(1)硫醣予體和添加劑二甲基甲醯胺及其衍伸物的a選擇性醣基化反應(2)二號位置的醚類保護基在腈類溶劑中的鄰基作用及其應用在a(1-5)阿拉巴醣寡糖上

Abstract

Part Ι.葡萄醣胺硫醣予體 (thioglucopyranoside donor)在二甲基甲醯胺 (Dimethylformamide,DMF) 媒介的醣基化反應中得到一個普通的a選擇性結果，但是伴隨著低產率和冗長的反應時間等缺點。為了尋求一個更好的添加劑取代二甲基甲醯胺 ，我們使用理論計算的方式分析雜原子在二甲基醯胺以及其衍伸物的電子密度。研究結果顯示，1-甲基吡咯烷酮 (1-methyl-2-pyrrolidinone)是一種可能替代二甲基甲醯胺的添加劑，基於較良好的產率以及可接受的反應時間。 Part ΙΙ. 阿拉巴醣硫予體 (thioarabinosyl donor ) 在 C-2位置的醚類取代基在腈類混合溶劑系統中被觀察到有鄰基效應的作用並且導致良好的1,2 反式選擇性醣苷鍵。我們揭示了似里特(Ritter-like)的結合關係來自於在C -2位置醚類取代基中的氧原子與腈類溶劑作用導致一個1,2 順式的中間物。這個觀念的應用可以使我們衍伸至開發a(1-5) 阿拉巴醣寡糖的高效率合成。

Part Ι. A modest a-selectivity in DMF-mediated glycosylation with thioglucopyranoside donor was obtained, which was accompanied by some drawbacks such as low reaction yield and longed reaction time. To seek for a better substitution for DMF additive, we used the computational calculation to analyze the electron density of heteroatom of selected derivatives. The results revealed that 1-methyl-2-pyrrolidinone was a possible substitution for DMF owing to the good yield and acceptable reaction time. Part ΙΙ. The C-2 ether protecting function of thioarabinosyl donor in nitrile co-solvent mixture was found to play a participation role and led to a 1,2-trans selectivity . We reveal a Ritter-like association of the oxygen atom in the C-2 ether function with the entrapped nitrile molecule, when they are configured in cis orientation. Application of this concept enables us to develop efficient strategy for the preparation of linear a(1-5) arabinan oligomers.