Chirality

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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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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Fischer Projection: hassle free way to depict a stereoformula in 2D projection 

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One of the major problems in organic chemistry is the representation of three-dimensional structures in a two-dimensional media (viz. sheet of paper, blackboard, etc.). Chemists sometimes represent structures for chiral molecules with two-dimensional formulas called Fischer projection formulas. These two-dimensional formulas are a quick way to show three dimensions without the hassle of having to draw 3-D. The Fischer projection, devised by the carbohydrate chemist Emil Fischer in 1891. This projection formula is a technique …

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Naming enantiomers: the left-(or right-) handed?

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Enantiomers are pair of molecules that exist in two forms that are mirror images of one another but cannot be superimposed one upon the other.  They are also referred to by chemists as chiral twins or handed molecules. Each twin is called an enantiomer. Naming of enantiomers is important to understand ‘which structure refers to which enantiomer?’. The chirality of organic molecules is described by the Cahn-Ingold-Prelog (CIP) system. This system is also referred to as the R/S convention …

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Thalidomide tragedy: the story and lessons …

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In the 1940s and early 1950s, pregnant women throughout the world who experienced morning sickness and other anxieties associated with the first term of pregnancy were given barbiturate sedatives for relief. The issue with these barbiturates, like most sedatives, was the fact that they were highly toxic in large doses. In 1957, Chemie Grunenthal of Germany launched thalidomide as a safer alternative to barbiturate sedatives. Thalidomide, as a new sedative, was a very “attractive” drug …

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