... Bioorganic & Medicinal Chemistry Letters. Volume 16, Issue 7, 1 April 2006, Pages 1947–1949. Cover image Cover image. Semisynthesis of C-ring modified triptolide analogues and their cytotoxic activities. ... b Yakult Central Institute for Microbiological Research, 1796 Yaho, Kunitachi-shi, Tokyo 186-8650, Japan. Received 1 November 2005, Revised 12 December 2005, Accepted 21 December 2005, Available online 7 February 2006. Abstract. ...