Coupling and decarboxylation mechanism of oxaloacetic acid and ethylenediamine: A theoretical investigation

Abstract

The decarboxylation mechanism of deprotonated oxaloacetate at pH = 8.0 in aid of protonated ethylenediamine was investigated systematically by full optimization at M06‐2X/6‐311++G(d,p) level combined with the CPCM solvation model to consider the effect of bulk water, where the roles of the carbinolamine and imine intermediates were elucidated. In the minimum energy path, the NH3+ group binds to the β‐carboxyl group of oxaloacetate via a hydrogen bond, and the amino group as both a nucleophile and an electrophile connects to the CO group by a hydrogen transfer process with a free‐energy barrier of 131.9 kJ/mol. Then the carbinolamine intermediate is dehydrated to form an imine with a total barrier of 164.2 kJ/mol, which is the rate‐limiting step in this energetically most favorable channel. After a proton transfer process, the β‐decarboxylation barrier is only 49.6 kJ/mol.

Theoretical study on the solvent‐free self‐catalyzed coupling mechanism of a chiral vicinal diamine and isobutyraldehyde mediated by the outgrowth H2O

“…The coupling mechanism of R1/R2 with R3 is illustrated in Figure 1. The carbonyl oxygen in R3 is linked to one of the amino hydrogen atoms via hydrogen bonding with a bond length of 2.371 Å in IM1 and 2.172 Å in IM1', respectively, which is in line with our previously reported coupling mechanism of oxaloacetic acid and ethylenediamine, [55] and the dimerization of the cyclic dimer of aziridine aldehyde with CH 2 = CHCHO. [56] Then this hydrogen atom transfers from N to the carbonyl O atom, and synchronously the carbonyl C atom connects to N with free energy barriers of 155.0 and 150.3 kJ/ mol, respectively.…”

Effect of Ammonium Salts on the Decarboxylation of Oxaloacetic Acid in Atmospheric Particles

“…Another interesting effect is the growth of a shoulder on the main absorption peak with the addition of ammonium sulfate (Figure S4), providing more absorption of tropospherically relevant wavelengths. This shoulder, characterized by an increase in absorbance between 270 and 315 nm, is attributable to the formation of an enamine, which would be particularly interesting if the enamine form is not active in the decarboxylation process as could be the case based on our and previous calculations. − Therefore, enamine formation may be a potential pathway for direct photolysis to compete with OAA’s decarboxylation. The enamine peak is only visible at pH values above about 3.5, as demonstrated by the ammonium chloride-containing absorbance spectra (Figure S6).…”

“…They found an uncatalyzed free energy barrier of about 24 kcal/mol and an ethylenediamine-catalyzed free energy barrier of approximately 14 kcal/mol, and the dehydration of the carbinolamine to form an imine was the rate-limiting step for the catalyzed reaction. A detailed mechanism for fully deprotonated OAA at pH 8.0 with and without catalysis by protonated ethylenediamine was calculated by Cheng . When fully deprotonated, the dehydration of the carbinolamine was still the rate-limiting step, but the free energy barrier was greater: 49 kcal/mol with ethylenediamine catalysis (the free energy barrier and the rate-limiting step without a catalyst were not discussed).…”

Computational insights into the binding modes, keto–enol tautomerization and stereo-electronically controlled decarboxylation of oxaloacetate in the active site of macrophomate synthase

“…In gluconeogenesis, the pyruvate carboxylase and phosphoenolpyruvate carboxykinase catalyze the decarboxylation of OAA. 5 Of the variety of OAA-involving reactions, decarboxylation has always been the issue of concerns, 6 because it is one of the most common processes in nature, and all of the carbon dioxide evolved in fermentation and respiration is generated by the decarboxylation of organic acids. Besides, decarboxylation is also a key step for the biosynthesis of terpenoids, steroids, and neurotransmitter amino compounds.…”