During the Fmoc-protection of H-alpha-Me-Val-OH, an unknown side product was found and isolated. The characterization using various analytical methods led unambiguously to the result that Fmoc-beta-Ala-OH was formed during the reaction. The reagent Fmoc-OSu was proven to be the source of Fmoc-beta-Ala-OH, following a mechanism that involved many deprotonation and elimination steps and a Lossen-type rearrangement as key sequence. The impurity Fmoc-beta-Ala-OH was found in a variety of reactions in which Fmoc-OSu was applied, either in the reaction mixture or as a contamination of the crude product. Purification of the Fmoc-amino acid derivatives from this impurity incurred high costs and significant reductions in yield.

中文翻译：

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在用Fmoc-OSu保护Fmoc的过程中形成Fmoc-β-丙氨酸。

在H-alpha-Me-Val-OH的Fmoc保护过程中，发现并分离出未知的副产物。使用各种分析方法进行的表征明确地导致了在反应过程中形成Fmoc-β-Ala-OH的结果。事实证明，试剂Fmoc-OSu是Fmoc-β-Ala-OH的来源，其机理涉及许多去质子化和消除步骤，以及以Lossen型重排为关键序列。在各种应用Fmoc-OSu的反应中都发现了Fmoc-β-Ala-OH杂质，无论是在反应混合物中还是对粗产物的污染。从该杂质中纯化Fmoc-氨基酸衍生物会导致高成本和产率的显着降低。