Synthetic vs. Natural: What’s the Difference?
When we say that Percy Julian and Josef Pikl synthesized the compound physostigmine in the lab, that might sound like he invented something that behaved very much like natural physostigmine and could be used as a substitute for it, but that it wasn’t the “real thing.” That’s not the case. They didn’t just make a substitute for physostigmine. They made physostigmine itself.
To explain what we mean, let’s look at a simple compound: water. We can make water molecules in the lab. All we need is some oxygen gas (O2) and some hydrogen gas (H2). Each molecule of oxygen is made of two oxygen atoms, and each molecule of hydrogen is made of two hydrogen atoms. If we put O2 and H2 in a tank together and set off a spark inside the tank, there will be a big ball of blue fire. This is the hydrogen gas burning. When it burns, each hydrogen molecule is being torn apart into two separate hydrogen atoms. Likewise, each oxygen molecule is being torn apart into two separate oxygen atoms.
All these atoms reassemble into new molecules. An oxygen atom will join with two hydrogen atoms. The new molecules formed are water molecules H2O. Our tank will have a small puddle of water at the bottom of it when we’re done, and there will be little drops of water all over the sides.
The liquid in the puddle was made by humans, but it isn’t some sort of “imitation water.” It’s real water. The water molecules we made here are identical to the water molecules found in the ocean, a river, raindrops, or any other natural source of water. What makes water act like water is its molecular structure, that is, the type of atoms its molecules contain and how they are arranged relative to each other, and not how the molecule was built in the first place.
This brings us back to Percy Julian. While a water molecule is a pretty simple thing, the physostigmine molecule is much more complicated. You can see a model of the molecule below.
(Don’t worry. You won’t have to draw it from memory on a test or anything.) This molecule is a very complicated assembly of carbon, oxygen, nitrogen, and hydrogen atoms. Julian and his coworkers figured out how to build, or synthesize, this exact molecule in their laboratory. Just like those molecules we made by burning hydrogen were true water molecules, the molecules that Julian built were real physostigmine, not “imitation” physostigmine. Julian’s synthesized physostigmine behaved exactly like natural physostigmine because Julian’s compound and the natural compound have exactly the same molecular structure.
So when we talk about “synthetic” substances versus “natural” substances, we’re referring the difference between how they are madehow they come into beingnot any difference between their molecules. The molecules are identical.
One important difference between substances found in nature and those synthesized in the lab, however, can be the difference in cost. Generally, substances like physostigmine occur in nature in small quantities that are hard to extract from the plant or animal in which they occur. So one great advantage of being able to unravel nature’s secrets and reproduce them in the lab is that, once the process is discovered, it becomes much cheaper to synthesize substances in the lab than it is to get them from nature. This is what Percy Julian did.