Chemical and Enantioselective Analysis of the Leaf Essential Oil from Varronia crenata Ruiz & Pav. Growing in Ecuador

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Abstract
Essential oils from species of the genus Varronia (Boraginaceae) are recognized for their chemical diversity and biological potential; however, phytochemical information on Varronia crenata Ruiz & Pav. remains scarce, despite its wide distribution in the Andean region. The aim of this study was to provide the first chemical and enantioselective characterization of the essential oil obtained from the leaves of V. crenata growing in Ecuador. Qualitative and quantitative analyses were carried out by GC–MS and GC–FID, respectively, using two columns with stationary phases of contrasting polarity. Compounds were identified by matching linear retention indices and mass spectra to literature references and quantified by external calibration using relative response factors (RRFs) calculated for each compound based on its combustion enthalpy. The most abundant constituents (≥3.0% on average between the two columns) of the essential oil of V. crenata, both in the nonpolar and polar stationary phases, were germacrene D (18.4%), (E)-β-caryophyllene (13.3%), α-copaene (10.4%), tricyclene (9.3%), δ-cadinene (8.9%), and α-pinene (8.3%). The volatile fraction was dominated by sesquiterpenes (60.2%) and monoterpenes (22.1%), while other chemical families were present in minor proportions. The enantioselective analysis was performed on two different columns, coated with stationary phases based on β-cyclodextrins: 2,3-diacetyl-6-tert-butyl-dimethylsilyl-β-cyclodextrin and 2,3-diethyl-6-tert-butyl-dimethylsilyl-β-cyclodextrin. Nine chiral compounds were analyzed; among them, (1R,5R)-(+)-α-pinene, (1R,5R)-(+)-sabinene, and (S)-(+)-β-phellandrene were detected as enantiomerically pure, while the other metabolites presented scalemic mixtures. Overall, the high content of bioactive sesquiterpenes and the observed stereochemical complexity highlight the potential pharmaceutical and agricultural relevance of V. crenata essential oil, while also providing novel chemotaxonomic information for the genus.

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