Brimonidine

Launched in the US for open-angle glaucoma and ocular hypertension, brimonidine is a relatively selective and potent α_2a,-adrenergic agonist with low affinity for the imidazoline l₁ receptor. Topical application reduces intraocular pressure. This bypasses any central hypotensive effects at the l₁ receptor (which can also give rise to a decrease in blood pressure and heart rate) if given systemically, since topical application results in low plasma levels concomitant with rapid systemic elimination. Brimonidine can be prepared in a four-step sequence from 4-nitrophenylenediamine.

Yellow Solid

Allergan (USA)

a2-Adrenoceptor agonist. Antiglaucoma

α2-Adrenoceptor agonist. Antiglaucoma.

coronary vasodilator calcium ion influx inhibitor

ChEBI: Brimonidine is a quinoxaline derivative, a secondary amine and a member of imidazoles. It has a role as an adrenergic agonist, an antihypertensive agent and an alpha-adrenergic agonist.

6-Aminoquinoxaline (2.08 g, 14.4 mmol) was dissolved in 11.5 ml glacial acetic acid. The solution was cooled in water while a solution of bromine (0.74 ml, 2.3 g, 14.4 mmol) in 1.5 ml glacial acetic acid was added slowly over 15 min. After stirring for an additional 30 min. the orange red solid formed was filtered off and washed thoroughly with dry ether. The solid was dried in vacuo overnight to yield 4.44 g crude product (a yield of 100%). The compound, 6- amino-5-bromoquinoxaline hydrobromide, had no definite melting point. A phase change (from fine powder to red crystals) was noticed at about 220°C. Decomposition was observed at about 245°C. It was used directly for the next step.
The crude 6-amino-5-bromoquinoxaline from above was dissolved in water and saturated sodium bisulfite solution was added until the resulting solution tested negative with starch-iodide paper. The solution was then basified with 2 N sodium hydroxide and extracted thoroughly with ethyl acetate. The organic extract was dried over magnesium sulfate and concentrated under reduced pressure to give the free base. The crude product was recrystallized from boiling benzene to give yellow crystals, m.p. 155°-156°C. Using various analytical procedures, the yellow crystals were determined to be 6-amino-5- bromoquinoxaline. The yield was 82%.
The crude hydrobromide product previously noted (4.27 g, 14.0 mmol) was dissolved in 60 ml of water and thiophosgene (1.28 ml, 16.8 mmol) was added in small portions with vigorous stirring. After 2 hours, the red color of the solution was discharged. The solid formed was filtered off and washed thoroughly with water. After drying in vacuo at 25°C 3.38 g (a yield of 90%) of brick red crystals was obtained, m.p. 157°-158°C. A portion of this material was further purified by column chromatography to give white crystals, m.p. 157°-158°C. Using various analytical procedures, these crystals were determined to be 5-bromo-6-isothiocyanatoquinoxaline.
A solution of the isothiocyanate (3.25 g, 12.2 mmol) in 145 ml benzene was added to a solution of ethylenediamine (5.43 g, 90.0 mmol) in 18 ml benzene at 25°C over 2 hours. After stirring for a further 30 min., the supernatant was poured off. The oil which remained was washed by swirling with dry ether three times and used directly for the next step. A portion of this product was further purified by column chromatography (SiO2, CHCl3) for characterization. A white solid was decomposed at 175°C. This white solid was determined to be 5-bromo-6-(N-2-(aminoethyl)thioureido)quinoxaline.
The crude product from above was dissolved in 100 ml dry methanol and the brown solution was refluxed for 19 hours until hydrogen sulfide gas was no longer evolved. The mixture was cooled to room temperature and concentrated to about 50 ml. The yellow solid was filtered off and dried in vacuo; weight 2.52 g (a yield of 70%), m.p. 242°-244°C. As the crude product was insoluble in most common organic solvents, initial purification was achieved by an acid-base extraction procedure. 23 g of the crude product was dissolved in 100 ml 0.5 N hydrochloric acid. The turbid yellow solution was filtered to give a clear orange yellow solution which was extracted twice with ethyl acetate (2x10 ml). The aqueous phase was cooled to 0°C and basified with 6 N sodium hydroxide, keeping the temperature of the solution below 15°C at all times. The yellow solid which precipitated was filtered off and washed thoroughly with water until the washings were neutral to pH paper. The solid was dried overnight in vacuo to give 1.97 g yellow solid, m.p. 249°-250°C. The recovery was about 88%.
Further purification was achieved by recrystallization as described below. The partially purified product from above was dissolved in N,N-dimethylformamide (about 17 ml/g) at 100°C with vigorous stirring. The solution was filtered hot and set aside to cool overnight. The bright yellow crystals were collected by filtration, m.p. 252°-253°C. Recovery was from 65-77%. Using various analytical procedures the bright yellow solid was determined to be 5-bromo-6- (2-imidazolin-2-ylamino)quinoxaline.

Alphagan (Allergan).

Antiglaucoma

A poison by ingestion.

Full α 2 adrenergic agonist. Centrally active following systemic administration in vivo . Also available as part of the α 2 -Adrenoceptor Tocriset™ and Mixed Adrenergic Tocriset™ .

UK 14,304 is an α2-adrenoceptor agonist. UK 14,304 inhibits hormone-sensitive lipase (HSL) activity and suppresses lipogenesis in adipose tissue.

Brimonidine is an alpha-adrenergic receptor agonist. It has a peak ocular hypotensive effect occurring at two hours post-dosing. Fluorophotometric studies in animals and humans suggest that brimonidine tartrate has a dual mechanism of action by reducing aqueous humor production and by and increasing uveoscleral outflow. After ocular administration of either a 0.1% or 0.2% solution, plasma concentrations peaked within 0.5 to 2.5 hours and declined with a systemic half-life of approximately 2 hours. In humans, systemic metabolism of brimonidine is extensive. It is metabolized primarily by the liver. Urinary excretion is the major route of elimination of the drug and its metabolites. Approximately 87% of an orally-administered radioactive dose was eliminated within 120 hours, with 74% found in the urine.

Store at RT