Ethambutol

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(S,S)-(+)-Ethambutol is powerful and selective antitubercular drug. It is a classical example of an old drug that was introduced for clinical use in its chirally pure form. Chirality and biological activity Ethambutol contains two constitutionally symmetrical stereogenic centers in its structure and exists in three stereoisomeric forms. An enantiomeric pair (S,S)- and (R,R)-ethambutol, along with the achiral stereoisomer called meso-form. The activity of the drug resides in the (S,S)-(+)-enantiomer which is 500 and 12 fold more …

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Levofloxacin

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Levofloxacin is a third generation fluoroquinolone that is widely used in the treatment of mild-to-moderate respiratory and urinary tract infections due to sensitive organisms.  Levofloxacin is an antibacterial prescription medicine approved by the U.S. Food and Drug Administration (FDA) for the treatment of certain bacterial infections, such as community-acquired pneumonia, acute worsening of chronic bronchitis, anthrax, urinary tract infections, acute sinus infections, and others. Chirality and biological activity Levofloxacin, the S-enantiomer of the previously marketed …

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Ascorbic acid

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L-(+)-Ascorbic Acid is another old chiral drug from natural source. It is a water-soluble vitamin (Vitamin C). Ascorbic acid is a potent reducing and antioxidant agent that functions in fighting bacterial infections, in detoxifying reactions, and in the formation of collagen in fibrous tissue, teeth, bones, connective tissue, skin, and capillaries. Found in citrus and other fruits, and in vegetables, Vitamin C cannot be produced or stored by humans and must be obtained in the …

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Quinine

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Most fascinating old chiral drug, from historical point of view, is Quinine. It is known that by early 1600s quinine was being used by South American natives, in Peru, Ecuador, as a crude preparation from the bark of the Cinchona tree for the treatment of malaria. Chirality and biological activity Quinine contains two major fused ring systems: aromatic quinoline and bicyclic quiniclidine. The molecule contains four stereogenic carbon centers at C-3, C-4, C-8 and C-9, respectively …

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Morphine

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Many medicinal agents important to life are combinations of mirror-image twins called chiral compounds. These twins may look very similar, yet their biological makeup might differ significantly. In other words, the pharmacokinetic and pharmacodynamic profiles of the individual enantiomers that make up a racemic chiral medication might drastically vary. The Chiral Molecule of the Week #cMOTW is an effort to highlight significant chiral compounds with therapeutic value. Follow us for more …… Nature is not even …

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Cis-trans and E-Z notation: choose your side

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“Pharmacological studies confirm the high activity of triprolidine and the superiority of (E) over corresponding (Z) isomers as H, antagonist” ( Ref:   – – – from “Wilson and Gisvold’s Textbook of organic medicinal and pharmaceutical chemistry, 2010”). “Triprolidine is 2-[(E)-1-(4-methylphenyl)-3-pyrrolidin-1-ylprop-1-enyl]pyridine”, the IUPAC name. To understand the above statements one need to be familiar with the “cis-trans and E-/Z- nomenclature. How to translate the name to structure and vice versa? This blog is basically to discuss …

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The meso compounds: finding plane of symmetry

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“If you immediately identified this as a molecule with an internal plane of symmetry (and hence an achiral molecule, incapable of having an enantiomer), congratulations. If not, you just fell into The Meso Trap”. Source: https://www.masterorganicchemistry.com/2011/01/12/the-meso-trap/ The meso concept is a common aspect in examinations and tests to evaluate how good you understand the concept of chirality So let us try to understand meso-compounds with case studies. It is suggested that the reader may first go through the earlier blog …

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Erythro- and Threo- prefixes: the (same-) or (opposite-) side?

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“Chloramphenicol possesses two chiral carbon atoms in the acylamidopropanediol chain. Biological activity resides almost exclusively in the D-threo-, isomer: the L-threo–and the D– and L-erythro– isomers are virtually inactive.”  – – – from “Wilson and Gisvold’s Textbook of organic medicinal and pharmaceutical chemistry”. In the name “D-threo– and L-threo-Chloramphenicol”, what does the prefix threo– and erythro– in the nomenclature mean? How do we translate the name to structure? This blog is basically to understand and …

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Atropisomers: things are tight, single bond won’t rotate

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Atropisomers are stereoisomers resulting from hindered rotation about single bonds where the steric strain barrier to rotation is high enough to allow for the separation of the conformers. Note: Butane, for example, has conformations that are atropisomers; however, unlike the biaryls, the barrier to rotation is so small that they are interconverted rapidly at room temperature, and they are, for practical purposes, achiral. As a general rule of thumb, chiral molecules must have at least …

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D-/L- system naming: the (left-) or (right-) hand side?

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The Fischer convention was introduced to specify the configuration of a stereogenic center and uses the symbols D and L. The use of capital letters is to differentiate from the “d” / “l” notation (optical descriptor) described earlier. This nomenclature system has become obsolete. In general the D/L system of nomenclature is superseded by the Cahn-Ingold-Prelog (CIP) rule to describe the configuration of a stereogenic/chiral center. But D-/L-system of naming is still employed to designate the configuration of amino acids …

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