Isotopic hydrogen exchange in purines—mechanisms and applications

Jones, John R.; Taylor, Scott

doi:10.1039/cs9811000329

Cited by 30 publications

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“…In a previous study (3) involving l-methyl[2-3~]imidaz~le (2a) the rate constants were found to increase with increasing pH in the lower pH region, while at intermediate pH (7)(8)(9)(10) the rate constants plateaued. If the rate-pH rofiles for …”

Section: Resultsmentioning

confidence: 99%

“…0.69). The poorer correlation is not surprising in that Jones and Taylor (10) found that various classes of substrates tended to show separate correlations. More specifically, compounds containing the purine nucleus seemed to show a separate correlation from that of substrates possessing the imidazole nucleus.…”

Section: Reactiviry Relationshipsmentioning

confidence: 97%

“…Jones and co-workers (10,21) have shown that there is a linear correlation between log k, the second-order rate constant for C(2)-proton exchange in azoles, and the pKa for N(3)-protonation; this relationship is followed by histidine (I), imidazole (2), benzimidazole, and their methyl derivatives. In fact, when the data for 1-methylimidazole and l-methylbenzimidazole are included with that originally presented (21), the slope and correlation coefficient only vary from -0.72 and 0.993 to -0.66 and 0.995, respectively, Fig.…”

Section: Reactiviry Relationshipsmentioning

confidence: 99%

“…In a study of the rates of detritiation of l-methyl [8-3H]inosine in the presence of cu2+, zn2+, and Ag+ ions, the metal ions were found to influence the rate of isotopic exchange in very different ways (10). For example, Zn2+ had virtually no effect on the rate of detritiation while Ag+ was found to suppress the rate of exchange to an even greater degree than Cu2+.…”

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Metal ion – biomolecule interactions. Part 14. Methylmercury and hydrogen ion catalysis of C(2)-H isotopic exchange in 1-methylhistidine

Buncel¹,

Joly²,

Yee³

1989

Can. J. Chem.

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. Can. J . Chem. 67, 1426Chem. 67, (1989. The rate constants for detritiation from the C(2) position of 1-meth~l[2-~~]histidine have been determined in a series of aqueous buffers at 8S0C. The resulting sigmoidal rate-pH profile was indicative of a mechanism involving hydroxide ion attack on the N(3)-protonated (4) and the amino-protonated (5) forms of 1-methylhistidine, and dissection of the kinetic data allowed the extraction of the second-order rate constants for the two pathways, k and k t . The unusually large value of k' for a species not protonated at N(3) of the imidazole ring suggested the involvement of a kinetically equivalent zwitterionic form of the substrate (7). Comparison of the rate constant k with values determined previously for closely related substrates, such as histidine, 1-methylimidazole, and imidazole, led to the use of FMO theory to explain the effect of the various structural changes, e.g., the effect of methylation and a positively charged side chain on k and k'. The addition of MeHgN03 resulted in a decrease in the pseudo-first-order rate constant for dehitiation. The rate retardation was discussed in terms of two mechanisms (Schemes 2 and 3). Analysis of the data in terms of the various metal-ion-coordinated species present under the experimental conditions showed that the reactivity of the protonated substrate greatly exceeds that of the metal-coordinated species. The difference in the catalytic ability of H+ vs. MeHg+ is discussed in terms of the extent of positive charge developed on the ligating heteroatom in the ylide (carbenoid) reaction intermediate.Key words: methylmercury, 1-methylhistidine, isotopic exchange, proton transfer, metal ion catalysis.ERWIN BUNCEL, HELEN A. JOLY et DIANE C. YEE. Can. J. Chem. 67, 1426Chem. 67, (1989.On a dktermink les constantes de vitesse de la dktritiation h partir de la position C(2) de la rn~th~l-l[~~-2]-histidine dans une skrie de solutions tampons ?i 85°C. Le profil sigmoidal de la courbe de vitesse en fonction du pH obtenue, tkmoigne I'existence d'un mkcanisme faisant intervenir l'attaque de l'ion hydroxyle sur les formes protonkes en N(3) (4) et amino-protonke (5) L'addition du MeHgN03 conduit h une diminution de la constante de vitesse de pseudo ordre un de la dktritiation. On discute de la diminution de la vitesse en fonction de deux mkcanismes (schkmas 2 et 3). L'analyse des donnkes en fonction des diverses espi?ces ion mktallique-coordonnk prksentes dans les conditions exp6rimentales dkcrites, montre que la rkactivitk du substrat proton6 exckde de beaucoup celle des espkces mktalliques coordonnkes. On discute de la diffkrence de pouvoir catalytique de H+ versus MeHg+ en fonction du taux de charge positive dkveloppke au niveau de l'hktkroatome jouant le r6le de ligand dans l'intermkdiaire (carbknoide) de rkaction de l'ylide.Mots clks : mercure-mkthyle, mtthyl-1-histidine, tchange isotopique, transfert de proton, catalyse d'ion mttallique.[Traduit par la revue]Histidine (1) is one of the most important amino acids found in biologi...

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Section: Resultsmentioning

confidence: 99%

Section: Reactiviry Relationshipsmentioning

confidence: 97%

Section: Reactiviry Relationshipsmentioning

confidence: 99%

mentioning

confidence: 99%

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Metal ion – biomolecule interactions. Part 14. Methylmercury and hydrogen ion catalysis of C(2)-H isotopic exchange in 1-methylhistidine

Buncel¹,

Joly²,

Yee³

1989

Can. J. Chem.

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“…The heterocyclic bases were chosen partly as a result of a parallel interest in the kinetic acidities of the C-2(H) proton in compounds such as the imidazoles and benzimidazoles (12,19) and the equivalent C-8(H) position in purines, and partly because of the opportunity they afforded of investigating structural factors not frequently made available in this kind of study. Thus imidazole, benzimidazole, purine, and pyrrole are all examples of T-excessive N-heteroatoms where the nitrogen is in an electron releasing environment (=CH-NH--€Hz).…”

Section: Resultsmentioning

confidence: 99%

Kinetics of ionisation of carbon acids in non-aqueous media: detritiation of [2-³H₁]diethyl malonate by heterocyclic bases

Davey¹,

Jones²,

Buncel³

1986

Can. J. Chem.

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. 64, 1246 (1986).To investigate proton transfer processes in non-aqueous media, two procedures have been developed of general applicability for the measurement of detritiation rates of carbon acids. One method is a variation of an existing solvent extraction procedure but with inclusion of a trace of trifluoroacetic acid, while the other involves the simple modification of a gas chromatograph so as to function as a radio-gas chromatograph. They have been established by studying the detritiation of [2-3~l]diethyl malonate in six different solvents (dimethylformamide, dimethyl sulfoxide, sulfolane, hexamethylphosphortriamide, tetrahydrofuran, ethanol) as catalyzed by various heterocyclic bases (substituted pyridines, imidazoles, benzimidazoles, pyrrole, pyrazole, purine, adenosine). The results are discussed in terms of solvation effects and catalyst structure. An approximate Bransted correlation is found to exist between log k$ for detritiation determined in DMSO and the pKa of the conjugate base measured in water at 25OC.

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1996

Chemistry of Heterocyclic Compounds: A Series of Monographs

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Isotopic hydrogen exchange in purines—mechanisms and applications

Cited by 30 publications

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Metal ion – biomolecule interactions. Part 14. Methylmercury and hydrogen ion catalysis of C(2)-H isotopic exchange in 1-methylhistidine

Metal ion – biomolecule interactions. Part 14. Methylmercury and hydrogen ion catalysis of C(2)-H isotopic exchange in 1-methylhistidine

Kinetics of ionisation of carbon acids in non-aqueous media: detritiation of [2-³H₁]diethyl malonate by heterocyclic bases

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Isotopic hydrogen exchange in purines—mechanisms and applications

Cited by 30 publications

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Metal ion – biomolecule interactions. Part 14. Methylmercury and hydrogen ion catalysis of C(2)-H isotopic exchange in 1-methylhistidine

Metal ion – biomolecule interactions. Part 14. Methylmercury and hydrogen ion catalysis of C(2)-H isotopic exchange in 1-methylhistidine

Kinetics of ionisation of carbon acids in non-aqueous media: detritiation of [2-3H1]diethyl malonate by heterocyclic bases

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Kinetics of ionisation of carbon acids in non-aqueous media: detritiation of [2-³H₁]diethyl malonate by heterocyclic bases