Theoretical studies on the conformation of saccharides

Conformations of 2-methoxytetrahydropyran as a model for the six-membered ring in aldopyranosides have been calculated by the PCILO method using the algorithm of the conjugated gradient to optimize the geometry. The calculated geometry of the fourteen basic forms of 2-methoxytetrahydropyran was found to be in agreement with the available data obtained by X-ray diffraction of pyranosides. The results indicate differences in the geometry of 2-methoxytetrahydropyran resulting from the change of the axial vs. equatorial position of the methoxyl group. These changes are particularly meaningful in the values of bond angles and they are in agreement with the anomeric and exoanomeric effects. The experimentally found differences in the energies of an axial (⁴ C ₁) and equatorial (¹ C ₄) conformer, G = 2.9–3.7 kJ/mol, and the dipole moment, = 1.20 ± 0.05 D (1D = 3.33 10^–30mAs) agree well with the calculated values E = 3.18 kJ/mol and <> = 1.18 D which, in turn, suggest that the axial conformer is preferred over the equatorial one by a ratio a:e = 78:22.     

Synthesis of (±)-cartorimine

Heating pyranulose 4 and cinnamate 2 in the presence of 2,6-di-t-butylpyridine in CH₃CN afforded the [5+2] cycloadduct, which was hydrolyzed to give 13% of cartorimine (1).     

A new enzyme catalysis: 3,4-dioxidation of some aryl β-d-glycopyranosides by fungal pyranose dehydrogenase

Quinone-dependent pyranose dehydrogenase presents a new tool for versatile conversions of numerous carbohydrates to their di- and tricarbonyl derivatives. This enzyme purified from the basidiomycete Agaricus meleagris catalysed dioxidation of several aromatic β-d-glucopyranosides and a β-d-xylopyranoside into the corresponding 3,4-didehydro-β-d-aldopyranosides (β-d-aldopyranosid-3,4-diuloses) in high yields, typically >80% for 4-nitrophenyl glycosides. These new compounds were doubly hydrated in aqueous solution. According to in situ NMR investigations, the reaction intermediates were the corresponding 3- and 4-dehydro compounds. The analogous anomeric α-glycosides underwent one-step oxidation only at C-3 to 3-dehydro-α-d-aldopyranosides (α-d-pyranosid-3-uloses).     

Electrochemical Activity Studies of Glucose Oxidase (GOx)‐Based and Pyranose Oxidase (POx)‐Based Electrodes in Mesoporous Carbon: Toward Biosensor and Biofuel Cell Applications

A simple study using a fixed amount of mesoporous carbon (MSU‐F‐C) was performed for the comparison of pyranose oxidase (POx) and glucose oxidase (GOx) in their electrochemical performance under biosensor and biofuel cell operating modes. Even though the ratio of POx to GOx in the glucose oxidation activity per unit weight of MSU‐F‐C was 0.35, the ratios of POx to GOx in sensitivity and power density were reversed to be 6.2 and 1.4, respectively. POx with broad substrate specificity and an option of large scale production using recombinant E. coli has a great potential for various electrochemical applications, including biofuel cells.     

单糖二级羟基的氧化及氧化剂的电化学行为

单糖二级羟基的氧化及氧化剂的电化学行为曹玲华,刘育亭（新疆大学化学系,乌鲁木齐,８３００４６）关键词吡喃糖,呋喃糖,氧化,氧化剂的电化学行为近年来,Ｃｏｒｅｙ等［１,２］研制的新试剂ＰＣＣ（Ｐｙｒｉｄｉｎｉｕｍｃｈｌｏｒｏｃｈｒｏｍａｔｅ）和ＰＤＣ（...     

Conversion of d‐Galactose to d‐threo‐Hexos‐2,3‐diulose by Fungal Pyranose Oxidase

Pyranose oxidase (pyranose:O₂ 2‐oxidoreductase, EC 1.1.3.10) purified from mycelia of the basidiomycete fungi Trametes versicolor and Oudemansiella mucida catalyzed oxidation of d‐galactose successively at C‐2 and C‐3 to d‐threo‐hexos‐2,3‐diulose (2,3‐dehydro‐d‐galactose, 2,3‐diketo‐d‐galactose) in the yields up to 80%. The sites of oxidation were deduced from structures of the N,N‐diphenylhydrazone derivatives of the reaction products. Under the reaction conditions used, the diulose was susceptible to non‐enzymatic oxidative decarboxylation to d‐threo‐pentos‐2‐ulose (2‐dehydro‐d‐xylose, 2‐keto‐d‐xylose) in yields of 5–10%.     

Ring conformations of d-glucose derivatives possessing two bulky silyl protecting groups at the 3,4-positions; the first observation of a stable full-axial chair conformer without bridge structures

The ring conformations of 3,4-bis-O-tert-butyldimethylsilyl- and 3,4-bis-O-tert-butyldiphenylsilyl-d-glucopyranoses as well as the corresponding phenyl 1-thio-d-glucopyranosides were investigated. Observations showed that the introduction of the two tert-butyldiphenylsilyl groups can flip the pyranose-ring into the ¹C₄ conformation possessing more axial substituents. All the substituents of the 3,4-bis-O-tert-butyldiphenylsilyl-β-d-glucopyranose were axially oriented.     

The first ring inversion of pyranoses induced by bulky silyl protections at the 2- and 3-positions

The pyranose rings of the 2,3-bis-O-tert-butyldiphenylsilyl-α- and β-d-glucopyranoses, and of the 2,3-bis-O-tert-butyldimethylsilyl-β-d-glucopyranose were in the ¹C₄ form. These findings indicate that the introduction of bulky silyl protecting groups at the 2- and 3-positions can flip a pyranose ring into the axial-rich chair form. Previous such ring inversions have been carried out by the silyl protections at the 3- and 4-positions.