Tolcapone

Absorption

Rapidly absorbed (absolute bioavailability is about 65%)

Toxicity

LD50 = 1600 mg/kg (Orally in rats)

Description

Tolcapone (134308-13-7) is a catechol O-methyltransferase inhibitor (COMT), inhibiting both brain and peripheral enzymes.1?Potent inhibitor of alpha-synuclein and beta-amyloid oligomerization and fibrillogenesis protecting against extracellular toxicity.2?Binds to transthyretin (TTR) with high affinity (21 to 58 nM) and inhibits TTR aggregation in human plasma and prevents TTR-induced cytotoxicity?in vitro. Stabilizes TTR in mice and humans?in vivo.3?Inhibits O-methylation of exogenous polyphenols such as EGCG.4?Cell permeable. Orally bioavailable.

Chemical properties

Yellow Solid

Originator

Tasmar,Roche

The Uses of Tolcapone

Tolcapone may be used in COMT-mediated cell signaling studies.
Tolcapone has been used in methyltransferase assay in human embryonic kidney 293 cells.

The Uses of Tolcapone

Orally active inhibitor of central and peripheral catechol-O-methyltransferase (COMT). Antiparkinsonian

Indications

Used as an adjunct to levodopa/carbidopa therapy for the symptomatic treatment of Parkinson's Disease. This drug is generally reserved for patients with parkinsonian syndrome receiving levodopa/carbidopa who are experiencing symptom fluctuations and are not responding adequately to or are not candidates for other adjunctive therapies.

Background

Tolcapone is a drug that inhibits the enzyme catechol-O-methyl transferase (COMT). It is used in the treatment of Parkinson's disease as an adjunct to levodopa/carbidopa medication. It is a yellow, odorless, non-hygroscopic, crystalline compound. Tolcapone is associated with a risk of hepatotoxicity.

What are the applications of Application

Tolcapone is an inhibitor of peripheral and central catechol-O-methyltransferase

Preparation

preparation by demethylation of 4-hydroxy-3-methoxy-4′-methyl-5-nitrobenzophenone with hydrobromic acid in refluxing aque-ous acetic acid.

Definition

ChEBI: Tolcapone is benzophenone substituted on one of the phenyl rings at C-3 and C-4 by hydroxy groups and at C-5 by a nitro group, and on the other phenyl ring by a methyl group at C-4. It is an inhibitor of catechol O-methyltransferase. It has a role as an EC 2.1.1.6 (catechol O-methyltransferase) inhibitor and an antiparkinson drug. It is a member of benzophenones, a member of 2-nitrophenols and a member of catechols.

Manufacturing Process

Condensation of 4-benzyloxy-3-methoxybenzaldehyde with 4-lithium-toluene (prepared from 4-bromotoluene and butyl lithium) leads to the corresponding benzhydrole. Oxidation of the new formed hydroxyl in benzhydrole gives the 4-benzyloxy-3-methoxyphenyl)-p-tolylmethanone. Treatment of this compound with hydrogen bromide selectively removes the benzyl ether that is additionally activated by the transannular carbonyl group. The intermediate is then nitrated under standart conditions to give the (4-hydroxy-3-methoxy-5- nitrophenyl)-p-tolylmethanone. A second treatment of the last compound with hydrogen bromide cleaves the ether group, which is now activated by the adjacent nitro group. This last step affords the (3,4-dihydroxy-5-nitrophenyl)(4-methylphenyl)methanone.

Therapeutic Function

Antiparkinsonian

General Description

Tolcapone, 3,4-dihydroxy-4'-methyl-5-nitrobenzophenone (Tasmar), is a yellow, odorless, nonhygroscopic,crystalline compound (pK_a＝4.78). Tolcapone israpidly absorbed after oral administration. Tolcapone ishighly bound to plasma albumin (＞98%), and its distributionis therefore restricted. Tolcapone has low first-pass metabolism.It is almost completely metabolized in the liver before excretion, and 60% is excreted by the kidney. The majormetabolite of tolcapone is an inactive glucuronide conjugate.COMT inhibitors increase chronotropic and arrhythmogeniceffects of epinephrine.Tolcapone is indicated as an adjunctto levodopa/carbidopa for the management of signs andsymptoms of PD.

Biochem/physiol Actions

Tolcapone is an orally active catechol-O-methyltransferase (COMT) inhibitor. It inhibits both central and peripheral COMT. Tolcapone crosses the blood-brain barrier, and has been used for L-DOPA adjunct therapy in the treatment of Parkinson′s Disease.

Pharmacokinetics

Tolcapone is a potent, selective, and reversible inhibitor of catechol-O-methyltransferase (COMT). In humans, COMT is distributed throughout various organs. COMT catalyzes the transfer of the methyl group of S-adenosyl-L-methionine to the phenolic group of substrates that contain a catechol structure. Physiological substrates of COMT include dopa, catecholamines (dopamine, norepinephrine, epinephrine) and their hydroxylated metabolites. The function of COMT is the elimination of biologically active catechols and some other hydroxylated metabolites. COMT is responsible for the elimination of biologically active catechols and some other hydroxylated metabolites. In the presence of a decarboxylase inhibitor, COMT becomes the major metabolizing enzyme for levodopa catalyzing it to 3-methoxy-4-hydroxy-L-phenylalanine (3-OMD) in the brain and periphery. When tolcapone is given in conjunction with levodopa and an aromatic amino acid decarboxylase inhibitor, such as carbidopa, plasma levels of levodopa are more sustained than after administration of levodopa and an aromatic amino acid decarboxylase inhibitor alone. It is believed that these sustained plasma levels of levodopa result in more constant dopaminergic stimulation in the brain, leading to greater effects on the signs and symptoms of Parkinson's disease in patients as well as increased levodopa adverse effects, sometimes requiring a decrease in the dose of levodopa.

Clinical Use

Catechol-o-methyltransferase inhibitor:
Treatment of Parkinson’s disease

Drug interactions

Potentially hazardous interactions with other drugs
Antidepressants: avoid with MAOIs.

Metabolism

The main metabolic pathway of tolcapone is glucuronidation

Metabolism

Extensively metabolised, mainly by conjugation to the inactive glucuronide, but methylation by catecholO-methyltransferase to 3-O-methyltolcapone and metabolism by cytochrome P450 isoenzymes CYP3A4 and CYP2A6 also occurs. Approximately 60
% of a dose is excreted in the urine with the remainder appearing in the faeces.

storage

Store at +4°C

References

1) Manisto?et al.?(1992),?Different in vivo properties of three new inhibitors of catechol O-methyltransferase in the rat; Br, J. Pharmacol.,?105?569 2) Giovanni?et al.?(2010),?Entacapone and tolcapone, two catechol O-methyltransferase inhibitors, block fibril formation of alpha-synuclein and beta-amyloid and protect against amyloid-induced toxicity;?J. Biol. Chem.,?285?14941 3) Sant’Anna?et al.?(2016),?Repositioning tolcapone as a potent inhibitor of transthyretin amyloidogenesis and associated cellular toxicity; Nat. Commun.,?7?10787 4) Forester and Lambert (2015),?The catechol-O-methyltransferase inhibitor, tolcapone, increases the bioavailability of unmethylated (-)-epigallocatechin-3-gallate in mice; Funct. Foods,?17?183