Chemical and enantioselective analyses of Protium amazonicum resin essential oil: featuring the first natural occurrence of 4-epi-eudesm-5-ene

Abstract

This study reports, for the first time, the chemical composition of an essential oil, distilled from the resin of Protium amazonicum collected in Ecuador within its native ecological context. Hydrodistillation gave an exceptionally high yield of 9.3% (w/w). GC analyses, using polar and non-polar stationary phases respectively, revealed an exclusively sesquiterpene profile, dominated by 4- epi -eudesm-5-ene (45.5–45.2%) and junenol (21.1–19.3%). Other major constituents were α-copaene (3.5% on both columns), trans -cadina-1(6),4-diene (7.2–7.0%), cis -β-guaiene (4.0–4.1%), δ-cadinene (2.1% on the polar phase only), and an unidentified compound (4.1% on the polar phase only). Enantioselective analyses showed enantiomerically pure (+)-α-copaene, whereas junenol occurred as an enantioenriched mixture. Notably, 4- epi -eudesm-5-ene is a novel natural product, while junenol contributes to the warm woody aroma of this essential oil. To the best of the authors’ knowledge, this is also the first chromatographic separation of junenol enantiomers using a β-cyclodextrin chiral selector. Methodologically, this essential oil was characterized through GC-MS (qualitatively) and GC-FID (quantitatively), whereas the enantiomeric ratios were determined using three different enantioselective columns. Furthermore, two major constituents were purified and characterized by NMR, MS, and FTIR. The high yield, unique composition, and warm woody aroma make this oil promising for perfumery, aroma industries and other commercial applications.