Cetirizine. Claire Förster Laura Euler Bueno Niels Hanau

Transcription

1 Cetirizine Claire Förster Laura Euler Bueno Niels Hanau

2 General information: Cetirizine is a second-generation antihistamine and the most used drug against hay fever. It is also used against other allergies, like Urticaria, Conjunctivitis, asthmatic conditions, itching and other skin responses. As the symptoms of these diseases are caused by histamine on the H1 receptor, Cetirizine blocks these receptors and disables them temporarily. As an antihistamine of the second generation Cetirizine is less able to cross the blood-brain barrier and so the effects on the central nervous system are much lower compared to first-generation antihistamine. Structure IUPAC name: (±)-[2-[4-[(4-chlorophenyl) phenylmethyl]-1- piperazinyl] ethoxy] acetic acid R- Cetirizine S- Cetirizine Cetirizine is a 1:1 racemate, but only the R enantiomer is an active component. Levocetirizine (R enantiomer) is also available as an own drug. Cetirizine is a derivative of ethylenediamine and piperazine. 3D structure of Cetirizine designed with ChemSketch

3 Differentiation of antihistamines The H1 histamines can be divided in three generations. The first generation operates sedating by damping off the central nerve system. The fact that the blood-brainbarrier can be crossed results in many adverse effects, e.g. fortige phenomenous. Besides these adverse effects all h1-receptors in the body are blocked. Due to all these side effects the H1-antihistamines are only in a rare oral usage today. The second generation antihistamines are marked as non sedating antihistamines. They are not specific for one H1-receptor and are less sedating. The blood-brain-barrier cannot be crossed which has the benefit of less adverse effects. One important advantage of the second generation is the fast and long persistent effect, resulting in the need of one oral taking only a day. Also they are not cardio toxic and anticholinergic. The last group of antihistamines is the third generation. This expression could be seen only as a marketing claim. These antihistamines have rarely therapeutic advantages. Often the enantomerical pure form is sold under a new name (Example: Levocetirizine). Synthesis of Cetirizine The first step of the synthesis of Cetirizine is a Friedel Crafts Acylation, followed by a reduction using sodium borhydride and a nucleophile substitution carried out using thionyl chloride. The reaction with component A results in another nucleophile substitution. In the next step a deprotonation with sodium hydride in presence of dimethylfurane. The last step to get Cetirizine is another nucleophile substitution. In an acidic solution Cetirizine builds a complex. The first step to synthesis component A is a nucleophile substitution of piperazine with Cl-CO 2-R, followed by a reaction with chloride ethanol in presence of sodium bicarbonate, under elimination of hydrochloric acid. The last step to synthesis component A is an acid inhibited substitution. Picture of synthesis:

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5 Effect and adverse effects Cetirizine has anti-allergic and anti-inflammatory properties. It has a high selectivity for the H1-receptor. As the symptoms of these diseases are caused by histamine on the H1 receptor, Cetirizine blocks these receptors and disables them temporarily. The effect of Cetirizine occurs quickly and is long persistent. By the fact that Cetirizine is not able to pass the blood-brain-barrier, Cetirizine causes less fortige and oscitancy than other first generation antihistamines. However both adverse effects could still appear. Further frequent adverse effects could be: headache, nausea, dizziness and lightheadedness. Rhinitis could occur by children. In addition occasionally itching and rash could be observed. But comparing all it can be summarized that antihistamines of the second generation have less adverse effects. References: Picture of synthesis: SciFinder