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Chemistry for a Healthier World

Lots of could-be medicines look good on paper—or on a computer screen—but a drug can only do its intended job of treating a symptom or fighting a disease if it gets to the right place in the body to do its job. That's where chemistry plays such a big role, in tweaking molecules to interact appropriately with the body.

A lot of the most important medical progress in recent history has come from the development of powerful antibiotics and vaccines to treat infectious diseases caused by bacteria, viruses and parasites. But those breakthroughs have come with a cost—microorganisms have learned how to fight back, and with a vengeance.

The misuse of antibiotics is the most common reason why antibiotic resistance is such a significant public health problem. These drugs are sometimes overprescribed by doctors, and many people fail to finish a full prescription.

Resisting Resistance

Staphylococcus aureus bacteria. Credit: Janice Haney Carr, CDC
MRSA is a strain of bacteria that has become resistant to antibiotics like methicillin. Credit: Janice Haney Carr, CDC

What's the problem? An antibiotic drug treats infection by knocking out hundreds of strains of "sensitive" bacteria in the body. But left behind are many nonsensitive, or resistant, strains. With no stops in place, the resistant microbes repopulate themselves rapidly.

Methicillin-resistant Staphylococcus aureus, or MRSA, is a bacterium that causes difficult-to-treat infections in humans, and its prevalence has been on the rise.

Making matters worse, MRSA has become resistant to most disinfectants and antiseptics used in hospitals.

Chemists are well aware of the public health danger posed by MRSA and other resistant organisms. They are working hard to outwit microbes that develop resistance. New forms of antibiotic drugs are currently in the pipeline, and researchers are trying to design them to target vulnerable molecular regions of enzymes within bacteria.

Not Your Local Library

As the name suggests, medicinal—also called pharmaceutical—chemistry is an area of research that focuses on designing and making drugs of all sorts. The first step in this process is identifying new molecules.

Years ago, medicinal chemists spent most of their time isolating interesting molecules from living organisms, mainly plants. Today, however, chemists working in this area are equally concerned with finding good ways to make these molecules in the lab. Medicinal chemists also work out the best way to deliver the new drug: as a capsule, tablet, aerosol or injection.

Illustration of combinatorial chemistry approach
Combinatorial chemistry helps narrow the search for new drugs.

Identifying a molecule with a specific medicinal effect—like lowering cholesterol or killing only tuberculosis bacteria—takes time and patience. But a strategy called combinatorial chemistry can help a lot. In this process, chemists create and then sift through immense collections, or "libraries," of molecules. The newly identified molecules, or "leads," are then tested for their usefulness in treating disease in animals and people.

Just like an online catalog helps you find books in the library or in a bookstore, combinatorial chemistry helps find molecules in a chemical library. It also usually involves computers to help a chemist find molecular matches that meet defined criteria.

Chemical libraries consist of a diverse matrix of thousands or even millions of different molecules made from just a few starting chemical building blocks. Each chemical has associated information about its chemical structure, purity or other characteristics stored in some kind of database.

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Two-Faced Drugs

Many properties help determine a molecule's potential as a drug. These include its chemical makeup, stability and solubility (how well it dissolves in water or body fluids).

Synthesizing new molecules or drugs involves much more than following a simple recipe. That's because chemical reactions turn out two, mirror-image results: a "left" and a "right" version of a molecule. The molecular building blocks of proteins, sugars, and DNA and RNA all have this property, which is called chirality. The term stems from the Greek word for "hands," the most familiar chiral objects.

Chemists call the two mirror images of a molecule enantiomers. Many chemical reactions generate a mixture of equal amounts of the two enantiomers. This matters when it comes to making a small molecule, such as a drug, that must fit precisely into a uniquely shaped cavity of a body protein. Whereas the left-handed version may fit perfectly into the correct space inside the protein, its right-handed counterpart couldn't squeeze in, no matter what.

Photo of a pair of hands
Hands are familiar chiral objects.

To manufacture products quickly and cost effectively, pharmaceutical companies used to produce medicines that contained equal portions of the left- and right-handed versions. That is because it is usually much less efficient and more expensive to produce only one enantiomer of a drug. Over time, however, chemistry research has taught us the importance of making single-handed compounds.

This solves two problems. The first is eliminating enantiomers that are dangerous. And in the vast majority of cases, most drugs produced as left- and right-handed mixtures are only half as strong as they could be, because one hand does nothing more than dilute the final mixture.

 

This page last reviewed on April 22, 2011