The high cost of enzymes for saccharification of lignocellulosic biomass is a major barrier to the production of second generation biofuels. Using a combination of genetic and biochemical techniques, we report that filamentous fungi use oxidative enzymes to cleave glycosidic bonds in cellulose. Deletion of cdh-1, the gene encoding the major cellobiose dehydrogenase of Neurospora crassa, reduced cellulase activity substantially, and addition of purified cellobiose dehydrogenases from M. thermophila to the Δcdh-1 strain resulted in a 1.6- to 2.0-fold stimulation in cellulase activity. Addition of cellobiose dehydrogenase to a mixture of purified cellulases showed no stimulatory effect. We show that cellobiose dehydrogenase enhances cellulose degradation by coupling the oxidation of cellobiose to the reductive activation of copper-dependent polysaccharide monooxygenases (PMOs) that catalyze the insertion of oxygen into C–H bonds adjacent to the glycosidic linkage. Three of these PMOs were characterized and s...

Cellobiose Dehydrogenase and a Copper-Dependent Polysaccharide Monooxygenase Potentiate Cellulose Degradation by Neurospora crassa

Synthesis of complex carbohydrates and glycoconjugates: enzyme-based and programmable one-pot strategies.

Solid-phase organic reactions: A review of the recent literature

Carbohydrates as ligands: coordination equilibria and structure of the metal complexes

Enzyme-mediated oxidations for the chemist

Pyranose oxidases are known to oxidise o-glucose, o-xylose and l- sorbose to keto-aldoses, biochemically interesting compounds that may also be used for synthetic purposes in a variety of reactions. In this study pyranose oxidase from the basidiomycete Penio- phora gigonteo was investigated, and it was found that this enzyme is able to oxidise a broad variety of substrates very effectively. ln analogy to its natural mode of action. most substrates are oxidised regioselectively in position 2. Certain compounds, however, are con- verted into 3-keto derivatives. and the enzyme even exhibits transfer potential, that is, disaccharides are formed from /j- glycosides of higher alcohols. Substrates that may be oxidised at C-2 in yields between 40-98"A are n-allose, o-galac- tose, 6-deoxy-o-glucose, D-gentiobiose, a-o-glucopyranosyl fluoride and the very interesting 3-deoxy-o-glucose. 1,5- Anhydro-o-glucitol ( 1 -deoxy-o-glucose) is very effectively oxidised in position 2 in 98 % yield and additionally gives a product of dioxidation at C-2 and C-3 upon prolonged reaction time. Selective oxidation at C-3 was found for 2-deoxv-

Rare Keto‐Aldoses from Enzymatic Oxidation: Substrates and Oxidation Products of Pyranose 2‐Oxidase

Rare sugars and sugar-based synthons by chemo-enzymatic synthesis

Keto aldoses usually form complex mixtures of equilibrating isomers in solution. This is due to the two different positions that may be used for ring closure in dicarbonyl sugars. The composition of various 2-keto aldoses 1–5 and 8, the 3-keto aldose 2-deoxy-D-erythro-hexos-3-ulose (9), and the ketose 1-deoxy-D-ribulose (10) in aqueous solution has been determined by NMR spectroscopy. The investigated keto aldoses form equilibria containing three to fifteen isomers. Among various furanose and pyranose ring structures stemming from 1,4-, 1,5-, 2,5-, and 2,6-cyclization, bicyclic forms were also found in several cases. The 2-keto aldoses mainly exist as hydrated isomers in H2O. Therefore, these forms and their proportions were compared to forms found in two homomorphous aldoses and one homomorphous ketose as model compounds. Besides the NMR data, also the composition of the 2-keto aldoses agreed with the average of forms found in the model compounds, a finding that might eventually be useful for deducing the composition of other keto aldoses.

Sabine Köpper

Papers

Rare Keto‐Aldoses from Enzymatic Oxidation: Substrates and Oxidation Products of Pyranose 2‐Oxidase

Rare sugars and sugar-based synthons by chemo-enzymatic synthesis

The Composition of Keto Aldoses in Aqueous Solution as Determined by NMR Spectroscopy

Convenient Chemo-Enzymatic Synthesis of d-Tagatose

Polymer-supported enzymic synthesis on a preparative scale