Synthesis and cytotoxicity of novel 20- O -linked homocamptothecin ester derivatives as potent topoisomerase I inhibitors. - Li, Di-Zao; Wang, Cun-Ying; Liu, Rui-Hua; Wang, Yan-Ming; Ji, Teng-Fei; Li, Yu-Rong; Pan, Xian-Dao (Journal of Asian Natural Products Research, 2013)