Oligosaccharides and derivatives--integrating biocatalyst selectivity and chemical diversity

Several biocatalytic pathways are available to synthesize rare sugars, oligosaccharides and derivatives. As examples selective hydrolysis, transglycosylation and regioselective oxidation are presented illustrating their potential. From inulin, difructose anhydrides and inulobiose are accessible via specific hydrolases with transglycosylation activity. Glycosyltransferases of the sucrase type utilise sucrose as a versatile substrate for the selective transfer of either glucosyl- or fructosyl units to a broad range of acceptors, sugars as well as derivatives, to yield oligosaccharides of different type. Kinetic analysis and reaction engineering can provide high product yields and concentration, as will be shown for glucose, yielding isomaltooligosaccharides as an example. Several new acceptor saccharides, including sugar alcohols and acids, have been shown to give new oligosaccharides. Regioselective oxidation of disaccharides like sucrose, lactose and others with resting cells of Agrobacterium tumefaciens yield 3-keto-disaccharides. These can further be functionalized in aquous systems without protecting groups via established chemical routes, such as catalytic hydration. As an example allosucrose is thus obtained from 3-keto-sucrose with high yield and stereochemical selectivity, which in turn can easily be hydrolysed and separated from fructose to give allose. Amino acid and peptide conjugates are accessible via reductive amination and acylation, as are building blocks for polymerisation.