Valliappan Kannappan

Chiral selectors

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Lead A wide range of chiral compounds have been examined as chiral selectors with regard to their ability to separate enantiomers using chromatography as part of the development of CSPs. From low-molecular-weight chemicals to polymers with both synthetic and biological origins, the chiral molecules investigated as potential CSs span almost the full spectrum of chemical and structural diversity. The search for effective CSs has so far led to the synthesis of more than 1400 CSPs, …

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Direct chiral HPLC separation on CSPs

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Chiral stationary phases (CSPs) The most convenient and most popular analytical methodology to assess chiral purity is the direct separation of enantiomers on so-called chiral stationary phases (CSPs). CSPs consists of an (ideally) inert chromatographic support ( usually silica micro-particles) on to which the chiral selector (CS; single enantiomer of a chiral molecule) is physically coated (adsorption) or immobilization (covalently linked).   Basic concept The column is packed with a chiral selector (viz. polysaccharide or …

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Chiral HPLC separation: strategy and approaches

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Strategy The basic aspect is to provide the right chiral environment where by the enantiomeric pair become distinguishable. In HPLC how do we construct the chiral environment? To understand this let us look at the variables available, in the HPLC system, that can be exploited for this purpose. The following is a schematic diagram of a typical HPLC system. The are three variables namely the analyte, mobile phase and stationary phase that can be alerted …

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Chiral chromatography

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What is chiral chromatography? Chiral chromatography is now widely understood and applied in daily life. The correct phrase, however, is “enantioselective chromatography”. Chiral chromatography has developed into the most popular method for enantiomeric purity assessment and pure enantiomer separation, both on an analytical and preparative scale. The initial step in any investigation into enantioselective synthesis or separation is a chiral chromatographic assay. This includes employing strategies like High performance liquid chromatography (HPLC), chiral supercritical fluid …

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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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