solvents by NMR spectroscopy as discussed by the authors.
Abstract: The solution conformation of the synthetic octapeptide Boc-Leu-Val-Val-D-Pro-Gly-Leu-Val-Val-OMe 1 and Boc-Leu-Val-Val-Pro-Gly-Leu-Val-Val-OMe 2 have been investigated in organic solvents by NMR spectroscopy. Peptide 1 adopts well-defined β-hairpin conformations in CDCl3, C6D6 and (CD3)2SO, nucleated by a D-Pro-Gly Type II′ β-turn, as demonstrated by the observation of characteristic nuclear Overhauser effects (NOEs) between backbone protons and solvent shielding of NH groups involved in cross-strand hydrogen bonding. Chemical shifts and coupling constants provide further support for the β-hairpin conformation, which is consistent with the observation of a single negative circular dichroism band at 216 nm in methanol. In peptide 2, there is no characteristic interstrand NOE observed in (CD3)2SO, while in CDCl3 pronounced aggregation results in line broadening. The observation of a low temperature coefficient for the Leu(6)NH proton favours a population of Pro-Gly Type II β-turn conformations. These results suggest that in short peptide sequences, the precise nature of the β-turn is critical for hairpin formation, with Type II′ β-turns being particularly effective.
TL;DR: A practical and versatile procedure for the solid-phase synthesis of N-linked glycopeptide T-cell epitope analogues 40–46 of the mouse haemoglobin-derived decapeptide Hb (67–76), VITAFNEGLK is demonstrated.
Abstract: In the present report a practical and versatile procedure for the solid-phase synthesis of N-linked glycopeptides from natural sources has been demonstrated. The approach is based on the mild hydrazinolysis procedure to release N-linked oligosaccharides in their intact unreduced form from the natural glycoproteins, e.g. fetuin and ribonuclease B and subsequent formation of the corresponding glycosylamines. Treatment of the reducing sugars 1–7 with a saturated solution of ammonium hydrogen carbonate in either water or dimethyl sulfoxide (DMSO) gives in almost quantitative yields the glycosylamines 8–14. Coupling of the unprotected glycosylamines 8–14 to the side-chain-activated aspartic acid derivative Fmoc-Asp(ODhbt)-OBut 16 affords the N-glycosylated asparagine derivatives 17–23. Subsequent acetylation of the carbohydrate hydroxy groups and cleavage of the tert-Bu ester by trifluoroacetic acid (TFA) treatment yields the glycosylated N-linked building blocks 31–37. The building blocks 31–37 are then incorporated into the multiple-column peptide-synthesis protocol of the glycopeptide T-cell epitope analogues 40–46 of the mouse haemoglobin-derived decapeptide Hb (67–76), VITAFNEGLK. The decapeptide sequence VITAFNEGLK binds well to the MHC Class II Ek molecule and is non-immunogenic in CBA/J mice. Syntheses of several natural and unnatural glycosylations, e.g. N-acetylglucosamine, N,N′-diacetylchitobiose, glucose, maltotriose, maltoheptose and di- and tri-antennary complex oligosaccharides on the decapeptide Hb (67–76) affording the N-linked glycopeptides 40–46 are described. The N-linked glycopeptides 40–46 have been fully characterised by 1D- and 2D-1H and 13C NMR spectroscopy and by ES-MS.
TL;DR: In this paper, a detailed kinetic and spectroscopic investigation has been made of the oxidation of 4-(4-sulfophenylazo)-1-naphthol (Orange I, 4) and a series of specially synthesised, substituted 1-arylazo-2-nAPHthol dyes (6a, 6b) by hypochlorite, peracids and hydrogen peroxide in aqueous media.
Abstract: A detailed kinetic and spectroscopic investigation has been made of the oxidation of 4-(4-sulfophenylazo)-1-naphthol (Orange I, 4) and 1-(4-sulfophenylazo)-2-naphthol (Orange II, 5) and a series of specially synthesised, substituted 1-arylazo-2-naphthol dyes (6a, 6b) by hypochlorite, peracids and hydrogen peroxide in aqueous media. In all cases, observed second-order rate constants exhibit maxima in alkaline media at a pH equal to the midpoint of the pKA values of dye and oxidant. It is found that substituents upon the aryl ring ortho to the azo group suppress dye reactivity towards hypochlorite and, in addition, it is shown that peracids exhibit similar trends. In contrast, oxidation by hydrogen peroxide is enhanced by ortho substituents, suggesting that it functions via a different mechanism. Surprisingly, the dye common anion has been identified as the form of the dye most susceptible to oxidation by peracids and hypochlorite, with the undissociated oxidant molecules acting as electrophiles. In contrast, dye oxidation by hydrogen peroxide proceeds via the perhydroxyl anion and the hydrazone tautomeric form of the dye. The main function of ortho substituents is to increase the dye pKA, thereby influencing observed rates (k2obs) by changing the equilibrium concentration of reactive species. Substituents also exert an electronic effect on absolute rate constants, k2, giving good Hammett plots for both ortho and para substituents. Reactive oxygen species, e.g. singlet oxygen, superoxide or hydroxyl radicals, are not implicated in the rate-controlling step of the reaction.
TL;DR: In this article, electron paramagnetic resonance (EPR) was used to detect reactive radical oxygen species (RROS) using three nitrones as spin traps and three water soluble amidino-azo-initiators as sources for alkylperoxyl and/or alkoxyl radicals.
Abstract: Spin trapping with nitrones coupled with the use of electron paramagnetic resonance (EPR) is one of the most effective techniques to observe reactive radical oxygen species (RROS), even though the distinction between, for example, alkoxyl and alkylperoxyl radicals is not an easy task. In the light of this very problem, this work summarizes our results using three nitrones as spin traps and three water soluble amidino-azo-initiators as sources for alkylperoxyl and/or alkoxyl radicals. The principal conclusion of this study is that only the corresponding alkoxyl radicals were found to add to the nitrones, and no evidence was found for the alkylperoxyl radical-spin adducts. The spin traps 5-(diethoxyphosphoryl)-5-methyl-4,5-dihydro-3H-pyrrole N-oxide (DEPMPO) as well as methyl-N-durylnitrone (MDN) rendered a discriminative spin adduct assignment much simpler as compared to 5,5-dimethyl-4,5-dihydro-3H-pyrrole N-oxide (DMPO), where liquid chromatography–electrospray mass spectrometry (LC–ESMS) was employed to substantiate the EPR results. For the kinetic decomposition behavior of the azo initiators it was found that at pH 6.2 2,2′-azobis(2-methylpropionamidine) dihydrochloride (AAPH) undergoes hydrolysis to the corresponding amides while the cyclic initiators 2,2′-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (VA-44) and 2,2′-azobis{2-[2-(4-methyl)imidazolin-2-yl]propane} dihydrochloride (Me-VA-44) are resistant towards hydrolysis over the employed timescale of 30 h.
TL;DR: In this article, the effects of substituent groups at the 4 and 7 positions of the benzofurazan skeleton on the fluorescence characteristics (fluorescence intensity, maximum excitation wavelength and maximum emission wavelength) were obtained for this purpose.
Abstract: To develop new fluorogenic reagents having the benzofurazan structure, we investigated the effects of the substituent groups at the 4- and 7-positions of the benzofurazan skeleton on the fluorescence characteristics (fluorescence intensity, maximum excitation wavelength and maximum emission wavelength). Seventy benzofurazan compounds substituted at the 4- and 7-positions were obtained for this purpose. The Hammett substituent constant (σp) was adopted as a parameter for electronic effects by substituent groups. The study using the sum and the difference of the Hammett substituent constants (σp) at the 4- and 7-positions revealed that the highly fluorescent benzofurazan compounds were classified into two groups and that singlet excitation energies, calculated by the maximum excitation and emission wavelengths, of the benzofurazan compounds were different between these two groups. The fluorescence characteristics of benzofurazan compounds substituted at the 4- and 7-positions were empirically predictable by these relationships and σp values. A new fluorogenic reagent, 4-phenylaminosulfonyl-7-fluoro-2,1,3-benzoxadiazole, for amines was developed based on this method and applied to the amino acids analysis.
TL;DR: This result supports a model in which the reactive methylene bridge of bilirubin points into the binding pocket of human serum albumin, and the two bulky p-fluorothiophenyl groups do not appear to impede interaction with the protein.
Abstract: Addition of excess (>500 equiv) of p-fluorothiophenol to bilirubin in the presence of toluene-p-sulfonic acid catalyst afforded 3,18-didevinyl-3,18-bis[2-(p-fluorothiophenyl)ethyl] bilirubin 2 from anti-Markovnikov addition to both the exo and endo vinyl groups of bilirubin Toluene-p-sulfonic acid is not essential as p-fluorothiophenol acts as the acid and nucleophile in the reaction In contrast, in the presence of toluene-p-sulfonic acid, regioselective Markovnikov addition of thioacetic S-acid to the exo vinyl group occurs, in agreement with previous studies of the addition of a range of oxygen and sulfur nucleophiles to bilirubin (P Manitto and D Monti, Experientia, 1973, 29, 137) Binding of 2 to human serum albumin was measured by circular dichroism The two bulky p-fluorothiophenyl groups do not appear to impede interaction with the protein This result supports a model in which the reactive methylene bridge of bilirubin, that connects rings B and C, points into the binding pocket of human serum albumin
TL;DR: In this article, the reaction site in arylazonaphthol dyes has been pinpointed by investigating k2E for substituted dyes with the 1-arylazo-2-naphthols and 2-aryl-azo-1-nophthol structural motifs.
Abstract: Kinetic and product analyses have been made of the oxidation of an activated azo dye, 4-(4-sulfophenylazo)-N,N-dimethylaniline (Methyl Orange, 1) and a series of tautomeric arylazonaphthol dyes by peracids at 40 °C in alkaline media, particularly peroxosulfate. The arylazonaphthol dyes are readily degraded into fragments (k2E = 102–103M–1 s–1) whereas the azo link in Methyl Orange is relatively inert (k2E 10–1M–1 s–1) consistent with the view that dyes that contain the azo or hydrazo link are more resistant to oxidation than the common anion form of arylazonaphthol dyes. Methyl Orange is decolourised by peroxosulfate (k2E = 7.6 M–1 s–1) simply via oxidation of the tertiary amine to amine oxide, resulting in a shift of the spectrum into the UV region. The reaction site in arylazonaphthol dyes has been pinpointed by investigating k2E for substituted dyes with the 1-arylazo-2-naphthol and 2-arylazo-1-naphthol structural motifs. In direct contrast to results for oxidation by hydrogen peroxide, the presence of an ortho-sulfonate in the aryl ring retards oxidation but an ortho-sulfonate in the naphthol ring does not. This suggests oxidation is initiated by electrophilic reaction by the negatively charged peroxosulfate at the nitrogen atom of the common dye anion that is in close proximity to the aryl ring. In contrast to oxidation by hypochlorite, the introduction of an amino group into the 8-position of 2-arylazo-1-naphthol dyes protects the dye against oxidation, via its influence upon the dye pKA.
TL;DR: In this article, a linear free energy relationship (LFER) has been found between the pseudorotaxane stability constants (Kas) and the Hammett substituent constants (σ).
Abstract: The crown ether dibenzo[24]crown-8 (DB24C8) is interpenetrated by a wide range of disubstituted dibenzylammonium cations to generate [2]pseudorotaxane complexes by virtue of, inter alia, hydrogen bonds. 1H NMR spectroscopic measurements indicate that the solution phase binding strengths of the pseudorotaxane complexes can be controlled accurately via judicious manipulation of the substituents attached to the dibenzylammonium cations’ aryl rings. A linear free energy relationship (LFER) has been found to exist between the complexes’ stability constants (Kas) and the Hammett substituent constants (σ). X-Ray crystallographic analyses of the pseudorotaxanes reveal that each of their discrete supramolecular units display similar solid state superstructures. However, these analyses also demonstrate that the pseudorotaxanes associate with one another, via a myriad of intersupramolecular packing motifs, to generate a wide range of novel superarchitectures.
TL;DR: In this article, the synthesis of 2-aroylbenzo[b]furans, 1,3-thiazoles and 3-aryl-5,6-dihydroimidazo[2,1-b][1,3]thiazole from α-tosyloxyketones and mineral oxides in processes accelerated by exposure to microwaves.
Abstract: The expeditious solventless syntheses of 2-aroylbenzo[b]furans, 1,3-thiazoles and 3-aryl-5,6-dihydroimidazo[2,1-b][1,3]thiazoles are described from readily accessible α-tosyloxyketones and mineral oxides in processes that are accelerated by exposure to microwaves The 2-aroylbenzo[b]furans are readily obtained from salicylaldehydes and α-tosyloxyketones in the presence of solid potassium fluoride doped alumina (KF–Al2O3) whereas montmorillonite K-10 clay provides 1,3-thiazoles from thioamides and α-tosyloxyketones Similarly, ethylenethiourea and α-tosyloxyketones provide bridgehead nitrogen heterocycles, 3-aryl-5,6-dihydroimidazo[2,1-b][1,3]thiazoles, in excellent yields which are not easily obtainable under classical heating conditions