合成硫酸化N-乙醯乳醣胺及其衍生物以用於半乳醣凝集素結合專一性之研究

半乳醣凝集素(galectin)是一種可以與beta-半乳醣苷有良好作用力的醣接合蛋白(carbohydrate-binding protein)。依照其醣辨識區(carbohydrate recognition domain, CRD)的型態以及從1974年以來發現的先後順序可以分成15種。近期的研究與臨床報導指出，半乳醣凝集素與許多須藉由辨識/辨認細胞表面醣類的生物現象有關，如免疫反應、細胞分化、細胞凋亡、個體發生、癌症轉移等。不過其詳細的作用機制及確切的功能還有待進一步研究。半乳醣凝集素在自然界中的配基大多是含有半乳醣結構的醣類或醣蛋白，其中以乳醣(lactose)或N-乙醯乳醣胺(N-acetyllactosamine)為佳。本實驗室與合作夥伴中研院基因體中心林國儀實驗室分別利用AlphaScreenTM與醣晶片為工具，進行半乳醣凝集素對資料庫中不同的醣類作結合能力測試發現：硫酸化N-乙醯乳醣胺及其衍生物對半乳醣凝集素的結合能力有顯著提升。這個初步結果提示了我們合成此類化合物的可能性。本篇論文的主題為合成Gal-beta(1-3)GlcNAc (type I)、Gal-beta(1-4)GlcNAc (type II)雙醣骨架，並在這些雙醣的6、6’、3’位置置換成硫酸根基團，試圖建立起一個小型、有規則的分子庫以提供更有系統的醣類-半乳醣凝集素結合能力測試。合成此類化合物將涉及有機醣化學合成中：(1) 醣予體(glycosyl acceptor)/醣受體(glycosyl donor)單元的設計與合成；(2) 醣苷鍵(glycosidic bond)的建立；(3) 如何選擇不會互相影響的醇類及胺類保護基；(4) 最佳化保護/去保護條件；(5) 選擇性在醣類一級醇或二級醇的硫酸化。配合各種光譜證據，以上合成已有了初步的成果。這類化合物在生物活性測試中發現可以抑止B淋巴細胞分化成分泌抗體的漿細胞，間接證明了半乳醣凝集素在B淋巴細胞分化過程中扮演了重要的角色。

關鍵字

硫酸化； N-乙醯乳醣胺；醣合成；半乳醣凝集素； B淋巴細胞分化

並列摘要

Galectins are a family of beta-galactoside-binding proteins that share significant sequence similarity in their carbohydrate-recognition domains (CRDs). So far fifteen galectins have been identified and categorized into three subgroups according to the type of CRDs. Accumulating evidence shows that galectins are related to numerous biological functions and corresponding diseases, such as immune responses, inflammation, cell apotosis, animal development and tumor progression. However, the function of galectins and the underlying mechanisms still remain unclear and need further investigations. In this thesis, a series of N-acetyllactosamine (LacNAc) sulfates and their analogues were synthesized. The critical reactions included protecting group manipulation, chemical glycosylation, and selective sulfation at a specific hydroxyl group. Different orthogonal protecting groups were introduced during the preparation of the building block synthesis to achieve the assembly of beta(1-3) or beta(1-4) glycosidic linkage, as well as selective sulfation at 3- or 6- position of Gal and 6-position of GlcNAc. Trichloroactaimidate and NIS/TfOH methods were studied for glycosylation with desired stereoselectivity and moderate yields. The final products were further studied for their binding specificity to galectins by AlphaScreenTM and immune assay. The preliminary results indicated that these compounds could impede B cell differentiation to antibody-secreting plasma cell, supporting the important role of galectin-glycan interaction.

並列關鍵字

sulfation ； N-acetyllactosamine ； carbohydrate synthesis ； galectins ； B cell differentiation

參考文獻

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合成硫酸化N-乙醯乳醣胺及其衍生物以用於半乳醣凝集素結合專一性之研究

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