Para-substituted Benzylamines Research Articles

Structure-function studies of substrate oxidation by bovine serum amine oxidase: relationship to cofactor structure and mechanism

The chemical mechanism of substrate oxidation, catalyzed by bovine serum amine oxidase, has been explored by a detailed investigation of structure-reactivity correlations. Past mechanistic studies, involving the reductive trapping of substrate to cofactor [Hartmann, C., & Klinman, J. P. (1987) J. Biol. Chem. 262, 962], implied the intermediacy of a substrate imine complex in the catalytic redox mechanism. These studies led to the proposal of a transamination mechanism for substrate oxidation, analogous to pyridoxal phosphate dependent enzymes. In pyridoxal phosphate catalyzed reactions, the transamination process involves the transient formation of a resonance-stabilized carbanion intermediate. Although evidence has been presented describing the participation of an active site base in bovine serum amine oxidase catalysis [Farnum, M. F., Palcic, M. M., & Klinman, J. P. (1986) Biochemistry 25, 1898], the nature of the intermediate derived from C-H bond cleavage has not been directly addressed. To examine this question, a structure-reactivity study was performed using a series of para-substituted benzylamines. Having prior knowledge of the intrinsic isotope effect for an enzymatic reaction permits calculation of microscopic rate constants from steady-state data [Palcic, M. M., & Klinman, J. P. (1983) Biochemistry 22, 5957]. Deuterium isotope effects on kcat and kcat/Km parameters were determined for all substrates, allowing for the calculation of rate constants for C-H bond cleavage (k3) and substrate dissociation constants (Kd). Pre-steady-state constants obtained for p-acetylbenzylamine, p-(trifluoromethyl)benzylamine, and unsubstituted benzylamine exhibited excellent agreement with values calculated from steady-state isotope effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanistic Study of the Oxidation of Substituted Benzylamines by N-Bromoacetamide

Abstract The oxidation of ortho-, meta-, and para-substituted benzylamines by N-bromoacetamide (NBA), to the corresponding benzaldehydes, is first order with respect to NBA and the amine. The pH dependence of the reaction rate suggests that the unprotonated benzylamine is the reductant. There is no effect of added acetamide. NBA itself has been postulated as the reactive oxidizing species. The oxidation of benzylamine-α,α-d2 exhibited a substantial primary kinetic isotope effect (kH⁄kD=5.81). The rates of the oxidation of the meta- and para-substituted benzylamines were separately correlated in Taft’s and Swain’s dual substituent parameter equations. For the para-substituted compounds, the best correlation is obtained with σI and σR+ values, while meta-substituted compounds correlated best with σI and σR° values. The reaction constants have negative values. The oxidation rates of the ortho-substituted compounds yield excellent correlation in a triparametric equation involving Taft’s σI and σR+ values and Charton’s steric parameter, V. A mechanism involving transfer of a hydride ion from the amine to NBA, in the rate-determining step has been proposed.

Kinetics and mechanism of the oxidation of substituted benzylamines by N-chlorosuccinimide

The oxidation of ortho-, meta-, and para-substituted benzylamines by N-chlorosuccinimide (NCS), to the corresponding benzaldehydes, is first-order with respect to NCS and the amine. The pH dependence of the reaction rate suggests that the unprotonated benzylamine is the reductant. There is no effect of added succinimide. NCS itself has been postulated as the reactive oxidising species. The oxidation of [α,α-2H2]benzylamine exhibited a substantial primary kinetic isotope effect (kH/kD= 6.20). The rates of oxidation of the meta- and para-substituted benzylamines were separately correlated in Taft and Swain's dual substituent parameter equations. For the para-substituted compounds, the best correlation is obtained with σI and σR+ values; meta-substituted compounds correlate with σI and σR0 values. The reaction constants have negative values. The oxidation rates of the ortho-substituted compounds yield an excellent correlation in a triparametric equation involving Taft's σI and σR+ values and Charton's steric parameter, V. A mechanism involving transfer of a hydride ion from the amine to the oxidant in the rate-determining step is proposed.

Oxidation of p-dimethylaminomethylbenzylamine by pig kidney diamine oxidase. A new method for spectrophotometric assay.

1. The oxidation of some para-substituted benzylamines by diamine oxidase produces the corresponding aldehydes. This was studied to develop a spectrophotometric method for following the enzyme reaction, as the aldehydes produced absorb strongly at 250nm where the substrates are almost optically transparent. 2. p-Dimethylaminomethylbenzylamine was the most useful substrate and full details of its preparation are given. The synthesis of its related oxidation product, p-dimethylaminomethylbenzaldehyde, is also described. 3. The effects of variations in pH, ionic strength, temperature and oxygenation on the reaction are described and the usefulness of the method is illustrated by several applications and assessed by comparison with the standard spectrophotometric assay.