Evidence for a second carbanion in the mecahnism of the thiamine catalysis

Mieyal, John J.; Votaw, Robert G.; Krampitz, Lester O.; Sable, Henry Z.

doi:10.1016/0304-4165(67)90267-x

Cited by 31 publications

(11 citation statements)

References 2 publications

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“…The >H NMR gave 1.69 (3 H, d), 2.42 (3 H, s), 2.58 (3 H, s), 3.33 (2 H, t), 4.22 (2 H, q), 5.43 (1 H, q), 5.55 (2 H, s), and 7.32 (1 H, s), in agreement with values reported by Kluger et al (1985) and Mieyal et al (1967).…”

Section: Methodssupporting

confidence: 91%

Synthesis and properties of 2-acetylthiamin pyrophosphate: an enzymatic reaction intermediate

Gruys¹,

Halkides²,

Frey³

1987

Biochemistry

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The synthesis of 2-acetylthiamin pyrophosphate (acetyl-TPP) is described. The synthesis of this compound is accomplished at 23 degrees C by the oxidation of 2-(1-hydroxyethyl)thiamin pyrophosphate using aqueous chromic acid as the oxidizing agent under conditions where Cr(III) coordination to the pyrophosphoryl moiety and hydrolysis of both the pyrophosphate and acetyl moieties were prevented. Although the chemical properties exhibited by acetyl-TPP are similar to those of the 2-acetyl-3,4-dimethylthiazolium ion examined by Lienhard [Lienhard, G.E. (1966) J. Am. Chem. Soc. 88, 5642-5649], significant differences exist because of the pyrimidine ring in acetyl-TPP. Characterization of acetyl-TPP by ultraviolet spectroscopy, 1H NMR, 13C NMR, and 31P NMR provided evidence that the compound in aqueous solution exists as an equilibrium mixture of keto, hydrate, and intramolecular carbinolamine forms. The equilibria for the hydration and carbinolamine formation reactions at pD 1.3 as determined by 1H NMR are strongly dependent on the temperature, showing an increase in the hydrate and carbinolamine forms at the expense of the keto form with decreasing temperature. The concentration of keto form also decreases with increasing pH. Acetyl-TPP is stable in aqueous acid but rapidly deacetylates at higher pH to form acetate and thiamin pyrophosphate. Trapping of the acetyl moiety in aqueous solution occurs efficiently with 1.0 M hydroxylamine at pH 5.5-6.5 to form acetohydroxamic acid and to a much smaller extent with 1.0 M 2-mercaptoethanol at pH 4.0 and 5.0 to form thio ester. Transfer of the acetyl group to 0.5 M dihydrolipoic acid at pH 5.0 and 1.0 M phosphate dianion at pH 7.0 is not observed to any significant extent in water. The kinetic and thermodynamic reactivity of acetyl-TPP with water and other nucleophiles is compatible with a hypothetical role for acyl-TPPs as enzymatic acyl-transfer intermediates.

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Section: Methodssupporting

confidence: 91%

Synthesis and properties of 2-acetylthiamin pyrophosphate: an enzymatic reaction intermediate

Gruys¹,

Halkides²,

Frey³

1987

Biochemistry

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“…Sable and co-workers considered this problem and suggested that the enzyme controls the course of the reaction. 55 A possible solution to this problem is control of the conformation OH of the side chain relative to the thiazolium ring by the enzyme so that the angle necessary for formation of a carbonyl group elimination of the thiamin ylide is maintained. This possibility should be considered in context of the information presented later in this review concerning conformational effects on reactivity.…”

Section: Tautomerization Of the Carbanion-enaminementioning

confidence: 99%

Thiamin diphosphate: a mechanistic update on enzymic and nonenzymic catalysis of decarboxylation

Kluger¹

1987

Chem. Rev.

254

158

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“…Sable and co-workers showed that hydroxyethylthiamin undergoes base-catalyzed proton exchange at the C-2a position and thus provided the first direct evidence for the existence of the free conjugate base. 13,14 The rate of the proton exchange reaction is very slow (half-life 5 h at pD 8.5, 50 °C, k = 4 X 10~4 S~'). This is consistent with the intermediate being a high-energy species due its very high basicity (estimated pK = 1715).…”

Section: Discussionmentioning

confidence: 99%

Chiral intermediates in thiamin catalysis. Stereochemical course of the decarboxylation step in the conversion of pyruvate to acetaldehyde

Kluger¹,

Karimian²,

Kitamura³

1987

J. Am. Chem. Soc.

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The stereochemical course of the nonenzymic decarboxylation of the adduct of pyruvate and thiamin was determined. Racemic ethyl 2-(lact-2-yl)thiamin was resolved as the 2,3-dibenzoyltartrate salt under slightly acidic conditions. The specific rotations of the free enantiomers of ethyl 2-(lact-2-yl)thiamin are +8.4 f 0.1' and -8.4 f 0.1'. These were converted to the parent acid, 2-(lact-2-yl)thiamin, by acid hydrolysis. The (+) ethyl ester gave the (-) acid ( [ a ] 2 5 D -4.7 f 0.1") while the (-) ethyl ester gave the (+) acid ([a]25D = +4.7 f 0.1'). The acids were allowed to undergo spontaneous decarboxylation under a variety of conditions: aqueous solution, ethanol solution, dimethylformamide solution, and dimethylformamide solution containing brucine. Under all conditions the product was racemic 2 4 I-hydroxyethy1)thiamin. These results require that the reaction proceed via an achiral intermediate or rapidly equilibrating achirally solvated enantiomeric intermediates. Since it is known that enzymic reactions produce a single enantiomer of 2 4 1-hydroxyethyl)thiamin, the stereospecificity of the enzymic reaction is due to the chirality of the protein and not the intrinsic mechanism of the decarboxylation reaction. ( 5 ) Ullrich, J.; Mannschreck, A. Eur. J . Biochem. 1967, 1 , 110. (6) Kiuger, R.; Karimian, K.; Gish, G.; Pangborn, W. A,; DeTitta, G. T. J. Am. Chem. SOC. 1987, 109, 618. The title and caption to Figure 1 contain a typographical error. The enantiomer of HETI shown has a negatiue (but very weak) specific rotation (circular dichroism is preferred for the assignment), as stated in the rest of the paper. This material results from (+)hydroxyethylthiamin and the configuration at the stereocenter is R as indicated. We thank Professor W. Shin for noting the error.

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Evidence for a second carbanion in the mecahnism of the thiamine catalysis

Cited by 31 publications

References 2 publications

Synthesis and properties of 2-acetylthiamin pyrophosphate: an enzymatic reaction intermediate

Synthesis and properties of 2-acetylthiamin pyrophosphate: an enzymatic reaction intermediate

Thiamin diphosphate: a mechanistic update on enzymic and nonenzymic catalysis of decarboxylation

Chiral intermediates in thiamin catalysis. Stereochemical course of the decarboxylation step in the conversion of pyruvate to acetaldehyde

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