1. Department of Chemistry, University of Dhaka, Dhaka 1000, Bangladesh
2. Faculty of Pharmaceutical Sciences, Kanazawa University, 13-1 Takara-Machi, Kanazawa 920, Japan. Present address: H. E. J Research Institute of Chemistry, Karachi University, Pakistan
3. Department of Pharmacognosy, Graduate School of Pharmaceutical Science, Kyoto University, Yoshida, Sakyo-Ku, Kyoto 606-8501 Japan. Present address: Tsukuba Medicinal Plant Research Station, National Institute of Health Sciences, 1-Hachimandal, Tsukuba, Ibaraki 305-0843, Japan
4. Department of Chemistry, University of Wisconsin-Milwaukee, Milwaukee, WI 53201, USA