1. Natural Products Division, Department of Chemistry, Sri Venkateswara University, Tirupati 517 502, India
2. Department of Chemistry, National Cheng Kung University, Tainan 701, Taiwan
3. Laboratoire de Chimie et Biochimie des Substances Naturelles, USM 0502 MNHN-UMR 5154, CNRS, 63 rue Buffon 75005, Paris, France