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Intramolecular aglycon delivery is a synthetic strategy for the construction of glycans. This methodology is generally applied to the formation of difficult glycosidic linkage. ==Introduction== Glycosylation reactions are very important reactions in carbohydrate chemistry leading to the synthesis of oligosaccharides, preferably in a stereoselective manner. The stereoselectivity of these reactions has been shown to be affected by both the nature and the configuration of the protecting group at C-2 on the glycosyl donor ring. While 1,2-trans-glycosides (e.g. alpha-mannosides and β-glucosides) can be synthesised easily in the presence of a participating group (such as OAc, or NHAc) at the C-2 position in the glycosyl donor ring, 1,2-cis-glycosides are more difficult to prepare. 1,2-cis-glycosides with the alpha configuration (e.g. glucosides or galactosides) can often be prepared using a non-participating protecting group (such as Bn, or All) at C-2 (OH). However, 1,2-cis-glycosides with the β configuration are the most difficult to achieve, and present the greatest challenge in glycosylation reactions. File:general information.gif One of the most recent approaches to prepare 1,2-cis-β-glycosides in a stereospecific manner is termed ‘Intramolecular Aglycon Delivery’, and various methods have been developed under this approach.〔Ian Cumpstey. Carbohydrate research, 343 (2008) 1553–1573〕 In this methodology, the glycosyl acceptor is tethered into the C-2-O-protecting group (X) in the first step. Upon activation of the glycosyl donor group (Y) (usually SR, OAc, or Br group) in the next step, the tethered aglycon traps the developing oxocarbenium ion at C-1 and is transferred from the same face as OH-2, forming the glycosidic bond stereospecifically. The yield of this reaction drops as the bulkiness of the alcohol increases. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Intramolecular aglycon delivery」の詳細全文を読む スポンサード リンク
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