Generally antimitotic agents such as colchicines and vinblastine bind to either the colchicine binding site or the vinca alkaloid binding site.1 On the other hand, paclitaxel promotes the polymerization of tubulin by binding to and stabilizing the resulting microtubule polymer, which differs from those of colchicines, podophyllotoxin, and the vinca alkaloids.1 In this study, it was found that isoplagiochins A (1) and B (2) remarkably inhibited the polymerization of tubulin (Table 1). Microtubule polymerization and depolymerization were monitored by the increase and the decrease in turbidity. Inhibitory effects of isoplagiochin B (2) to tubulin polymerization
are shown in Fig. 1, in which tubulin polymerization was inhibited in a concentration-dependent manner. On the other hand, dihydroisoplagiochins A (3) and B (4), which were derived by hydrogenation of 1 and 2 in the presence of PtO2, respectively, were found to be less potent (IC50, >100 lM, respectively) than 1 and 2, indicating that the restricted biaryl ring system of bis(bibenzyls) may be favorable for tubulin binding.
Generally antimitotic agents such as colchicines and vinblastine bind to either the colchicine binding site or the vinca alkaloid binding site.1 On the other hand, paclitaxel promotes the polymerization of tubulin by binding to and stabilizing the resulting microtubule polymer, which differs from those of colchicines, podophyllotoxin, and the vinca alkaloids.1 In this study, it was found that isoplagiochins A (1) and B (2) remarkably inhibited the polymerization of tubulin (Table 1). Microtubule polymerization and depolymerization were monitored by the increase and the decrease in turbidity. Inhibitory effects of isoplagiochin B (2) to tubulin polymerizationare shown in Fig. 1, in which tubulin polymerization was inhibited in a concentration-dependent manner. On the other hand, dihydroisoplagiochins A (3) and B (4), which were derived by hydrogenation of 1 and 2 in the presence of PtO2, respectively, were found to be less potent (IC50, >100 lM, respectively) than 1 and 2, indicating that the restricted biaryl ring system of bis(bibenzyls) may be favorable for tubulin binding.
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