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Nature's Products

Our world is full of molecules with natural healing power. Chemists examine substances produced for self-defense by microbes, algae, plants and animals to learn how to make powerful antibiotics, painkillers, cancer treatments and other medicines.

Snakes, spiders and sea snails use venom to kill their prey. Poisonous dart frogs, wasps and hemlock trees protect themselves with chemicals. Penicillin is a "bacterial poison" made by a mold. The process of evolution has shaped inventive ways for organisms to keep themselves safe from predators.

Earth's Pharmacy

Photo of 'Conus geographus' cone snail. Credit: Kerry Matz
Scientists have retooled cone snail poisons to make the painkiller Prialt®. Credit: Kerry Matz

The enzymes in our bodies are also shaped by millions of years of evolution. Because all living things share the same basic biochemistry, natural products frequently interact with the same molecules in people as they do in other organisms.

So chemists want to understand much more about natural products, and a key step in doing that is figuring out how the molecules are made. That information is important for two reasons.

First, it can uncover related, and sometimes even more desirable, molecules. Second, understanding natural processes helps chemists learn how to make and refine chemicals in the lab.

Biology Labs

Human use of microorganisms extends back to prehistoric times, when people began making wine and leavened bread. Recently, in an area of chemistry called metabolic engineering, researchers have used the tools of molecular biology to produce chemical substances that, in many cases, never before existed in nature. Sometimes, these are referred to as "unnatural" natural products.

Metabolic engineers use living systems to turn simple sugars and other small molecules into promising new antibiotic medicines, biofuels and other agricultural and veterinary products.

Unlike a factory production scheme, metabolic "labs" carry out multiple chemical reactions in a single pot-a cell-without the need for time- and labor-intensive separation and purification steps.

To work their magic, chemists need to understand and be able to reproduce the biochemical circuits these organisms routinely use to break down food and produce energy, as well as those pathways that re-use the building blocks to make bigger molecules. The products of metabolism are called metabolites.

Illustration of erythromycin made by enzyme modules, each of which adds two carbons to the growing chain of atoms.
Erythromycin is made by enzyme modules, each of which adds two carbons to the growing chain of atoms.

More than a hundred metabolites are currently used as common medicines for people and animals. Examples include the antibiotics erythromycin and tetracycline, a cholesterol-lowering drug called lovastatin (Mevacor®) and a flea-busting pet medicine called avermectin. All of these are polyketides, a class of metabolites that soil bacteria manufacture naturally and abundantly.

Chemicals from nature have also proven effective against not-so-obvious conditions like heart disease, depression and epilepsy. Sometimes, a natural substance will inspire medicines for two or more diseases.

Photo of an yew tree's bark. Credit: NIH
Scientists make Taxol from the bark of yew trees. Credit: NIH

There are also many natural products that look good but simply can't be made in the lab. Many have very complex structures that are too difficult and expensive to manufacture on an industrial scale. One example is the painkiller morphine.

Another is the cancer drug paclitaxel (Taxol®). An entire Pacific yew tree would have to be cut down to extract enough active ingredient from the bark to make a single dose of this medicine.

But this slow-growing tree is an environmentally threatened species.

Thankfully, synthetic chemists have figured out a way to make the drug from a readily available ingredient that is abundant in the more plentiful European yew tree.

Chemists also get creative by inventing techniques unavailable to woodland or jungle creatures. Using lab tools and tricks—changing reaction conditions or adding catalysts—chemists can make huge quantities of molecules whose structures are slight variations of a natural product.

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An Interesting Prospect

Photo of a rainforest
Tropical rainforests are often rich sources of chemical diversity.

Researchers travel the world to obtain natural samples to analyze and evaluate for the purposes of drug discovery. Collecting natural materials can involve harvesting reptile venom, diving for poisonous marine life and hiking through jungles to identify rare plants. Scientists have already found lots of promising substances, but they think that many more are still out there.

Having an appreciation for different cultures is really important for this kind of work. Often, talking with locals gives key insights about potential uses for natural products.

"Bioprospecting" has to be thoughtful and respectful. Many of the areas of rich biodiversity are in tropical forests and coral reefs in some of the poorest parts of the world, and these ecosystems must be protected. One way to do this is through chemistry that synthesizes natural products and helps minimize the use of natural resources.

 

This page last reviewed on April 22, 2011