As the world moves towards a cleaner green bioeconomy, new research on the uses of poplar bark and leaves, and its potential phytochemicals as value-added co-products are being developed through biorefinery.
Recently a team of researchers led by the biochemistry professor John Ralph PhD’82, based in the Great Lakes Bioenergy Research Center (GLBRC), in Wisconsin (USA) has been awarded a patent for a method to synthesize paracetamol— also known as acetaminophen — from a molecule found on the lignin from poplar trees. This new method offers a renewable alternative to the present manufacturing process that uses chemicals from coal tar.
The Great Lakes Bioenergy Research Center (GLBRC) is a U.S. Department of Energy-funded Bioenergy Research Center led by the University of Wisconsin–Madison. Its mission is to create economically viable and environmentally sustainable biofuels and bioproducts.
Paracetamol from poplar
Paracetamol’s structure is relatively simple, explains the scientists: a six-carbon benzene ring with two small chemical groups attached. Poplar trees naturally make a remarkably similar structure, called p-hydroxybenzoate, which is attached to lignin. The plant material offers the chemical advantage of starting from a molecule that already has some of the desired structures, whereas more complex petrochemicals first must be stripped down to basic molecular pillars before being built back up into the desired compounds.
According to the research team, the new method is inexpensive and builds on a biomass pre-treatment process previously developed at GLBRC. “Making money off any side product helps drive the economics of the biorefinery. In many cases, these products are even more valuable than the fuel”, Ralph explains.
But what is biorefining?As defined by the International Energy Agency, biorefining is “the sustainable processing of biomass into a spectrum of bio-based products (food, feed, chemicals, materials) and bioenergy (biofuels, power and/or heat)”.
“As industries prepare to shift away from a fossil fuel–based economy, having biomass-based pathways at the ready will be an essential piece of that process,” Ralph declares. For him, this is an opportunity “to make a high-demand, ‘green’ pharmaceutical from plants rather than from fossil fuels.”
A tree with medicinal properties
Poplar is no stranger to medical uses. The Greek physician Pedanius Dioscorides, (born c. AD 40, Anazarbus, Cilicia—died c. 90) wrote about the use of poplar in the treatment of gout. His work De materia medica was the most important pharmacological text for 16 centuries.
Throughout history, other renowned scientists such as the English physician and apothecary Nicholas Culpeper (1616-1654), and the Swedish naturalist and botanist Carl von Linné, wrote extensively on the medicinal properties of poplar and its uses in the treatment of various illnesses, from ear pain to dysentery, burns and arthritic pain.
One of the reasons for this is that poplar is rich in salicin. This is an anti-inflammatory agent found in the bark of Populus species and willows, as well as in poplar leaves. Salicin also contains flavonoids – which are plant compounds that reduce inflammation – and antibacterial tannins. When ingested, salicin is metabolized by the intestinal flora to saligenin. This is further metabolized by the liver to salicylic acid. Historically, the origin of aspirins that we use today, is salicin.