Study on Conformation of Three Cyclic Peptides and Their Correspondent Linear Peptides with CD Spectroscopy

We used CD spectroscopy to study the conformations of three cyclic peptides (CP10E cyclo GiniOBz))-Pro-Gly-Glu(OBz]}-Gly(2). CP10K : Cyclo [Lys(Z)-Pro Gly-Lys(Z)-Gly(12). OP12K: cyclo Phe-Lys(Z)-Pro-Gly Lys(Z) Gly(jz) and their correspomdemt linear peptides (LP10E: Boc Clu(OBzl)-Pro-Gly-Glu(OBzl)-Gly](2)OPac, LP10K; Boc[Lys(Z)-Pro-Lys(Z)-Pro(2-)MOc, LP12K: Bao-[-Lys(Z)-Pro-Gly-Lys(Z)-Gly(jz)-MOc] is three solvents of different polarity (chloroform, aretonitrile, 2,2,2-trifluorethanpl), abd it was found that all of lines and cyclicpeptides exist as gamma-turn conformation in chloroform, however, in TFE & Ch(3)CN solutions, the three linear peptides are in beta Pi- turn conformation. CP10E os beta 1 - urn conformation, CP10K & CP12K exist in more than one types of turn conformations. On the basis of our experiments, it was concluded: 1) In the presence of conformational constrained amino acids sport linear peptides form obvoius secondary structure: 2) The solvent polarity has influence on the peptide conformation and this influence on linear peptides is greater than that on cyclic peptides; 3) The backbone ofcyclic peptide has constraint effect on its confirmatio and makes the secondary structure of cyclic peptide different from rare of its relative peptide. this information might give some clues in the design of bioactive peptides with different receptor selectivity.