Ohwada, Tomohiko; Nonomura, Taro; Maki, Keisuke; Sakamoto, Kazuho; Ohya, Susumu; Muraki, Katsuhiko; Imaizumi, Yuji Bioorganic and Medicinal Chemistry Letters, 2003 , vol. 13, # 22 p. 3971 - 3974