Not All Plant-Based Medications Actually Come from Plants
Acetaminophen, the active ingredient in popular pain reliever Tylenol, stems from a surprising source: coal tar, a thick, sticky liquid produced when oxygen-deprived coal is subjected to high heat.
Fortunately, a new method, developed by researchers at the University of Wisconsin
—Madison's Great Lakes Bioenergy Research Center (GLBRC) offers an environmentally friendly alternative to the currently fossil-fuel heavy one. It draws upon a natural compound derived from plant material to synthesize the popular medication. According a press release, the process is outlined in a patent awarded to a team led by Biochemist John Ralph.
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Along with University of Kentucky Biochemist Justin Mobley and GLBRC research scientist Steven Karlen, the trio decided to experiment with clipoffs. Clipoffs are small molecules attached to lignin, an abundant yet difficult-to-manage polymer that makes the cell walls of plants rigid. This came after having a light bulb moment in the middle of a conversation.
"Ralph started talking about clipoffs, and I said why don't we make something out of these. So we chose acetaminophen as a catchy target that people have heard and care about."University of Kentucky Biochemist Justin Mobley
Ralph describes lignin as an "extremely complex, messy polymer...very effective for providing structure and defense for the plant" but hard to break down into usable components. This quality makes lignin a researcher's headache. They rely on plant sugars found in bioenergy crops to produce biofuels but find themselves unable to effectively use the leftover polymer. It is then burned for energy.
To overcome this issue of wastefulness, a string of chemical reactions capable of converting clipoff molecules, so called because a structure attached to lignin known as p-hydroxybenzoate is "fairly easy to clip off as a quite pure stream," into acetaminophen has been created. It only took three steps to accomplish the task. Adhering to the same process used with coal tar, the only part that changed was the source material.
Acetaminophen and p-hydroxybenzoate are both relatively simple molecules. given the similarities in their structures, the plant-based material boasts an advantage of the fossil-fuel derived one. Whereas this more complex petrochemical must be stripped down to its bare molecular bones before being built back up into the desired compound, the lignin-based molecules already bear some of the desired structure.
Now, the team is working on refining their method, to improve both yield and purity. Although the more expensive, renewable alternative is unlikely to replace the cheaper method anytime soon, Ralph says that
"...at some point , it may be the case that we are completely prevented from using fossil fuels. We are not close to that now...but it is almost inevitable. Preparing for a future in which our resources are derived sustainably seems prudent."University of Wisconsin
—Madison's Great Lakes Bioenergy Research Center Biochemist John Ralph