The mechanism of imine–enamine tautomerism of 2- and 4-phenacylquinolines

Carey, A. R. Edwin; Fukata, Gouki; O’Ferrall, Rory A. More; Murphy, Michael G.

doi:10.1039/p29850001711

Cited by 31 publications

(34 citation statements)

References 8 publications

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“…The distribution of ionic speciation of MC‐LR was calculated as a function of medium pH following Carey et al and is depicted in Figure A.…”

Section: Methodsmentioning

confidence: 99%

“…However, time-dependent pH changes were observed in both pH levels, suggesting that experimental data regarding the effects of water pH on the toxicity of MC-LR provided only partial information. The distribution of ionic speciation of MC-LR was calculated as a function of medium pH following Carey et al [29] and is depicted in Figure 1A.…”

Section: Toxicity Evaluation Under Varying Water Ph Conditionsmentioning

confidence: 99%

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Combined effects of the cyanobacterial toxin microcystin‐LR and environmental factors on life‐history traits of indigenous cladoceran Moina macrocopa

Kim

Seo

Yoon

et al. 2014

Enviro Toxic and Chemistry

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Environmental factors are important in that they might interact with toxicants and could affect the concentration-response relationship of the toxicants in the water environment. Microcystins (MCs) produced by algal blooming are natural toxins that exert severe impacts on aquatic organisms. Despite the possibility of interaction effects between environmental factors and MCs, very few studies have been carried out to date. In the present study, the authors evaluated the effect of 3 environmental factors on chronic toxicity of MC-leucine-arginine (MC-LR; 0 µg/L, 0.8 µg/L, 4 µg/L, 20 µg/L, 100 µg/L, 500 µg/L) to the freshwater invertebrate Moina macrocopa. Three environmental factors were determined to reflect the reasonable worst conditions of the water body in South Korea: high water temperature (25 °C), the highest concentration of nutrients (ammonia-nitrogen [NH3 -N] = 3.8 mg/L; nitrate-nitrogen [NO3 -N] = 8.5 mg/L) during the occurrence of algal bloom, and 2 pH conditions of 7.0 and 9.0, which satisfy the test acceptance criteria for the Daphnia test. Among the various environmental factors being tested, high water temperature and NO3 -N elevated chronic toxicity of MC-LR, whereas NH3 -N reduced toxicity. Water pH did not influence chronic toxicity of MC-LR to M. macrocopa. This observation suggests that those environmental factors are responsible for changing the trend of MC-LR toxicity.

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“…The distribution of ionic speciation of MC‐LR was calculated as a function of medium pH following Carey et al and is depicted in Figure A.…”

Section: Methodsmentioning

confidence: 99%

Section: Toxicity Evaluation Under Varying Water Ph Conditionsmentioning

confidence: 99%

Combined effects of the cyanobacterial toxin microcystin‐LR and environmental factors on life‐history traits of indigenous cladoceran Moina macrocopa

Kim

Seo

Yoon

et al. 2014

Enviro Toxic and Chemistry

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“…The measurements in DCl lead to a pH-independent rate constant 1.53 × 10 -3 s -1 and corresponding solvent isotope effect k H2O /k D2O ) 7.0, which is consistent with rate-determining proton transfer from H 3 …”

Section: +2mentioning

confidence: 68%

“…For acetic acid buffers, the reaction scheme in eq 18 is modified to that in eq 20 in which the metal-enolate complex is now protonated by acetic acid instead of H 3 The exchange equilibrium constants K x for copper and zinc ions are conveniently converted to equilibrium constants K B for binding the metals to the enolate anion by making use of the thermodynamic cycle shown in Scheme 3. Again the equilibria are represented by single arrows to show the directions of reactions to which the pKs refer.…”

Section: Correlation Of Pk a Values For Substituted Pyridines Andmentioning

confidence: 99%

Binding Catalysis and Inhibition by Metal Ions and Protons in the Enolization of Phenylacetylpyrazine

et al. 2009

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A study of the enolization of phenylacetylpyrazine (PzCOCH(2)Ph) catalyzed by acid, base and metal ions in aqueous solution shows, unusually, that metal ions are more effective catalysts than protons, e.g., for zinc k(Zn)/k(H) = 600. Such behavior contrasts with that of the structurally related phenacylpyridine (PyCH(2)COPh) for which k(Zn)/k(H) = 0.0065. To interpret this difference, equilibrium constants for the tautomerization of phenylacetylpyrazine and for binding of protons and metal ions to its keto tautomer and enolate anion have been measured or estimated and are compared with existing measurements for phenacylpyridine. A tautomeric constant, K(E) = 1.2 x 10(-3) (pK(E) = 2.9), is derived by combining forward and reverse rate constants for enolization measured, respectively, by iodination or bromination of the keto tautomer and relaxation of the less stable enol. For the keto tautomer, NMR measurements yield a pK(a) = -0.90 for N-protonation, and spectrophotometric measurements give pK(a) = 11.90 for ionization to an enolate anion. For the enol, pK(a) values of 0.44 and -4.80 for mono- and diprotonation are obtained from the pH profile for ketonization and absorbance measurements for the transient enol reactant. Binding constants for metal ions (Cu(2+), Ni(2+), Zn(2+), Co(2+), and Cd(2+)) are derived from the saturation of their catalysis of the ketonization reaction. It is found that ketonization is efficiently catalyzed by metal ions but inhibited by acid. These findings, and the striking difference from phenacylpyridine, are ascribed to differences in thermodynamic driving force arising from stronger binding of the proton to the more basic pyridine than pyrazine nitrogen atom in both the reactant keto tautomer and in the enaminone or zwitterion product of the rate-determining (proton transfer) step of the enolization.

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“…Tautomerism in 2-acylmethylquinolines and 2-acylmethylpyridines has been studied by various spectroscopic methods and ketimine-enaminone and ketimine-enolimine equilibria (Scheme 1) were reported for these compounds, respectively [5][6][7][8][9][10][11].…”

Section: Introductionmentioning

confidence: 99%

Synthesis of 6-acylmethylphenanthridine enaminones

Khouzani

Sadeghi²,

Mehrabi

et al. 2005

JICS

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A series of 6-acylmethylphenanthridine derivatives were synthesized by reaction of aliphatic and aromatic esters with 6-methylphenanthridine in the presence of phenyllithium. Enaminone form of the obtained compounds was investigated by spectroscopic methods. The results revealed that the presence of aromatic rings on 3-and 4-position of 2-acylmethylquinolines (6-acylmethylphenanthridines) is the most important factor for the preference of the enaminone form b. It was found that the intramolecular hydrogen bonding is the only factor that can damage aromaticity of the phenanthridine moiety.

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The mechanism of imine–enamine tautomerism of 2- and 4-phenacylquinolines

Cited by 31 publications

References 8 publications

Combined effects of the cyanobacterial toxin microcystin‐LR and environmental factors on life‐history traits of indigenous cladoceran Moina macrocopa

Combined effects of the cyanobacterial toxin microcystin‐LR and environmental factors on life‐history traits of indigenous cladoceran Moina macrocopa

Binding Catalysis and Inhibition by Metal Ions and Protons in the Enolization of Phenylacetylpyrazine

Synthesis of 6-acylmethylphenanthridine enaminones

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