Rüegg U T, Jarvis D, Rudinger J
Biochem J. 1979 Apr 1;179(1):127-34. doi: 10.1042/bj1790127.
S-2-Sulphobenzylcysteine and S-2-(sulphomethyl)benzylcysteine are prepared by alkylation of cysteine with omega-toluenesultone and 2,3-benzo-1,4-butanesultone respectively. Owing to the presence of the sulphonic acid group, these protected cysteine derivatives are extremely water-soluble and are stable to acid hydrolysis. The groups can be removed by treatment with sodium in liquid NH3. Reduction with tributylphosphine and simultaneous alkylation of insulin with toluenesultone under mild conditions (pH 8.3, aq. 50% propanol) gives the fully S-substituted derivatives in excellent yield; they can be separated by isoelectric precipitation of the S-sulphobenzylated B-chain. Treatment of the latter with sodium in liquid NH3 led simultaneously to the removal of the protecting groups and to the well-documented cleavage at the threonine-proline bond which can be prevented by addition of sodium amide. When deprotected A-chain was recombined with B-chain, insulin was isolated in the same yield and with the same degree of biological activity as that in the control experiment.
S - 2 - 磺苄基半胱氨酸和S - 2 - （磺甲基）苄基半胱氨酸分别通过半胱氨酸与ω - 甲苯磺内酯和2,3 - 苯并 - 1,4 - 丁烷磺内酯的烷基化反应制备。由于磺酸基团的存在，这些受保护的半胱氨酸衍生物极易溶于水且对酸水解稳定。这些基团可用液氨中的钠处理除去。在温和条件下（pH 8.3，50% 丙醇水溶液）用三丁基膦还原并同时使胰岛素与甲苯磺内酯烷基化，可得到产率极高的完全S - 取代衍生物；它们可通过S - 磺苄基化B链的等电沉淀分离。用液氨中的钠处理后者会同时导致保护基团的去除以及在苏氨酸 - 脯氨酸键处发生已充分记录的裂解，而添加氨基钠可防止这种裂解。当脱保护的A链与B链重新组合时，分离得到的胰岛素产率和生物活性程度与对照实验相同。
