The Essential Oil from Cupules of Aiouea montana (Sw.) R. Rohde: Chemical and Enantioselective Analyses of an Important Source of (–)-α-Copaene

The present study described, for the first time, the chemical and enantiomeric composition of an essential oil, distilled from the cupules of <i>Aiouea montana</i> (Sw.) R. Rohde. On the one hand, chemical analyses were carried out through GC-MS (qualitative) and GC-FID (quantitative), on two stationary phases of different polarity. Major components (≥3.0%) were <i>S</i>-methyl-<i>O</i>-2-phenylethyl carbonothioate (23.1%), α-copaene (20.3%), α-phellandrene (18.7%), (<i>E</i>)-β-caryophyllene (6.1%), and α-pinene (4.5%). On the other hand, enantioselective analyses were conducted, through GC-MS, on two columns with different chiral selectors, based on derivatised β-cyclodextrins. A total of 12 chiral components were analysed, of which (1<i>S</i>,5<i>S</i>)-(-)-α-pinene and (1<i>R</i>,2<i>S</i>,6<i>S</i>,7<i>S</i>,8<i>S</i>)-(-)-α-copaene were found to be enantiomerically pure. All the other chiral components were present as scalemic mixtures. Finally, both chemical and enantiomeric profiles were compared to the ones previously described in the literature for the leaf essential oil of <i>A. montana</i>. In conclusion, cupules of <i>A. montana</i> produced an essential oil with a higher yield in comparison with leaves but with a lower content of <i>S</i>-methyl-<i>O</i>-2-phenylethyl carbonothioate. On the other hand, to some extent, the enantiomeric compositions of these volatile fractions were somewhat different. To the best of the authors' knowledge, the cupule essential oil of <i>A. montana</i> could be the second main natural source of (-)-α-copaene so far described in the literature.