Alkaloids of the Australian Rutaceae: Pentaceras australis Hook. F. I. Isolation of the Alkaloids and Identification of Canthin-6-one

Abstract

Three alkaloids, with molecular formulae C14H8ON2, C15H10O2N2, and C15H10OSN2,, have been isolated from the ram-forest tree Pentaceras australis Hook. f. All three are present in the bark of mature trees, the total yield of alkaloids varying from c. 0.2 per cent. (branch bark) to c. 1 per cent. (root bark). The wood contains 0.2 per cent. of a mixture of two of the alkaloids, C14H8ON2 and C15H10OSN2, while the leaves contain less than 0.01 per cent. of a mixture in which the alkaloids C14H8ON2 and C15H10O2N2 are present.The alkaloid C14H8ON2 is shown to be representative of a ring system not previously found In the plant kingdom. It is canthm-6-one (II). The principal reactions on which this structure is based are (a) oxidation of the alkaloid to β-carboline-1-carboxylic acid and (b) the reversible opening of a lactam ring with alkali to give cis-2-(1'-β-carbolyl) acrylic acid (III) which may be transformed to the trans-isomer from which the alkaloid is not regenerated. Other reactions of the alkaloid support the canthinone structure. Among the compounds described is a dihydro-derivative (XI) of the parent base canthine