Other Cyclic and Bicyclic Protecting Systems for Sialyl Donors

SCHEME 5.16 Use of an ALacetyl-4-0,5-ALoxazolidinone-protected sialyl phosphate in a one-pot trisaccharide synthesis. 

8 OTHER CYCLIC AND BICYCLIC PROTECTING SYSTEMS FOR SIALYL DONORS 

Seeking to emulate the benzylidene effect in p-mannosylation [68] (see Section 4.2.6), David Crich and Baolin Wu [87] and Hiromune Ando and coworkers [88] prepared 5-.V,7-(9-oxazinone-protecled thiosialosides 69 and 70 (Fig. 5.5). Unfortunately, both groups found this class of donors to be moderately p-selective under a variety of activating conditions and even in the presence of acetonitrile. 

FIGURE 5.5 Oxazinone-protected sialoside donors. TBS, terf-butyldimethylsilyl. 

SCHEME 5.18 Use of a tricyclic sialyl donor and the influence of the acceptor protecting system on stereoselectivity. PMP, p-methoxyphenyl. 

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