Korry has a Ph.D. in organic chemistry and teaches college chemistry courses.
Have you ever stopped to consider just how vast the number of FDA (Federal Drug Administration) approved drugs on the market really is? And even more than that, the number of drugs that are put into clinical trials each year is even larger. Where did they all come from? How do you get ideas as to what kind of organic compound might make a good drug candidate? Although those are certainly very broad questions that could take a lot of time to explain, using nature to help aid in drug discovery efforts is actually a very important way to discover new therapeutic agents.
Just like a gold miner goes out and tries to find gold among the rubble, scientists take plants and try to find natural products with biologically active properties that could help in the treatment of clinical conditions. Sometimes this is called 'bio-prospecting,' just like prospecting for gold! The class of natural products we are going to learn about in this lesson are called alkaloids. We will talk about what an alkaloid is, then get a short survey of how they are extracted from the plant sources they are commonly found inside of.
An alkaloid is simply a naturally occurring organic compound that contains at least one basic nitrogen atom. The first individual alkaloid isolated was in 1804, and is probably one you've heard of before-- morphine. Morphine (a powerful pain killer) was first extracted and isolated from the poppy seeds of opium poppy plants. Notice the basic nitrogen atom of morphine labeled in red, thus making it an alkaloid.
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Two other common examples of alkaloids you're familiar with are nicotine and caffeine. Nicotine is a stimulant, and the compound responsible for the effects of tobacco use. Caffeine, as we all know, is found in coffee and sodas and is also a stimulant that helps us get going in the morning or get through that afternoon drowsy period. Notice that again, both nicotine and caffeine contain at least one basic nitrogen atom, making them alkaloids.
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Let's say you know for a fact that a plant you've brought back from the rainforest contains an alkaloid that is active against cancer. The task at hand now is to successfully extract and isolate the alkaloid from the rest of the other thousands of organic compounds inside the plant. An analogy would be something like you have 10,000 pieces of straw and there is 1 small needle among them. Find the needle. Sounds impossible right? But that's the task natural product chemists are faced with. Trying to find the one piece of 'gold' among rubble!
The first thing you'll want to do is take the dried plant material and crush it up into as fine of a powder as possible. The greater the surface area and the finer the material, the better the extraction goes. We need to get rid of all the fats, oils, terpenes, etc. from the alkaloids. Basically all of the non-polar 'junk' we're not after. How we can do this is extract these compounds with hexanes or petroleum ether from the powdered material. We aren't really interested in these compounds so they can be discarded.
To extract the alkaloids that are left, we will take methanol (ethanol can also be used) and repeatedly wash the crude plant material. This pulls all of the alkaloids out of the plant material. A machine called a rotary evaporator is then used to evaporate the alcohol solvent and this gives us our crude alkaloid mixture (plants rarely contain only one alkaloid).
Once we have the crude alkaloid mixture, we will use an analytical technique called high-performance liquid chromatography (HPLC) to fractionate the mixture repeatedly until we have pure individual alkaloids. When we have the pure alkaloids, we can test them in a cancer assay to find out exactly which one is our 'gold nugget' that we were looking for!
In this lesson, we learned that an alkaloid is a naturally occurring organic compound that has at least one basic nitrogen atom. Alkaloids such as morphine, nicotine, and caffeine have been known for decades, and new alkaloids with desirable medicinal properties are being discovered frequently by natural products chemists. Extracting of alkaloids from their natural sources includes:
1. Separation of the alkaloid mixture from the fats, oils, terpenes, and other non-polar compounds by extracting them with either hexanes or petroleum ether.
2. Extraction of the alkaloid mixture with either methanol or ethanol.
3. Isolation of the pure alkaloids by HPLC (high performance liquid chromatography).
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