By Chiamaka Egwu
Scientists at Stellenbosch University, SU, South Africa, have detected, for the first time, evidence of a rare group of natural compounds known as flavoalkaloids in Cannabis leaves.
The discovery was made by analytical chemists studying the complex chemical composition of commercially grown Cannabis from South Africa.
The researchers said the finding could draw fresh scientific attention to Cannabis leaves, which are often regarded as low-value plant material or waste, because they may contain a wider range of potentially useful compounds than previously recognised.
The study, published in the Journal of Chromatography A, identified 79 phenolic compounds across three commercially grown Cannabis strains in South Africa.
Of these, 25 had not previously been reported in Cannabis, while 16 were tentatively identified as flavoalkaloids.
According to the researchers, most of the newly detected flavoalkaloids occurred predominantly in one of the three strains, highlighting significant differences in the phenolic profiles of Cannabis varieties.
Dr Magriet Muller, analytical chemist at the LC-MS laboratory of SU’s Central Analytical Facility and first author of the study, said the discovery was particularly significant because flavoalkaloids are rarely found in nature.
“Most plants contain highly complex mixtures of phenolic compounds, and while flavonoids occur widely in the plant kingdom, the flavoalkaloids are very rare in nature,” she said.
Muller said the complexity of Cannabis had made the finding unexpected.
“We know that Cannabis is extremely 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 very exciting.”
Phenolic compounds are naturally produced by plants and are involved in processes including pigmentation, defence and protection against environmental stress.
Flavonoids, a major subgroup of phenolic compounds, have attracted scientific interest because several members of the group have been associated with antioxidant, anti-inflammatory and anti-carcinogenic properties.
Flavoalkaloids, however, are considerably less common.
The researchers said detecting the compounds required advanced analytical techniques capable of separating closely related substances in the chemically complex Cannabis samples.
Muller developed the analytical methods during her postgraduate studies in SU’s Department of Chemistry and Polymer Science. The techniques combine comprehensive two-dimensional liquid chromatography with high-resolution mass spectrometry.
Liquid chromatography separates compounds in a mixture, while the two-dimensional approach separates them according to two different characteristics, providing greater resolving power. High-resolution mass spectrometry then enables researchers to determine molecular masses with high precision.
Muller said she initially developed and tested the methods on rooibos tea, grapes and wine before applying them to Cannabis.
“We were looking for a new application for the methods that 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 that Cannabis phenolics have not been well characterized,” she said.
The lead of the study, Prof. André de Villiers, Muller who is also the main author of the paper, said the separation achieved through the advanced technique was critical to the discovery.
“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 said.
The researchers said rare compounds can easily remain undetected when they occur alongside substances present in much higher concentrations.
The findings therefore demonstrate how improved analytical techniques can reveal previously overlooked components of plant chemistry.
While scientific attention on Cannabis has historically centred largely on cannabinoids, the researchers said the study points to the need for greater investigation of the plant’s non-cannabinoid chemistry.
De Villiers said Cannabis leaves currently regarded as waste could warrant further scientific investigation because of their phenolic composition.
“Our analysis again highlights the medicinal potential of Cannabis plant material, currently regarded as waste. Cannabis exhibits a rich and unique non-cannabinoid phenolic profile, which could be relevant from a biomedical research perspective,” he said.
