Are there differences in the chemical composition of the essential oils from different vegetative parts of Piper mollicomum Kunth?

Piper mollicomum Kunth (Piperaceae) is recognized as medicinal plant in Brazil since the early 19th century with its therapeutic properties¹. Its vegetative parts have several popular uses as anesthetics associated with root chewing; the leaves infusion is used to treat problems associated with digestive systems; the inhalation of the aerial parts is used against respiratory problems; and the decoction and smoke of the stems and/ or leaves are used in the ritualistic ceremonies of African mothers religion in Brazil²,³. Observing the diverse applications of P. mollicomum and their descriptions as species rich in essential oil (EO), the following questions is made: Are there differences in the chemical composition of the EO of different vegetative parts of P. mollicomum? To answer this question, leaves, main stem, secondary stem (branches), roots, inflorescences and fruits were collected in January 2018 in the Tijuca Forest, Rio de Janeiro. These vegetative parts (150g) were separately submitted to EO extraction by hydrodistillation in a modified Clevenger-type apparatus. The volatile compounds were identified and quantified by Gas Chromatography coupled to Mass Spectrometry (GC-MS) and Gas Chromatography coupled to Flame Ionization Detector (GC-FID). GC-MS and GC-FID analyzes were performed using an HP-5ms column (30m x 0.32mm id x 0.25 µm, particle size), programmed temperature from 60 °C to 240 °C (3 °C / min) and flow rate at 1mL/ min. The retention indices were calculated from a homologous series of hydrocarbons (C8 -C22, Sigma-Aldrich) to confirm the identification of compounds. In order to verify the differences in the EO compositions, principal component analysis (PCA) and hierarchical component (clauster) were performed. EO yields were lower on the main stems (0.12%) and branches (0.18%) and the highest for inflorescences (1.8%), fruits (1.5%), roots (1.0%) and leaves (0.87%). The presence of the major compounds were achieved: Leaves: 1,8-cienole (5.75%), δ-elemene (5.40%) and β-elemene (5.29%); linalool (15.65%), cis-calamenen-10-ol (8.98%), phellandrene (7.51%) and nerolidol (7.57%); Main stem: α-phellandrene (15.71%), linalool (12.33%), β-phellandrene (8.06%) and nerolidol (6.03%); Roots: myristicine (55.65%), dillapiol (25.20%) and apiol (16.71%); Inflorescence: linalool (20.69%); eupatoriochromene (19.66%) and nerolidol (8.04%); and fruits: linalool (35.55%), eupatoriochromene (14.65%) and nerolidol (9.55%). In the chemometric analyzes it was possible to register a division of the analyzed samples following the biosynthetic production of their compounds, as follow: I - predominance of the pathways acetate-mevalonate and/ or methyltrithritol phosphate (EO from leaves, main stem and branches); II - predominance of the polycetidic pathways and acetate-mevalonate and/ or methyltrithritol phosphate (EO from inflorescence and fruits); and III - predominance of the shikimate pathway (EO from roots). Therefore, there are significant differences in chemical compositions that may direct the various future multi-target applications in the research of this medicinal plant that already has different popular uses for vegetative parts.