1. Natural Products Division, Department of Chemistry, Sri Venkateswara University, Tirupati 517 502, India
2. Organic Chemistry Division II, Indian Institute of Chemical Technology, Hyderabad 500 007, India
3. Center for Magnetic Resonance, Indian Institute of Chemical Technology, Hyderabad 500 007, India
4. Laboratoire de Chimie et Biochimie des Substances Naturelles, USM 0502 MNHN-UMR 5154, CNRS, 63, rue Buffon 75005 Paris, France