Staudinger Ligation of Peptides at Non-Glycyl Residues
作者:Matthew B. Soellner、Annie Tam、Ronald T. Raines
DOI:10.1021/jo0620056
日期:2006.12.1
The Staudinger ligation provides a means to form an amide bond between a phosphinothioester and azide. This reaction holds promise for the ligation of peptides en route to the total chemical synthesis of proteins. (Diphenylphosphino) methanethiol is the most efficacious of known reagents for mediating the Staudinger ligation of peptides, providing high (> 90%) isolated yields for equimolar couplings in which a glycine residue is at the nascent junction. Surprisingly, the yields are lower (< 50%) for non-glycyl couplings due to an aza-Wittig reaction that diverts the reaction toward a phosphonamide byproduct. Here, the partitioning of the reaction toward Staudinger ligation (and away from the aza-Wittig reaction) is shown to increase with increasing electron density on phosphorus. This electron density can be tuned either by installing functional groups on the phenyl substituents of (diphenylphosphino) methanethiol or by changing the polarity of the solvent. Installing p-methoxy groups and using a solvent of low polarity (such as toluene or dioxane) provide especially high (> 80%) isolated yields for the ligation of two non-glycyl residues. These conditions retain the high chemoselectivity of the reaction and do not lead to a substantial change in reaction rate. The traceless Staudinger ligation is now poised to enable the iterative ligation of peptides with little regard for their sequence, as well as the synthesis of amide bonds for other purposes.
Electronic and steric effects on the rate of the traceless Staudinger ligation
作者:Annie Tam、Matthew B. Soellner、Ronald T. Raines
DOI:10.1039/b802336k
日期:——
Interplay between electronic effects imparted by phosphinothiol substituents and steric effects imposed by amino-acid reactants affects the rate of the tracelessStaudingerligation of peptides in a predictable manner.
Reaction Mechanism and Kinetics of the Traceless Staudinger Ligation
作者:Matthew B. Soellner、Bradley L. Nilsson、Ronald T. Raines
DOI:10.1021/ja060484k
日期:2006.7.1
in the Staudingerligation of glycyl residues mediated by (diphenylphosphino)methanethiol was the formation of the initial phosphazide intermediate. Less efficacious coupling reagents and reaction conditions led to the accumulation of an amine byproduct (which resulted from a Staudinger reduction) or phosphonamide byproduct (which resulted from an aza-Wittig reaction). The Staudingerligation mediated
无痕施陶丁格连接能够在硫代膦酸酯(或膦酸酯)和叠氮化物之间形成酰胺键,而不会掺入残留原子。在这里,详细表征了通过该反应进行的肽偶联。[(18)O]H(2)O 的实验表明,由(二苯基膦基)甲硫醇介导的反应是通过亚氨基膦中间体的 S-->N 酰基转移以形成氨基鏻盐,而不是通过氮杂-维蒂希反应进行的然后水解所得的硫代亚氨酸盐。基于连续 (13) C NMR 的测定表明,由(二苯基膦基)甲硫醇介导的甘氨酰残基 Staudinger 连接中的决定速率步骤是初始磷酰化物中间体的形成。不太有效的偶联试剂和反应条件导致胺副产物(由施陶丁格还原产生)或膦酰胺副产物(由氮杂-维蒂希反应产生)的积累。由(二苯基膦基)甲硫醇介导的施陶丁格结扎以二级速率常数(7.7 x 10(-3)M(-1)s(-1))和产量(95%)进行,通过添加外源性亲核试剂。由膦醇介导的连接具有较低的速率常数或较低的化学选择性。因此,(二苯