1. Department of Chemistry, Quaid-I-Azam University Islamabad, Islamabad, Pakistan
2. Institute of Organic Chemistry, Hannover University, Schneiderberg 1B, D-30167 Hannover, Germany
3. Institute of Pharmaceutical Chemistry, University of Münster. Hittorfstr. 5 8 -6 2 , D-48149 Münster, Germany