1. Peptide Chemistry Research Center; K. N. Toosi University of Technology; P.O. Box 15875-4416 Tehran Iran
2. Department of Chemistry; Sharif University of Technology; P.O. Box 11365-9516 Tehran Iran
3. Organisch-Chemisches Institut der Universität Heidelberg; Im Neuenheimer Feld 270 D-69120 Heidelberg Germany