From Poplar to Painkiller A new, renewable way to make acetaminophen also improves the bottom line for biorefining With a new method to synthesize a popular painkiller from plants rather than fossil fuels, a team of researchers led by biochemistry professor John Ralph PhD’82 has found a way to relieve two headaches with one process. The group has been awarded a patent for a method to synthesize acetaminophen — the active ingredient in Tylenol — from a natural compound derived from plant material. The approach offers a renewable alternative to the current manufacturing process, which uses chemicals derived from coal tar. It also creates a useful product from an abundant but difficult-to-manage component of plant cell walls called lignin. “Lignin is an extremely complex, messy polymer. No two molecules in a plant are exactly the same,” says Ralph, who is also affiliated with the Great Lakes Bioenergy Research Center (GLBRC), where the research team is based. “It’s very effective for providing structure and defense for the plant, but it’s challenging Photo by Chelsea Mamott for us to break down into useable materials.” The lignin in bioenergy crops, such as poplar, can material, the newly patented process improves the create a headache for bioenergy researchers due to overall bottom line for biorefining — that is, producits recalcitrant tendencies, Ralph says. Once plant ing fuels and other industrial materials from plants. sugars are used to produce biofuels, the lignin that “Making money off any side product helps drive remains is typically burned for energy. the economics of the biorefinery,” Ralph explains. The patent application, filed by the Wisconsin “In many cases, these products are even more valuable Alumni Research Foundation, describes a way to than the fuel.” convert a molecule found on lignin into acetaminoThe plant material also offers the chemical phen. It was awarded in May 2019 to Ralph, GLBRC advantage of starting from a molecule that already scientist Steven Karlen, and Justin Mobley, a has some of the desired structure. More complex former GLBRC postdoctoral fellow who is now at petrochemicals must first be stripped down to basic the University of Kentucky. molecular backbones before being built back up into Structurally, acetaminophen is a relatively simple the desired compounds. compound: a six-carbon benzene ring with two small “As industries prepare to shift away from a fossil chemical groups attached. Poplar trees naturally fuel–based economy, having biomass-based pathways make a very similar structure, called p-hydroxybenat the ready will be an essential piece of that process,” zoate, attached to lignin. Ralph says. “Here is an opportunity to make a high“Although lignin itself is a challenge to break demand, ‘green’ pharmaceutical from plants rather down, the p-hydroxybenzoate is fairly easy to clip off than from fossil fuels.” as a quite pure stream,” Ralph says. Acetaminophen and related molecules are also From there, the researchers devised a short series useful as commodity chemicals, the industrial buildof chemical reactions to convert the molecule into ing blocks used to make products, including other acetaminophen. The method is inexpensive and pharmaceuticals, plastics, and fuels. builds on a biomass pretreatment process previously The researchers are now working on refining the developed at GLBRC. process to improve the yield and purity of the plantIn addition to charting a way to synthesize derived acetaminophen. acetaminophen from a renewable, sustainable source —Jill Sak ai
Lignin samples in a lab at the Wisconsin Energy Institute, which houses the Great Lakes Bioenergy Research Center. This research was supported by a grant from the Department of Energy (DE-SC0018409).
FALL 2019
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