New insights into the chemical composition of Baccharis palustris Heering (Asteraceae) essential oil

Abstract

B. palustris Heering (Asteraceae), has been previously characterized as having an unusual essential oil composition with C9-/C10-polyacetylenes as main components, and mono- and sesqui terpenes/terpenoids at minor or trace levels. In this work, new insights into the chemical composition of this oil are presented: 1. TLC profiles using different visualization reagents for their characterization, 2. chemical analyses combining HRGC/qMS, HRGC/HRMS-TOF and HRGCxHRGC/HRMS-TOF, and 3. radical scavenging activity assay using the DPPH methodology were performed. The best TLC visualization conditions for the polyacetylenic components of the oil were obtaining using UVλ= 365 nm and vanillin/H3PO4, while the original application of NaDi (1-naphtol + N,N-dimethyl-p-phenylendiamine) demonstrated to be the best option to visualize the lachnophyllum acid methyl esters fraction. Gas chromatography/mass spectrometry protocols allowed the detection of 63 components in B. palustris oil: 39 of them were identified, 6 tentatively assigned without LRI information, and 18 could not be identified. Most of the identified components were mono- and sesquiterpenes and their derivatives. Ten of them are informed for the first time in B. palustris oil [α-pinene epoxide, rosefuran, epi-cubebol, cubebol, germacrene D-4-ol, junenol, epi-α- cadinol, epi-α-muurolol, germacra-4(15),5,10(14)-trien-1-β-ol and oplopanone]. C9-/C10-polyacetylenes (baccharisdyine/lachnophyllum acid derivatives) were confirmed as the main components of the oil, while other polyacetylenes were tentatively identified and their possible structures are discussed. The deconvolution analyses on HRGCxHRGC/HRMS-TOF allowed the identification of a lachnophyllum lactone isomer (undefined stereochemistry), co-eluting with the (cis)-lachnophyllum acid methyl ester peak. Finally, B. palustris oil was found to be an inactive DPPH radical scavenger.