Oxidation, Reduction, and Deoxygenation
2.2
195
⊡ Scheme 12
⊡ Scheme 13
and cellobiose also undergo this selective C3 oxidation [119]. The active enzyme, a 3-dehydrogenase, has been isolated and purified. In addition to disaccharides this enzyme also oxidizes
D-glucose, D-galactose and their methyl glycosides at C3 [120].
Selective oxidation at C2 in pyranoses can in some cases be carried out with the enzyme
pyranose 2-oxidase, which can be isolated from several wood-degrading fungi [121]. The natural substrate for the enzyme is D-glucose, but significant activity towards C2 oxidation in
D-galactose, D-xylose, and D-allose has also been observed ( > Scheme 13) [121]. In contrast, L-sorbose undergoes very selective oxidation at C5 [121]. In some cases, the formed
2-keto-D-aldose is not the oxidation end-product, but is accumulated in the mixture and then
further converted into another product. In this way, D-glucose, D-galactose, and D-xylose have
been converted into the corresponding 2,3-diketo-aldoses by oxidation with pyranose 2-oxidase from various sources [122].
2.2
195
⊡ Scheme 12
⊡ Scheme 13
and cellobiose also undergo this selective C3 oxidation [119]. The active enzyme, a 3-dehydrogenase, has been isolated and purified. In addition to disaccharides this enzyme also oxidizes
D-glucose, D-galactose and their methyl glycosides at C3 [120].
Selective oxidation at C2 in pyranoses can in some cases be carried out with the enzyme
pyranose 2-oxidase, which can be isolated from several wood-degrading fungi [121]. The natural substrate for the enzyme is D-glucose, but significant activity towards C2 oxidation in
D-galactose, D-xylose, and D-allose has also been observed ( > Scheme 13) [121]. In contrast, L-sorbose undergoes very selective oxidation at C5 [121]. In some cases, the formed
2-keto-D-aldose is not the oxidation end-product, but is accumulated in the mixture and then
further converted into another product. In this way, D-glucose, D-galactose, and D-xylose have
been converted into the corresponding 2,3-diketo-aldoses by oxidation with pyranose 2-oxidase from various sources [122].