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.