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Natural Products

Fungal compound has the power to deskunk

Pericosine A quashes potent odors by reacting with skunk thiols

by Lauren Gravitz, special to C&EN
August 1, 2019

20190731lnp2-skunk.jpg
Credit: Wikimedia Commons/C&EN
Thiols in a skunk’s spray are some of the most persistent and difficult odors to neutralize.

If you or your pet has ever had the misfortune of a tail-end encounter with a skunk, you’ve likely tried everything in the book to vanquish the smell. Tomato juice overwhelms the nose and turns everything pink, but the odor is back the following day. Commercial treatments largely fail. And the most common folk remedy—baking soda combined with dish soap and hydrogen peroxide—works but also irritates and bleaches everything it touches. Now, researchers have found that a compound produced by fungi found in Alaskan soil may solve this stinky dilemma (J. Nat. Prod. 2019, DOI: 10.1021/acs.jnatprod.9b00415).

Robert H. Cichewicz, a natural products chemist at the University of Oklahoma, and his colleagues were investigating fungal products from soil samples collected as part of a citizen science project, looking for molecules with potential anticancer or antimicrobial activity. But what they found was a very strange-looking thing, a molecule with two distinct halves—one a shikimate, something commonly found in plants, and one a polyketide, something typically produced by microbes. “The two halves looked like things we’d seen before,” Cichewicz says, “but how they connected, the way it was put together—we had never seen that before.”

20190731lnp2-pericosine.jpg

The group found that one particular piece of the shikimate half—a compound called pericosine A—had the ability to attack and neutralize a variety of antifungal compounds and toxins (Angew. Chem., Int. Ed. 2016, DOI: 10.1002/anie.201511348). So he and his colleagues brainstormed about noxious things in the human environment that pericosine A might be able to neutralize. They thought it might have an aptitude for neutralizing thiols, the type of organosulfur compounds that make skunk spray so smelly.

“I probably would have just looked at [pericosine A], said ‘oh, it’s too reactive and doesn’t have human health applications,’ and put it on a shelf,” says Sandra Loesgen of Oregon State University, who was not part of the study. She notes that the innovative thought process is par for the course for Cichewicz, who has a long history of “going the extra mile and tickling out new structures.”

The researchers reacted pericosine A with different skunk thiols and found that it converted them into odorless compounds, reducing the thiol levels to a point at which they were undetectable by the human nose. They also tested the competition: out of six products marketed as skunk deodorizing solutions, five did little to neutralize the thiols. The sixth, marketed as an all-natural, mineral-based solution, worked, but the team’s analysis revealed that it contained little more than chloramine-T, a strong commercial biocide and disinfectant with the same potential to irritate as hydrogen peroxide.

Finally, the group blended pericosine A with typical cosmetic ingredients that might be used to deliver it to skin or hair in a smell-removal product and subjected it to a battery of standard, in vitro tests, all of which showed that the compound caused no skin or eye irritation.

Cichewicz and his colleagues have laid all the groundwork for anyone interested in doing something with the compound, but he has no plans to pursue commercialization. Still, in choosing to tackle this stinky problem, the team has gone the extra mile: the thiols in skunk secretions are not just particularly stable, which makes them hard to break down, they’re also so powerful that the human nose can pick them out when they’re present at just 10 ppb. (In contrast, our noses can only detect ammonia—the primary ingredient of smelling salts—at around 46 ppm.) There’s nothing like skunk odor, Cichewicz says, to expose the shortcomings of a lab’s hood system. And once he made the mistake of wafting his hand over a sample of pure anal gland secretions. It was, he says, “the nasal equivalent of staring at the sun.”

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