Influence of Protecting Group on Donor Reactivity

The enhanced lability of the methyl-6-deoxygalactopyranoside is mirrored by the acid-sensitivity of a-fucosyl linkages in general [20]. 

Inductive effects, however, were all too evident to early researchers Fletcher et al. demonstrated that increasing numbers of ester protecting groups reduced the reactivity of glycosyl halides under methanolysis conditions (Table 3) [23]. 

The ratio of the product disaccharides AC and BC was determined by H NMR (each disaccharide had already been prepared discretely) thus providing a quantitative analysis of reactivity of the various protecting group patterns (Table 5). 

As a simplifying approximation, the individual contributions from each protecting group can be treated as being independent of any other protecting groups in the system. Although the validity of this approximation is questionable [28] it does 

That the predicted result is of similar magnitude to the observed value is indicative of the usefulness of this approximation the difference cannot, however, be explained away merely as statistical error and should in part be attributed to the failure of the approximation. 

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Influence of Protecting Group on Donor Reactivity Electronic Effects. 40... 

Influence of Protecting Group on Donor Reactivity 431 Table 2. Comparison of the rates of hydrolysis of methyl glycosides and their 6-deoxy analogs. 

Aubry S, Sasaki K, Sharma I, Crich D (2011) Influence of protecting groups on the reactivity and selectivity of glycosylation chemistry of the 4,6-O-benzylidene protected mannopyr-anosyl donors and related species. In Topics in current chemistry. Springer, Heidelberg. 

Influence of Protecting Groups on the Reactivity and Selectivity of Glycosylation Chemistry of the 4,6-O-BenzyIidene Protected Mannopyranosyl Donors and Related Species... 

While the preceeding section discussed the influence of protecting groups on the relative reactivity of glycosyl donors, the present section deals with the possibility of tuning the reactivity by incorporating different anomeric LGs. The same promotor is used for both the donor and acceptor. Thus, additional distinct levels of anomeric reactivity of glycosides are achieved. 

INFLUENCE OF HYDROXY PROTECTING GROUPS ON SIALYL DONOR REACTIVITY 147... 

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