ABSTRACT

Bracken (Pteridium spp.) is a ubiquitous fern which has been described as one of the five most common plants on the earth. The toxic effects of bracken on livestock have been recorded since the end of the 19th century, and extensive and intensive investigations for the bracken toxin(s) led to the isolation of ptaquiloside in 1983 as the major, but unstable, toxin of bracken. This review concentrates mainly on the results of the scientific investigations into ptaquiloside, and cites 133 references.

No abstract

Okadaic acid (OA) is a potent non-12-O-tetradecanoyl-phorbol-13-acetate (non-TPA) type tumor promoter on mouse skin. OA acts on cells through inhibiting the activity of protein phosphatases and results in the increase of phosphorylation of proteins. Seventeen OA derivatives were evaluated as possible tumor promoters by means of three biochemical tests: inhibition of specific [3H]OA binding to a particulate fraction of mouse skin containing protein phosphatases, inhibition of protein phosphatase activity, and induction of ornithine decarboxylase in mouse skin. Potency in each of these biochemical tests correlated well for each of these derivatives. We present results indicating that the carboxyl group as well as the four hydroxyl groups at C-2, C-7, C-24 and C-27 of OA are important for activity. Acanthifolicin, which gave positive responses in these three biochemical tests as strong as those of OA and dinophysistoxin-1, is predicted to be an additional member of the OA class of tumor promoters.

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Aplyronine A is a macrolide isolated from Aplysia kurodai. By monitoring fluorescent intensity of pyrenyl-actin, it was found that aplyronine A inhibited both the velocity and the degree of actin polymerization. Aplyronine A also quickly depolymerized F-actin. The kinetics of depolymerization suggest that aplyronine A severs F-actin. The relationship between the concentration of total actin and F-actin at different concentrations of aplyronine A suggests that aplyronine A forms a 1:1 complex with G-actin. From these results, it is concluded that aplyronine A inhibits actin polymerization and depolymerizes F-actin by nibbling. Comparison of the chemical structure of aplyronine A and another actin-depolymerizing macrolide, mycalolide B, suggests that the side-chain but not the macrolide ring of aplyronine A may account for its actin binding and severing activity.

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Bioassay-guided fractionation of the cytotoxic constituents of the Japanese sea hare Dolabella auricularia led to the isolation of two novel cytotoxic compounds, aurisides A (1) and B (2). Their gross structures were established by spectroscopic analysis including the 2D NMR technique. On the basis of the NOESY spectral analysis and the degradation experiments, their absolute stereostructures were determined to be 14-membered macrolide glycosides that contain a bromine-substituted conjugated diene structure, a cyclic hemiacetal moiety, and a 2,4-di-O-methyl-L-rhamnopyranoside part. Aurisides A (1) and B (2) show cytotoxicity against HeLa S(3) cells with IC(50) values of 0.17 and 1.2 &mgr;g/mL, respectively.