4-(Aminomethyl)-1-aryl-2-pyrrolidinones, a new class of monoamine oxidase B inactivators

A computational study on the amine-oxidation mechanism of monoamine oxidase: Insight into the polar nucleophilic mechanism

The proposed polar nucleophilic mechanism of MAO was investigated using quantum chemical calculations employing the semi-empirical PM3 method. In order to mimic the reaction at the enzyme's active site, the reactions between the flavin and the p-substituted benzylamine substrate analogs were modeled. Activation energies and rate constants of all the reactions were calculated and compared with the published experimental data. The results showed that electron-withdrawing groups at the para position of benzylamine increase the reaction rate. A good correlation between the log of the calculated rate constants and the electronic parameter (sigma) of the substituent was obtained. These results agree with the previous kinetic experiments on the effect of p-substituents on the reduction of MAO-A by benzylamine analogs. In addition, the calculated rate constants showed a correlation with the rate of reduction of the flavin in MAO-A. In order to verify the results obtained from the PM3 method single-point B3LYP/6-31G*//PM3 calculations were performed. These results demonstrated a strong reduction in the activation energy for the reaction of benzylamine derivatives having electron-withdrawing substituents, which is in agreement with the PM3 calculations and the previous experimental QSAR study. PM3 and B3LYP/6-31G* energy surfaces were obtained for the overall reaction of benzylamine with flavin. Results suggest that PM3 is a reasonable method for studying this kind of reaction. These theoretical findings support the proposed polar nucleophilic mechanism for MAO-A.

Orientation of oxazolidinones in the active site of monoamine oxidase

Oxazolidinone inhibitors of monoamine oxidase (MAO) and oxazolidinone antibacterials are two distinct classes of drug, often with linear structures and overlapping activities for some derivatives. By synthesizing novel dimerised derivatives with identical substitution of the two C-5 side chains, we have obtained experimental evidence for the orientation of oxazolidinones in the active site of MAO A. Two types of spectral changes, either increasing the absorbance at 510 nm or decreasing it at 495 nm depending on the group nearest to the flavin cofactor, were seen on ligand binding to MAO A. Side chain derivatives with amine substituents are very poor substrates so that it was possible to examine the spectral change due to binding of a substrate before reduction of the flavin occurred. Binding of these amino derivative substrates to MAO A induced a spectral change characterized by a strong decrease in absorbance at 495 nm. These substrates reduced the enzyme fully without any trace of a semiquinone intermediate. Only oxazolidinone inhibitors with a bromo-imidazole substituent increased the yield of semiquinone intermediate obtained during chemical reduction. In accord with the experimental data, results of docking experiments showed that binding of the oxazolidinone ring in the aromatic cage close to the flavin was favored and that the nitrogen of the derivatives that were substrates was within van der Waals distance of N-5 of the flavin.

Effect of the locus of the oxygen atom in amino ethers on the inactivation of monoamine oxidase B

Monoamine oxidase is a flavoenzyme that catalyzes the oxidation of a variety of primary, secondary, and tertiary amines. Although primary alkylamines, such as heptylamine, and primary arylalkyl amines, such as phenylethylamine, are excellent substrates for MAO, their analogues having an electron withdrawing group near the aminomethyl methylene group (1-8) are known to inactivate the enzyme. Inactivation has been attributed to the inductive effect of the electron-withdrawing group of these analogues. To determine the extent of the proposed inductive effect of a heteroatom on MAO B inactivation, a series of oxaheptylamine analogues (9-12) were synthesized and tested as inactivators of MAO B. The analogues in which the oxygen atom is closest to the alpha-carbon (9 and 10) inactivate MAO B, but activity slowly returns with time. The analogues with the oxygen atom farther from the alpha-carbon inactivate the enzyme, but activity rapidly returns. These results support the inductive effect hypothesis for inactivation.

Structure-activity studies on monoamine oxidase inhibitors by calorimetric and quantum mechanical calculations

Structure-activity relationship studies were carried out on a new series of hydrazino-thiosemicarbazide derivatives, which inhibit monoamino oxidase (MAO). Fifty-five compounds were synthesized and tested "in vitro" for their inhibitory effects on rat liver mitochondrial MAO. The most efficient MAO inhibitors were the benzylidene derivatives (sequence: see text] where R is the piperonyl radical and ethyl or isopropyl substituents are in R1 position. Correlation of MAO activity with hydrophobic, electronic and steric properties of tested compounds, evaluated by means of Quantum Mechanical calculations and calorimetric analysis (DSC) suggest that electronic and steric parameters give a better fit than hydrophobicity with the biological activity.

SAR studies of fluorine-substituted benzylamines and substituted 2-phenylethylamines as substrates and inactivators of monoamine oxidase B

To test whether addition of electron-withdrawing substituents to good substrates of monoamine oxidase (MAO) will transform them into inactivators, a series of fluorine-substituted benzylamines and a series of substituted 2-phenylethylamines were synthesized and tested as substrates and inactivators of monoamine oxidase B. All of the compounds were substrates. None of the benzylamines was an inactivator, but several of the phenethylamines were. These results suggest that either stronger electron withdrawing character or additional stabilizing factors are needed to stabilize the hypothesized enzyme adduct.