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PubMed2001

4-([(1E)-(2-Hydroxyphenyl)methylidene]amino)-1,5-dimethyl-2-phenyl-2,3-dihydro-1H-pyrazol-3-one.

In the title compound, C18H17N3O2, a strong intramolecular O-H...N hydrogen bond [N...O 2.607 (3), O-H 0.97 (3) and H...N 1.71 (3) A, and O-H...N 153 (2) degrees ] was observed, which leads to a unique phenol-imine tautomerism in the solid state. The C=N imine bond distance and the C-N-C bond angle [1.287 (2) A and 121.7 (1) degrees, respectively] indicate the existence of this phenol-imine tautomer. In solution, the phenol-imine tautomer of the title free Schiff base ligand is dominant in both polar and non-polar solvents, as supported by 1H NMR and UV-visible spectroscopic data.

Journal Article↗

PubMed2003

Effects of continuous positive airway pressure on upper airway inspiratory dynamics in awake patients with sleep-disordered breathing.

Continuous positive airway pressure (CPAP) is the main treatment of the obstructive sleep apnoea syndrome (OSAS). We assessed its effects on the upper airway (UA) dynamics in response to bilateral anterior magnetic phrenic nerve stimulation (BAMPS) in 17 awake untreated OSAS patients (15 males; 52 +/- 7 years) whose effective CPAP (P(eff)) had been determined beforehand by a conventional titration sleep study. All twitch-related inspirations were flow-limited, flow first rising to a maximum (V(Imax)), then decreasing to a minimum (V(Imin)), and then increasing again (M-shaped pattern). Up to V(Imin), the relationship between driving pressure (P(d)) and flow (V) could adequately be fitted to a polynomial regression model (V = k(1)P(d) + k(2)P(d)(2); r(2) = 0.71-0.98, P < 0.0001). At atmospheric pressure V(Imax) was 700 +/- 377 ml s(-1), V(Imin) was 458 +/- 306 ml s(-1), k(1) was 154.5 +/- 63.9 ml s(-1) (cmH(2)O)(-1), and k(2) was 10.7 +/- 7.3 ml s(-1) (cmH(2)O)(-1). CPAP significantly increased V(Imax) and V(Imin) (peak values 1007 +/- 332 ml and 837 +/- 264 ml s(-1), respectively) as well as k(1) and k(2) (peak values 300.9 +/- 178.2 ml s(-1) (cmH(2)O)(-1) and 55.2 +/- 65.3 ml s(-1) (cmH(2)O)(-1), respectively). With increasing CPAP, k(1)/k(2) increased up to a peak value before decreasing. We defined as P(eff,stim) the CPAP value corresponding to the highest k(1)/k(2) value. P(eff,stim) was correlated with P(eff) (P(eff) = 7.0 +/- 2.0; P(eff,stim) = 6.4 +/- 2.6 cmH(2)O; r = 0.886; 95 % CI 0.696-0.960, P < 0.001). We conclude that CPAP improves UA dynamics in OSAS and that the therapeutic CPAP to apply can be predicted during wakefulness using BAMPS.

Adult↗

PubMed2000

A catalytic asymmetric strecker-type reaction promoted by Lewis acid-Lewis base bifunctional catalyst.

A general asymmetric Strecker-type reaction is reported, catalyzed by the Lewis acid-Lewis base bifunctional catalyst 1. The reaction of trimethylsilyl cyanide (TMSCN) with various fluorenyl imines, including n-aldimines and alpha,beta-unsaturated imines, proceeds with good to excellent enantioselectivities in the presence of a catalytic amount of phenol as additive (20 mol%) (catalytic system 1). The products were successfully converted to the corresponding amino acid derivatives in high yields without loss of enantiomeric purity. Furthermore, hydrogenation or dihydroxylation of the products from alpha,beta-unsaturated imines afforded saturated or functionalized aminonitriles also without loss of enantiomeric purity. The absolute configuration of the products and a control experiment using catalyst 2 supported the proposed dual activation of the imine and TMSCN by the Lewis acid (Al) and the Lewis base moiety (phosphine oxide) of 1. From the mechanistic studies including kinetic and NMR experiments of the catalytic species, the role of PhOH seems to be a proton source to protonate the anionic nitrogen of the intermediate. Specifically, we have found that TMSCN is more reactive than HCN in this catalytic system, probably due to the activation ability of the phosphine oxide moiety of 1 toward TMSCN. This fact prompted us to develop the novel catalytic system 2, consisting of 1 (9 mol%), TMSCN (20 mol%) and HCN (1.2 mol eq). This new system afforded comparable results with obtained by system 1 (1 (9 mol%)-TMSCN (2 mol eq)-PhOH (20 mol%)).

Acids↗

PubMed2004

[Asymmetric reactions based on activation and structure control of molecule--asymmetric reaction of lithiated nucleophiles].

The methodology we developed relies on an external chiral coordinating reagent that forms a deaggregated chelate complex with organolithium reagents. Under the positive control of a chiral dimethyl ether of stilbenediol 4, an asymmetric conjugate addition reaction of organolithium reagents with unsaturated imines and esters proceeded successfully to yield the corresponding addition products with reasonably high stereoselectivity. The sense of stereochemistry is predictable based on a coordination model. The methodology has been extended to a catalytic asymmetric 1,2-addition reaction of organolithium reagents with imines. An enantiotopic group differentiating the opening of cyclohexene oxide with organolithium was also mediated by a chiral ligand. The asymmetric Horner-Wadsworth-Emmons reaction of phosphonates and Peterson reaction of alpha-silylester with 4-substituted cyclohexanone were another successful extension of the methodology. A three-component reagent of lithium ester enolate, lithium amide, and chiral diether reacts with imines to afford beta-lactam with reasonably high enantioselectivity. Tridentate aminoether ligands were also shown to affect the catalytic asymmetric addition of lithium ester enoaltes to imines, giving beta-lactams with high enantioselectivity. Asymmetric conjugate addition of lithium amide to enoates was mediated by a chiral diether ligand to give the beta-aminoester with high yield and enatioselectivity. The methodology has been successfully applied to an asymmetric synthesis of biologically potent compounds. Dihydrexidine, a promising anti-Parkinsonism candidate, and salsolidine, a representative isoquinoline alkaloid, have been synthesized using asymmetric addition reactions of organolithium reagents as the key steps.

Antiparkinson Agents↗

PubMed1996

Hypothesis on a casual link between EMF and an evolutionary class of cancer and spontaneous abortion.

A biophysical theory is presented that supports a causal link between EMF exposures and the different biological endpoints of cancer and spontaneous abortion. The model for time-dependent instability of DNA specificity [Biochem. Genet. 32, 383 (1994)] is assumed to have been operational since DNA became selected as the molecular structure for the genome. Species were consequently required to adapt mechanisms to protect haploid gene pools from the continuous time-dependent accumulation of evolutionary base substitutions. To this end, conserved genetic domains containing mutation-intolerance thresholds are a result of natural selection operating on time-dependent base substitutions. "P53-type" genes are examples of such conserved domains with point mutation thresholds. When the oocyte is fertilized, conserved domains express wild type keto-amino genetic information. During subsequent development and growth, time-dependent evolution events populate G-C sites with enol-imine stationary states that can be transcribed and/or replicated to express transversion and transition mutations. As the level of evolution events would approach the intolerance threshold in the haploid genome, point mutation sensitive genes from conserved diploid domains, e.g. "p53-type" genes, would generate amino acid substituted proteins that have been evolutionarily selected to participate in species preservation by removing from the gene pool those haploid genomes containing advanced levels of mutation which, if propagated, would be inconsistent with survival. Consistent with the evolutionary origin of cancer hypothesis [Cancer Biochem. Biophys: 13, 147 (1993)], perturbations that would enhance rates of populating G-C sites with enol-imine states could accelerate point mutation "activation" of "p53-type" genes that could be manifested as premature cancer in living populations or expressed as spontaneous abortion in unborn populations. The evolution event "rate constant" is (gamma/h)2 where gamma is the quantum mechanical energy shift between G-C states. This expression implies that "additional" magnetic fields could increase rates of populating enol-imine states due to Lorentz force momentum transfer to metastable proton oscillators where induced electric fields and local currents would subject elevated energy proton oscillators to collisional de-exciatations which would increase the energy density of chemical bonds that support hydrogen bonds in DNA, thereby introducing larger energy shift values in (gamma/h)2. This hypothesis is explored for "additional" magnetic fields in the range of 0.15 to 0.01 gauss where the influence of magnetic enhancement energies on rates of populating enol-imine stationary states is evaluated, using Gurney and Condon tunneling time calculations for unperturbed and magnetically enhanced protons to escape metastable keto-amino energy wells. Model calculations are qualitative and are consistent with the experimentally testable hypothesis that "additional" magnetic fields could cause increased rates of accumulating evolutionary base substitutions, thereby increasing probabilities of activating "p53-type" genes which could cause increased incidence of spontaneous abortion in unborn populations and increased incidence of cancer in living populations.

Abortion, Spontaneous↗

PubMed2004

Formation of iminium ions by fragmentation of a2 ions.

Tandem mass spectrometric experiments have been carried out on the protonated amides H-Gly-Ala-NH2, H-Ala-Gly-NH2, H-Ala-Val-NH2, H-Val-Ala-pNA, H-Leu-Phe-NH2, H-Phe-Leu-NH2, H-Phe-Tyr-NH2 and H-Tyr-Phe-NH2 with particular emphasis on the fragmentation of the isomeric a2 ions derived therefrom. Primary fragmentation reactions of the protonated amides involve formation of the y1" and b2 ions with further fragmentation of the b2 ion to form the a2 ion which fragments to form iminium ions. Collision-induced dissociation studies of the mass-selected a2 ions were carried out. For the Gly-Ala, Ala-Gly and Val-Ala a2 ions, weak signals were observed corresponding to loss of CO from the a2 ion. With the exception of the Gly-Ala, Ala-Gly and Val-Ala a2 ions, both possible iminium ions (a1 and the internal iminium ion) are observed with the most abundant being that formed by proton attachment to the imine of higher proton affinity. The results provide strong support for the recently proposed (El Aribi et al. J. Am. Chem. Soc. 2003; 125: 9229) mechanism of fragmentation of a2 ions which involves elimination of CO from the a2 ion to form a proton-bound complex of two imines. Based on this mechanism ab initio calculations of the total energies of the a2 ions and the transition states for fragmentation have been carried out giving the energy barrier for fragmentation of each a2 ion. The experimental results are interpreted in terms of these energetics data, unimolecular rate constants calculated by using the RRKM theory, and the imine proton affinities.

Gas Chromatography-Mass Spectrometry↗

PubMed2000

5a-formylbicyclomycin: studies on the bicyclomycin-Rho interaction.

Bicyclomycin (1) is a commercial antibiotic whose primary site of action is the rho transcription termination factor. A new bicyclomycin irreversible inactivator, 5a-formylbicyclomycin (3), was prepared to provide information concerning the bicyclomycin-rho inactivation process and the drug's binding pocket within rho. The apparent I(50) value for 3 was 35 microM, showing that 3 was a more effective inhibitor of rho poly C-dependent ATPase activity than 1 (I(50) = 60 microM). Mechanistic studies demonstrated that 3 inhibited poly C-dependent ATP hydrolysis, in part, by a reversible, noncompetitive pathway with respect to ATP (K(i) = 62 microM). Incubation of 3 with rho led to efficient imine formation. Adding excess 1 to solutions containing 3 and rho prevented imine formation, demonstrating that 1 and 3 bind to the same active site in the protein. The 3-rho imine was stabilized by either ATP or ADP or by both, and was converted to the nonreversible 3-rho amine adduct upon treatment with NaBH(4). Mass spectrometric analysis of the amine provided a stoichiometry of approximately five bound 3 per rho hexamer indicating the number of bicyclomycin binding sites for the rho hexamer is between five and six. Monomer exchange experiments using modified 3-rho amine and wild type rho demonstrated that no more than two modified subunits per rho hexamer are sufficient to halt poly C-dependent rho ATPase activity.

Adenine Nucleotides↗

PubMed2002

Structure-based analysis and optimization of a highly enantioselective catalyst for the strecker reaction.

A mechanistic investigation of the asymmetric Strecker reaction catalyzed by a metal-free Schiff base catalyst was conducted. The active site of the catalyst, the relevant stereoisomer of the imine substrate, and the solution structure of the imine-catalyst complex were elucidated using a series of kinetics, structure-activity, and NMR experiments. An unusual bridging interaction between the imine and the urea hydrogens of the catalyst was identified and supported by computation. Rational optimization of catalyst structure based on the mechanistic insight led to an improved catalyst for the asymmetric Strecker reaction.

Catalysis↗

PubMed2002

Structural features of azidopyridinyl neonicotinoid probes conferring high affinity and selectivity for mammalian alpha4beta2 and Drosophila nicotinic receptors.

The higher toxicity of neonicotinoid insecticides such as N-(6-chloropyridin-3-ylmethyl)-2-nitroiminoimidazolidine (imidacloprid) to insects than mammals is due in large part to target site specificity at the corresponding nicotinic acetylcholine receptors (nAChRs). We propose that neonicotinoids with a protonated N-unsubstituted imine or equivalent substituent recognize the anionic subsite of the mammalian alpha4beta2 nAChR whereas the negatively charged (delta(-)) tip of the neonicotinoid insecticides interacts with a putative cationic subsite of the insect nAChR. This hypothesis can be tested by using two photoaffinity probes that differ only in the N-unsubstituted imine vs negatively charged (delta(-)) tip. Synthesis methodology was developed for compounds combining three moieties: pyridin-3-ylmethyl or 6-chloropyridin-3-ylmethyl and their 4- and 5-azido analogues; imidazolidine, 4-imidazoline or 4-thiazoline; and N-unsubstituted imine, nitroimine, cyanoimine, or nitromethylene. Structure-activity studies compared displacement of [(3)H]nicotine binding in mammalian alpha4beta2 nAChR and [(3)H]imidacloprid binding in Drosophila nAChR. Preferred compounds are N-(5-azido-6-chloropyridin-3-ylmethyl) with 2-iminothiazoline for alpha4beta2 (K(i) = 0.47 nM) and with 2-nitroiminothiazoline or 2-nitromethyleneimidazolidine for Drosophila (K(i) = 0.72-3.9 nM).

Animals↗

PubMed2005

Practical enantioselective synthesis of beta-substituted-beta-amino esters.

[reaction: see text] A practical, large-scale synthesis of a beta-amino ester 1 was developed. A chiral imine derived from (S)-phenylglycinol and 3-trimethylsilylpropanal was coupled with the Reformatsky reagent 3 with high diastereoselectivity (de > 98%) to give (SS)-4a as the major isomer. The amino alcohol residue of the coupling product 4 was oxidatively cleaved with sodium periodate in the presence of methylamine. An unusual selective oxidative cleavage of the (SS)-isomer was observed and the imine 6 was obtained with ee > 99% while the (RS)-4b isomer was not cleaved. Reaction with p-toluenesulfonic acid monohydrate allowed for the hydrolysis of the imine and the isolation of the amine as its salt. The title compound 1 was then obtained by transesterification, desilylation, and hydrochloride salt formation in a one-pot process. The method was successfully applied toward the synthesis of a wide variety of beta-amino esters.

Aldehydes↗

PubMed2006

Asymmetric synthesis of 2-(2-pyridyl)aziridines from 2-pyridineimines bearing stereogenic N-alkyl substituents and regioselective opening of the aziridine ring.

The addition of chloromethyllithium to the imine derived from 2-pyridinecarboxaldehyde and (S)-valinol, protected as its O-trimethylsilyl ether, gave the 1,2-disubstituted aziridine with good yield and diastereoselectivity. The analogous reaction performed on the imine derived from (S)-valine methyl ester gave the product containing the aziridine ring and the alpha-chloro ketone group coming from the attack of chloromethyllithium to the ester function. Other stereogenic alkyl substituents at nitrogen gave less satisfactory results. Moreover, the aziridination protocol did not work on other aromatic imines which were not capable of bidentate chelation, e.g., 3- and 4-pyridineimine and benzaldimine. Preliminary studies showed the possibility to carry out regio- and stereospecific opening reactions of 2-(2-pyridyl)aziridines by attack of internally generated or external nucleophiles.

Aziridines↗

PubMed2001

Double-level "orthogonal" dynamic combinatorial libraries on transition metal template.

Dynamic combinatorial libraries are mixtures of compounds that exist in a dynamic equilibrium and can be driven to compositional self adaptation via selective binding of a specific assembly of certain components to a molecular target. We present here an extension of this initial concept to dynamic libraries that consists of two levels, the first formed by the coordination of terpyridine-based ligands to the transition metal template, and the second, by the imine formation with the aldehyde substituents on the terpyridine moieties. Dialdehyde 7 has been synthesized, converted into a variety of ligands, oxime ethers L(11)-L(33) and acyl hydrazones L(44)-L(77), and subsequently into corresponding cobalt complexes. A typical complex, Co(L(22))(2)(2+) is shown to engage in rapid exchange with a competing ligand L(11) and with another complex, Co(L(22))(2)(2+) in 30% acetonitrile/water at pH 7.0 and 25 degrees C. The exchange in the corresponding Co(III) complexes is shown to be much slower. Imine exchange in the acyl hydrazone complexes (L(44)-L(77)) is strongly controlled by pH and temperature. The two types of exchange, ligand and imine, can thus be used as independent equilibrium processes controlled by different types of external intervention, i.e., via oxidation/reduction of the metal template and/or change in the pH/temperature of the medium. The resulting double-level dynamic libraries are therefore named orthogonal, in similarity with the orthogonal protecting groups in organic synthesis. Sample libraries of this type have been synthesized and showed the complete expected set of components in electrospray ionization MS.

Aldehydes↗

PubMed2000

Adventures with heterocycles.

Elucidation of mechanisms and discovery of novel reactions are interconnected, as four research chapters from the Munich laboratory demonstrate. 1) In a new opening of the furan ring, 2-methoxyfuran and tetra-acceptor-substituted ethylenes furnish methyl acrylates, which are cis-3-substituted by a cyclopropyl ring that bears the four acceptor groups. Experiments with trans- and cis-1,2-bis(trifluoromethyl)-1,2-dicyanoethylenes (BTE) clarify the role of zwitterionic intermediates. 2) The concerted nature of 1,3-dipolar cycloaddition is well established. On reacting thiocarbonyl S-ylides as electron-rich 1,3-dipoles with tetra-acceptor-substituted ethylenes, the switching to a two-step pathway via zwitterion was diagnosed from a loss of stereospecificity and the formation of strained 7-membered cyclic ketene imines. 3) Stable as crystals, these ketene imines rearrange to 5-membered thiolanes in solution. In contrast to open-chain ketene imines, the cyclic representatives add vinyl ether at the C=N bond and show a novel pathway of dimerization. 4) Cycloadducts of isoquinolinium N-phenylimide with ethylenic dipolarophiles undergo an acid-catalyzed [3.3] sigmatropic hydrazo rearrangement. An exception is the conversion of the dimethyl maleate adduct (C21H20N2O4) by acid into a yellow compound C24H22N2O6; the structure and the astounding mechanism were clarified.

Heterocyclic Compounds↗

PubMed1983

Reactive metabolites of phenacetin and acetaminophen: a review.

Phenacetin can be metabolized to reactive metabolites by a variety of mechanisms. (1) Phenacetin can be N-hydroxylated, and the resulting N-hydroxyphenacetin can be sulfated or glucuronidated. Whereas phenacetin N-O sulfate immediately rearranges to form a reactive metabolite which may covalently bind to protein, phenacetin N-O glucuronide slowly rearranges to form reactive metabolites. Incubation of the purified phenacetin N-O glucuronide under a variety of conditions suggests that N-acetyl-p-benzoquinone imine is a reactive metabolite. This metabolite covalently binds to protein, reacts with glutathione to form an acetaminophen-glutathione conjugate, is reduced by ascorbate to acetaminophen or is partially hydrolyzed to acetamide. (2) Phenacetin can be O-deethylated to acetaminophen, and acetaminophen can be converted directly to a reactive metabolite which may be also N-acetyl-p-benzoquinone imine. (3) Phenacetin can be sequentially N-hydroxylated and O-deethylated to N-hydroxyacetaminophen which spontaneously dehydrates to N-acetyl-p-benzoquinone imine. (4) Phenacetin can be 3, 4-epoxidated to form an alkylating and an arylating metabolite. In the presence of glutathione, a S-ethylglutathione conjugate and an acetaminophen-glutathione conjugate are formed. In the absence of glutathione, the alkylating metabolite may bind to protein and the arylating metabolite is completely hydrolyzed to acetamide and another arylating metabolite which may bind to protein. The structures of the alkylating and arylating metabolites are unknown. Control experiments have shown that in pathway (1) the phenolic oxygen of the acetaminophenglutathione conjugate is derived from water, whereas in pathways (2) and (3) the phenolic oxygen of this metabolite is derived from phenacetin. In pathway (4) the phenolic oxygen was 50% derived from molecular oxygen and 50% from phenacetin. Administration of [p-(18)0]phenacetin to hamsters revealed only a 10% loss of (18)0 in the acetaminophen mercapturic acid (the further metabolic product of the glutathione conjugate) which suggests that, in the hamster, pathways (2) and/or (3) are the primary mechanism of conversion of phenacetin to reactive metabolites in vivo.

Acetaminophen↗

PubMedDate not supplied

[Growth and DNA synthesis inhibition and superoxide anion formation by iminoquinones in Trypanosoma cruzi].

Despite its epidemiological importance, chemotherapy of Chagas' disease is still an unsolved problem. Many drugs have been assayed for their trypanocidal action on T. cruzi, but, so far, naftoquinone-imines have not been included in drug screenings. Fernández A.E. et al., prepared a series of 4-(aminomethylisoxazolyl)-1,2-naftoquinones. Some of these, namely, IIIA (2-hydroxy-N-(3,4-dimethyl-5-isoxazolyl)-1,4-naftoquinone-4- imine), IIIC hydroxy-N-3,5-dimethyl-4-isoxazolyl)-1,4-naftoquinone-4-i min e, IIIE (2-hydroxy-N-(3-methyl-5-isoxazolyl)-1,4-naftoquinone-4-i min e), and IVD (5-methyl-3-isoxazolyl)-1,2-naftoquinone-4-imine) were assayed on T. cruzi epimastigotes. Parasite growth and DNA synthesis were inhibited 12-36% and 14-49%, respectively, by 18-19 microM quinones or 44-83% and 37-73%, respectively, by 60-78 microM quinones (Table 1). The assayed compounds (37-100 microM concentration) stimulated oxygen uptake (Figs. 2 and 3) and superoxide anion generation by epimastigotes to 0.20-0.70 nmol/min/mg of cell protein (O2- measured by the adrenochrome method, Table 2). In the presence of quinones, T. cruzi mitochondrial fraction supplemented with 0.42 mM NADH produced O2- at a rate of 1.10-1.45 nmol/min/mg of protein (31 and 75 microM quinone, respectively; Table 3) whereas, under the same experimental conditions, the microsomal fraction supplemented with NADPH produced O2- at rate of 0.85 and 1.03, respectively (same units). The kinetics of O2- generation by the mitochondrial fraction supplemented with quinone IIIC and NADH revealed two interacting sites (Fig. 5). The corresponding Km(s) were 5.2 and 17 microM and the Vm, 13 and 17 nmoles O2-/min/mg of protein, respectively. The quinone interaction with the mitochondrial membranes involved a "quinone reductase" located on the substrate site of the antimycin site, as shown by the 3.6-fold increase of the oxygen uptake rate induced by quinone IIIE in Fig. 2. Apparently, the quinone excess inhibited the reductase since by varying the quinone concentration in the 0-500 microM range, the oxygen uptake versus quinone concentration plots showed a maximum at 100-150 microM quinone (Fig. 3). O2- generation by quinones depended on the latter redox-cycling, as shown by a) the decrease of quinone absorption at 480-500 nm after incubation with T. cruzi epimastigotes for the time necessary to exhaust the reaction mixture oxygen, and b) the reappearance of the quinone absorption band after oxygenation of the anaerobic reaction mixture (Fig. 6).

Animals↗

PubMed1998

Protein displacement in dye-ligand chromatography using neutral and charged polymers.

Displacement chromatography was demonstrated to perform separations efficiently under mass-overloaded conditions, offering advantages such as increased product recovery and purity, superior resolving power, and concentration and purification in a single processing step. The use of water-soluble polymers for protein displacement in dye-ligand chromatography was initiated in our laboratory. The polymers for displacement were selected using differences spectroscopy to monitor their interactions with a dye-ligand in solution. Non-charged polymers such as poly(N-vinyl pyrrolidone) and poly(N-vinyl caprolactam) efficiently displaced lactate dehydrogenase from porcine muscle from a Blue Sepahrose column. The latter polymer, being thermosensitive, could be easily removed from the eluate and recovered by precipitation at 45 degrees C and low-speed centrifugation. The positively charged polymer poly(ethylene imine) proved to be an even more efficient displacer. The dye-ligand column could be regenerated after application of displacer either by washing with a solution of the soluble ligand Cibacron Blue (in the case of non-charged polymers) or by washing with highly alkaline solutions containing polyanions (in the case of poly(ethylene imine)) The latter formed a soluble complex with poly(ethylene imine) and stripped the column from the polymer.

Animals↗

PubMed2001

Addition of a phosphinidene complex to C=N bonds: P-ylides, azaphosphiridines, and 1,3-dipolar cycloadditions.

The terminal phosphinidene complex PhPW(CO)5 adds to the imine bond of PhHC=N-Ph to give 3-membered ring azaphosphiridines, which undergo ring-expansion with an additional imine to yield a set of four isomeric five-membered ring diazaphospholanes. Treatment with the diimines PhHC=N-(CH2)n-N=CHPh (n=2,3,4) results instead-in all three cases-in only a single isomer of the (CH2)n bridged diazaphospholane. For n=2 or 3, this aminal group is easily hydrolyzed to afford new 6- and 7-membered ring heterocycles. No intermediate azaphosphiridine complex is observed during the addition reaction to the diimines. B3LYP/6-31G* calculations on an unsubstituted, uncomplexed system suggest that the initially formed P,N-ylide of the H2C=N-(CH)2-N=CH2 diimine both kinetically and thermodynamically favors an intramolecular 1,3-dipolar cycloaddition over an imine insertion into the CPN ring of an intermediate azaphosphiridine. Single-crystal X-ray structures for the (CH2)2-bridged azaphospholane complex and the HCl adduct of the 7-membered hydrolysis product are presented.

Journal Article↗

PubMed1985

Intermolecular cross-linking in fibrotic collagen.

The extent, nature and location of the cross-links involved in the stabilization of collagen in fibrotic lesions are crucial to its subsequent removal, naturally or induced by treatment. Stabilization is achieved initially by divalent aldimine and keto-imine intermolecular cross-links located at the end-overlap region in the quarter-stagger alignment of the molecules in the fibre. Elucidation of the location of the cross-links also provides chemical evidence for the organization of the collagen molecule in the fibre. All the fibrous collagens are stabilized by these cross-links, the more stable keto-imine cross-link predominating in the types I and II collagens present in the initial stages of fibrosis. Further stabilization of the lesion usually follows, increasing the resistance to degradative enzymes, thus rendering the fibrosis irreversible. This maturation process, which also occurs in normal ageing, involves the formation of multivalent cross-links derived from the initial aldimine and keto-imine cross-links to form a three-dimensional network through a polymeric peptide (poly-alpha 1CB6 in type I collagen). The nature of these cross-links has not yet been elucidated. The so-called mature cross-link, 3-hydroxypyridinoline, could not be identified in this polymeric network. A secondary process involving non-enzymic glycosylation of lysine residues and subsequent intermolecular cross-linking has also been demonstrated, although the nature and extent of this type of cross-link remain to be determined.

Aging↗