Stellenbosch University (SU) researchers have uncovered the first evidence of a rare class of phenolic compounds in cannabis leaves long prized in the pharmaceutical industry for their antioxidant, anti-inflammatory and anti-carcinogenic properties.
The study, recently published in the Journal of Chromatography A, identified 79 phenolic compounds in three strains of cannabis grown commercially in South Africa.
Of these, 25 were reported for the first time in the plant, with 16 tentatively identified as flavoalkaloids, a rare class of phenolics found mainly in the leaves of one of the strains.
Analytical chemist in the LC-MS laboratory of the Central Analytical Facility at SU and first author of the paper, Dr Magriet Muller, said characterising phenolics in plants is notoriously challenging due to their structural diversity and low concentration.
“Most plants contain highly complex mixtures of phenolic compounds and while flavonoids occur widely in the plant kingdom, the flavoalkaloids are rare in nature.”
She said the discovery was unexpected.
“We know cannabis is complex, it contains more than 750 metabolites, but we did not expect such high variation in phenolic profiles between only three strains, nor to detect so many compounds for the first time in the species. Especially the first evidence of flavoalkaloids in cannabis was exciting,” she said.
For her postgraduate research in SU’s department of chemistry and polymer science, Muller developed powerful analytical methods that combined two-dimensional liquid chromatography with high-resolution mass spectrometry to profile phenolics in detail.
“We were looking for a new application for the methods I developed, after successfully testing them on rooibos tea, grapes and wine. I then decided to apply the methods to cannabis because I knew it was a complex sample and cannabis phenolics have not been well characterised,” she said.
Her supervisor Prof André de Villiers, who leads the analytical chemistry research group in SU’s department of chemistry and polymer science, said he was astonished by the results.
“The excellent performance of two-dimensional liquid chromatography allowed separation of the flavoalkaloids from the much more abundant flavonoids, which is why we were able to detect these rare compounds for the first time in cannabis.”
He added that the findings reinforce the untapped medicinal potential of cannabis beyond its more widely studied cannabinoids.
“Our analysis again highlights the medicinal potential of cannabis plant material, regarded as waste. Cannabis exhibits a rich and unique non-cannabinoid phenolic profile, which could be relevant from a biomedical research perspective,” he said.
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