1. PeptLab, Department of Organic Chemistry “Ugo Schiff”, University of Florence, Via della Lastruccia 13, 50019 Sesto Fiorentino, Florence, Italy, Department of Chemistry, University of Florence, Via della Lastruccia 3, 50019 Sesto Fiorentino, Florence, Italy, and Department of Chemistry, University of Siena, Via De Gasperi 2, 53100 Siena, Italy