21802-85-7Relevant articles and documents
1-(2-aminoethyl)-1,4-cyclohexadiene: A probe to examine the chemistry and energetics of the C-H bond cleavage in dopamine β-monooxygenase catalysis
Wimalasena, Kandatege,Alliston, Kevin R.
, p. 1220 - 1224 (2007/10/02)
The chemistry and energetics of the initial C-H bond cleavage step in dopamine β-monooxygenase (DβM, E.C. 1.14.17.1) catalysis has been explored using 1-(2-aminoethyl)-1,4-cyclohexadiene (CHDEA) as a probe. DβM has been previously shown (Wimalasena, K.; May, S. W. J. Am. Chem. Soc. 1989, 111, 2729) to catalyze the aromatization of CHDEA to phenylethylamme (PEA). We now report that the side chain hydroxylated product, 2-amino-1-(1,4-cyclohexadiene)ethanol (CHDEA-OH), is also a direct product of the DβM/CHDEA reaction. The PEA:CHDEA-OH product ratio is 2.7 at pH 5.2 and 37 °C for the DβM/CHDEA reaction. The side chain deuterated analog, 1-(2-amino-1,1-dideuterioethyl)-1,4-cylohexadiene, undergoes aromatization almost exclusively. The ring deutefated analog, 1-(2-aminoethyl)-3,3,6,6-tetradeuterio-1,4-cyclohexadiene, favors side chain hydroxylation 2.6 times over aromatization. The hexadeuterio derivative, 1-(2-amino-1,1-dideuterioethyl)-3,3,6,6-tetradeuterio-1,4-cyclohexadiene (CHDEA-d6), prefers aromatization 3.9 times. The apparent kinetic isotope effects of CHDEA-d6 are small, 1.8 for kcat and 1.3 for kcat/Km, suggesting that the initial C-H bond cleavage is only partly rate limiting in the CHDEA/DβM reaction analogous to the normal DβM hydroxylation reaction. The intrinsic isotope effects for the exocyclic and ring methylene hydrogens are estimated to be 9.9 and 7.0, respectively. The alteration of the product ratiodue to deuterium substitution suggests that activation energies of the initial C-H bond cleavage steps for the two pathways are similar. In contrast to the high thermodynamic driving force for the ring methylene hydrogen abstraction, the similar activation energies must be a consequence of the proximity and/or the relative orientation of the corresponding hydrogens of the enzyme-bound CHDEA with respect to the activated copper oxygen species.
