title: Cyclization of several linear penta- and heptapeptides with different metal ions studied by CD spectroscopy.
abstract: A cyclic pentapeptide c(Tyr-Leu-Ala-Gly-Pro) (I), which was isolated and identified from Pseudostellaria heterophylla medicinal herbs, and two cyclic heptapeptides, c(Gly-Tyr-Gly-Gly-Pro-Phe-Pro) (II) and c(Gly-Ile-Pro-Tyr-Ile-Ala-Ala) (III), which were isolated and identified from Stellaria yunnanensis Franch (M), were synthesized by using 3-(diethoxyphosphoryloxy)-1,2,3-benzotriazin-4(3 H)-one (DEPBT) as a coupling reagent in solution, and mediated by different metal ions, from their linear peptide precursors H-Tyr-Leu-Ala-Gly-Pro-OH (I-1) and H-Ala-Gly-Pro-Tyr-Leu-OH (I-2), H-Gly-Tyr-Gly-Gly-Pro-Phe-Pro-OH (II-1) and H-Gly-Ile-Pro-Tyr-Ile-Ala-Ala-OH (III-1), respectively. The results show that alkali metal ions can improve the cyclization yields and/or the cyclization rates of linear peptide precursors, such as Na(+) ion is favorable for the cyclization of linear pentapeptides and Cs(+) ion is favorable for the cyclization of linear heptapeptides, while some bivalent and trivalent metal ions, such as Mg(2+), Ca(2+), Zn(2+), Fe(2+), Ni(2+) and Cr(3+) reduced/inhibited both the cyclization yields and the cyclization rates of the linear peptide precursors. The circular dichroism spectra of I-1, II-1 and III-1 with different metal ions were studied to elucidate the changes in their secondary structures. It is shown that Cs(+) can induce and stabilize the type I beta-turn conformation in the linear heptapeptide II-1 and the type II beta-turn conformation in the linear heptapeptide III-1.
authors.affiliation: Laboratory of Bioorganic Chemistry and Molecular Engineering, Ministry of Education, College of Chemistry and Molecular Engineering, Peking University, Beijing, China.
authors.forename: M
authors.initials: M
authors.lastname: Liu
authors.forename: Y-C
authors.initials: YC
authors.lastname: Tang
authors.forename: K-Q
authors.initials: KQ
authors.lastname: Fan
authors.forename: X
authors.initials: X
authors.lastname: Jiang
authors.forename: L-H
authors.initials: LH
authors.lastname: Lai
authors.forename: Y-H
authors.initials: YH
authors.lastname: Ye
mesh_terms: D002942:Circular Dichroism; D003500:Cyclization; D007477:Ions / Q000737:chemistry; D008670:Metals / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D010456:Peptides, Cyclic / Q000138:chemical synthesis / Q000737:chemistry*; D013696:Temperature
chemical_list: D007477:Ions; D008670:Metals; D010456:Peptides, Cyclic