The preparation of amino sugars by nucleophilic displacement

The reactivity of a leaving group also depends on the substitution and configuration of the saccharide.59 For example, displacement at the C(2) position of mannosides is hindered by unfavourable dipolar interactions 

Azide ions are by far the most common nucleophilic species employed in substitution reactions for the preparation of amino sugars. An azido moiety is stable under many reaction conditions but can be reduced to an amino group by a variety of reagents. The nucleophilicity of azido ions can be increased by the addition of a suitable crown ether to complex the counterion.36c,63b In the past, ammonia and hydrazine were used as nucleophiles to overcome unfavourable dipolar interactions that arise when charged nucleophiles were used. However, a drawback of the use of these nucleophiles is that the product is still nucleophilic and can perform a second displacement. Phthalimide ions have successfully been applied in displacement reactions to yield a protected amino sugar derivative.58 63f 

During the opening of an epoxide, an alkoxide is liberated which may then be the cause of undesired side reactions. Ammonium chloride is often added to the reaction mixture to neutralise the alkoxide produced. 

It has been shown75 that the stereochemical outcome of the reduction of 2-oxime sugars is influenced by the configuration of the anomeric centre. An interesting approach developed by Lichtenhaler et n/.,75a entails the use of 2-(benzoyloxyimino)glycosyl bromides as glycosyl 

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