Solvent Independent Conformational Propensities of [1,2,3]Triazolyl- Bridged Parathyroid Hormone-Related Peptide-Derived Cyclo-nonapeptide Analogues Mario Scrima, 1 Manuela Grimaldi, 1 Sara Di Marino, 1 Chiara Testa, 2,3 Paolo Rovero, 2,4 Anna Maria Papini, 2,3 Michael Chorev, 5,6 Anna Maria D’Ursi 1 1 Department of Pharmaceutical and Biomedical Sciences, Via Ponte Don Melillo 11C, Salerno, I-84084, Italy 2 Laboratory of Peptide & Protein Chemistry & Biology, Polo Scientifico e Tecnologico, University of Firenze, Sesto Fiorentino I-50019, Italy 3 Department of Chemistry ‘‘UgoSchiff,’’ Polo Scientifico e Tecnologico, University of Florence, Via della Lastruccia 13, Sesto Fiorentino I-50019, Italy 4 Department Pharmaceutical Sciences, University of Firenze, Via Ugo Schiff 3, Polo Scientifico e Tecnologico, Sesto Fiorentino I-50019, Italy 5 Laboratory for Translational Research, Harvard Medical School, One Kendal Square, Building 600, Cambridge, Massachusetts 02139 6 Department of Medicine, Brigham and Women’s Hospital, 75 Francis Street, Boston, Massachusetts 02115 Received 6 July 2012; accepted 23 July 2012 Published online 18 August 2012 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/bip.22139 Solvent Independent Conformational Propensities of [1,2,3]Triazolyl- Bridged Parathyroid Hormone-Related Peptide-Derived Cyclo- nonapeptide Analogues Additional Supporting Information may be found in the online version of this article. Correspondence to: Anna Maria D’Ursi, Department of Pharmaceutical and Biomedical Sciences, Via Ponte Don Melillo 11C, Salerno, I-84084, Italy; e-mail: dursi@unisa.it V V C 2012 Wiley Periodicals, Inc. ABSTRACT: The recently introduced Cu(I)-catalyzed azide–alkyne 1,3-dipolar Huisgen cycloaddition as a prototypic ‘‘click chemistry reaction’’ presented an opportunity for introducing the 1,4-disubstituted-[1,2,3]triazolyl moiety as a new isostere for peptide bonds in the backbone. Previous study in our lab focused on the synthesis of a model i-to-i+4 side chain-to-side chain 1,4- and 4,1- disubstituted-[1,2,3]triazolyl-bridged cyclo-nonapeptide I (Scheme 1) as analogues of its structurally related helical i-to-i+4 lactam-bridged cyclo-nonapeptide [Lys 13 (& 1 ),Asp 17 (& 2 )]parathyroid hormone related peptide (PTHrP)(11–19)NH 2 1 a truncated version of the a-helical and potent parathyroid hormone receptor 1 agonist [Lys 13 (& 1 ),Asp 17 (& 2 )]PTHrP(1-34)NH 2 , 2,3 N a - Ac-Lys-Gly-Lys(& 1 )-Ser-Ile-Gln-Asp(& 2 )-Leu-Arg- NH 2 ]. Systematic [1,2,3]triazolyl-containing bridge structure–conformation relationship studies in hexafluoroacetone/water mixture included incorporation of bridges varied in size and position and orientation of the triazolyl ring within the bridge. These studies revealed that the size of methylene bridge flanking triazolyl moiety is critical to reproduce in the heterodetic cyclo- nonapeptides. The conformational features of the analogues cyclo-nonapeptide in which Lys 13 and Asp 17 are bridged by the isosteric lactam. Here, we extend our conformational analysis to dimethyl sulfoxide/water mixture in an effort to characterize inherent conformational properties of the heterodetic cyclopeptides that are solvent independent. Our present study shows that the physicochemical properties of the structure- supporting solvent cannot override the effect of the size of methylene bridge to form helical mimetic structures. PeptideScience Volume 98 / Number 6 535