A novel coumarin, 6,7-methylenedioxy-8-methoxycoumarin [1], and four known coumarins, umbelliferone, scopoletin, bergapten, and xanthotoxin, have been isolated from the aerial parts of Asterolasia trymalioides. Asterolasia trymalioides (Rutaceae) F. Muell., a prostrate to erect shrub in alpine heaths, is a south-eastern Australian species (occurring in the Snowy Mountains of southern New South Wales and eastern Victoria) (1). Of 11 species of Asterolasia (2), three have recently been studied (3,4), as part of our ongoing chemotaxonomic survey of Australian Rutaceae. In this paper we wish to report on the major secondary metabolites found in a sample of the aerial parts of A. trymalioides and to discuss their chemotaxonomic significance.Five coumarins have been isolated, four from an n-hexane extract and one from an EtOAc extract, by a combination of cc, circular tlc, and prep. tlc. They were characterized as umbelliferone (e), 6,7 methylenedioxy-8-methoxycoumarin [1], bergapten (4,7,8), xanthotoxin (4,7,8), and scopoletin (44). All except 1 were characterized by direct comparison of their physical and spectroscopic properties with published data (4-8) and co-tlc with commercially available samples.The novel coumarin 1 was identified and characterized by spectroscopic methods. It was observed on tlc as a bluishwhite fluorescent spot under uv light (366 nm) and showed uv absorption maxima at 321 and 231 nm, suggestive of a coumarin (9). The empirical formula was found to be C11H8O5 from high-resolution eims data. The H-nmr spectrum (Table 1) revealed the typical H-3 and H-4 protons of the coumarin nucleus (9). The chemical shift for H-4 (δ 7.56) indicated the absence of any oxygenation at C-5 (9). Three more signals indicated an aromatic proton, a methylenedioxy group, and a methoxyl substituent. As there was no oxygenation at C-5, the aromatic singlet must be assigned as H-5and this was confirmed by an nOe difference experiment, where irradiation ofthe signal at δ 6.58 enhanced the signal for the H-4 proton. The ¹H-nmr chemical shift data for 1 differed significantly from those published for 7,8 methylenedioxy-6-methoxycoumarin (10), the most notable feature being the highly deshielded resonance for the methoxyl, indicative of the steric hindrance encountered at C-8. The attachment of the methoxyl group at C-8 was further supported by an nOe experiment, since irradiating the methoxyl protons gave no enhancement of the H-5 signal. The methylenedioxy group must therefore be at the 6,7 positions and thus the structure of this coumarin can unambiguously be assigned as 1, which is novel.Inclusive of the present results, all four species of Asterolasia examined to date (3,4) have yielded coumarins. However, these show considerable structural diversity between species. A. drummondii yielded a range of 5,7-oxygenated-6,8 prenylated coumarins; A. squamuligera gave a 3-prenyl-7-oxygenated coumarin; A. phebalioides and A. trymalioides produce coumarins with 6-prenylation and oxygenation at the 5,7, and 8 positions but with no 8-prenylation. Cyclization of the 6-prenyl group, leading to the formation of a furan but not a pyran ring system has been observed in A. phebalioides and A. trymalioides but not in the other two species. These furocoumarins and other oxygenated simple coumarins are also present in many species of the genus Phebalium (11). Thus, the co-occurrence ofthese coumarins in the genus Phebalium, and in extracts from two species of Asterolasia, lends some support to the taxonomic affinity between these two genera proposed by Armstrong's cladistic study (12).