In addition to several known constituents and their artefacts, the root of Dictamnus albus L. has yielded the new natural products, isomaculosidine (9) and preskimmianine (15, R = Me). In connection with our interest in the biogenetic origin of fraxinellone (1), we have made a thorough examination of the root of the plant in the hope of finding intermediates in the conversion of limonin (2) to fraxinellone (1), since both of these compounds are constituents of this plant. Dictamnus albus L., a member of the Rutaceae, occurs widely and, because of ignition of the gas given off by the plant, it has been known as the 'gas plant' or the 'burning bush.' Considerable claims have been made for the powdered root as a folk remedy and the plant has a photosensitising action on the skin. Previous chemical studies have shown the plant to contain the limonoids limonin (2), fraxinellone (1) and obacunone (3) as well as a lactone dictamnolide (C28H30-32O9) of unknown structure. The furanoquinoline alkaloids dictamnine (4, R = Me), skimmianine (5, R = Me) and γ-fagarine (6, R = Me) have been isolated from the plant and various amines, anthocyanins, monoterpenes and flavonol glycosides have also been found. Further constituents are the furocoumarin bergapten (7) and the coumarin auraptene (8). We have extracted the powdered root of Dictamnus albus L. by the method of Pailer et al. The root was extracted with ethanol in a Soxhlet and the extracts were treated with base to saponify any lactones present. The non-base-soluble material was separated into acid-soluble and neutral fractions. Chromatography of the acid-soluble fractions on silica gel yielded four compounds, three of which were quickly identified from UV and NMR spectroscopy as O-ethylnordictamnine (4, R = Et), O-ethylnor-γ-fagarine (6, R = Et) and O-ethylnorskimmianine (5, R = Et). These were readily converted into the known natural products dictamnine (4, R = Me), γ-fagarine (6, R = Me) and skimmianine (5, R = Me) respectively on treatment with acidic methanol. The O-ethyl compounds can be assumed to be artefacts of the isolation procedure, since treatment of dictamnine (4, R = Me), skimmianine (5, R = Me) and γ-fagarine (6, R = Me) with ethanolic potassium hydroxide is known to result in exchange of this type and other furanoquinoline alkaloids behave in similar fashion. The fourth compound, C14H13NO4 (m.p. 170-172 °C), had an NMR spectrum characteristic of a linear furanoquinoline in the iso-series with α- and β-furan protons (J = 2 Hz) at 2.76 and 3.01 τ, meta-coupled aromatic protons at 2.42 and 3.28 τ, and OMe and N-Me singlets at 5.90, 6.08 and 6.10 τ. Isomaculosidine (9) (m.p. 167-168 °C), a known degradation product of the alkaloid maculosidine (10), has a reported NMR spectrum which corresponds well with these data but the UV spectrum has not been reported. That we have found isomaculosidine for the first time as a natural product was proved by hydrogenolysis to the hydroxyquinolone (11, R = H) which had a characteristic blue shift in base in the UV spectrum. The hydroxyquinolone (11, R = H) was methylated by diazomethane to 11 (R = Me) the structure of which was proven by synthesis. Reaction of 2,4-dimethoxyaniline with diethylethylmalonate yielded the quinolone (12, R = H). Attempts to methylate this quinolone with methyl iodide and sodium hydride in benzene resulted mainly in alkylation of the ambident anion at position 3, the major product (13) having both ketonic and amide CO bands in the IR spectrum and C-Me and N-Me singlets at 8.60 τ and 6.51 τ respectively in the NMR spectrum. There was a smaller amount of 11 (R = Me) present, identical in its spectra to the degradation product of isomaculosidine. This compound, the product of N,O-dialkylation, was the sole product when the reaction was carried out with dimethylsulphate and potassium hydroxide in dimethylformamide. Isofuranoquinoline alkaloids are very rare in nature but there is no reason to suppose that our extraction procedure could have produced isomaculosidine as an artefact, and so the compound must be a natural product. The neutral fraction of the non-base-soluble portion of the extract of the root of D. albus was chromatographed to yield fraxinellone (C14H16O3, m.p. 117 °C, [α]D -45.6 °), and a solid (C29H50O, m.p. 143-144 °C, [α]D -35.3 °) which formed an acetate (m.p. 137-138 °C, [α]D -40.1 °) on treatment with acetic anhydride and pyridine; this latter compound was concluded to be sitosterol, isolated previously from the root of Dictamnus albus by Kuwada. A further solid material (m.p. 69-71 °C) was a mixture of fatty acids with the highest molecular weight acid having molecular weight 424; esterification with diazomethane followed by GLC analysis showed the solid to be a mixture of seventeen esters in two homologous series. The final product of this neutral fraction proved to be a new alkaloid, C17H21NO4 (m.p. 151-152 °C), with NH and amide absorption in the IR spectrum and a UV spectrum typical of a 2-quinolone. The NMR spectrum had an exchangeable (N-H) proton at 0.85 τ, two ortho-coupled aromatic protons at τ = 2.52 and 3.15 (J 9 Hz), methoxyl singlets at τ = 6.03 (6H) and 6.06 (3H), vinylic Me singlets at τ = 8.20 and 8.31, and a one-proton triplet at 4.69 τ (J = 6.5 Hz) coupled to a two-proton doublet at τ = 6.63. From these data only two structures (14 or 15, R = Me) are possible for the alkaloid. Structure 15 (R = Me) has the same OMe substitution pattern as skimmianine (5, R = Me), a constituent of Dictamnus albus L. Furanoquinoline alkaloids have long been assumed to be derived from isopentenyl precursors, an assumption proven recently by the radioactive feeding work of Grundon, so we assumed that 15 (R = Me) was the more likely structure and commenced synthesis. 1-Chloro-3-methylbut-2-ene was synthesised conveniently by addition of hydrochloric acid to isoprene; the chloride was reacted with sodium diethylmalonate to yield diethyl 2-(3-methylbut-2-enyl)malonate. 2,3-Dimethoxyaniline was prepared by Hofmann rearrangement of 2,3-dimethoxybenzamide. Condensation of 2,3-dimethoxyaniline with diethyl 2-(3-methylbut-2-enyl)malonate in refluxing diphenyl ether yielded 4-hydroxycarbostyril (15, R = H) (m.p. 214-216 °C) with expected spectral data. Treatment of 15 (R = H) with diazomethane afforded 3-(3-methylbut-2-enyl)-4,7,8-trimethoxy-2-quinolone (15, R = Me) which was identical in all respects to the alkaloid from Dictamnus albus L.; we named this alkaloid preskimmianine. The base-soluble portion of the saponification of the Dictamnus albus L. extract yielded limonin (2) and fraxinellone (1) as the only characterisable products.