Tranylcypromine

Tranylcypromine (Parnate, Jatrosom) is a drug of the substituted phenethylamine and amphetamine classes which acts as a monoamine oxidase inhibitor (MAOI)—it is a non-selective and irreversible inhibitor of the enzyme monoamine oxidase (MAO). It is used as an antidepressant and anxiolytic agent in the clinical treatment of mood and anxiety disorders, respectively.

History
Tranylcypromine was originally developed as an analogue of amphetamine. Although it was first synthesized in 1948, its MAOI action was not discovered until 1959. Precisely because tranylcypromine was not, like isoniazid and iproniazid, a hydrazine derivative, its clinical interest increased enormously, as it was thought that it might have a more acceptable therapeutic index than previous MAOIs.

The drug was introduced by Smith, Kline & French in the United Kingdom in 1960 and approval in the United States soon followed in 1961. It was withdrawn from the market in February 1964 due to a number of patient deaths involving hypertensive crises with intracranial bleeding. However, it was reintroduced later that year with more limited indications and specific warnings of the risks.

Clinical use
Despite their well-established efficacy, indications for monoamine oxidase inhibitors are currently very limited, due to their significant potential for adverse effects, many interactions, and the availability of newer and safer (although not necessarily more efficacious) antidepressants. Tranylcypromine is indicated primarily for the treatment of major depressive disorder, and can also be used in the management of various mood and anxiety disorders, typically as a last resort after conventional antidepressants have been tried without success.

Contraindications
Therapeutic contraindications of tranylcypromine include:


 * Cardiovascular or cerebrovascular disease
 * Drug abuse (due to the potential for interactions with certain agents, especially stimulants)
 * Low body weight, anorexia, or eating disorders of the sort
 * Pheochromocytoma
 * Pre-existing and chronic headaches or migraines
 * Psychosis such as schizophrenia or bipolar disorder

Dietary restrictions
Foods high in endogenous monoamine precursors or exogenous monoamine compounds may cause adverse reactions. The most common example of this, is the hypertensive crisis caused by the ingestion of tyramine, which is found in foods like aged cheeses, cured meats, tofu and certain red wines. Some, such as yeast extracts, contain enough tyramine to be potentially fatal in a single serving. Spoiled food is also likely to contain dangerous levels of tyramine.

Adverse effects
Adverse effects of tranylcypromine may include anxiety or nervousness, irritability, anorexia and subsequent weight loss, insomnia, mydriasis, tachycardia, hypertension or hypotension, hyperthermia, increased perspiration, muscle tremors, sexual dysfunction consisting of erectile dysfunction and/or anorgasmia, and orthostatic or postural hypotension.

Tranylcypromine is typically considered to have fewer side effects than the hydrazines, such as phenelzine (Nardil).

Overdose
Symptoms of tranylcypromine overdose are generally more intense manifestations of its usual effects. They may include exacerbated anxiety, muscle tremors, tachycardia, hypertension or hypotension, and hyperthermia, among others. Rare cases have been reported of hypertensive crisis, serotonin syndrome, myoclonus, hyperpyrexia, psychosis, and delirium, some of which progressed to coma. Additionally, in sensitive individuals or at extreme dosages, hypotension may lead to shock.

Pharmacology


Tranylcypromine acts as a nonselective and irreversible inhibitor of monoamine oxidase. Regarding the isoforms of monoamine oxidase, it shows slight preference for the MAOB isoenzyme over MAOA. In addition, tranylcypromine functions as a norepinephrine and dopamine releasing agent (NDRA) with approximately 1/10 the potency of amphetamine.

As a result of these actions, tranylcypromine considerably boosts the concentrations and activity of the monoamine neurotransmitters serotonin and dopamine, along with paradoxical and varying effects on norepinephrine and epinephrine. It increases the levels of the trace amines phenethylamine, tyramine, octopamine, and tryptamine as well. It is believed to be tranylcypromine's action on these neurochemicals that is responsible for its therapeutic efficacy.

Tranylcypromine has also been shown to inhibit the histone demethylase, BHC110/LSD1. Tranylcypromine inhibits this enzyme with an IC50 < 2 µM, thus acting as a small molecule inhibitor of histone demethylation with an effect to derepress the transcriptional activity of BHC110/LSD1 target genes.

Synthesis
Several methods of chemical synthesis for tranylcypromine are known.

Traditional:


 * 1) Styrene is reacted with ethyl diazoacetate to give ethyl 2-phenylcyclopropanecarboxylate.
 * 2) Hydrolysis of ethyl 2-phenylcyclopropanecarboxylate in the presence of alkali forms  2-phenylcyclopropanecarboxylic acid.
 * 3) 2-phenylcyclopropanecarboxylic acid is reacted with thionyl chloride (SOCl2) to form 2-phenylcyclopropanecarbonyl chloride.
 * 4) 2-phenylcyclopropanecarbonyl chloride is reacted with sodium azide (NaN3).
 * 5) The resulting azide of the above step is then the subject of a Curtius rearrangement.
 * 6) The resulting isocyanate of the above step is hydrolyzed in a Schmidt reaction to realize 2-phenylcyclopropylamine as the product.
 * 7) There are now four stereoisomers of the final compound:
 * 8) *(1S,2R)-trans-2-phenylcyclopropylamine
 * 9) *(1R,2S)-trans-2-phenylcyclopropylamine
 * 10) *(1R,2R)-cis-2-phenylcyclopropylamine
 * 11) *(1S,2S)-cis-2-phenylcyclopropylamine
 * 12) The required racemate of (1S,2R)- and (1R,2S)-trans-2-phenylcyclopropylamine is separated from (1R,2R)- and (1S,2S)-cis-2-phenylcyclopropylamine by crystalization with enantiopure tartaric acid, resulting in tranylcypromine.



Modern:


 * 1) Styrene is reacted with ethyl diazoacetate to give ethyl 2-phenylcyclopropanecarboxylate.
 * 2) Product is 3-4 parts trans isomer and 1-2 parts of cis isomer.
 * 3) Ethyl 2-phenylcyclopropanecarboxylate is epimerized by refluxing in sodium/ethanol. At the end of the reflux, ratio = 95% trans and 5% cis.
 * 4) Further purification through recrystallization at this stage results in pure racemic trans product.
 * 5) Hydrolysis of ethyl 2-phenylcyclopropanecarboxylate in the presence of alkali forms 2-phenylcyclopropanecarboxylic acid.
 * 6) 2-phenylcyclopropanecarboxylic acid is reacted with thionyl chloride (SOCl2) to form 2-phenylcyclopropanecarbonyl chloride.
 * 7) 2-phenylcyclopropanecarbonyl chloride is reacted with sodium azide (NaN3).
 * 8) The resulting azide of the above step is then the subject of a Curtius rearrangement.
 * 9) The resulting isocyanate of the above step is hydrolyzed to 2-phenylcyclopropylamine.
 * 10) The racemate can be purified further into the (–)-enantiomer via crystalization with the (+)-enantiomer of tartaric acid.