A 1,2-trans-Selective Glycosyl Donor Bearing Cyclic Protection at the C-2 and C-3 Hydroxy Groups

作者：Yagami Nahoko; Tamai Hideki; Udagawa Taro; Ueki Akiharu; Konishi Miku; Imamura Akihiro; Ishida Hideharu^*; Kiso Makoto; Ando Hiromune^*

来源：European Journal of Organic Chemistry, 2017, 2017(32): 4778-4785.

DOI：10.1002/ejoc.201700671

• Carbohydrates
• Glycosylation
• Conformation analysis
• Protecting groups
• Diastereoselectivity
• Glycosides

A new 1,2-trans-selective glycosylation reaction is described. Glucosyl donors protected cyclically at the C-2 and C-3 hydroxy groups as six- (butane diacetal), seven- (tetraisopropyldisiloxanylidene), or eight- (2,3-o-xylylene) membered fused rings were synthesized in a straightforward manner. The glycosylation reactions of the glucosyl donors with various acceptors mainly generated -glycosides under conventional reaction conditions. The results show that the o-xylylene group is a suitable 1,2-trans-directing group from the points of view of stereoselectivity and chemical stability. A conformational study of the oxocarbenium ion of an o-xylylene-protected glucose derivative by NMR spectroscopy and computational simulation was carried out. The results imply that the oxocarbenium ion mainly adopts a H-4(3) conformation owing to the rigid trans-fused ring at C-2 and C-3, while a noncyclically protected derivative might fluctuate between conformations. These results suggest that an eclipsing interaction between the pseudoequatorial xyloxy group at C-2 and the incoming nucleophile hampers 1,2-cis attack.

• 出版日期2017-9-1