The chemical constituents of Idiospermum australiense (Diels) S.T. Blake

This blog has been set up so that results of the study of the chemical constituents of Idiospermum australiense that we carried out at Sydney University in 1972 and 1973 may be more widely accessed. This blog is also a testimony to the pioneering work into natural product chemistry in Australia by the late Prof Ern Ritchie and the late Prof Wal Taylor who were my supervisors. Prof Taylor passed away just under a year ago and was working towards publishing the results of my study. In the event these results are not actually published in a recognized scientific journal then this blog makes available some the results that can otherwise be sourced from my thesis. It is well documented that in 1912 Diels described the tree as Calycanthus australiense Diels from a specimen collected in northern Queensland at Harvey Creek near the Russell River. Then in 1971 the plant was rediscovered in the Daintree area after a case of stock poisoning. T.S. Blake, a taxonomist with the Queensland herbarium, reclassified the plant into a new genus and family, Idiospermum australiense, Idiospermaceae.

This first post will briefly describe the results concerning the alkaloids found in the plant.
The bark, cotyledons, wood and leaves all yielded (+)-calycanthine
Bark: 0.1% calycanthine
Cotyledons: 0.05% calycanthine
Wood: 0.03% calycanthine
Leaves: 0.38% crude alkaloid fraction (calycanthine plus another alkaloid)

This result is significant in that it indicates that the plant is closely related to the calycanthaceae since according to Hegenauer, members of this family characteristically contain calycanthine type alkaloids (Hegnauer, R., Chemotaxonomie der Pflanzen, Band 3, p338 (Birkhauser Verlag: Basel 1964).

After exhaustive counter current separation of the alkaloid fraction from the leaves of the plant a new alkaloid, idiospermine (0.002%) was isolated.

Idiospermine (C34H40N6) can be viewed as a trimer of methyltryptamine plus an additional methyl group. From spectral data it was concluded that its structure is that of a calycanthine moiety linked via one of its para positions to the alpha position of methyltryptamine where the indole nitrogen has been methylated.

I moved on from chemistry in 1973 and I hope that in a future post I can obtain the assistance of a friend to post the actual chemical structures.

The uv spectrum displayed the presence of an alpha-aryl indole chromophore. Prof Taylor subsequently confirmed the structure via X-ray crystallography carried out by Prof Trevor Hambley of Sydney University.

Idiospermine is different from idiospermuline (extracted from the seeds of this plant) which is a chimonanthine analogue - Rujee K. Duke, Robin D. Allan, Graham A.R. Johnston, Kenneth N. Mewett and Ann D. Mitrovic, "Idiospermuline, a trimeric pyrrolidinoindoline alkaloid from the seed of Idiospermum australiense, Journal of Natural Products, vol 58 (no.8), 1995, pp1200-1208.

Idiospermine is, however, similar to idiospermamine B recently reported by Anthony R. Carroll, Gregory A. Feshner, Sandra Duffy and Vicky M. Avery at the 50th Annual Meeting of the American Society of Pharmocognosy held in Hawaii in June of 2009. This alkaloid was isolated from the bark of the plant and displays antimalarial, antitrypanosomal and cytoxic activities.

The structure of idiospermamine B ( C34H38N6) is that of a calycanthine moiety coupled at the beta position of methytryptamine followed by cyclisation (formation of a pyrrolidine ring). This work from researchers at Griffith University is about to be published in the very near future.

In 2001 Bremner published results into study of a Psychotria sp from Lombok, Indonesia - http://www.mdpi.com/1420-3049/6/2/117/pdf. He referred to an alkaloid with a molecular weight of 574. My guess is that this compund has the molecular formula ( C37H46N6). Bremner does not seem to have published a structure for this alkaloid but my guess is that it is a trimethylated compound from idiospermine.