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d‐Allulose has potential as a low‐calorie sweetener which can suppress fat accumulation. Several enzymes capable of d‐allulose production have been isolated, including d‐tagatose 3‐epimerases. Here, we report the isolation of a novel protein from Methylomonas sp. expected to be a putative enzyme based on sequence similarity to ketose 3‐epimerase. The synthesized gene encoding the deduced ketose 3‐epimerase was expressed as a recombinant enzyme in Escherichia coli, and it exhibited the highest enzymatic activity toward l‐ribulose, followed by d‐ribulose and d‐allulose. The X‐ray structure analysis of l‐ribulose 3‐epimerase from Methylomonas sp. (MetLRE) revealed a homodimeric enzyme, the first reported structure of dimeric l‐ribulose 3‐epimerase. The monomeric structure of MetLRE is similar to that of homotetrameric l‐ribulose 3‐epimerases, but the short C‐terminal α‐helix of MetLRE is unique and different from those of known l‐ribulose 3 epimerases. The length of the C‐terminal α‐helix was thought to be involved in tetramerization and increasing stability; however, the addition of residues to MetLRE at the C terminus did not lead to tetramer formation. MetLRE is the first dimeric l‐ribulose 3‐epimerase identified to exhibit high relative activity toward d‐allulose.

D-allose is a rare sugar that has been reported to up-regulate thioredoxin-interacting protein (TXNIP) expression and affect the production of intracellular reactive oxygen species (ROS). However, the antitumor effect of D-allose is unknown. This study aimed to determine whether orally administered D-allose could be a candidate drug against bladder cancer (BC). To this end, BC cell lines were treated with varying concentrations of D-allose (10, 25, and 50 mM). Cell viability and intracellular ROS levels were assessed using cell viability assay and flow cytometry. TXNIP expression was evaluated using Western blotting. The antitumor effect of orally administered D-allose was assessed using a xenograft mouse model. D-allose reduced cell viability and induced intracellular ROS production in BC cells. Moreover, D-allose stimulated TXNIP expression in a dose-dependent manner. Co-treatment of D-allose and the antioxidant L-glutathione canceled the D-allose-induced reduction in cell viability and intracellular ROS elevation. Furthermore, oral administration of D-allose inhibited tumor growth without adverse effects (p < 0.05). Histopathological findings in tumor tissues showed that D-allose decreased the nuclear fission rate from 4.1 to 1.1% (p = 0.004). Oral administration of D-allose suppressed BC growth in a preclinical mouse model, possibly through up-regulation of TXNIP expression followed by an increase in intracellular ROS. Therefore, D-allose is a potential therapeutic compound for the treatment of BC.

The racemic title compound, C6H12O6, consisting of C-4 epimers of psicose, was crystallized from an aqueous solution of an equimolar mixture of d- and l-sorboses. It was confirmed that d-sorbose (or l-sorbose) formed α-pyranose with a 4C1 (or 1C4) conformation where the anomer position was designated as carbon-1. The asymmetric unit comprises two crystallographically independent molecules. In the crystal, molecules are linked by O—H...O hydrogen bonds, forming a three-dimensional framework. The unit-cell volume of the title racemic α-d,l-sorbose is 1450.86 (6) Å3 (Z = 8), which is about 41 Å3 smaller than that of twice the amount of chiral α-l-sorbose [V = 745.942 Å3 (Z = 4)].

A practical synthesis of the very rare sugar d-idose and the stable building blocks for d-idose, d-iduronic, and d-idonic acids from ido-heptonic acid requires only isopropylidene protection, Shing silica gel-supported periodate cleavage of the C6-C7 bond of the heptonic acid, and selective reduction of C1 and/or C6. d-Idose is the most unstable of all the aldohexoses and a stable precursor which be stored and then converted under very mild conditions into d-idose is easily prepared.

The title compound, C6H12O5, was crystallized from an aqueous solution of 6-deoxy-l-psicose (6-deoxy-l-allulose, (3S,4S,5S)-1,3,4,5-tetrahydroxyhexan-2-one), and the molecule was confirmed as α-furanose with a 3T4 (or E4) conformation, which is a predominant tautomer in solution. This five-membered furanose ring structure is the second example in the field of the 6-deoxy-ketohexose family. The cell volume of the title compound [742.67 (7) Å3, Z = 4 at room temperature] is only 1.4% smaller than that of β-d-psicopyranose, C6H12O6 (753.056 Å3, Z = 4 at room temperature).

The title compound, C6H12O6, was crystallized from an aqueous solution of equimolar mixture of d- and l-fructose (1,3,4,5,6-pentahydroxyhexan-2-one, arabino-hexulose or levulose), and it was confirmed that d-fructose (or l-fructose) formed β-pyranose with a 2C5 (or 5C2) conformation. In the crystal, two O—H...O hydrogen bonds between the hydroxy groups at the C-1 and C-3 positions, and at the C-4 and C-5 positions connect homochiral molecules into a column along the a axis. The columns are linked by other O—H...O hydrogen bonds between d- and l-fructose molecules, forming a three-dimensional network.

The title compound, C6H12O6, a C-3 position epimer of fructose, was crystallized from an aqueous solution of equimolar mixture of d- and l-psicose (1,3,4,5,6-pentahydroxyhexan-2-one, ribo-2-hexulose, allulose), and it was confirmed that d-psicose (or l-psicose) formed β-pyranose with a 2C5 (or 5C2) conformation. In the crystal, an O—H...O hydrogen bond between the hydroxy groups at the C-3 and C-2 positions connects homochiral molecules into a column along the b axis. The columns are linked by other O—H...O hydrogen bonds between d- and l-psicose molecules, forming a three-dimensional network. An intramolecular O—H...O hydrogen bond is also observed. The cell volume of racemic β-d,l-psicose [763.21 (6) Å3] is almost the same as that of chiral β-d-psicose [753.06 Å3].

X-ray crystallography showed that the title compound, C6H12O5, crystallizes in the α-pyranose form with the six-membered ring in a chair conformation. The crystal structure exists as a three-dimensional hydrogen-bonded network of molecules with each molecule acting as a donor and aceptor for four hydrogen bonds. The absolute configuration was determined by the use of l-fucose as starting material.

1-Deoxy-d-galactitol, C6H14O5, exists in the crystalline form as hydrogen-bonded layers of molecules running parallel to the ac plane, with each molecule acting as a donor and acceptor of five hydrogen bonds.

Allitol is a hexitol produced by reducing the rare sugar D-allulose with a metal catalyst under hydrogen gas. To confirm the safe level of allitol, we conducted a series of safety assessments. From the results of Ames mutagenicity assay using Salmonella typhimurium strains TA98, TA100, TA1535, and TA1537, Escherichia coli strain WP2uvrA, and an in vitro chromosomal aberration test on cultured Chinese hamster cells, allitol did not show any significant genotoxic effect. No significant effects on general condition, urinalysis, hematology, physiology, histopathology, or at necropsy were observed at a dose of 1500 mg/kg body weight of allitol in the acute and 90-day subchronic oral-toxicity assessments for rats. A further study performed on healthy adult humans showed that the acute use level of allitol for diarrhea was 0.2 g/kg body weight for both men and women. The results of current safety assessment studies suggest that allitol is safe for human consumption. [ABSTRACT FROM AUTHOR]

d-Aldotetroses are rare sugars that are obtained via chemical synthesis in low yield. In this study, we demonstrated that d-aldotetroses could be produced using 3 isomerases. First, l-erythrulose was epimerized using d-tagatose 3-epimerase from Pseudomonas cichorii ST-24. The specific optical rotation of the reaction solution gradually decreased to zero, indicating that approximately 50% of the l-erythrulose was converted to d-erythrulose. d, l-Erythrulose mixture was isomerized with d-arabinose isomerase from Klebsiella pneumoniae 40bXX to produce d-threose, resulting in a conversion rate of 9.35%. d-Erythrose production using l-rhamnose isomerase from Pseudomonas stutzeri LL172 resulted in a conversion rate of 12.9%. Because of the low purity of the purchased d-erythrose, the product was reduced by the Raney nickel catalyst compared with authentic erythritol. We confirmed the products using HPLC and 13C-NMR spectra. This is the first report of d-aldotetrose production using an enzymatic reaction. [ABSTRACT FROM AUTHOR]

Glucotoxicity, impaired insulin secretion, suppression of insulin gene expression, and apoptosis, in pancreatic β-cells caused by chronic hyperglycemia is a key component of the pathogenesis of type 2 diabetes. Recently, it has been reported that rare sugar D-allulose has antihyperglycemic and antihyperlipidemic effects in diabetic rats. However, the direct effects of rare sugars including D-allulose on pancreatic β-cell function are unclear. In this study, we investigated whether chronic exposure to ketohexoses causes glucotoxicity, suppression of insulin gene expression, and apoptosis, in INS-1 rat pancreatic insulinoma cells. D-Fructose, D-tagatose, L-allulose, and L-sorbose treatment for 1-week reduced insulin gene expression, whereas D-allulose, D-sorbose, L-fructose, and L-tagatose did not. All ketohexoses were transported into INS-1 cells, but were not metabolized. In addition, the ketohexoses did not induce apoptosis and did not affect glucose metabolism. These results suggest that long-term administration of D-allulose, D-sorbose, L-fructose, and L-tagatose does not affect pancreatic β-cell function. [ABSTRACT FROM AUTHOR]

D-Allulose (d-psicose) is a rare sugar, that contains no calories and exhibits 70% relative sweetness when compared with sucrose. Recently, several studies have demonstrated the anti-obesity effect of dallulose, mediated by suppressing lipogenesis and increasing energy expenditure. Medium-chain triacylglycerols (MCTs) are lipids formed by 3 medium-chain fatty acids (MCFAs) with 6-12 carbon atoms attached to glycerol. MCTs have been expensively studied to reduce body fat accumulation in rats and humans. The anti-obesity effect of MCTs was not confirmed depending on the nutritional conditions because MCT might promote lipogenesis. In the present study, we examined the effects of simultaneous intake of diets containing low (5%) or high (13%) MCTs, with or without 5% d-allulose, on body fat accumulation in rats (Experiment 1). Furthermore, we assessed the interaction between 5% MCT and 5% d-allulose in the diet (Experiment 2). In Experiment 1, intra-abdominal adipose tissue weight was significantly greater in the high MCT diet groups than in the commercial diet (control) group. d-Allulose significantly decreased weights of intra-abdominal adipose tissue, carcass fat, and total body fat, however, these weights increased as the amount of MCT added increased. In Experiment 2, d-allulose significantly decreased almost all body fat indicators, and these values were not influenced by the presence or absence of MCT addition. The antiobesity effect of d-allulose was observed with or without dietary MCT, and no synergistic effect was detected between d-allulose and MCT. These results suggest that d-allulose is a beneficial food ingredient in diets aimed at reducing body fat accumulation. However, further research is required on the synergistic effects between d-allulose and MCTs. [ABSTRACT FROM AUTHOR]

Sweetspire (Itea) is the only plant that accumulates rare sugars d-allulose and allitol. However, no reports have indicated that sweetspire has a beneficial physiological activity in mammalians. We have examined the effect of dietary dried sweetspire powder (SP) on body fat accumulation in rats fed with a high-fat diet. Twenty-four male Wistar rats were randomized into three groups, the control (C), SP, and rare sugar (RS) groups. The SP diet contained 5% SP (contained 0.4% d-allulose and 0.6% allitol in the diet), and the RS diet contained the same amount of rare sugars as the SP diet. All rats were given free access to the experimental diets for 8 weeks. The percentages of intra-abdominal adipose tissue and total body fat were significantly lower in the SP group than in the C group, suggesting that SP has an anti-obesity effect. Furthermore, this anti-obesity effect may be attributed to the rare sugars in SP. [ABSTRACT FROM AUTHOR]

Ease of separation of petrol-soluble acetonides derived from the triacetonide of methyl glucoheptonate allows scalable syntheses of rare sugars containing the l-gluco or d-gulo structural motif with any oxidation level at the C6 or C1 position of the hexose, usually without chromatography: meso-d-glycero-d-guloheptitol available in two steps is an ideal entry point for the study of the biotechnological production of heptoses. [ABSTRACT FROM AUTHOR]

The article presents a study that determines the enzymatic production of three 6-deoxy-aldohexoses from L-rhamnose. It offers details of the study which uses L-rhamnose isomerase and P-tagatose 3-epimerase (TT-PcDTE). It outlines the findings of the research which indicates that aldose isomerase has acted on 6-deoxy aldohexoses.

L-Ribulose 3-epimerase (L-RE) from Mesorhizobium loti has been identified as the first ketose 3-epimerase that shows the highest observed activity towards ketopentoses. In the present study, the crystal structure of the enzyme was determined to 2.7 A resolution. The asymmetric unit contained two homo-tetramers with the monomer folded into an (α/β)8-barrel carrying four additional short a-helices. The overall structure of M. loti L-RE showed significant similarity to the structures of ketose 3-epimerases from Pseudomonas cichorii, Agro-bacterium tumefaciens and Clostridium cellulolyticum, which use ketohexoses as preferred substrates. However, the size of the C-terminal helix (α8) was much larger in M. loti L-RE than the corresponding helices in the other enzymes. In M. loti L-RE the α8 helix and the following C-terminal tail possessed a unique subunit-subunit interface which promoted the formation of additional intermolecular interactions and strengthened the enzyme stability. Structural comparisons revealed that the relatively small hydrophobic pocket of the enzyme around the substrate was likely to be the main factor responsible for the marked specificity for ketopentoses shown by M. loti L-RE. [ABSTRACT FROM AUTHOR]

The equilibrium tautomeric composition in aqueous solution of 6-deoxy-L-psicose and 1-deoxy-D-tagatose was elucidated by means of 13CNMR spectroscopy at 15-50°C. The molar absorption coefficient of their respective carbonyl group, εC=O was determined from the linear relationship between the absorbance around 280 nm and molar concentration of the acyclic carbonyl form. It was found that εC=O for 6-deoxy-L-psicose was almost the same as for D-psicose, whereas εC=O for 1-deoxy-D-tagatose was reduced by ca. 25% compared to D-tagatose. [ABSTRACT FROM AUTHOR]

Medium-chain triglycerides, lipids containing three 6−12 carbon medium-chain fatty acids, have antiobesity effects because they do not promote lipogenesis. d-Allulose, a low-calorie epimer of fructose commercially used as a low-calorie sweetener, suppresses hepatic lipogenesis and enhances postprandial fat oxidation. Therefore, we have explored whether a simultaneous intake of medium-chain fatty acids and d-allulose may exhibit a greater reduction in de novo lipogenesis and increase their antiobesity effects. To this end, 32 male Wistar rats were divided into four treatment groups of equal sizes: control, 3% d-allulose-treated, 5% medium-chain triglycerides-treated, and 3% d-allulose + 5% medium-chain triglycerides-treated. After 8 weeks of ad libitum exposure to these diets, d-allulose significantly decreased intra-abdominal adipose tissue and total body fat weight, with or without medium-chain triglyceride supplementation. The antiobesity effect of d-allulose was observed with or without dietary medium-chain triglyceride supplementation in high-fat diet-induced obese rats, but no synergistic effect was detected between d-allulose and medium-chain triglycerides. [ABSTRACT FROM AUTHOR]