Successful manual synthesis of the TD2.2 peptide acting as a blood–brain barrier shuttle was achieved. TD2.2 was successfully synthesised by sequential condensation of four protected peptide fragments on solid-phase settings, after several unsuccessful attempts using the stepwise approach. These fragments were chosen to minimise the number of demanding amino acids (in terms of coupling, Fmoc removal) in each fragment that are expected to hamper the overall synthetic process. Thus, the hydrophobic amino acids as well as Arg(Pbf) were strategically spread over multiple fragments rather than having them congested in one fragment. This study shows how a peptide that shows big challenges in the synthesis using the common stepwise elongation methodology can be synthesised with an acceptable purity. It also emphasises that choosing the right fragment with certain amino acid constituents is key for a successful synthesis. It is worth highlighting that lower amounts of reagents were required to synthesise the final peptide with an identical purity to that obtained by the automatic synthesiser.

中文翻译：

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在固相树脂上通过片段缩合方法成功合成神经胶质特异性血脑屏障穿梭肽

实现了作为血脑屏障穿梭器的 TD2.2 肽的成功人工合成。在使用逐步方法进行了几次不成功的尝试后，通过在固相设置上连续缩合四个受保护的肽片段成功合成了 TD2.2。选择这些片段是为了最大限度地减少每个片段中预计会阻碍整个合成过程的要求氨基酸（在偶联、Fmoc 去除方面）的数量。因此，疏水性氨基酸以及 Arg(Pbf) 战略性地分布在多个片段上，而不是让它们拥挤在一个片段中。本研究展示了如何合成具有可接受纯度的肽，该肽在使用常见逐步延伸方法的合成中显示出巨大挑战。它还强调选择具有特定氨基酸成分的正确片段是成功合成的关键。值得强调的是，合成与自动合成仪获得的纯度相同的最终肽所需的试剂量较少。