1. Research Group of Peptide Chemistry, Hungarian Academy of Sciences, and Department of Organic Chemistry, Eötvös L. University, P.O. Box 32, 1518 Budapest 112, Hungary, Laboratory for Medical Microbiology, Universiteit Groningen, 9713 GZ Groningen, The Netherlands, Laboratory of Analytical Chemistry and Biopolymer Structure Analysis, and Zukunftskolleg, University of Konstanz, 78457 Konstanz, Germany, and Department of Experimental and Health Sciences, Pompeu Fabra University, 08028 Barcelona, Spain