Pyranose oxidases are known to oxidise d-glucose, d-xylose and lsorbose 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 Peniophora gigantea was investigated, and it was found that this enzyme is able to oxidise a broad variety of substrates very effectively. In analogy to its natural mode of action, most substrates are oxidised regioselectively in position 2. Certain compounds, however, are converted into 3-keto derivatives, and the enzyme even exhibits transfer potential, that is, disaccharides are formed from bglycosides of higher alcohols. Substrates that may be oxidised at C-2 in yields between 40 ± 98 % are d-allose, d-galactose, 6-deoxy-d-glucose, d-gentiobiose, a-d-glucopyranosyl fluoride and the very interesting 3-deoxy-d-glucose. 1,5-Anhydro-d-glucitol (1-deoxy-d-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-deoxyd-glucose in very good yields and for methyl b-d-gluco-and methyl b-galactopyranoside in lower yields. All oxidation products were unequivocally characterised by NMR spectroscopy and/or chemical derivatisation. In addition, the kinetic data of the enzymatic reactions were determined for all substrates. On the basis of these data and the structural characteristics of the substrates, a model for the minimal structural requirements of the enzyme ± substrate interaction is suggested. The enzyme presumably uses two different binding modes for the regioselective C-2 and the C-3 oxidations, which are described.

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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 H 2 O. 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.1. Introduction. ± The composition of carbohydrates in solution is of major importance for their chemical, physical, and biological properties. Common reducing and nonreducing sugars have been studied extensively by NMR spectroscopy, and their equilibria in H 2 O are well-documented [1] [2]. Aldoses and ketoses mainly form two pyranose and two furanose anomers, which are rarely accompanied by open-chain or other forms. The analysis of the NMR spectra of these common sugars is, therefore, relatively straightforward. This is not the case for carbohydrates that have a second CO function. In keto aldoses, ring closure can take place at two different positions, and, accordingly, these compounds exist as complex mixtures of isomeric forms. For this reason, the composition of keto aldoses has been analyzed thoroughly in only a few cases [3 ± 14].Keto aldoses are important intermediates in biological and chemical processes. In mammals, the keto aldose d-glucosone (1) is believed to be formed by auto-oxidation of glucose [15] or by other processes [16], and 3-deoxy-d-glucosone (5) occurs in blood and urine [17] in concentrations that are elevated in diabetic patients [18]. The hexosulose 5 also plays an important role in the Maillard reaction [19]. The chemical interest in keto aldoses stems from the fact that they combine the high number of functional groups and the inherent information on chirality of carbohydrates that have a higher degree of diversity than normal hexoses. They are consequently very interesting synthons for a variety of chemical procedures [20 ± 22], and some of them have been effectively used for the synthesis of antibiotics [23 ± 26] and amino sugars [27]. Therefore, the composition in solution is of interest for both the chemistry and

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