Synthesis and properties of 2-acetylthiamin pyrophosphate: an enzymatic reaction intermediate
The synthesis of 2-acetylthiamin pyrophosphate (acetyl-TPP) is described. The synthesis of this compound is accomplished at 23/sup 0/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, significant differences exist because of the pyrimidine ring in acetyl-TPP. Characterization of acetyl-TPP by ultraviolet spectroscopy, /sup 1/H NMR, /sup 13/C NMR, and /sup 31/P 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 /sup 1/H 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.
- Research Organization:
- Univ. of Wisconsin, Madison
- OSTI ID:
- 5301978
- Journal Information:
- Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 26:24; ISSN BICHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
62 RADIOLOGY AND NUCLEAR MEDICINE
AQUEOUS SOLUTIONS
BARYONS
BIOCHEMICAL REACTION KINETICS
BIOSYNTHESIS
CARBON 13
CARBON ISOTOPES
CHEMICAL REACTIONS
CHROMIUM COMPOUNDS
DISPERSIONS
ELEMENTARY PARTICLES
EVEN-ODD NUCLEI
FERMIONS
HADRONS
HEAVY WATER
HYDROGEN COMPOUNDS
ISOTOPES
KINETICS
LIGHT NUCLEI
MAGNETIC RESONANCE
MIXTURES
NMR SPECTRA
NUCLEAR MAGNETIC RESONANCE
NUCLEI
NUCLEONS
ODD-EVEN NUCLEI
OXIDATION
OXYGEN COMPOUNDS
PHOSPHORUS 31
PHOSPHORUS COMPOUNDS
PHOSPHORUS ISOTOPES
PROTONS
PYROPHOSPHATES
REACTION INTERMEDIATES
REACTION KINETICS
RESONANCE
SOLUTIONS
SPECTRA
STABLE ISOTOPES
SYNTHESIS
TRANSITION ELEMENT COMPOUNDS
ULTRAVIOLET SPECTRA
WATER