Leaf essential oil from IvorianIsolona dewevrei(Annonaceae): Chemical composition and structure elucidation of four new natural sesquiterpenes

This work is a contribution to the characterization of aromatic and medicinal plants from Cote d'Ivoire. To date, no phytochemical investigation was reported onIsolona dewevrei. Thus, the aim of this study was to investigate for the first time, the chemical composition of the leaf essential oil fromI dewevrei. Two essential oil samples (S1, S2) were analysed by combination of chromatographic [GC(FID) and GC(RI)] and spectroscopic [MS,C-13-NMR] techniques. As several compounds remained unidentified, particularly in sample S1, this oil was fractionated on silica gel column, leading to the isolation and structural elucidation of four new natural compounds by QTOF-MS, 1D and 2D-NMR analyses. These new natural sesquiterpenes were identified as (5 alpha H,10 beta Me)-6,12-oxido-elema-1,3,6,11(12)-tetraene, 6,12-oxido-germacra-1(10),4,6,11(12)-tetraene, (1 beta H,5 beta H)-6,12-oxido-guaia-6,10(14),11(12)-trien-4 alpha-ol and germacra-1(10),4,7(11)-trien-6,12-gamma-lactone. Finally, sixty-eight constituents were identified in both investigated essential oil samples. They accounted for 96.1 and 97.3%, respectively, of the whole chemical composition of S1 and S2. Leaf essential oil fromIdewevreiis very rich in sesquiterpenes. Indeed, its majority compounds were germacrene B (20.8 and 24.8%), (5 alpha H,10 beta Me)-6,12-oxido-elema-1,3,6,11(12)-tetraene (10.3 and 0.3%, new compound), germacrene D (7.5 and 17.8%), (Z)-beta-ocimene (7.8 and 9.7%),gamma-elemene (6.9 and 7.5%) and (E)-beta-caryophyllene (6.8 and 3.5%). The contents of thermolabile components were assessed by combination of GC(FID) and(13)C-NMR.