The Fukuyama–Mitsunobu alkylation procedure is widely used to introduce alkyl substituents to amino groups in general and N-alkylation of peptides in particular. Here we have investigated the procedure in detail for N-alkylation of peptides with N-terminal glycine residues, based on the observation that standard conditions lead to substantial bis-nosylation of the glycine amino group. A systematic evaluation of this observation was carried out and it was demonstrated that for peptides with alanine, β-alanine or γ-aminobutyric acid (GABA) as N-terminal residues mono-nosylation was observed under the same conditions. Moreover, bis-nosylation was independent of the type of resin, neighboring amino acid and nature of the peptide. Calculations suggest that the reason for the bis-nosylation is the fact that the deprotonated mono-nosyl species is particularly stable in the case of the terminal Gly residue because the N− residue can become closer to the SO2 unit. Finally, the mono-nosylated N-terminal glycine could be obtained by careful optimization of the procedure, adding only one equivalent of 2-nitrobenzenesulfonyl chloride.
Fukuyama-Mitsunobu 烷基化程序被广泛用于在
氨基上引入烷基取代基,特别是肽的 N-烷基化。在此,我们根据标准条件会导致甘
氨酸
氨基发生大量双烷基化的观察结果,详细研究了该程序对具有 N 端甘
氨酸残基的肽进行 N- 烷基化的过程。我们对这一观察结果进行了系统评估,结果表明,在相同条件下,以丙
氨酸、
β-丙氨酸或γ-
氨基
丁酸(
GABA)为 N 端残基的肽也会发生单烷基化。此外,
双糖基化与
树脂类型、邻近
氨基酸和肽的性质无关。计算结果表明,
双糖基化的原因是,在末端 Gly 残基的情况下,去质子化的
单糖基物种特别稳定,因为 N-残基可以变得更接近 SO2 单元。最后,通过仔细优化程序,只加入一个当量的
2-硝基苯磺酰氯,就可以得到单 Nosyl 化的 N 端甘
氨酸。