1. A novel prosthetic group for site-selective labeling of peptides for positron emission tomography
Joseph Arukwe, Alan Cuthbertson, Ole Kristian Hjelstuen, Magne Solbakken, Hege Karlsen, Dag Erlend Olberg Bioconjug Chem . 2008 Jun;19(6):1301-8. doi: 10.1021/bc800007h.
Efficient methodologies for the radiolabeling of peptides with [(18)F]fluoride are a prerequisite to enabling commercialization of peptide-containing radiotracers for positron emission tomography (PET) imaging. It was the purpose of this study to investigate a novel chemoselective ligation reaction comprising conjugation of an [(18)F]-N-methylaminooxy-containing prosthetic group to a functionalized peptide. Twelve derivatives of general formula R1-CO-NH-Lys-Gly-Phe-Gly-Lys-OH were synthesized where R1 was selected from a short list of moieties anticipated to be reactive toward the N-methylaminooxy group. Conjugation reactions were initially carried out with nonradioactive precursors to assess, in a qualitative manner, their general suitability for PET chemistry with only the most promising pairings progressing to full radiochemical assessment. Best results were obtained for the ligation of O-[2-(2-[(18)F]fluoroethoxy)ethyl]-N-methyl-N-hydroxylamine 18 to the maleimidopropionyl-Lys-Gly-Phe-Gly-Lys-OH precursor 10 in acetate buffer (pH 5) after 1 h at 70 degrees C. The non-decay-corrected isolated yield was calculated to be 8.5%. The most encouraging result was observed with the combination 18 and 4-(2-nitrovinyl)benzoyl-Lys-Gly-Phe-Gly-Lys-OH, 9, where the conjugation reaction proceeded rapidly to completion at 30 degrees C after only 5 min. The corresponding non-decay-corrected radiochemical yield for the isolated (18)F-labeled product 27 was 12%. The preliminary results from this study demonstrate the considerable potential of this novel strategy for the radiolabeling of peptides.
2. Structural characterization of lipopeptide agonists for the bradykinin B2 receptor
E Nardi, C Giragossian, A M Papini, D F Mierke, C A Maggi, S Meini, C Savery, M Pellegrini Biopolymers . 2001 Apr 15;58(5):511-20. doi: 10.1002/1097-0282(20010415)58:53.0.CO;2-Z.
The conformational features of Pam-Lys(0)-Arg(1)-Pro(2)-Pro(3)-Gly(4)-Phe(5)-Ser(6)-Pro(7)-Phe(8)-Arg(9)-OH (PKD) and Pam-Gly(-1)-Lys(0)-Arg(1)-Pro(2)-Pro(3)-Gly(4)-Phe(5)-Ser(6)-Pro(7)-Phe(8)-Arg(9)-OH (PGKD), the Pam-Lys and Pam-Gly-Lys analogues of bradykinin, have been determined by high-resolution NMR in a zwitterionic lipoid environment. Radical-induced relaxation of the (1)H NMR signals was used to probe the topological orientation of the peptides with respect to the zwitterionic lipid interface. The radical-induced relaxation and molecular dynamics (MD) data indicated that the palmitic acid and N-terminal amino acid residues embed into the micelles, while the rest of the polypeptide chain is closely associated with the water-micelle interface. Throughout the entire nuclear Overhauser effect restrained MD simulation, a nonideal type I beta-turn was observed in the C-terminus of PKD between residues 6 and 9, and a gamma-turn was observed in the C-terminus of PGKD between residues 6 and 7. Therefore, the additional glycine has a dramatic effect on the structural preferences of the biologically important C-terminus, an effect brought about by the interaction with the lipid environment. These structural features are correlated to the biological activity at the bradykinin B2 receptor.
3. Peptide ionophores: synthesis and cation-binding properties of a bicyclic peptide containing glycine and lysine residues
E Crusi, D Andreu, E Giralt Pept Res . 1995 Mar-Apr;8(2):62-9.
Peptide 1, cyclo(1,5-epsilon-succinoyl) (Lys-Gly-Gly-Gly)2, is a representative member of a family of polycyclic peptide ionophores characterized by C2 symmetry and a relatively flexible structure resulting from its high Gly content. Peptide 1 has been synthesized by two different solid-phase protocols from its linear precursors, H-Gly-Gly-Lys(Fmoc)-Gly-Gly-Gly-Lys(Fmoc)-Gly-OH and H-Gly-Gly-Lys(Z)-Gly-Gly-Gly-Lys(Z)-Gly-OH), and satisfactorily characterized by chemical means. The CD spectrum of 1 is compatible with a beta-folded structure, stabilized by two internal hydrogen bonds. The complexation behavior of 1 toward alkaline and alkaline-earth cations can be envisaged as an equilibrium between inclusion (1:1) and sandwich (2:1) complex models, with affinities in the 10(6) M-1 and 10(11) M-2 range, respectively. A slight preference of 1 for Sr2+ over other cations has been found.
