Glycine enolates:: The large effect of iminium ion formation on α-amino carbon acidity
Glycine enolates:: The large effect of iminium ion formation on α-amino carbon acidity
复制标题
DOI：
10.1021/ja016250c
复制
发表时间：
2001-08-15
影响因子：
15
通讯作者：
Richard, JP
中科院分区：
文献类型：
--
作者：
Rios, A;Crugeiras, J;Richard, JP
我们希望报道简单的酮丙酮对甘氨酸甲酯的R-氨基碳的去质子化的非常有效的催化作用，这是由于亚胺离子加合物IH+（pKCH）14）的碳去质子化的酸度常数KCH比N-质子化的甘氨酸甲酯GH+（pKCH）21）的大107倍。碳酸的催化去质子化是一个有争议和非常感兴趣的主题。1酶催化的R-氨基酸的碳去质子化的速率加速主要是氨基酸烯醇（酯）相对于非常弱的母体碳酸稳定的结果。1.甘氨酸阴离子H_2NCH_2CO_2 ~-的R质子的酸性增加约10%。1012-通过N-质子化和O-甲基化（O-质子化的模型）的组合作用，将反应进行10倍，得到+H3 NCH 2CO 2 Me（GH+）。2，3众所周知，R-氨基酸与复合酶辅因子磷酸吡哆醛形成加合物导致R-氨基碳的酸度大幅增加。4我们现在表明，R-氨基酸酯的碳酸度通过形成
We wish to report extraordinarily efficient catalysis of deprotonation of the R-amino carbon of glycine methyl ester by the simple ketone acetone that is the result of a 107-fold larger acidity constant KCH for carbon deprotonation of the iminium ion adduct IH+(pKCH) 14) than for deprotonation of N-protonated glycine methyl ester GH+(pKCH) 21).The mechanism for enzyme-catalyzed deprotonation of carbon acids is a subject of some controversy and much interest. 1 The bulk of the rate acceleration for enzyme-catalyzed carbon deprotonation of R-amino acids is the result of stabilization of the amino acid enol (ate) relative to the very weak parent carbon acid. 1 We have shown that the acidity of the R-proton of glycine anion H2NCH2CO2-is increased ca. 1012-fold by the combined effects of N-protonation and O-methylation (a model for O-protonation) to give+ H3NCH2CO2Me (GH+). 2, 3 It is well-known that formation of adducts of R-amino acids to the complex enzyme cofactor pyridoxal phosphate results in a large increase in the acidity of the R-amino carbon. 4 We now show that the carbon acidity of an R-amino acid ester is increased dramatically by formation of the