1. a Department of Pharmaceutical Chemistry, Faculty of Pharmacy , Silpakorn University , Nakorn-Pathom 73000 , Thailand
2. b Office for Research and Development, Faculty of Medicine , Siriraj Hospital, Mahidol University , Bangkok 10700 , Thailand
3. c Department of Pharmacognosy, Faculty of Pharmacy , Mahidol University , Bangkok 10400 , Thailand
4. d Graduate School of Pharmaceutical Sciences , Chiba University , Chiba 263-8522 , Japan