Trimethylsilyl bromide (TMSBr) in trifluoroacetic acid (TFA) was found to have the ability to cleave benzyl-type protecting groups, i.e., benzyloxycarbonyl (Z), benzyl (O-Bzl) and p-methoxybenzyl (S-MBzl). The reaction was best accelerated by addition of thioanisole, compared with other soft nucleophiles so far examined. The rate of the cleavage reaction with TMSBr/TFA was judged to be somewhat slower than that with trimethylsilyl trifluoromethanesulfonate/TFA. However, TMSBr/TFA reduced Met (O) efficiently and gave almost no side reaction of Asp (succinimide formation). This deprotecting procedure was applied to the synthesis of human gastrin-releasing peptide.
研究发现,
三氟乙酸(TFA)中的三甲基
溴化
硅(TMSBr)能够裂解苄基保护基,即苄氧羰基(Z)、苄基(O-Bzl)和对甲氧基苄基(S-MBzl)。与迄今研究的其他软亲核试剂相比,添加
硫代
苯甲醚能够最好地加速反应。TMSBr/TFA的裂解反应速度被认为比三甲基
硅基
三氟甲磺酸酯/TFA的裂解反应速度稍慢。然而,TMSBr/TFA能够有效还原Met(O),并且几乎没有Asp(琥珀
酰亚胺形成)的副反应。这种脱保护程序被应用于人类胃泌素释放肽的合成。