以醣為模板的分子內矽基酮自由基環化反應之研究

Abstract

在本論文當中，以具有高單一對掌性之醣分子為模板，以不會改變分子上的立體中心之合成步驟，將還原端轉化成矽基酮官能基，非還原端轉成溴基，其它之二級烴基皆保護成醚類，製備出自由基環合前驅物矽基酮，並完成了自由基環化。一開始以先前尚未被研究之五碳醣-木醛糖為起始物，運用不同的保護基合成了矽基酮，完成五員環之自由基環合反應；接下來利用相同合成路徑，分別以葡萄糖、甘露糖兩種六碳醣為模板，順利的合成自由基環合前驅物，並完成了六員環之自由基環合，這是首次將矽基酮的自由基化學應用在六碳醣之環合反應上，但是六員環的自由基環合效率並不是很理想，除了環化速率較五員環化為慢之外，分子內1,5-氫轉移亦是應注意的競爭反應；接下來，結合之前的研究結果，我們討論了在不同醣分子上之取代基立體位向的不同，對於自由基環合前驅物的製備以及自由基環化中間體抓氫位向的影響，並利用重氘三丁基錫烷做為自由基環化試劑，證明了在核糖體系中分子內氫轉移。最後，我們以來蘇糖做為起始物進行自由基環化所得到之五員環產物為先趨研究，利用官能基轉換，將多羥五碳環轉換成具有潛在生理活性之生物鹼。

In this thesis, we described the synthesis of four kinds of acylsilanes that are derived from xylose, mannose, and glucose. Our method conserved the orginal stereochemistry of carbohydrate molecules in this route. The reducing ends were converted to an acylsilane functionality whereas the non-reducing ends were transformed into a halide. All the secondary hydroxyl groups were protected as ethers. By using these carbohydrate-derived acylsilanes, the radical cyclizations were accomplished. It is the first case about radical cyclizations of acylsilanes using hexoses as templates. However, the cyclization efficiencies are not as good as the pentose system. Combined with previous research, we disscussed the influence of the substituents on the stereoselectivity of radical cyclizations. Finally, to demonstrate the synthetic utility of our synthetic method, one of the polyhydroxylated cyclopentanes was converted to an amino sugar mimics that may exhibit useful biological activities.