Chirality

Rediscovery of stereochemistry

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Stereochemistry, in particular chirality, is known to us as early as 1809, when Malus, Arago and Biot discovered plane polarized light and its characteristics. It is observed that during 1950s to the 1970s, the “Golden Age” of drug discovery & development, stereochemistry was largely ignored resulting in approximately 57% of pharmaceuticals being marketed as racemates by the 1980s. Before going further let us examine the stereospecific awareness level that existed during 1980s’. Stereospecific Awareness level  …

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Levamisole

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Levamisole is used as anthelmintic agent to get rid of the intestinal worms. It is (S)-(-)-enantiomer of tetramisole. This drug is used in veterinary to treat hookworm infections.  Levamisole also finds therapeutic application in the treatment of colon cancer when given in conjunction with fluorouracil.   Chirality and biological activity Tetramisole carries one chiral stereogenic center and exists as an enantiomeric pair. The anthelmintic activity resides in the (S)-(-)-enantiomer, levamisole. The (R)- isomer harbors undesirable …

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Beta-Blockers

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Beta blockers, also spelled β-blockers, used as antihypertensive agents (lowering blood pressure), represent a class of chiral drugs that are marketed as racemates since the distomer exhibits no undesirable adverse effects. Three most important β-blockers viz. propranolol, atenolol, and metoprolol are marketed as racemic mixture. Chirality and biological activity β-blockers are aryloxy propanolamines with one stereogenic center and exists as a pair of enantiomers. It is observed that their therapeutic effect resides entirely in the (S)-enantiomer …

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L-Dopa

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Levodopa, L-Dopa, belong to a class of medications called dopamine agonists.  L-Dopa is used to increase dopamine concentrations in the treatment of  Parkinson’s disease. Most commonly, clinicians use levodopa as a dopamine replacement agent for the treatment of Parkinson disease. L-dopa is the precursor to dopamine and crosses the blood-brain barrier to increase dopamine neurotransmission. Chirality and Biological activity L-dopa, the (S)-enantiomer, is a chiral drug with one stereogenic center. It exists as a pair of enantiomers. The initial use …

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Terodiline

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(±)-Terodiline, the antianginal agent, perhaps represents the best authenticated example of a drug that had to be withdrawn from the world market as consequence of proven stereospecific toxicity. Terodiline has a close similarity to prenylamine from a structural and pharmacological view point. It was firs marketed as an antianginal agent but it exhibited urinary retention as a frequent and worrying side-effect. It was decided to exploit the the side-effect. Therefore the drug was redeveloped and …

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Prenylamine

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(±)-Prenylamine, an antianginal agent, was introduced in the market since early 1960. Reports associating Prenylamine with prolongation of the QT interval, ventricular tachycardia, and ventricular fibrillation started to appear. Some of these events had a fatal outcome and the drug was withdrawn from the market world-wide in 1988.  Chirality and drug withdrawals Prenylamine is chemically diphenyl-propyl derivative of phenylalkylamine. The drug is optically active with one stereogenic center (indicated by a red arrows), giving rise …

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Dilevalol

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Dilevalol is the (R,R)-diastereoisomer of labetalol. Labetalol has been in clinical use since 1977 for the treatment of hypertension.  Labetalol is an adrenergic antagonist used to treat high blood pressure. It has a role as an antihypertensive agent, a sympatholytic agent, an alpha-adrenergic antagonist and a beta-adrenergic antagonist. Chirality and drug withdrawals Labetalol has two stereogenic centers and consequently exists as four stereoisomers. It is a diastereoisomeric mixture of approximately equal amounts of all four possible stereoisomers …

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Thalidomide

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Thalidomide was a racemic therapeutic and prescribed to pregnant women to control nausea and vomiting. The drug was withdrawn from world market when it became evident that the use in pregnancy causes phocomelia (clinical conditions where babies are born with deformed hand and limbs). Later in late 1970s, the thalidomide enantiomers were separated and enantioselective studies indicated that the (R)- enantiomer, the good partner, is an effective sedative, the (S)-enantiomer, the evil partner, harbors teratogenic …

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Indacrinone

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Indacrinone is an orally active, indanone-based loop diuretic patented by American pharmaceutical company Merck and Co as mixture of two enantiomers. In healthy volunteers, the racemic mixture of indacrinone exhibited greater natriuretic potency than furosemide, with a slower onset and longer duration of action. Furthermore, single doses of indacrinone decreased serum uric acid concentrations and increased uric acid clearance, while similar doses of furosemide generally had the opposite effects. Differences in the pharmacologic effects of …

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Levocetirizine

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Levocetirizine, is chiral switch cetirizine, employed for allergies. It is a third generation, non-sedating, selective histamine H1 receptor antagonist, with antihistamine, anti-inflammatory and potential anti-angiogenic activities. Levocetirizine is used to relieve the symptoms of hay fever and hives of the skin. It is an antihistamine that works by preventing the effects of a substance called histamine, which is produced by the body.  Chirality and Biological activity Cetirizine carries one stereogenic carbon (indicted by an red arrow mark) and …

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