IngentaConnect Cyclization of several linear penta- and heptapeptides with diffe...

Authors: M. Liu; Y.-C. Tang; K.-Q Fan; X. Jiang; L.-H Lai; Y.-H Ye

Source: Journal of Peptide Research, Volume 65, Number 1, January 2005 , pp. 55-64(10)

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 Mg²⁺, Ca²⁺, Zn²⁺, Fe²⁺, Ni²⁺ and Cr³⁺ 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 -turn conformation in the linear heptapeptide II-1 and the type II -turn conformation in the linear heptapeptide III-1.

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Cyclization of several linear penta- and heptapeptides with different metal ions studied by CD spectroscopy