Seventeen pyrrolizidine alkaloids were studied with the hepatocyte primary culture-DNA repair test using rat hepatocytes. DNA repair synthesis was elicited by 15 alkaloids, including 11 of unknown carcinogenicity, i.e., senecionine, seneciphylline, jacobine, epoxyseneciphylline, senecicannabine, acetylfukinotoxin, syneilesine, dihydroclivorine, ligularidine, neoligularidine, and ligularizine. The positive results with these alkaloids of unknown carcinogenicity suggest that they are possibly genotoxic carcinogens. The two pyrrolizidine alkaloids that did not elicit DNA repair were retronecine which lacks a necic acid component and ligularinine which lacks the unsaturated double bond at the 1,2-position of the pyrrolizidine ring. Five pyrrolizidine alkaloids, retronecine, monocrotaline, seneciphylline, senkirkine, and clivorine, were also tested in the DNA repair test with hamster or mouse hepatocytes. These alkaloids, except retronecine, showed a positive response in the test with hamster hepatocytes, but in the test with mouse hepatocytes clivorine in addition to retronecine was also negative. The results indicate a species difference in liver bioactivation of pyrrolizidine alkaloids, implying that there could be species differences in their carcinogenic activities.
A new cyclopropane-containing sesquiterpenoid, phellilane L (1), was isolated from the medicinal mushroom Phellinus linteus ("Meshimakobu" in Japanese), a member of the Hymenochaetaceae family and a well-known fungus that is widely used in East Asia. The planar structure of 1 was determined on the basis of spectroscopic analysis. The authors achieved the first total synthesis of 1. Our protecting group-free synthesis features a highly stereoselective one-pot synthesis involving an intermolecular alkylation/cyclization/lactonization strategy for construction of the key cyclopropane-γ-lactone intermediate. Additionally, our synthesis determined the absolute configuration of phellilane L (1).
Four new pyrrolizidine alkaloids, ligularidine, neoligularidine, ligularizine and ligularinine, were isolated together with the known compound clivorine from the roots and aerial parts of Ligularia dentata. Their structures were elucidated on the basis of the spectral data and chemical conversion of clivorine into these alkaloids. A useful epoxidation of pyrrolizidine alkaloids was achieved by using performic acid.
In this study, we found that two sesquiterpene lactones, isobutyroylplenolin and arnicolide D, from Centipeda minima L. (Compositae) exerted stronger cytotoxic activity than cisplatin on the human colon carcinoma HT-29 cell line. Furthermore, the cytotoxicity of these two compounds on normal cells was weaker than that of cisplatin. Treatment with isobutyroylplenolin and arnicolide D increased the levels of intracellular reactive oxygen species and decreased the levels of nuclear factor-κB protein, resulting in cell cycle arrest in G1 phase and apoptosis. We also discuss the difference in structure and activity between these two compounds.
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