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PubMed1997

Electron affinities of p-benzoquinone, p-benzoquinone imine and p-benzoquinone diimine, and spin densities of their p-benzosemiquinones computed by several quantum chemical models.

Restricted and unrestricted (U) Hartree-Fock (HF), second-order Møller-Plesset perturbation (MP2), density functional (DF), hybrid HF/DF and semiempirical (half-electron (HE) method) models have been used to calculate adiabatic electron affinities (EAad values) of p-benzoquinone (I), p-benzoquinone imine (VI) and p-benzoquinone diimine (XI), as well as expectation values ( ) and spin density distributions in the radical anions of I, VI and XI. The AM1/AM1-HE and ab initio calculated structures are found to be in accord with each other. The ROHF/6-31G(d) method gave the poorest EAad result. The UHF and UMP2 wave functions were found to be substantially spin contaminated (for the radicals) and the accuracies of the EAad values calculated were also poor. The use of molecular energies obtained after spin annihilation did not lead to significant improvement of the UHF and UMP2 results. In contrast to the ROHF, UHF and UMP2 results, the DF(USVWN, UBVWN, UBLYP) and hybrid HF/DF(UB3LYP) methods, as well as the AM1-HE, gave much better results. The calculated EAad values decreased, as predicted by most of the models, in the order EAad(I) > EAad(VI) > EAad(XI). The differences in the EAs, EAad(I)-EAad(VI) and EAad(I)-EAad(XI), were consistently predicted to be about 8-9 and 17-18 kcal/mol, respectively, by the DF, B3LYP and AM1-HE models. The performance of the PM3 and SAM1 models was not as good as the AM1 model. Of all the methods tested, the B3LYP/6-311G(d,p) model is concluded to give the most accurate quantitative trend (I(42.6) > VI(33.1) > XI(23.7)) in EAad. The predicted trend in EA can satisfactorily be rationalized by the calculated LUMO orbital energies, atomic charges and spin density distributions. Analysis of the spin density data predicts that phenoxyl- and anilino-type radical anions predominate in the p-benzosemiquinones of I and XI, respectively, while both phenoxyl- and anilino-type radicals contribute to the structure of the p-benzosemiquinone of VI, with the anilino-type predominating.

Benzoquinones↗
PubMed2005

The chemistry of trifluoromethyl imines and related acetals derived from fluoral.

Trifluoromethylated nitrogen-containing molecules have been shown to have important biological effects and their synthesis is in the focus of the pharmaceutical industry. In the last few years, simple nitrogen derivatives of fluoral, i.e. imines, acetals and oxazolidines, have emerged as powerful building blocks to synthesize these target molecules and relevant precursors. This review summarizes the chemistry of these "N-derivatives of fluoral", with special highlight on the syntheses of peptidomimetic units (amino alcohols, amino acids...) and heterocycles (piperidines, beta-lactams...).

Acetaldehyde↗
PubMed2004

Mechanistic studies on the formal aza-Diels-Alder reactions of N-aryl imines: evidence for the non-concertedness under Lewis-acid catalysed conditions.

The reaction of a para-methoxyaniline, ethyl glyoxalate-derived imine with a series of dienes has resulted in products, which initially suggest the operation of different modes of aza-Diels-Alder reaction. However, a more likely explanation is that a common reaction mechanism is operating, involving a step-wise Lewis-acid catalysed process, which only appears to behave similarly to alternative concerted cycloaddition reactions.

Catalysis↗
PubMed2005

Zinc-mediated carbon radical addition to glyoxylic imines in aqueous media for the synthesis of alpha-amino acids.

The addition of carbon radicals to glyoxylic imines was studied using zinc dust as a radical initiator. The zinc-mediated radical reaction of glyoxylic oxime ethers and hydrazones proceeded smoothly to give the alkylated products via a carbon-carbon bond-forming process in aqueous media. The reaction of the oxime ethers and hydrazones having an Oppolzer's camphorsultam group provided the corresponding alkylated products, which could be converted into enantiomerically pure alpha-amino acids. The diastereoselectivities observed in the reaction of hydrazones were better than those obtained in the reaction of oxime ethers.

Amino Acids↗
PubMed2006

[6 + 6] Schiff-base macrocycles with 12 imines: giant analogues of cyclohexane.

Hexagon-shaped [6 + 6] Schiff-base macrocycles with 12 imine bonds are reported. These giant macrocycles possess 6 N2O2 coordination environments and mass spectrometry evidence for hexametallation of one macrocycle is provided. Semi-empirical calculations reveal two stable conformations with boat and chair geometries for the macrocycles metallated with Ni(II), analogous to the conformations observed for cyclohexane.

Cyclohexanes↗
PubMed2006

Direct addition of alkynes to imines and related C=N electrophiles: A convenient access to propargylamines.

Propargylic amines are highly useful building blocks in organic synthesis, and the corresponding structural motif has been found in various natural products and compounds of pharmaceutical relevance. This article provides an overview of the most significant advances in the preparation of propargylic amines via the direct addition of alkynes to imines and related carbon-nitrogen electrophiles in the presence of metal catalysts or promoters.

Alkynes↗
PubMed1995

Escherichia coli dihydrodipicolinate synthase: characterization of the imine intermediate and the product of bromopyruvate treatment by electrospray mass spectrometry.

Simplified procedures for assaying and purifying dihydrodipicolinate synthase (EC 4.2.1.52), the first enzyme of the lysine biosynthetic pathway, have been developed and electrospray ionization m.s. has been used to observe the imine intermediate with pyruvate and to investigate the reaction of the enzyme with bromopyruvate and fluoropyruvate.

Aspartic Acid↗
PubMed1984

N-acetyl-p-benzoquinone imine: a cytochrome P-450-mediated oxidation product of acetaminophen.

N-acetyl-p-benzoquinone imine (NAPQI) has been proposed as the toxic metabolite of acetaminophen for the past 10 years, although it has never been detected as an enzymatic oxidation product of acetaminophen. We report (i) direct detection of NAPQI formed as an oxidation product of acetaminophen by cytochrome P-450 and cumene hydroperoxide and (ii) indirect evidence that is compelling for NAPQI formation from acetaminophen by cytochrome P-450, NADPH, and NADPH-cytochrome P-450 reductase. Evidence is provided for the rapid reduction of NAPQI back to acetaminophen by NADPH and NADPH-cytochrome P-450 reductase such that steady-state levels of NAPQI were below our detection limits of 6.7 X 10(-8) M. In mouse liver microsomal incubations, radiolabeled analogs of both NAPQI and acetaminophen bound covalently to microsomal protein with the loss of approximately equal to 20% of the acetyl group as acetamide. The binding in each case was decreased by glutathione with concomitant formation of 3-S-glutathionylacetaminophen. The binding also was decreased by L-ascorbic acid, NADPH, and NADH with reduction of NAPQI to acetaminophen. Results of partitioning experiments indicate that NAPQI is a major metabolite of acetaminophen, a considerable fraction of which is rapidly reduced back to acetaminophen.

Acetaminophen↗
PubMed2000

Hepatotoxicity of acetaminophen and N-acetyl-p-benzoquinone imine and enhancement by fructose.

1. Although oral administration of 400 mg/kg acetaminophen (APAP) or 1.8-3.4 g/kg sucrose had no effect on serum levels of alanine aminotransferase (ALT) and sorbitol dehydrogenase (SDH), their co-administration resulted in 20-fold increases in ALT/SDH activities. APAP alone (1250 mg/kg, p.o.) caused the elevation hepatotoxicity parameters, but the levels were lower than observed with co-administration of APAP (400 mg/kg) and sucrose (2.6 or 3.4 g/kg). 2. Sucrose-associated increase in serum ALT/SDH activities was selective with APAP and not detected with carbon tetrachloride (160 mg/kg, i.p.), D-galactosamine (400 mg/kg, i.p.) or alpha-naphthyl isothiocyanate (100 mg/kg, p.o.). 3. To verify the synergistic mechanism of sucrose, a major reactive intermediate of APAP, N-acetyl-p-benzoquinone imine (NAPQI), was given via the portal vein to rat pretreated with sucrose. Clear elevation of ALT/SDH activities was detected in the co-treated group. These results, together with an allopurinol-inhibition experiment, suggest the involvement of high-dose sucrose at a step(s) occurring after the metabolic activation of APAP. 4. Co-administration of glucose or fructose as well as sucrose elevated APAP-induced hepatotoxicity parameters in rat. Fructose but not glucose elevated APAP- or NAPQI-induced LDH leakage in a primary hepatocyte system. The results suggest the primary role of fructose is on the sucrose enhancement of APAP toxicity in rat.

Acetaminophen↗
PubMed1999

Cytotoxic metabolite of acetaminophen, N-acetyl-p-benzoquinone imine, produces cataract in DBA2 mice.

Acetaminophen, or N-acetyl-p-aminophenol (APAP), is metabolized to N-acetyl-p-benzoquinone imine (NAPQI) by cytochrome P450 enzymes in the liver. The biotransformation of APAP is enhanced in P450-inducible C57BL6 (B6) mice but not in non-inducible DBA2 (D2) mice. Our previous studies showed that high doses of APAP administered to B6 mice pretreated with beta-naphthoflavone (BNF), a P450 inducer, produced ocular tissue damage but not in D2 mice similarly treated. We then proposed that the ocular toxicity of APAP is due to accumulation of its metabolite, NAPQI. In the present work, we tested this hypothesis by injecting NAPQI (50 microg in 2 microl propyleneglycol/eye) intracamerally into B6 and D2 mice. NAPQI produced cataract within a few hours (mean = 4 hr) both in B6 and D2 mice. Lower concentrations of NAPQI did not produce lens opacification. Injection of the solvent propyleneglycol only did not cause cataract. Thus, when NAPQI was injected, P450 inducibility was not essential for cataract formation. In addition to vacuole formation in the lens epithelial cells, alterations were observed in the corneal endothelium and ciliary epithelium. The retinal cell layers remained intact. Extensive mitochondrial damage and changes in chromatin structure in the nucleus were evident in the affected lens epithelial cells. The present result dissociates APAP ocular toxicity from its metabolic potentiation by P450 enzymes and will allow us to investigate the mechanism of cataractogenesis in in vitro lens culture systems.

Acetaminophen↗
PubMed1997

99Tcm-phenylene imine phenol as a potential leukocyte labelling agent.

The aim of this study was to evaluate 99Tcm-labelled phenylene imine phenol (99Tcm-Ph(IP)2) as a leukocyte label. The 99Tcm complex exhibits a neutral lipophilic character. The radiochemical purity of the 99Tcm-Ph(IP)2 was high both soon after labelling (94.5 +/- 1.2%, n = 7) and at 24 h (89.7 +/- 1.0%, n = 7). In a comparative study, the labelling efficiency of 99Tcm-Ph(IP)2 and 99Tcm-hexamethylpropylene amine oxime (99Tcm-HMPAO) labelled leukocytes was 47.1 +/- 3.5% (n = 7) and 58.5 +/- 7.0% (n = 7) respectively. The viability of labelled leukocytes was greater than 90% for both 99Tcm complexes. The elution ratios of labelled leukocytes with 99Tcm-Ph(IP)2 at 1, 4 and 24 h were 10.1 +/- 3.5%, 17.2 +/- 2.7% and 23.0 +/- 2.4% (n = 7) respectively, while those with 99Tcm-HMPAO were 10.8 +/- 1.2%, 18.3 +/- 2.0% and 37.0 +/- 3.7% (n = 7) respectively. In conclusion, 99Tcm-Ph(IP)2, with good stability and significant leukocyte labelling efficiency, is a potential leukocyte label.

Animals↗
PubMed1967

Imine-bonding in membrane transport of monosaccharides: invalidity of kinetic evidence.

The proposition that carrier mediation of sugar transport may involve formation of imine complexes with specific cell membrane proteins has recently been advanced. However, the primary data presented accord more quantitatively with the presumption of a nonspecific reaction and furnish no evidence for the existence of the high-affinity glucose-binding sites which are essential to the proposed interpretation.

Binding Sites↗
PubMed2005

The crystal structure and physicochemical characteristics of 2-hydroxy-N-[3(5)-pyrazolyl]-1,4-naphthoquinone-4-imine, a new antitrypanosomal compound.

This study was designed to investigate the physical characteristics and crystalline structure of 2-hydroxy-N-[3(5)-pyrazolyl]-1,4-naphthoquinone-4-imine (PNQ), a new active compound against Trypanosoma cruzi, the causative agent of American trypanosomiasis. Methods used included differential scanning calorimetry, thermogravimetry, hot stage microscopy, polarized light microscopy (PLM), Fourier-transform infrared (FTIR) spectroscopy, and high-resolution X-ray powder diffraction (HR-XRPD). According to PLM and HR-XRPD data, PNQ crystallized as red oolitic crystals (absolute methanol) or prisms (dimethyl sulfoxide [DMSO]-water) with the same internal structure. The findings obtained with HR-XRPD data (applying molecular location methods) showed a monoclinic unit cell [a = 18.4437(1) A, b = 3.9968(2) A, c = 14.5304(1) A, alpha = 90 degrees , beta = 102.71(6) degrees , gamma = 90 degrees , V = 1044.9(1) A(3), Z = 4, space group P2(1)/c], and a crystal structure (excluding H-positions) described by parallel layers in the direction of the b-axis, with molecules held by homochemical (phenyl-phenyl and pyrazole-pyrazole) van der Waals interactions. In addition, FTIR spectra displayed the NH-pyrazole stretch overlapped with the OH absorption at 3222 cm(-1), typical of -NH and -OH groups associated through H-bondings; and a carbonyl stretching absorption at 1694 cm(-1), indicating a nonextensively H-bonded quinonic C=O, which was in accordance with the solved crystal structure of PNQ. The existence of such cohesive forces shed light on the thermoanalytical data, which revealed that PNQ is a stable solid, unaffected by oxygen that decomposed without melting above 260 degrees C.

Antiprotozoal Agents↗
PubMed2000

Controlling factors in chiral bisoxazoline-catalyzed asymmetric lithium ester enolate-imine condensation producing a beta-lactam.

A catalytic amount of external chiral bisoxazoline ligand 3a bearing an isopropyl group as a stereocontrolling group catalyzed a reaction of a lithium ester enolate 4b, generated from 3-pentyl 2-methylpropionate, with benzaldehyde anisidine-imine 5 to afford corresponding beta-lactam 6 in higher 70% ee than that obtained by the reaction using a stoichiometric amount of the ligand. A bulkier ligand 3d bearing a phenyl group gave 81% and 6% ees in stoichiometric and catalytic reactions, respectively. Examination of the varying factors suggested the involvement of mixed aggregates as a reactive species. A working model is presented for prediction of the sense of asymmetric induction.

Catalysis↗