p-Nitrobenzyl Protection for Cysteine and Selenocysteine: A More Stable Alternative to the Acetamidomethyl Group
p-Nitrobenzyl Protection for Cysteine and Selenocysteine: A More Stable Alternative to the Acetamidomethyl Group
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DOI：
10.1002/bip.21502
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发表时间：
2010-01-01
期刊：
影响因子：
2.9
通讯作者：
Alewood, Paul F.
中科院分区：
文献类型：
--
作者：
Muttenthaler, Markus;Ramos, Yesica Garcia;Alewood, Paul F.
研究了在叔丁氧羰基（Boc）化学固相合成催产素（OT）的过程中，乙酰氨基甲基（Acm）、三甲基乙酰氨基甲基（Tacm）和对硝基苄基（pNB）作为半胱氨酸和硒代半胱氨酸（Sec）保护基的酸不稳定性。本研究开发了两种新型的Sec结构单元（N-α-叔丁氧羰基-Se（乙酰胺基甲基）-L-硒代半胱氨酸（Boc-L-Sec（Acm）-OH）和N-α-叔丁氧羰基-S（4-硝基苄基）-L-硒代半胱氨酸（Boc-L-Sec（pNB）-OH））。合成六种部分保护的硫代和硒代OT类似物，纯化，并在25、40、50和60 ℃的温度下暴露于纯三氟乙酸（TFA）1小时，并在0 ℃下暴露于HF处理1小时。在大于25 ℃的温度下和在0 ℃的HF处理期间，观察到Acm和Tacm组在TFA中的显著损失，而pNB组保持完整。通过在溶液中用乙酸中的锌还原成对氨基苄基或通过在固体载体上的盐酸中的氯化锡还原成对氨基苄基，然后用碘氧化裂解，产生相应的二硫键或二硒键，实现pNB的去除。未观察到重大副反应。该研究证实了偶尔描述的Acm不稳定性，并支持pNB基团作为半胱氨酸和Sec保护的替代物的发展。(C)2010 Wiley Periodicals，Inc. Biopolymers（Pept Sci）94：423-432，2010.
This study evaluated the acidic lability of the acetamidomethyl (A cm), trimethylacetamidomethyl (Tacm), and the p-nitrobenzyl (pNB) as protecting groups for cysteine and selenocysteine (Sec) during the tert-butyloxycarbonyl (Boc)-chemistry solid-phase peptide synthesis of oxytocin (OT). Two novel Sec building blocks (N-alpha-tert-butyloxycarbonyl-Se(acetamidomethyl)-L-selenocysteine (Boc-L-Sec(Acm)-OH) and N-alpha-tert-butyloxycarbonyl-S(4-nitrobenzyl)-L-selenocysteine (Boc-L-Sec(pNB)-OH)) were developed for this study. Six partially protected thio- and seleno-OT analogues were synthesized, purified, and exposed to neat trifluoroacetic acid (TFA) at temperatures of 25, 40, 50, and 60 degrees C for 1 h, and HF treatment at 0 degrees C for 1 h. Significant losses were observed for the Acm and Tacm group in TFA at temperatures greater than 25 degrees C and during HF treatment at 0 degrees C, whereas the pNB group remained intact. Removal of the pNB was achieved via reduction to the p-aminobenzyl group either with zinc in acetic acid in solution or via tin chloride in hydrochloric acid on solid support, followed by oxidative cleavage with iodine yielding the corresponding disulfide or diselenide bond. No major side reactions were observed. This study confirms the occasionally described Acm instability and underpins the development of the pNB group as an alternative for cysteine and Sec protection. (C) 2010 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 94: 423-432, 2010.