Amino-acids and peptides. Part XXV. The mechanism of the base-catalysed racemisation of the p-nitrophenyl esters of acylpeptides
作者:I. Antonovics、G. T. Young
DOI:10.1039/j39670000595
日期:——
“direct exchange” mechanism of racemisation and that through the oxazolone, and it is concluded that such racemisation proceeds through the intermediate formation, racemisation, and coupling of the corresponding oxazolone. Evidence is also given that the conversion of benzyloxycarbonylglycyl-L-phenylalanine into its p-nitrophenyl ester by means of diphenyl-keten is accompanied by racemisation.
的p苯甲酰基和苄氧羰基甘氨酰的硝基苯基酯大号-苯丙氨酸由三乙胺在二氯甲烷中速度远远超过是苄氧羰基和邻苯二甲酰基的类似酯外消旋大号-苯丙氨酸。结果表明,酰基肽酯与三乙胺可逆地反应,生成相应的恶唑酮,该平衡极大地有利于该酯。通过加入大量过量的苄氧羰基缩水甘油基苯丙氨酸衍生的恶唑酮,抑制了三乙胺对苯甲酰基缩水甘油基-L-苯丙氨酸对硝基苯酯的消旋作用,建议立即与p-硝基苯氧根阴离子,因此可防止形成外消旋酯的逆反应。该实验清楚地区分了外消旋的“直接交换”机理和通过恶唑酮的机理,得出的结论是,这种消旋通过相应的恶唑酮的中间体形成,消旋和偶联而进行。也有证据表明,通过二苯基-酮将苄氧羰基甘氨酰基-L-苯丙氨酸转化成其对硝基苯酯伴随着消旋作用。