The structure of monatin, a hig h-intensity sweetener isolated from Schlerochiton ilicifolius was elucidated by 'H and 13C NMR spectroscopy as 4-hydroxy-4-(indol-3-ylmethyl)glutamic acid. The 2R*,4R* relative configuration of the two chiral centres in monatin was determined by NOE studies on a derivative, met hy I 2 -( i ndol -3 -y lmet hyl) -4-(2,4-d in itroa n i I i no) -5 -0x0 -2,3,4,5 -tetra h ydrof u ran -2-carboxylate. The assignment of the 2s configuration to monatin, through application of the Clough-Lutz-Jirgenson rule, established the 2S,4S configuration for the compound.The detrimental effects of high consumption of sucrose and glucose-based sugars, such as obesity and tooth decay in humans,'a2 have resulted in the present day extensive research on synthetic, non-nutritive sweeteners with the aim to develop a safe, high-intensity, non-calorific sweetener, stable for a wide range of pH and temperatures, with a long shelflife and no aftertaste. None of the present products on the market, e.g. saccharin, cyclamate, acesulfame-K and aspartame fulfil all these requirement^.^ The concern about long-term effects of some of these products has resulted in a search for high-intensity sweeteners from natural source^.^ Three of the more promising 4975298 Al1988. 1961, V O ~. 1, pp. 83-93.

Geigeria poisoning, referred to as 'vermeersiekte' is an important plant poisoning in southern Africa. Three sesquiterpene lactones, isogeigerin acetate (1) ivalin(2) and geigerin (3) were isolated and purified from Geigeria aspera Harv.(Asteraceae). Structures were deduced using 1 and 2D, 1 H-and 13 C-NMR spectroscopy and mass spectrometry, while the absolute configurations of compounds 1 and 3 were determined for the first time by X-ray crystal diffraction analyses. Cytotoxicity of isogeigerin acetate, ivalin and geigerin were compared by exposing a murine skeletal myoblast (C2C12) cell line to varying concentrations of the three sesquiterpene lactones isolated. Cell viability was assessed using the methyl-thiazolyl-tetrazolium (MTT) assay. The EC 50 s were 3.746 mM, 0.0029 mM and 3.792 mM for isogeigerin acetate (1), ivalin (2) and geigerin (3), respectively. The results indicate that ivalin is much more toxic, approximately 1000 times, in vitro compared to isogeigerin acetate and geigerin.

Diplodiosis is an important neuromycotoxicosis of ruminants in South Africa when grazing on harvested maize fields in winter. It is believed to be caused by mycotoxin(s) synthesised by Stenocarpella (Diplodia) maydis. Although several metabolites have been isolated from S. maydis culture material, none of these have been administered to ruminants to reproduce the disease. The objectives of this study were to isolate diplodiatoxin and to administer it to juvenile goats. Diplodiatoxin, considered as a major metabolite, was purified from S. maydis-infected maize cultures (Coligny 2007 isolate). Following intravenous administration of 2 mg and 4 mg diplodiatoxin/kg body weight for five consecutive days to two juvenile goats, no clinical signs reminiscent of diplodiosis were observed. Based on previous experimental results and if diplodiatoxin was the causative compound, the dosage regimen employed was seemingly appropriate to induce diplodiosis. In addition, intraruminal administration of 2 mg/kg diplodiatoxin to one goat for three consecutive days also did not induce clinical signs. It appears as if diplodiatoxin alone is not the causative compound. Other metabolites and/or mixtures of diplodiatoxin and other mycotoxins, when available in sufficient quantities, should also be evaluated.

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