Simultaneous regio- and enantiodifferentiation in carbohydrate coupling

The glycosylation of 1, 2 - trans-diequatorial diols derived from tetrabenzoylated and tetrabenzylated D- and L-chiro-inositol with several glycosyl donors has been investigated. An unprecedented dependence of the regioselectivity on the absolute configuration of the acceptor has been found. However this trend is also modulated by the nature of the protecting groups on both the donor and acceptor, with benzoylated acceptors affording higher levels of regioselectivity. Most of the results have been rationalized by DFT calculations which indicate that stereoelectronic factors and hydrogen bonding between the donor and acceptor govern their relative orientation and determine the regiochemical outcome of the process. These studies also highlight the role of the acyl group adjacent to the OH to be glycosylated in facilitating the glycosylation reaction. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)