Influence of the N5 Protecting Group on Reactivity and Selectivity

The most important advances in stereoselective sialylation in the last 15 years, beginning with the work of Geert-Jan Boons and Alexei Demchenko in 1998 [31], have centered around the discovery that modification of the N5 protecting group influences both the reactivity of sialyl donors and the stereoselectivity of their coupling reactions. In view of their importance to the field, the most important features of modifications of the N5 protecting groups are discussed in some detail here even if they have been reviewed previously [32, 33], 

SCHEME 5.3 Effect of (V,(V-diacetylation of a thioglycoside donor on sialylation. Bz, benzoyl TMS, trimethylsilyl Ts, toluenesulfonyl. 

SCHEME 5.4 Beneficial effect of the imide function on acceptor reactivity. Bn, benzyl. 

SCHEME 5.6 Sialylation with an iV-acetyl-iV-Boc-protected donor. TFA, trifluoroacetyl. 

SCHEME 5.7 Use of a phthalimide-protected sialyl donor. All, allyl Phth, phthaloyl. 

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