Fragrant Sesquiterpene Ketones as Trace Constituents in Frankincense Volatile Oil of Boswellia sacra.

In a previous study, two highly potent yet unidentified odorants were detected that were present at trace levels in the volatile fraction of Boswellia sacra gum resin. These two compounds were isolated semipreparatively from the volatile oil by a sensory-guided fractionation process involving microscale bulb-to-bulb distillation, countercurrent chromatography, and preparative gas chromatography. In this manner, the two oxygenated sesquiterpenes could be identified as rotundone (1) and mustakone (2). Compound 2 is described for the first time as a potent odorant with a very low odor threshold.