Dihydrotagetone, an Unusual Fruity Ketone, is Found in Enantiopure and Enantioenriched Forms in Additional Australian Native Taxa of Phebalium (Rutaceae: Boronieae)

Abstract

Here we report for the first time hydrodistillation of leaf essential oils from Phebalium squamulosum subsp. verrucosum, P. glandulosum subsp. eglandulosum, P. glandulosum subsp. nitidum and P. glandulosum subsp. angustifolium (Rutaceae: Boronieae). Essential oils were analysed using gas-chromatography/mass spectrometry (GC-MS) and nuclear magnetic resonance spectroscopy (NMR). With the exception of P. glandulosum subsp. angustifolium, all taxa yielded essential oils in relatively high amounts (1–3%, w/w) made up predominantly of 2,6-dimethyloct-7-en-4-one (dihydrotagetone). The essential oil from P. squamulosum subsp. verrucosum contains either (+)-dihydrotagetone ( ee 94–100%) or (-)-dihydrotagetone ( ee 17–18%). Taxonomically, these results support the proposal that P. squamulosum subsp. verrucosum may be specifically misplaced, phytochemically resembling the P. glandulosum complex. Similarly, P. glandulosum subsp. angustifolium phytochemically resembles P. distans or P. longifolium and also appears to be assigned incorrectly to the P. glandulosum group.