Stereoselective synthesis of beta-mannopyranosides via the temporary silicon connection method
Stereoselective synthesis of beta-mannopyranosides via the temporary silicon connection method
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DOI：
10.1021/ja9532291
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发表时间：
1996-01-10
影响因子：
15
通讯作者：
LaClair, JJ
中科院分区：
文献类型：
--
作者：
Stork, G;LaClair, JJ
Increasing interest in the synthesis of biologically significant carbohydrate glycosides and conjugates has led to the development of ever more selective methods for the control of stereochemistry at the anomeric center. The stereospecific formation of β-mannopyranosides has proved particularly difficult to achieve, however, in spite of considerable effort, because the vicinal cis (axial) β-hydroxyl group blocks access to the β-face. 1 The presence of the β-mannopyranoside entity, inter alia, in the core region of N-linked glycoproteins (cf. Figure 1) warrants significant attention toward its construction. A general solution to this type of problem was introduced in 1983, with the demonstration that a carbon substituent could be introduced, regio-and stereospecifically, in many ring systems by using the temporary attachment of the desired substituent to a stereochemistry-controlling hydroxyl within the ring system. 2 Internal transfer of the substituent by cyclization cis to the controlling hydroxyl then allowed completion of the process by removal of the temporary connector. Possible choices for the latter are limited. We made use of a temporary acetal link in a prostaglandin synthesis3 and a temporary silyl ether connection in a method for the controlled introduction of methyl groups. 4 In these particular examples, the tethered entities were cyclized by free-radical processes. In the carbohydrate area, the temporary connection method was first applied in the acetal version to the stereospecific synthesis of C-glycosides. 5 We, in turn, explored the temporary silyl ether version for the same purpose6 and found it especially significant that the approach was successful even for the synthesis of a β-C-mannopyranoside, thus obtained free from its R-isomer (cf. 1 f 2, Figure 2).So far as the synthesis of typical β-mannopyranosides, the first applications of the temporary tethering concept were carried out, independently, by Hindsgaul7 and us, 8 using respectively mixed acetals and silyl ether connectors. More recently, Ito and Ogawa demonstrated the efficient use of p-methoxybenzylidene acetals. 9
