The evaluation of N-propargylamine-2-aminotetralin as an inhibitor of monoamine oxidase.

Monoamine oxidase B (MAO-B) inhibitors are established therapy for Parkinson's disease and act, in part, by blocking the MAO-catalysed metabolism of dopamine in the brain. Two propargylamine-containing MAO-B inhibitors, selegiline [(R)-deprenyl] and rasagiline, are currently used in the clinic for this purpose. These compounds are mechanism-based inactivators and, after oxidative activation, form covalent adducts with the FAD co-factor. An important consideration is that selegiline and rasagiline display specificity for MAO-B over the MAO-A isoform thus reducing the risk of tyramine-induced changes in blood-pressure. In the interest of discovering new propargylamine MAO inhibitors, the present study synthesises racemic N-propargylamine-2-aminotetralin (2-PAT), a compound that may be considered as both a six-membered ring analogue of rasagiline and a semi-rigid N-desmethyl ring-closed analogue of selegiline. The in vitro human MAO inhibition properties of this compound were measured and the results showed that 2-PAT is a 20-fold more potent inhibitor of MAO-A (IC50 = 0.721 µM) compared to MAO-B (IC50 = 14.6 µM). Interestingly, dialysis studies found that 2-PAT is a reversible MAO-A inhibitor, while acting as an inactivator of MAO-B. Since reversible MAO-A inhibitors are much less liable to potentiate tyramine-induced side effects than MAO-A inactivators, it is reasonable to suggest that 2-PAT could be a useful and safe therapeutic agent for disorders such as Parkinson's disease and depression.

A Review of the Pharmacological Properties of 3,4-dihydro-2(1H)- quinolinones.

The 3,4-dihydro-2(1H)-quinolinone moiety is present in a number of pharmacologically active compounds. These include FDA approved drugs such as cilostazol, carteolol and aripiprazole as well as numerous experimental compounds. Compounds containing the 3,4-dihydro-2(1H)-quinolinone moiety also exhibit a variety of activities in both the peripheral and central tissues, which includes phosphodiesterase inhibition, blocking of ß-adrenergic receptors, antagonism of vasopressin receptors and interaction with serotonin and dopamine receptors. Based on its versatility in drug design and action, this paper reviews the pharmacological actions of compounds containing the 3,4-dihydro-2(1H)- quinolinone scaffold with emphasis being placed on the most important and significant members of each activity class.

C6- and C7-Substituted 3,4-dihydro-2(1H)-quinolinones as Inhibitors of Monoamine Oxidase.

Purpose Monoamine oxidase (MAO) inhibitors are considered to be useful therapeutic agents and isoform specific inhibitors are employed for the treatment of depression and Parkinson's disease. MAO inhibitors are also under investigation for the treatment of disorders ranging from Alzheimer's disease, prostate cancer and certain cardiomyopathies. While a number of irreversible MAO inhibitors are available in the clinic, reversible inhibitors, particularly of the MAO-B isoform are still being developed. Based on our interest in discovering reversible inhibitors with specificity for MAO-B, we have recently reported that, among a series of 10 3,4-dihydro-2(1H)-quinolinone derivatives, are high potency MAO-B inhibitors, with a number of homologues displaying good selectivities for MAO-B over the MAO-A isoform. Methods and Findings: To expand on these promising findings and to derive structure-activity relationships, the current study synthesizes a series of 14 3,4-dihydro-2(1H)-quinolinone derivatives. An evaluation of their MAO inhibition properties shows that all derivatives are MAO-B specific with the most potent inhibitor (3a) displaying an IC50 value of 0.0014 µM. Selectivities for MAO-B ranged from 99 to 40 000-fold. Conclusions: It may thus be concluded that substitution of 3,4-dihydro-2(1H)-quinolinone on C6 and C7 with a variety of side chains yields highly potent and selective MAO-B inhibitors, compounds with existing and prospective therapeutic applications.

Inhibition of monoamine oxidase by 3,4-dihydro-2(1H)-quinolinone derivatives.

In the present study, a series of 3,4-dihydro-2(1H)-quinolinone derivatives were synthesized and evaluated as inhibitors of recombinant human monoamine oxidase (MAO) A and B. The 3,4-dihydro-2(1H)-quinolinone derivatives are structurally related to a series of coumarin (1-benzopyran-2-one) derivatives which have been reported to act as MAO-B inhibitors. The results document that the quinolinones are highly potent and selective MAO-B inhibitors with most homologues exhibiting IC50 values in the nanomolar range. The most potent MAO-B inhibitor, 7-(3-bromobenzyloxy)-3,4-dihydro-2(1H)-quinolinone, exhibits an IC50 value of 2.9 nM with a 2750-fold selectivity for MAO-B over the MAO-A isoform. An analysis of the structure-activity relationships for MAO-B inhibition shows that substitution on the C7 position of the 3,4-dihydro-2(1H)-quinolinone scaffold leads to significantly more potent inhibition compared to substitution on C6. In this regard, a benzyloxy substituent on C7 is more favourable than phenylethoxy and phenylpropoxy substitution on this position. It may be concluded that C7-substituted 3,4-dihydro-2(1H)-quinolinones are promising leads for the therapy of Parkinson's disease.