ABSTRACT
References ..................................................................................................................................... 85
Protecting groups and protection strategies are important components of all total syntheses of
organic molecules. This is particularly true in carbohydrate chemistry and oligosaccharide
synthesis because of the large number of functional groups present. Most of them are of the same
sort — hydroxyl groups — which necessitates (sometimes quite laborious) regioselective
protecting strategies. Several books have been written on protecting groups in organic synthesis
[1-4], and new groups and methodologies are continually being developed [5,6]. A large part of
this literature deals with protecting group manipulations applied to carbohydrate chemistry. In
addition to the problems associated with protecting the various functional groups so as to expose the
functionality to be reacted (most often glycosylation of a hydroxyl group), several other issues have
to be considered. Protecting groups not only protect; they also confer other effects to the molecule.
For example, they can increase or decrease the reactivity and they can also participate in reactions,
thus affecting the stereochemical outcomes. Important examples of such effects are that acylated
glycosyl donors are less reactive than their alkylated counterparts. Furthermore, the use of 2-O-
participating groups in donors has been developed to ensure 1,2-trans selectivity in glycosylation
reactions. These factors should be taken into account when planning the protective group strategy.
However, due to the large number of protecting groups present in a fully protected sugar, it is
almost impossible to predict all effects introduced by the protecting group pattern, and often
unexpected reactivity is found requiring the study of alternative strategies.
