N-连接糖基化是一种非常重要的蛋白质翻译后修饰过程，对维持蛋白和多肽的结构和功能有重要意义，获得高纯度、均一结构糖蛋白是进行相关基础研究和药化应用的一个关键问题。目前均一结构的N-连接糖蛋白很难通过生物技术来有效获取，而高效地化学合成的方法仍然有限。针对此问题，本项目拟在我们前期工作基础上，继续发展高效多片段连接的方法学和策略，通过收敛法合成均一结构的复杂N-连接糖蛋白。主要研究内容为：（1）发展基于分子内N到S酰基迁移合成多肽硫酯的方法；（2）应用选择性光化学脱硫反应以拓展自然化学连接策略；（3）发展基于活泼酯胺解反应的收敛法以合成均一结构N-连接糖肽；（4）综合运用新发展的的方法学和策略，合成均一结构的重要糖蛋白，即白细胞介素IL-3和IL-5，并研究其构效关系。本项目工作将为高效化学合成均一结构的复杂糖蛋白提供新方法和新策略，为研究和应用糖蛋白的生物医药功能提供有效化学工具。

N-Linked glycosylation is regarded as a kind of important post-translational modification for many proteins，and has significant influences on the structural properties and biomedical functions of proteins and peptides. Thus, it is essential obtain high quality, structure-defined glycoproteins for the basic research and biochemical applications. However, it is very difficult obtain enough homogenous N-linked glycoproteins via biological methods, and the chemical methods are also very limited. Regarding to this challenge and on the basis of our previous study, we plan to develop the methodologies and strategies of multi-fragment ligation, and synthesize structure-defined complex N-linked glycoproteins using convergent strategy.. The main contents of this research proposal are listed as the following: (1) to develop intramolecular N-to-S acyl shift to synthesize thioester of C-terminal peptide; (2) to apply visible-light-induced specific desulfurization to expand the scope of native chemical ligations; (3) to develop aminolysis of active ester for convergent synthesis of homogeneous N-linked glycopeptides; (4) to synthesize structure-defined important glycoproteins - interleukin-3 & interleukin-5 using our new methodologies and strategies, and study the relations between their structures and functions. The work of this proposal will provide new methodologies and strategies to synthesize structure-defined complex glycoproteins, and provide useful chemical tools for the study and application of glycoproteins' biomedical functions.