Is Curzerene Responsible for the Bioactive Properties of Eugenia uniflora? A Possible Misinterpretation of Bioactive Markers.

Essential oils are a complex matrix of volatile compounds produced by many plants of different families with diverse bioactivities. Eugenia uniflora (Myrtaceae), popularly known as the pitangueira, is native to Brazil and a source of essential oils, mainly composed of sesquiterpenes such as Furanodiene. Curzerene is the major contributor to most of the bioactive properties assigned to E. uniflora. Gas chromatography (GC) is the primary technique for characterizing essential oils. However, sesquiterpenes of the germacrene type may undergo a [3,3]-sigmatropic rearrangement in GC, converting into Elemene-type, leading to these compounds' misidentification. Curzerene is an Elemene-type compound known to result from the sigmatropic rearrangement of furanodiene. Aiming to demonstrate this evidence, the objective of this study was to perform a thermal treatment of the essential oil from E. uniflora, to simulate the heating conditions during GC to identify the chemical transformations in this essential oil. Essential oil from E. uniflora leaves were obtained by hidrodistillation and was characterized by GC-MS. Nine major sesquiterpenes were identified in the GC-MS analysis of the oil, with the most prevalent being Germacrene B (16.19%), Curzerene (13.28%), and Germacrene D (12.64%). Additionally, β-Elemene and β-Elemenone were identified in lower concentrations. In the NMR analysis, it was possible to identify only four germacrene-type compounds and a small amount of Curzerene. After thermal treatment (240 °C), the Elemenes resulting from the sigmatropic rearrangement were identified. These results suggest that most of the properties assigned to Curzerene throughout the years, which do not combine cold techniques, such as NMR spectroscopy, to characterize the essential oil of E. uniflora, were incorrectly assigned and likely belong to furanodiene, evidencing the importance of apply different methods of analysis in some situations.