Synthesis of Sichuan pepper chemical allows new uses

HKU professor envisages applications including painkillers, cosmetics or sweets

PUBLISHED : Sunday, 23 September, 2012, 12:00am
UPDATED : Sunday, 23 September, 2012, 3:10pm

A Sichuan hotpot dinner has inspired a local chemist's discovery of how to synthesise the chemical that tingled his tongue.

The pleasurable tingling sensation and numbing of tongue and lips when eating Sichuan peppercorns is caused by hydroxyl alpha sanshool (HAS).

Patrick Toy, associate professor at the University of Hong Kong's chemistry department, said the synthesis might be used as pain reliever, wrinkle remover, or for sweets in future.

He synthesised HAS, and results were recently published in the chemistry journal Synlett.

"A couple of colleagues and I were having a hotpot dinner, we're drinking a lot of beer, and were talking about this tingling effect and how it is produced," he said.

"I got onto Wikipedia the next morning and realised, even though the chemical had been known to exist for 20 years, nobody had made it in the past."

One factor currently limiting research on HAS is the difficulty in obtaining it in a highly pure form. Isolating pure HAS from the pepper is difficult, expensive and low-yielding.

Isolating pure HAS is "sort of like picking needles out of a haystack", he said.

The method Toy and his colleagues used for producing HAS not only provides access to large quantities of it in high purity, but also may help identify more potent compounds.

Researchers around the world are currently studying the use of HAS in applications ranging from medicine (as a painkiller) to cosmetics (skin lifter).

Toy even envisions using the synthetic HAS in sweets, without containing the pepper's bitter components.

"Being able to synthesise the compound may have many, many uses because it's difficult to extract the pure form of it from the peppercorns, not to mention [that] the crude extract of it may have other, unintended side- effects," Toy said.

"We have spoken to several food companies and we are looking at ways to make candies with it, so that, for instance, the dentist can pop one in your mouth before he injects into your gum."