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Chiral Drugs

Jermaine P. Serrano

Drug chirality is now a major theme in the design, discovery, development, launching and

marketing of new drugs. The human body is made up of chiral receptors. Chirality in the human

body makes it selectively affinitive to the drugs being introduced to the body. Chiral drugs haveenantiomers that affect its therapeutic efficiency. Most of the chiral drugs made nowadays are amixture of enantiomers. That is, it is most probable that each enantiomer or the drug will exhibit

different physiological effects. It is important to know whether both enantiomers of a drug

exhibit desirable effect or if one exhibits harmful effect and the other does not.

A chiral carbon is an sp3carbon atom with four unidentical groups attached to it. This is a type of

molecule that has a non-superposable mirror image. The presence of an asymmetric carbon atom

is often the feature that causes chirality in molecules. A chiral carbon should have an enantiomer.

An enantiomer is one of two stereoisomers that are mirror images of each other that are non-

superposable, much as one's left and right hands are the same except for opposite orientation.

In a more scientific definition by Evans ( 2014), Enantiomers are molecular entities which are

non-superimposable mirror images. The chirality (handedness) of enantiomeric molecules iscaused by the presence of one or more chiral elements (chirality axis, chirality plane, or chirality

centre, e.g., asymmetric carbon atom) in the structure. The chirality and optical activity of the

enantiomers is determined by their absolute configuration, i.e., the spatial arrangement of the

atoms in the molecule.

Two enantiomers of the same compound, despite having the same physical and chemical

properties, show different interactions with other chiral molecules due to differences in spatial

arrangement of the atoms and therefore binding affinity. This phenomenon is particularly

significant in biological interactions as all proteins, enzymes and carbohydrates are chiral. Thus

organisms might respond uniquely to each enantiomer.

Majority of the receptors in the human body is chiral. Thus, a chiral receptor can only bind with

one pair of an enantiomer. According to Tian (2012), Chiral drugs, which took more than 50%

of all current drugs, have been paid more and more attention for their clinical applications. A pairof enantiomers would be discriminated as different molecules by chiral environment such as

enzymes, receptors, carries, etc. Bio membrane permeability and cellular uptake of chiral drugs

may be also stereo selective if intracellular macromolecules recognize the enantiomers in chirallydiscriminative ways. Therefore, the pharmacodynamics, pharmacokinetics and toxicology

between the enantiomers could be stereoselective.

The drugs are categorized into three classes: natural products a chemical compound or

substance produced by a living organismfound in nature; natural products that have been

modified in the laboratory; synthetic compounds produced by chemical synthesis, especially

not of natural origin. Most drugs obtained from natural sources consist of a single enantiomer.

Most of the drugs being produced nowadays are a mixture of enantiomers. The biologicalresponse produced by enantiomers is rarely similar. There is an evidence that the human body is

capable of convertingRenantiomer into desired S enantiomer. Jamalis (1997) study found the

following: The R enantiomers of some of the 2-arylpropionic acid non-steroidal

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