Transesterification and amide cis–trans isomerization in Zn and Cd complexes of the chelating amino acid ligand Boc–Asp(Dpa)–OBzl
作者:Nicole Niklas、Achim Zahl、Ralf Alsfasser
DOI:10.1039/b611873a
日期:——
significantly more reactive than the cadmium complex (k=(1.41+/-0.03)x10(-6) s-1). In order to study their tertiary amide cis-trans isomerization, the cadmium complex [(-OCH3)Cd(NO3)2] was synthesized, and the zinc complex [(-OCD3)Zn(NO3)2] was generated in situ in (CD3)2CO:CD3OD (3:1). The barriers to rotation were determined (:14.1 kcal mol-1 in CD3OD;: 13.4 kcal mol-1 in (CD3)2CO:CD3OD (3:1)). Our results
氨基酸衍生物Boc-Asp-OBzl(Boc = N-丁氧基羰基; Asp =天冬氨酸; Bzl =苄基)通过将其羧酸酯侧链偶联至二聚烯丙基胺而官能化。这产生了三齿氮供体配体Boc-Asp(Dpa)-OBzl(-OBzl)。化合物-OBzl包含三个不同的羰基:Asp和Dpa之间的叔酰胺键,C末端的苄基酯官能团和N末端的氨基甲酸酯保护基团。NMR光谱用于比较这些部分的反应性。Boc保护基产生两个异构体,(E,9%)和(Z,91%)。Cd(NO3)2和Zn(NO3)2的配位生成配合物和。与游离配体相比,这些化合物的绕叔酰胺CN键旋转的障碍显着减少(-CDz3中-OBzl:18.5 kcal mol-1;(CD3)2CO中12.9 kcal mol-1 ;: 13。8 kcal mol-1 in(CD3)2CO)。两种复合物都容易在甲醇或CD3OD中进行酯交换反应。实验伪准一级速率常数在CD3O