Capasso S, Sica F, Mazzarella L, Balboni G, Guerrini R, Salvadori S
Department of Chemistry, University of Naples Federico II, Italy.
Int J Pept Protein Res. 1995 Jun;45(6):567-73. doi: 10.1111/j.1399-3011.1995.tb01321.x.
The kinetics of the spontaneous formation of 2,5-dioxopiperazines from peptides containing the Tic (1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid) residue in the 2-position of the sequence has been studied in DMSO and water solution. The reaction is first order in Tic-peptide and subject to general-acid catalysis. Moreover, only the fraction of peptide having the amino terminal group in the deprotonated state reacts with appreciable rate. In pure organic solvent, and in aqueous solution with low buffer concentration, the degradation reaction of Tic-peptides is very low; at 20 degrees C for the peptide H-Tyr-Tic-Phe-Phe-NH2, in DMSO and in neutral water in the absence of buffer, the half-lives (t1/2) are 3 x 10(4) and 1.2 x 10(4) h, respectively. The addition of carboxylic acids or buffers to the reaction solutions markedly increases the reaction rate; in 0.01 m HAc in DMSO and in 0.1 M phosphate buffer in water, pH 7.1, t1/2 values for the tetrapeptide are 61 and 121 h, respectively.
对序列中2位含有Tic（1,2,3,4-四氢异喹啉-3-羧酸）残基的肽自发形成2,5-二氧代哌嗪的动力学在二甲基亚砜（DMSO）和水溶液中进行了研究。该反应对Tic-肽为一级反应，并受到广义酸催化。此外，只有氨基末端基团处于去质子化状态的那部分肽才以可观的速率反应。在纯有机溶剂中以及在低缓冲浓度的水溶液中，Tic-肽的降解反应非常缓慢；在20℃下，对于肽H-Tyr-Tic-Phe-Phe-NH2，在DMSO中和在无缓冲剂的中性水中，半衰期（t1/2）分别为3×10⁴和1.2×10⁴小时。向反应溶液中加入羧酸或缓冲剂会显著提高反应速率；在DMSO中的0.01 m HAc中和在pH 7.1的水中的0.1 M磷酸盐缓冲液中，该四肽的t1/2值分别为61和121小时。
