Removal of t-butyl and t-butoxycarbonyl protecting groups with trifluoroacetic acid. Mechanisms, biproduct formation and evaluation of scavengers.
Removal of t-butyl and t-butoxycarbonyl protecting groups with trifluoroacetic acid. Mechanisms, biproduct formation and evaluation of scavengers.
复制标题
用三氟乙酸除去叔丁基和叔丁氧羰基保护基。
DOI：
10.1111/j.1399-3011.1978.tb02896.x
复制
发表时间：
2009
期刊：
影响因子：
--
通讯作者：
J. Markussen
中科院分区：
文献类型：
--
作者：
B. Lundt;N. L. Johansen;A. Vølund;J. Markussen
三氟乙酸介导的去除受保护氨基酸中的t-丁基导致形成三氟乙酸t-丁基。这种t-丁基酯在三氟乙酸、蛋氨酸和色氨酸中发生烷基化。常用的t-丁基阳离子清除剂可以破坏三氟乙酸t-丁酯，并以清除剂与酯的反应速率作为评价清除剂的依据。具有硫化物结构的清除剂与三氟乙酸丁酯反应生成具有烷基化性质的磺化化合物。在酸解过程中，在有清除剂存在的情况下，三氟乙酸和清除剂将与t-丁基阳离子竞争反应。动力学研究表明，与噻吩作为清除剂的反应速率相当。在三氟乙酸中加入清除剂在解封反应中的作用是由于除了去除t-丁基阳离子外，还可以去除三氟乙酸t-丁基。异丁烯与三氟乙酸反应生成三氟乙酸丁酯。在室温下，反应达到有利于酯的平衡。因此，在三氟乙酸的解封反应中，不可能有异丁烯逸出。
The trifluoroacetic acid-mediated removal of t-butyl groups in protected amino acids leads to the formation of t-butyl trifluoroacetate. This t-butyl ester alkylates in trifluoroacetic acid methionine and tryptophan. The t-butyl trifluoroacetate ester can be destroyed by scavengers commonly employed for t-butyl cations, and the reaction rates of the scavengers with the ester are used in the evaluation of scavengers. Scavengers of sulphide structure react with t-butyl trifluoroacetate to form sulphonium compounds, which possess alkylating properties. In the presence of a scavenger during acidolysis, the trifluoroacetic acid and the scavenger will compete in reacting with the t-butyl cations. Kinetic studies show comparable reaction rates with thiophenol as scavenger. The usefulness of adding scavengers to trifluoroacetic acid in deblocking reactions is due to the removal of t-butyl trifluoroacetate in addition to the removal of t-butyl cations. Isobutene reacts with trifluoroacetic acid and yields t-butyl trifluoroacetate. The reaction reaches an equilibrium displaced in favour of the ester at room temperature. Hence no isobutene can be expected to escape during a deblocking reaction in trifluoroacetic acid.