Mechanism of hydrolysis of N-methylacetimidate esters

Pletcher, Terry C.; Koehler, Siegmund; Cordes, E. H.

doi:10.1021/ja01027a033

Cited by 21 publications

(8 citation statements)

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“…The p K a value for protonation of carbonyl oxygen of the imidic acid form was estimated as around 0 ( 10 ), and that of protonation/deprotonation of nitrogen was estimated as 4.5 to 7.5 ( 11 , 12 ). Thus, the nitrogen atom of the imidic acid form of asparagine can act as a base in Pc Cel45A, although it is not yet clear how the oxygen atom of asparagine is protonated.…”

Section: Resultsmentioning

confidence: 99%

“Newton’s cradle” proton relay with amide–imidic acid tautomerization in inverting cellulase visualized by neutron crystallography

et al. 2015

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Section: Resultsmentioning

confidence: 99%

“Newton’s cradle” proton relay with amide–imidic acid tautomerization in inverting cellulase visualized by neutron crystallography

et al. 2015

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“…ethanol. In alkaline dioxane solutions the reaction follows the rate law of eq 5, where k0 is the rate of the +bsd -hi, + &OH [OH ] (5) pH independent reaction, and k0h is the catalytic coefficient of hydroxide ion. Kinetic data for hydrolysis of ethyl V-arylformimidates in alkaline 20% dioxane are collected in Table IV, and catalytic coefficients and activation parameters derived from them appear in Table V.…”

Section: Resultsmentioning

confidence: 99%

“…products change differs from that at which reaction rate changes. [4][5][6][7][8][9]16 Product composition is also influenced by the presence of bifunctional catalysts such as phosphate, bicarbonate, and carboxylate ions, which catalyze the formation of esters and amines. 4,8,10,15 In acidic solutions, ethyl m-toluimidate3 and 2-methyl-A2-oxazoline13 hydrolyze about twice as fast in H20 as in D20.…”

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confidence: 99%

Kinetics and mechanism of hydrolysis of N-arylimidic esters

DeWolfe¹

1971

J. Org. Chem.

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The influence of aryl substituents, pH, temperature, general acid-base catalysts, and solvent polarity on the kinetics of hydrolysis of ethyl A-arylformimidates and ethyl A-arylacetimidates was studied in aqueous and aqueous dioxane solutions. The data indicate that hydrolysis of these imidates involves rate-limiting reaction of the conjugate acids of the imidates with water in acidic solutions, and with hydroxide ion in alkaline solutions. Although alkoxyanilinocarbinols are probably intermediates in alkaline solutions, they may not be intermediates in acidic solutions. Hydrolysis at low pH may be a concerted process involving simultaneous C-0 bond formation and C-N bond cleavage. The falloff in hydrolysis rate in strongly acidic solutions may be due to the diminished water activity of the solvent, rather than to a change in the rate-limiting step. The two sets of products formed in alkaline imidate hydrolyses may arise from competing reactions of a single intermediate, rather than from reactions of two different intermediates in acid-base equilibrium.

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“…An obvious upper bond for the latter is the diffusion-limited rate, which is ~5 X 1012 M'1 min"1 for the recombination of D+ and OD" (Eigen et al, 1962). According to the Eigen formulation of proton-exchange rates (Eigen, 1964), the pXa of Tyr2 NH must be lowered by 2 units to bring the primary structure corrected k0D for this residue to within 5% of the diffusion-controlled limit, a shift consistent with those induced by electron-withdrawing substituent groups and with the pXa's of N-substituted imidic acid esters (Hartigan & Cloke, 1945;Fletcher et al, 1968). By use of this estimate for fcracc, eq 9a then yields Xacc = 2.3.…”

Section: Discussionmentioning

confidence: 99%

Hydrogen-deuterium-exchange kinetics of the amide protons of oxytocin studied by nuclear magnetic resonance

Krauss

Cowburn

1981

Biochemistry

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The contribution of intramolecular hydrogen bonding to the solution structure of oxytocin was evaluated by study of amide hydrogen exchange rates in D2O by Fourier transform 1H NMR spectroscopy. Resolution enhancement filtering was employed in the determination of individual pseudo-first-order rate constants. Apparent barriers to exchange of 0.5 and 0.6 kcal mol-1 were measured for Asn5 and Cys6 peptide NH, respectively. The slowing is best explained by steric hindrance to solvent access in the case of Asn5, while for the Cys6 participation in a weak intramolecular hydrogen bond is possible. Fourfold acceleration of base-catalyzed exchange was observed for Tyr2 NH; it is proposed that this is the result of electronic effects induced by hydrogen bonding of Cys1 C=0, either to Cys6 NH or to the N-terminal amino group. Exchange proceeds near the random coil limit for each of the remaining residues. Comparison with exchange data for the model tripeptide N-acetyl-L-prolyl-L-leucylglycinamide demonstrates no evidence of noncovalent association of the tocin ring with the tripeptide tail of the hormone.

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Mechanism of hydrolysis of N-methylacetimidate esters

Cited by 21 publications

References 0 publications

“Newton’s cradle” proton relay with amide–imidic acid tautomerization in inverting cellulase visualized by neutron crystallography

“Newton’s cradle” proton relay with amide–imidic acid tautomerization in inverting cellulase visualized by neutron crystallography

Kinetics and mechanism of hydrolysis of N-arylimidic esters

Hydrogen-deuterium-exchange kinetics of the amide protons of oxytocin studied by nuclear magnetic resonance

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