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November 30, 2018

Germany: Wuppertal, Bayer


The tracks for Wuppertal’s suspension railway head past the Bayer plant.

As it heads along the Wupper River the Wuppertal Suspension Railway passes by a large chemical plant owned by the pharmaceutical giant Bayer. It is in this area of Germany that several notable pharmaceuticals were discovered or first manufactured at scale for the market. Many of these drugs, including Aspirin, acetaminophen, phenobarbital, and Heroin are still used today.

It is commonly believed that the drug Aspirin is derived from salicylic acid found in the leaves of willow trees. Though it is true that willow trees do produce salicylic acid, it is not the full story. Bayer did not need willow trees. It had an abundance of salicylic acid produced as a by product from processing the coal mined in the nearby Ruhr Valley. It was the salicylic acid from coal that Bayer was working with, not salicylic acid from willow trees. In an effort to make salicylic acid a better drug chemists at Bayer discovered that “acetylating” the phenolic hydroxyl produced an effective painkiller.

A suspension railway car approaches a station.

The suspension railway’s track above the Wupper River

Then and now the masking of hydrophilic functional groups to give a medicinal compound better absorption and distribution characteristics is common practice in medicinal chemistry. Indeed, this is exactly what Bayer did in converting naturally occurring morphine to the semi-synthetic drug diacetylmorphine, better known as Heroin.

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Salicylic acid (left) and acetylsalicylic acid or Aspirin (right)

And in the case of Aspirin, acetylating the phenol of salicylic acid did produce a better drug. But unlike what usually happens, the acetylation of salicylic acid had an unexpected consequence. Aspirin, the trade name for acetylated salicylic acid, works predominantly by a different mechanism than its parent compound salicylic acid. The acetyl group of Aspirin is critical: It is chemically transferred to cyclooxygenase 1 and 2, enzymes important for human inflammation. Irreversibly blocking this pathway has been proven to reduce inflammation and pain. This is a mechanism of action not possible for salicylic acid itself as it lacks Aspirin’s acetyl group.

A railway train leaves a station.

Of course none of this was understood at the time of Aspirin’s discovery. It was more than 70 years after Bayer’s synthesis that Aspirin’s mechanism of action was elucidated in work that was the basis for a Nobel Prize.

The discovery of Aspirin as a pain reliever by Bayer was serendipitous. It works by an entirely unexpected mechanism. And in the end, though salicylic acid from willow trees was the inspiration for Aspirin, it was not the source of the starting material. The Aspirin produced by Bayer came from coal, not willow trees.

The story of Aspirin took a curious turn after its discovery. Some at Bayer initially believed that Aspirin had an adverse cardiovascular effect based on experiences with the parent compound salicylic acid. Consequentially Bayer promoted its new wonder drug that they believed had less risk. This drug, Heroin, was thought to be a less addictive form of morphine. But in both cases Bayer was wrong. Heroin is generally now considered to be more addictive than morphine and today Aspirin has been shown to statistically reduce heart attacks.

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We rode the Wuppertal Suspension Railway past Bayer’s plant in October of 2017.

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