RESUMO
An investigation on the constituents of the callus tissues of Ternstroemia gymnanthera has led to the isolation of five phytosterols, 15 known triterpenoids, and four new triterpenoids (1-4). The new compounds were characterized by spectroscopic study as 3-epi-corosolic acid lactone (2 alpha,3 alpha-dihydroxyurs-11-en-13 beta,28-olide) (1), 3-epi-ternstroemic acid (2 alpha,3 alpha-dihydroxyurs-12-en-11-on-28-oic acid) (2), ternstroemic acid (2 alpha,3 beta-dihydroxyurs-12-en-11-on-28-oic acid) (3), and gymnantheraic acid (2 alpha,3 alpha-dihydroxy-11 alpha-methoxyurs-12-en-28-oic acid) (4). The isolated triterpenes were compared with those from actinidiaceous plant callus tissues from a chemotaxonomic point of view.
Assuntos
Ácido Oleanólico/análogos & derivados , Fitosteróis/isolamento & purificação , Plantas Medicinais/química , Theaceae/química , Triterpenos , Japão , Estrutura Molecular , Ressonância Magnética Nuclear Biomolecular , Ácido Oleanólico/química , Ácido Oleanólico/isolamento & purificação , Fitosteróis/química , Caules de Planta/química , Estereoisomerismo , Triterpenos/química , Triterpenos/classificação , Triterpenos/isolamento & purificaçãoRESUMO
We found that some triterpene compounds could not only selectively inhibit the activities of mammalian DNA polymerase alpha (pol alpha) and beta (pol beta), but could also potently inhibit DNA topoisomerase II (topo II) [Biochem. J. 350 (2000) 757]. Here, we report that natural triterpenes produced by callus from an ancient Chinese medicinal plant were also inhibitors of the enzymes, and some were more selective than others. The natural triterpenes with a carboxyl group equally inhibited the activities of pol alpha, pol beta, and topo II, while the olide-type triterpenes with a ketone group suppressed the activities of pol beta and topo II, but not pol alpha. The other triterpenes from the callus hardly influenced these enzyme activities. As also described previously [J. Biochem. 130 (2001) 657], pol beta and topo II have a three-dimensionally similar triterpene-binding region, which is a pocket in which specific compounds can insert. The newly found triterpene inhibitors might structure-dependently insert into the pocket, and the pocket structure of each enzyme might, three-dimensionally but slightly, differ among them. The triterpene frames could be used for screening new inhibitors of the enzymes, and computer-simulated drug design using the frame and pocket structure may in theory be a possible approach to develop new inhibitors.