Unusual Amino Acids and Monofluoroacetate from Dichapetalum michelsonii (Umutambasha), a Toxic Plant from Rwanda

Abstract

In the course of our investigations on Umutambasha in order to identify its convulsant principles, small quantities of monofluoroacetate were observed in stem bark, leaves, and fruits of this plant newly identified as Dichapetalum michelsonii Hauman. Conclusive evidence for a monofluoroacetate presence came from its isolation from the freeze-dried extract of stem bark. Three free unusual amino acids, named N-methyl-α-alanine, N-methyl-β-alanine, and 2,7-diaminooctan-1,8-dioic acid, described for the first time in a plant, and known trigonelline were also isolated from the stem bark of D. michelsonii. Structure elucidations were mainly achieved by spectroscopic methods (1H-NMR, 2D-NMR, MS) and by comparison with authentic references. These unusual amino acids were detected by a fast, reliable TLC analysis in all our batches of Umutambasha, suggesting that they could be used for identification purposes in case of human or livestock intoxications. Finally, EEG recordings and behavioural observations performed in mice suggested that the convulsive patterns produced by Umutambasha are the consequence of monofluoroacetate presence in D. michelsonii.

Monofluoroacetate-Containing Plants That Are Potentially Toxic to Livestock

“…3 Dichapetalum cymosum (Gifblaar) causes sudden death or "Gifblaar poisoning" and is the third most important toxic plant in South Africa. 3 Seven Dichapetalum spp., D. barteri, 43 D. braunii, 44 D. cymosum, 45 D. edule, 44 D. heudelotii, 46 D. michelsonii 44,47 (possibly the same as D. stuhlmanii), and D. toxicarium, 48 have been documented to contain monofluoroacetate (Table 1), and three of these, D. cymosum, D. barteri, and D. toxicarium, are reported to be lethally toxic to livestock. 3 D. ruhlandii has also been reported to be lethally toxic, but, apparently, has not been shown to contain monofluoroacetate.…”