Coumarins from Phebalium aff. brachycalyx

The genus Phebalium Vent. (Rutaceae, tribe Boronieae) includes some 45 species of shrubs and undershrubs, distributed in the southwest and southeast regions of Australia and in the northern island of New Zealand ( [Bentham and Mueller, 1863] and [Engler, 1896]). A consistent feature of all investigated species is the presence of coumarins ( [Quader et al., 1992] and [Ghisalberti, 1997]). In a major taxonomic revision, the genus was divided into four sections, Phebalium, Eristemoides, Gonioclados, and Leionema (Wilson, 1970). The species Phebalium brachycalyx P. G. Wilson is included in the section Phebalium, which comprises 19 species characterized by stem, leaves, and outside petals lepidote, and by an inflorescence in terminal umbel. Several taxa of this section previously led to the isolation of 7-geranyloxycoumarins, 8-prenylated coumarins, and linear furocoumarins ( [Rashid et al., 1992] and [Quader et al., 1992]). It was recognised (Wilson, 1970) that a number of the West Australian species of Phebalium sect. Phebalium hybridised and intergraded into one another and in that context P. brachycalyx underwent introgressive hybridisation with both P. filifolium and P. tuberculosum. More recently, Wilson (1998) has indicated that it may not be possible to maintain those taxa separated within this group. Accordingly, we refer to the collection here as P. aff. brachycalyx as it exhibits many of the characteristics ascribed to that taxon but clearly falls within the boundaries of the “super-species”. In a continuation of our studies on Australian Rutaceous plants (Girard et al., 2002), we report here the isolation and structure determination of two new heraclenol derivatives from P. aff. brachycalyx leaves and twigs, together with the identification of 22 other coumarins.