Kinetics of Amide Formation through Carbodiimide/<i>N-</i>Hydroxybenzotriazole (HOBt) Couplings
作者:Lai C. Chan、Brian G. Cox
DOI:10.1021/jo701558y
日期:2007.11.1
similar rate constants measured in water. The subsequent catalytic cycle, involving reaction of O-acylisourea with HOBt to give HOBt ester, which then reacts with the amine to give the amide with regeneration of HOBt, determines the product distribution. In the case of the amino acid, 3, reaction of the O-acylisourea with MIPE to give amide, 4, is increasingly favored at higher pH values over that with the
形成酰胺,的动力学4通过与异丙酯甲硫氨酸(MIPE)的,通过碳二亚胺EDCI,介导的反应,从相应的羧酸1,和HOBt,2,都在1-甲基-2-吡咯烷酮进行了研究( NMP),使用反应量热法。已经发现反应速率与HOBt的浓度无关,这表明确定速率的步骤是羧酸与EDCI之间的反应,得到相应的O-酰化脲。pH依赖性的O-酰基尿素形成速率常数与双质子化EDCI(EDCIH 2 2 +,6)和羧酸根基团。观察到的速率常数在高pH下急剧下降,因为EDCI占EDCIH 2 2+的比例继续大幅下降,而羧酸基团已被完全电离。速率常数,ķ P,对于羧酸酯基酸之间的反应3,和EDCIH 2 2+具有的值ķ P = 4.1×10 4中号- 1个小号- 1在20℃下,约10 5倍以上比在水中测得的类似速率常数要大。随后的催化循环,涉及O的反应用HOBt生成酰化脲,生成HOBt酯,然后与胺反应生成酰胺,并随HOBt的再生