Functionalization of Carbohydrates in Water

Carbohydrate chemistry and chemistry in water go well with each other for three main reasons. First, the synthesis of carbohydrate derivatives of biological relevance has profited from the advances in the use of aqueous media as solvents, leading to new compounds with improved reactivity and selectivity. Second, carbohydrates, being water soluble, have been used as water solubility inducers for water-promoted reactions. Third, part of the chemistry devoted to the use of carbohydrates as raw materials, as an alternative to fossil resources, is performed in water. Indeed, it is now strategic to combine different key principles of green chemistry, namely the use of clean solvents and the use of renewable starting materials in synthetic chemistry. Moreover, it can be connected with the design of new derivatives with improved environmental properties. The chapter focuses on the chemistry of small carbohydrates (not polysaccharides), reviewing CC bond formation reactions involved in multi-step syntheses of complex structures or in direct processes towards functional derivatives, CN and CO bond formation reactions. The latter aspect, which deals with the reactivity of sugars as polyols, is an extremely large topic, and for reasons of conciseness the main issues of this chemistry will be illustrated by focusing on the example of sucrose, the most available small carbohydrate. Also, some approaches in which a carbohydrate serves as a polar appendage which provides the water solubility necessary to take advantage of hydrophobic effects are described, in addition to the use of aqueous solutions of sugars as media in which hydrophobic effects are intensified. Keywords: carbohydrates; water; functionalization; C-glycosides; renewable resources; sucrose; green chemistry