@article {M.:January 2005:1397-002X:55,
	author = "M. Liu",
	author = "Y.-C. Tang",
	author = "K.-Q Fan",
	author = "X. Jiang",
	author = "L.-H Lai",
	author = "Y.-H Ye",
	title = "Cyclization of several linear penta- and heptapeptides with different metal ions studied by CD spectroscopy",
	journal = "Journal of Peptide Research",
	volume = "65",
	year = "January 2005",
	abstract = ": <P></P>A cyclic pentapeptide c(Tyr-Leu-Ala-Gly-Pro) (<B>I</B>), which was isolated and identified from <I>Pseudostellaria heterophylla</I> medicinal herbs, and two cyclic heptapeptides, c(Gly-Tyr-Gly-Gly-Pro-Phe-Pro) (<B>II</B>) and c(Gly-Ile-Pro-Tyr-Ile-Ala-Ala) (<B>III</B>), which were isolated and identified from <I>Stellaria yunnanensis</I> Franch (M), were synthesized by using 3-(diethoxyphosphoryloxy)-1,2,3-benzotriazin-4(3 <I>H</I>)-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 (<B>I-1</B>) and H-Ala-Gly-Pro-Tyr-Leu-OH (<B>I-2</B>), H-Gly-Tyr-Gly-Gly-Pro-Phe-Pro-OH (<B>II-1</B>) and H-Gly-Ile-Pro-Tyr-Ile-Ala-Ala-OH (<B>III-1</B>), 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<SUP>+</SUP> ion is favorable for the cyclization of linear pentapeptides and Cs<SUP>+</SUP> ion is favorable for the cyclization of linear heptapeptides, while some bivalent and trivalent metal ions, such as Mg<SUP>2+</SUP>, Ca<SUP>2+</SUP>, Zn<SUP>2+</SUP>, Fe<SUP>2+</SUP>, Ni<SUP>2+</SUP> and Cr<SUP>3+</SUP> reduced/inhibited both the cyclization yields and the cyclization rates of the linear peptide precursors. The circular dichroism spectra of <B>I-1</B>, <B>II-1</B> and <B>III-1</B> with different metal ions were studied to elucidate the changes in their secondary structures. It is shown that Cs<SUP>+</SUP> can induce and stabilize the type I <I><IMG SRC="/iso-ents/isogrk1/bgr-s.gif" ALT="bgr"></I>-turn conformation in the linear heptapeptide <B>II-1</B> and the type II <I><IMG SRC="/iso-ents/isogrk1/bgr-s.gif" ALT="bgr"></I>-turn conformation in the linear heptapeptide <B>III-1</B>.",
	pages = "55-64(10)",
	url = "http://www.ingentaconnect.com/content/mksg/jpr/2005/00000065/00000001/art00009"
	doi = "doi:10.1111/j.1399-3011.2004.00199.x"
}