Protecting Groups at the Primary Position of Carbohydrates
Résumé
Protecting group strategies are at the heart of carbohydrate chemistry as the only means available for the selective transformation of hydroxyl groups. The 6-position is the only primary alcohol present in saccharides, and a literature survey of regioselective and/or chemoselective methods for the introduction of a protecting group gathered more than 200 references. The typical protecting groups introduced are trityl or large silyl ethers, and these are extensively reviewed. Methods for the sulfonylation of the primary alcohol are also presented, providing an insight toward further chemical modifications (e.g. halogenation and azidation). A large group of chemoenzymatic conditions for the introduction or removal of ester at the primary positions is also discussed. Oxidations to the corresponding aldehydes or carboxylic acids are presented both from chemical and/or from chemoenzymatic methodologies.