| 摘要: | 醣鍵結反應一直在醣化學當中位居重要的地位，化學家多年來致力於發展出可以有效製備多醣的方法。而如今如何合成出純度好、產率高且能夠有效控制其產物立體選擇性的策略是正在面臨的困境。
近年來，有許多研究團隊發現，當 C-3、C-4、C-6 上利用酯基基團保護時能得到大量特定的立體選擇性產物，其中透過應用於特定醣體之位向上，可以得到傾向生成 1,2-順式醣苷鍵的結果。經過研究顯示認為是因遠端參與效應而得此結果，但由於遠端參與效應如何去影響反應的生成以及對於反應的影響程度不明確，許多研究團隊利用光譜學、理論計算與實驗操作等方法，試圖釐清遠端參與效應的發生與成果卻仍存在著爭議，無法對遠端參與效應有統一的論述，也因此無法廣泛利用遠端參與效應於合成多醣上。
而在本文研究當中先選用 C-3、C-4、C-6 上利用苯甲醯基保護之葡萄糖醣予體進行醣鍵結反應，並將其實驗結果帶入本實驗室建立的預測性模型，以系統性分析的角度觀察醣鍵結反應後產物之立體選擇性，實驗流程概括四個部分，製備苯甲醯基與其衍生物之葡萄糖醣予體以及葡萄糖醣受體、測量醣予體之反應性 (RRV) 與受體之反應性 (Aka)、進行醣鍵結反應、將其結果帶入模型分析。
且通過與本實驗室先前的例子，C-3、C-4、C-6 上分別以乙醯基基團保護的葡萄糖醣予體與不同型態之葡萄糖醣受體和甲醇進行醣鍵結反應的結果進行比較。鑒於先前的研究只針對葡萄糖醣受體與甲醇作為受體反應，因此在本文實驗中選用更多不同型態的受體進行醣鍵結反應，期望能更加全面的探討受體帶來的影響外，更加以透過於 C-6 上保護使用苯甲醯基衍生物之葡萄糖醣予體進行醣鍵結反應，以利用不同位置進行保護以及使用不同保護基團的角度，探討遠端參與效應於反應中對產物之立體選擇性的影響以及其影響程度。;In the realm of glycoscience, the synthesis of polysaccharides stands as a critical endeavor, necessitating the attainment of high purity, optimal yield, and precise stereoselectivity. While the construction protocols of 1,2-trans linkages rely on neighboring group effect, there is no straightforward solution for the formation of 1,2-cis glycosidic bonds.
Recent investigations have underscored the strategic introduction of C-3, C-4, C-6 ester groups on various glycosyl donors as a way to facilitate the formation of 1,2-cis glycosidic linkages, attributed to the remote participation. However, the elucidation of the mechanism and impact of the remote participation remains enigmatic, prompting dispute within the scientific community. Employing an array of analytical techniques including NMR (Nuclear Magnetic Resonance), IR (Infrared Spectroscopy), and theoretical calculations researcher have strived to unravel the intricacies of remote participation, yet consensus remains elusive, impeding its practical application in polysaccharide synthesis.
In this study, we present our investigation into the utilization of benzoyl group-modified glucosyl donors in glycosylation reactions with various acceptors, leveraging a predictive model developed in our laboratory to analyze stereoselectivity. Through meticulous experimentation, we assessed the occurrence of remote participation and compared the outcomes with those obtained using glucosyl donors bearing acetyl groups at corresponding positions.
Furthermore, we scrutinized the impact of benzoyl group derivatives in the glycosylation processes, enriching our understanding the role of remote participation.
Our workflow encompassed the synthesis of glucose acceptors and donors bearing benzoyl group substituents, carried out glycosylation reactions, a systematic evaluation of stereoselectivity and remote participation effect. The findings underscore the potential of remote participation in directing glycosylation outcomes and shed light on the modulatory influence of benzoyl group substituents on glycosylation stereochemistry. |
