6706-15-6Relevant academic research and scientific papers
Mechanisms of Decarboxylation of Carboxybiotin
Tipton, Peter A.,Cleland, W. W.
, p. 5866 - 5869 (2007/10/02)
Carboxylation is decarboxylated by two different mechanisms at low pH, where the N 1' carboxyl is protonated (pK 4.25 at 2 deg C) and at high pH where it is ionized.The low-pH mechanism has a rate constant of 5.9 X 10-3min-1 at 2 deg C (activation energy 33 kcal/mol), while the high - pH one has a rate constant of 4.6 X 10-3min-1 at 25 deg C, with the two mechanisms showing equal rates at 25 deg C at pH 6.4.At pH 8 the D2O solvent isotope effect is 1.1 with a curved proton inventory, while at pH 3.4 the value is 1.6 with a linear proton inventory.The 13C isotope effect on decarboxylation is 1.023 at pH 8.2, but 1.012 for the lo w-pH reaction.The low-pH mechanism probably involves concerted protonation of N 1' and C - N bond cleavage, with an early transition state in which proton motion is ahead of C - N bond breaking.The high - pH mechanism has a moderately early transition state and gives the enolate as the product, with the small solvent isotope effect presumably arising from changes in the fractionation factors of protons in water hydrogen-bonded to the ureido oxygen.
