以連續性正交錯保護方法合成含甘露醣之分支寡醣

Abstract

N-聚醣在生物體中扮演所多重要的角色，如免疫、細菌與病毒的感染、癌細胞轉移等生理反應。由於N-聚醣結構上複雜的鍵結分支和醣體非還原端上的特殊修飾(硫酸根和唾液酸)，這些特點對醣類化學合成無一不是巨大的挑戰。因此發展一個通用且多用途的合成策略並可應用於大部分的N-聚醣是有不可或缺的必要性。 而本論文的目標是合成由核心三甘露醣體透過β1-6鍵結延伸兩個N-乙醯乳醣胺的雙分支的N-聚醣，並且在非還原端引入硫酸根和岩藻糖的修飾。在開發的過程中我們完成：(1) 發展連續性保護基策略並串聯醣基化反應，藉由此策略可快速完成具有正交錯保護的甘露醣單醣構築體和多樣的醣受體；(2) 而具有正交錯保護的甘露醣構築體，可以幫助我們使用最少的單醣體，即可合成多種不同鍵結的直線型三醣體30, 37或是分支型結構的三醣26, 40, 或五醣體28；(3) 成功結合具有正交錯保護的雙醣醣予體和三醣醣受體進行[2+3+2] 醣基化反應，完成所需的七醣體46；(4) 於七醣體中選擇性的引入修飾硫酸根基團，完成具有硫酸根修飾的七醣體；利用酵素合成的方式，以減少合成步驟和反應時間，進行選擇性的岩藻醣化反應，合成具有岩藻醣修飾的九醣體。 而所合成最終的產物可用於半乳糖凝集素-7的結合力測試，用以探討醣體上: (1)直線與分支結構;(2)醣體還原端上的修飾，如硫酸化和岩藻醣化對於半乳糖對於結合力的影響性。

N-Glycans play an important role in numerous biological activities, such as immunity, pathogen-host interaction and cancer metastasis. Their syntheses represent a great challenge in a carbohydrate chemistry because the structures of N-glycans are often complicated by the presence of branching structures and various modifications in the non-reducing termini (e.g. sulfation, fucosylation and sialylation). It is thus indispensible to develop a simple but versatile approach that is applicable to the preparation of most N-glycans. This thesis aims at the synthesis of biatennary N-acetyl lactosamine attached to the trimammose core via β1-6 linkage, and futher introduction of sulfate group and L-fucose residues to the non-reducing end. We developed a facile method to prepare orthogonally protected mannose building blocks, make it to carry out consecutive protection/glycosylation steps with high overall yields without the necessity of purification of products. This developed procedure led to the formation of linear/branched tri -(26, 30, 37 and 40), penta-(28) and heptasaccharides (46). Further deprotection, sulfation and/or enzymatic fucosylation steps led to formation of several hepta- and nonasaccharides that were subjected to the binding assay of human galectin-7.With these saccharides available, we are able to address important features of galectin-7 binding affinity, such as linear and branched structures, the effect of sulfation or fucosylation.