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Ethnobotany and phytochemistry of Tropaeolum tuberosum and lepidium meyenii from Andean South America Johns, Timothy Allan


A systematic investigation of the ethnopharmacology of Tropaeolum tuberosum Ruiz & Pavon and Lepidium meyenii Walp., in the Tropaeolaceae and Erassicaceae respectively, was undertaken to determine the physical basis for the medicinal and nutritional uses of these species by natives of the Andes mountains. The domestication of T. tuberosum in relation to these uses was considered from the perspective of the glucosinolate cherootaxonomy of the two subspecies, tuberosum and Silvestre. High Performance Liquid Chromatography (HPLC) was used as the primary tool for determining the isothiocyanates hydrolyzed enzymatically from glucosinolates of the tubers, seeds, flowers and leaves of both subspecies of T. tuberosum, and from the roots of L. meyenii. On the basis of HPLC, paper chromatography of thiourea derivatives, mass spectrometry and nuclear magnetic resonance spectrometry it was concluded that the sole isothiocyanate liberated from T. tuberosum subsp. tuberosum is p—methoxybenzyl isothiocyanate. T. tuberosum subsp. silvestre is characterized by benzyl, 2-propyl and 2-butyl isothiocyanates. This difference in glucosinolates supports the existence of two distinct subspecies. Hydroilysates of L. meyenii contain benzyl isothiocyanate as the primary constituent, and p-methoxybenzyl isothiocyanate as a minor constituent. N,N,Di(methoxy, 4- benzyl)thiourea was detected in the isothiocyanate extracts of T. tuberosum subsp. tuberosum. A statistical survey of the ethnobotanical uses of Glucosinolate-containing plants from around the world was carried out. The significant medicinal uses for glucosinolate- containing plants in general correlates positively with the uses from the Andes of T. tuberosum and L. meyenii. Pharmacological studies on crude plant material and extracts of T. tuberosum and on pure compounds were carried out in relation to the reputed uses of these species. Tropaeolum tuberosum and Lepidium meyenii are believed to affect human fertility. Feeding studies of female guinea pigs and in vitro studies to test the 17-estradiol binding inhibition of extracts and of pure isothiocyanates failed to substantiate any estrogenic activity of these taxa. However, preliminary results for N,N,Di(methoxy, 4-benzyl)thiourea suggest that this confound competitively inhibits estradiol binding and may have estrogenic activity. The antiaphrodisiac beliefs associated with T. tuberosum subsp. tuberosum were examined in male rats fed a diet containing tubers of this taxon. Experimental animals and controls showed equal capability in impregnating females, although animals fed T. tuberosum showed a 45% drop in their blood levels of testosterone/dihyrotestosterone. This drop appears to be related to the antimetabolic effects of isothiocyanates in the tubers. Tubers of Tropaeolum tuberosum and purified isothiocyanates were shown to be antibiotic but not phototoxic against yeast and bacteria. Benzyl isothiocyanate was shown to be nematocidal. Tests of a tuber extract against Herpes Type I virus failed to substantiate possible antiviral activity for this species. Analysis of free amino acids in tubers of T. tuberosum failed to detect any non-protein or unusual amino acids.

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