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 doi: 10.1016/j.bmcl.2003.08.072