Essential oils can sometimes be surprising. It so happens that well-known species that have been frequently studied yield, in particular conditions, peculiar volatile molecules that are otherwise not widely recognized to be characteristic of the plant. When such an observation is made, it is useful to publish the results, so that further occurences of these observations can stand on firm scientific ground and dissipate suspicions of contamination, misidentification or adulteration.
Figure 1. Schinus molle branch and fruits. The|
resemblance of the latter with peppercorns gave
the plant its common, name, but it is unrelated
to black pepper. Source: Wikimedia commons.
In the course of a collaboration with Socodevi, a Canadian cooperative specialized in international economic development in 2014, we had to analyze samples from a Bolivian essential oil distillation facility operated by UNEC S. A., a company owned by local farmers to produce added-value products from their crops. The samples were distilled from locally picked Peruvian Peppertree, Schinus molle (figure 1).
Oil from both the leaves and fruits of Molle have been studied in numerous scientific papers (see our article for full list of references), as the plant is found throughout South America and has been planted widely elsewhere. What surprised us was the observation in the first oil that we analyzed of several rare sesquiterpenes. More batches were analyzed, and the same observations came back. We thus suggested to publish these results, which we did in Natural Product Communications recently (click here to read the abstract) .
Identification of the plants was confirmed by local agronomists, who are also coauthors of the study. Contamination of the plant material with others is also unlikely, given that the other species distilled by UNEC are oregano and thyme, which are devoid of the molecules that caught our interest. These were a set of oxygenated sesquiterpenes that are usually found in sweet flag, Acorus calamus, with names revolving around shyobunol and calamendiol. The whole set is depicted in figure 2.
|Figure 2. Structures of the uncommon oxygenated sesquiterpenes observed in Bolivian Schinus molle essential oils.|
Hints of their presence in Schinus molle were already present in literature. Indeed, a study conducted on a plant extract from a single tree grown in a botanical garden in Germany had previously lead to the isolation of preisocalamendiol , while shyobunol and dehydroxyisocalamendiol had been reported in essential oils of Molle in, respectively, Mexico and Saudi Arabia [3,4]. Never before though was the whole group of compounds observed at once in an essential oil from S. molle. The fact that the same observation was made on several batches produced months apart from each other further strenghtens our confidence in the results that a peculiar shyobunol/preisocalamendiol chemotype likely exists in Peruvian Peppertree, and that it can be found at the very least in Bolivia.
Figure 3. Acorus calamus, better known as
sweet flag. Source: Wikimedia commons.
Preisocalamendiol has been bolded out in figure 2 since it was one of the main constuents of the oils studied (5.6-11%). As I previously mentioned, these compounds are normally more characteristic of sweet flag, Acorus calamus (e. g. , see article for full references), a somewhat controversial plant. Sweet flag (figure 3) has a long history of use in aromatherapy from Asia to Europe, but has raised serious safety concerns. That is because the plant exists under three different forms, which are distinguished by the number of copies of each chromosome they bear (a phenomenon called ploidy). Diploid plants, which are native to some parts of North America, are not dangerous. However, triploid and especially tetraploid plants, which are more abundant, respectively produce an essential oil containing about 10% and 85-90% β-asarone , a toxic mutagenic molecule [6,7]. Sweet flag was once widely used as a flavouring agent, but is now banned by the FDA and Health Canada due to its asarone content.
Yet, sweet flag was used as a light sedative and tranquilizer. A recent paper studied the ability of several constituents of A. calamus oils to modulate the brain molecular target of several analgesic and anesthetic drugs, called GABAA. In this assay, β-asarone asarone was very efficient, but so were a few other compounds, including preisocalamendiol and shyobunone. This studied provided a good rationale for the tranquilizing properties of sweet flag , but this does not solve the safety concerns.
The fact that preisocalamendiol can be found in interesting concentrations in some S. molle essential oils, which is devoid of β-asarone, could point to putative tranquilizing properties with a favourable safety profile in aromatherapy, given the proper chemotype is employed. It might also in part explain why S. molle was sometimes used to treat rheumatisms, tooth pain or depression by natives. Of course, at this point, this is a mere hypothesis, and we cannot make any firm assessment of the efficiency of this oil in this regard.
We look forward to establish such collaborations with other people, too. If any oil we analyze is original enough to be published, we will be pleased to write a joint manuscript, free of charge. Only this way can the knowledge of essential oils be brought further, for our collective enjoyment!
 A. St-Gelais, M. Mathieu, V. Levasseur, J. F. Ovando, R. Escamilla and H. Marceau. (2016) Preisocalamendiol, shyobunol and related oxygenated sesquiterpenes from Bolivian Schinus molle essential oil. Nat. Prod. Comm., 11(4), 547-550. D. M. Delvalle and G. Schwenker. (1987) Preisocalamenediol, a constituent of Schinus molle. Planta Medica, 53, 230.
 L. Guerra-Boone, R. Álvarez-Román, R. Salazar-Aranda, A. Torres-Cirio, V. M. Rivas-Galindo, N. Waksman de Torres, G. M. González González and A. L. Pérez-López. (2012) Chemical compositions and antimicrobial and antioxidant activities of the essential oils from Magnolia grandiflora, Chrysactinia mexicana, and Schinus molle found in northeast Mexico. Nat. Prod. Comm., 8, 135-138.
 E. Abdel-Sattar, A. A. Zaitoun, M. A. Farag, S. H. Gayed and F. M. H. Harraz. (2010) Chemical composition, insecticidal and insect repellent activity of
Schinus molle L. leaf and fruit essential oils against Trogoderma granarium and Tribolium castaneum. Nat. Prod. Res., 24, 226-235.
 F. X. Garneau, G. Collin, H. Gagnon, A. Bélanger, S. Lavoie, N. Savard and A. Pichette. (2008) Aromas from Quebec. I. Composition of the essential oil of the rhizomes of Acorus calamus L. J. Ess. Oil Res., 20, 250-254.
 G. Abel. (1987) Chromosome damaging effect on human lymphocytes by β-asarone. Planta Medica, 53, 251-253.
 W. Göggelmann and O. Schimmer. (1983) Mutagenicity testing of beta-asarone and commercial calamus drugs with Salmonella typhimurium. Mut. Res., 121, 191-194.
 J. Zaugg, E. Eickmeier, S. N. Ebrahimi, I. Baburin, S. Hering and M. Hamburger. (2011) Positive GABAA receptor modulators from Acorus calamus and structural analysis of (+)-dioxosarcoguaiacol by 1D and 2D NMR and molecular modeling. J. Nat. Prod., 74, 1437-1443.