Structure Design of Polysaccharides by Selective Conversion: Old Hat or Topical?
Keywords:Activating groups, Blocking groups, Bulky silyl ethers, Chemoselectivity, 6-halogeno-6-deoxy polysaccharides, Medium-controlled selectivity, Regioselectivity, Structure-property relationships, Sulfonic acid esters, Triphenylmethyl ethers
The functionalization pattern in polysaccharide derivatives is an important factor that determines their properties and, thus, their functions in applications. Regioselectively functionalized polysaccharide derivatives are used in material science because they may form lamellar structures in microscale by self-assembling. Intrinsically chiral polysaccharide derivatives are used for the separation of enantiomers by chromatography, and the separation efficiency is influenced by the regioselective distribution of substituents attached. Due to the multi-functionality of polysaccharides, their derivatization reactions usually yield products with random distribution of substituents. Thus, establishment of unambiguous structure-property relationships cannot be achieved. This review article summarizes recent developments in this topic. In addition to the blocking group techniques, synthesis methods applying activating substituents will be summarized. Moreover, the reaction medium itself may direct the substituent in a certain position without laborious multistep reactions.