1. Department of Organic Chemistry, Royal Institute of Technology, S-100 44 Stockholm, Sweden
2. Department of Medicinal Chemistry, Royal Danish School of Pharmacy, DK- 2100 Copenhagen, Denmark
3. Department of Structural Chemistry, University of Stockholm, S-106 91 Stockholm, Sweden
4. Dipartimento di Chimica, Università di Napoli, Federico II Via Mezzocannone 4, 80134 Napoli, Italy