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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.

d-Aldotetroses are rare sugars are obtained via chemical synthesis in low yield. In this study, we demonstrated that D-aldotetroses could be produced using three 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.

Some rare sugars can be potently medicinal, such as l -gulose. In this study, we present a novel alditol oxidase (fAldOx) from the soil fungus Penicillium sp. KU–1, and its application for the effective production of l -gulose. To the best of our knowledge, this is the first report of a successful direct conversion of d -sorbitol to l -gulose. We further purified it to homogeneity with a ∼108-fold purification and an overall yield of 3.26%, and also determined the effectors of fAldOx. The enzyme possessed broad substrate specificity for alditols such as erythritol (kcat/KM, 355 m −1 s−1), thus implying that the effective production of multiple rare sugars for medicinal applications may be possible.

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 d-allulose, 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 anti-obesity 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.

We found that l-gulose, a rare sugar, was produced from d-sorbitol efficiently, using a wheat-bran culture extract of the fungus Penicillium sp. KU-1 isolated from soil. The culture extract showed enzyme activity for the oxidation of d-sorbitol to produce l-gulose; a high production yield of approximately 94% was achieved.

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‐Allulose has potential as a low‐calorie sweetener which can suppress fat accumulation. The enzymes capable of d‐allulose production have attracted attention. Here, we report the X‐ray structure of a novel l‐ribulose 3‐epimerase from Methylomonas sp. (MetLRE) which also has enzymatic activity towards d‐allulose, showing that MetLRE is the first dimeric l‐ribulose 3‐epimerase identified to exhibit high relative activity toward d‐allulose. ​

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.

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.

Transketolase is a key enzyme in the pentose phosphate pathway in all organisms, recognizing sugar phosphates as substrates. Transketolase with a cofactor of thiamine pyrophosphate catalyzes the transfer of a 2-carbon unit from D-xylulose-5-phosphate to D-ribose-5-phosphate (5-carbon aldose), giving D-sedoheptulose-7-phosphate (7-carbon ketose). Transketolases can also recognize non-phosphorylated monosaccharides as substrates, and catalyze the formation of non-phosphorylated 7-carbon ketose (heptulose), which has attracted pharmaceutical attention as an inhibitor of sugar metabolism. Here, we report the structural and biochemical characterizations of transketolase from Thermus thermophilus HB8 (TtTK), a well-characterized thermophilic Gram-negative bacterium. TtTK showed marked thermostability with maximum enzyme activity at 85 °C, and efficiently catalyzed the formation of heptuloses from lithium hydroxypyruvate and four aldopentoses: D-ribose, L-lyxose, L-arabinose, and D-xylose. The X-ray structure showed that TtTK tightly forms a homodimer with more interactions between subunits compared with transketolase from other organisms, contributing to its thermal stability. A modeling study based on X-ray structures suggested that D-ribose and L-lyxose could bind to the catalytic site of TtTK to form favorable hydrogen bonds with the enzyme, explaining the high conversion rates of 41% (D-ribose) and 43% (L-lyxose) to heptulose. These results demonstrate the potential of TtTK as an enzyme producing a rare sugar of heptulose. KEY POINTS: • Transketolase catalyzes the formation of a 7-carbon sugar phosphate • Structural and biochemical characterizations of thermophilic transketolase were done • The enzyme could produce non-phosphorylated 7-carbon ketoses from sugars.

The rare sugar d-tagatose is a safe natural product used as a commercial food ingredient. Here, we show that d-tagatose controls a wide range of plant diseases and focus on downy mildews to analyze its mode of action. It likely acts directly on the pathogen, rather than as a plant defense activator. Synthesis of mannan and related products of d-mannose metabolism are essential for development of fungi and oomycetes; d-tagatose inhibits the first step of mannose metabolism, the phosphorylation of d-fructose to d-fructose 6-phosphate by fructokinase, and also produces d-tagatose 6-phosphate. d-Tagatose 6-phosphate sequentially inhibits phosphomannose isomerase, causing a reduction in d-glucose 6-phosphate and d-fructose 6-phosphate, common substrates for glycolysis, and in d-mannose 6-phosphate, needed to synthesize mannan and related products. These chain-inhibitory effects on metabolic steps are significant enough to block initial infection and structural development needed for reproduction such as conidiophore and conidiospore formation of downy mildew., Mochizuki, Fukumoto, Ohara, et al. study the protective role of the rare sugar d-tagatose against plant disease. They focus on its effects against the downy mildews and delineate the metabolic pathway that blocks the initial infection. Their work paves the way for the development of safe fungicidal agrochemicals using natural products.

D-Allose (D-All), C-3 epimer of D-glucose, is a rare sugar known to suppress reactive oxygen species generation and prevent hypertension. We previously reported that D-allulose, a structural isomer of D-All, prolongs the lifespan of the nematode Caenorhabditis elegans. Thus, D-All was predicted to affect longevity. In this study, we provide the first empirical evidence that D-All extends the lifespan of C. elegans. Lifespan assays revealed that a lifespan extension was induced by 28 mM D-All. In particular, a lifespan extension of 23.8 % was achieved (p < 0.0001). We further revealed that the effects of D-All on lifespan were dependent on the insulin gene daf-16 and the longevity gene sir-2.1, indicating a distinct mechanism from those of other hexoses, such as D-allulose, with previously reported antiaging effects.

The key step in the syntheses of highly substituted trans-3,4-dihydroxypyrrolidines is introduction of bromide by stereospecific and regiospecific Hanessian-Hullar reactions; benzylidene lactones of l -rhamnonolactone and 6-deoxy-this should be small unnpercase d not l why can I not correct this-gulonolactone allow introduction of N at C2 with inversion or retention of configuration. Initially a protecting group, the benzylidene acetal then provides a bromide at C5 to allow formation of the pyrrolidine ring. With silyl protecting groups, bromide was introduced at C5 with inversion of configuration whereas benzoyl protection gave a mixture of retention and inversion, indicative of neighbouring group participation in a Hanessian-Hullar reaction. Four stereoisomeric pyrrolidines - iminosugar mimics of α- and β- l -rhamnulose and α- and β-6-deoxy- d -sorbose were prepared. Only the α- l -rhamnulose mimic showed moderate inhibition of rhamnosidase but some were good inhibitors of α-glucosidases; none inhibited rhamnose isomerase and they had a small effect as synthetic inducers of the rhamnose catabolic operon in E. coli.

Dietary restriction (DR) is an effective intervention known to increase lifespan in a wide variety of organisms. DR also delays the onset of aging-associated diseases. DR mimetics, compounds that can mimic the effects of DR, have been intensively explored. d- Allulose ( d- Alu), the C3-epimer of d- fructose, is a rare sugar that has various health benefits, including anti-hyperglycemia and anti-obesity effects. Here, we report that d- Alu increased the lifespan of Caenorhabditis elegans both under monoxenic and axenic culture conditions. d- Alu did not further extend the lifespan of the long-lived DR model eat-2 mutant, strongly indicating that the effect is related to DR. However, d- Alu did not reduce the food intake of wild-type C. elegans. To explore the mechanisms of the d- Alu longevity effect, we examined the lifespan of d -Alu-treated mutants deficient for nutrient sensing pathway-related genes daf-16, sir-2.1, aak-2, and skn-1. As a result, d- Alu increased the lifespan of the daf-16, sir-2.1, and skn-1 mutants, but not the aak-2 mutant, indicating that the lifespan extension was dependent on the energy sensor, AMP-activated protein kinase (AMPK). d -Alu also enhanced the mRNA expression and enzyme activities of superoxide dismutase (SOD) and catalase. From these findings, we conclude that d- Alu extends lifespan by increasing oxidative stress resistance through a DR mechanism, making it a candidate DR mimetic.

The biological activities of deoxy sugars (deoxy monosaccharides) have remained largely unstudied until recently. We compared the growth inhibition by all 1-deoxyketohexoses using the animal model Caenorhabditis elegans. Among the eight stereoisomers, 1-deoxy- d -allulose (1d- d -Alu) showed particularly strong growth inhibition. The 50% inhibition of growth (GI50) concentration by 1d- d -Alu was estimated to be 5.4 mM, which is approximately 10 times lower than that of d -allulose (52.7 mM), and even lower than that of the potent glycolytic inhibitor, 2-deoxy- d -glucose (19.5 mM), implying that 1d- d -Alu has a strong growth inhibition. In contrast, 5-deoxy- and 6-deoxy- d -allulose showed no growth inhibition of C. elegans. The inhibition by 1d- d -Alu was alleviated by the addition of d -ribose or d -fructose. Our findings suggest that 1d- d -Alu-mediated growth inhibition could be induced by the imbalance in d -ribose metabolism. To our knowledge, this is the first report of biological activity of 1d- d -Alu which may be considered as an antimetabolite drug candidate.

Pseudomonas cichorii D-tagatose 3-epimerase (PcDTE), which has a broad substrate specificity, efficiently catalyzes the epimerization of not only D-tagatose to D-sorbose but also D-fructose to D-psicose (D-allulose) and also recognizes the deoxy sugars as substrates. In an attempt to elucidate the substrate recognition and catalytic reaction mechanisms of PcDTE for deoxy sugars, the X-ray structures of the PcDTE mutant form with the replacement of Cys66 by Ser (PcDTE_C66S) in complexes with deoxy sugars were determined. These X-ray structures showed that substrate recognition by the enzyme at the 1-, 2-, and 3-positions is responsible for enzymatic activity and that substrate-enzyme interactions at the 4-, 5-, and 6-positions are not essential for the catalytic reaction of the enzyme leading to the broad substrate specificity of PcDTE. They also showed that the epimerization site of 1-deoxy 3-keto D-galactitol is shifted from C3 to C4 and that 1-deoxy sugars may bind to the catalytic site in the inhibitor-binding mode. The hydrophobic groove that acts as an accessible surface for substrate binding is formed through the dimerization of PcDTE. In PcDTE_C66S/deoxy sugar complex structures, bound ligand molecules in both the linear and ring forms were detected in the hydrophobic groove, while bound ligand molecules in the catalytic site were in the linear form. This result suggests that the sugar-ring opening of a substrate may occur in the hydrophobic groove and also that the narrow channel of the passageway to the catalytic site allows a substrate in the linear form to pass through.

We compared the growth inhibitory effects of all aldohexose stereoisomers against the model animal Caenorhabditis elegans. Among the tested compounds, the rare sugars d-allose (d-All), d-talose (d-Tal), and l-idose (l-Ido) showed considerable growth inhibition under both monoxenic and axenic culture conditions. 6-Deoxy-d-All had no effect on growth, which suggests that C6-phosphorylation by hexokinase is essential for inhibition by d-All.

Biological activities of unusual monosaccharides (rare sugars) have largely remained unstudied until recently. We compared the growth inhibitory effects of aldohexose stereoisomers against the animal model Caenorhabditis elegans cultured in monoxenic conditions with Escherichia coli as food. Among these stereoisomers, the rare sugar D-arabinose (D-Ara) showed particularly strong growth inhibition. The IC50 value for D-Ara was estimated to be 7.5 mM, which surpassed that of the potent glycolytic inhibitor 2-deoxy-D-glucose (19.5 mM) used as a positive control. The inhibitory effect of D-Ara was also observed in animals cultured in axenic conditions using a chemically defined medium; this excluded the possible influence of E. coli. To our knowledge, this is the first report of biological activity of D-Ara. The D-Ara-induced inhibition was recovered by adding either D-ribose or D-fructose, but not D-glucose. These findings suggest that the inhibition could be induced by multiple mechanisms, for example, disturbance of D-ribose and D-fructose metabolism.

The X-ray structure of ketose 3-epimerase from Arthrobacter globiformis M30, which was previously reported to be a D-allulose 3-epimerase (AgD-AE), was determined at 1.96 Å resolution. The crystal belonged to the hexagonal space group P6522, with unit-cell parameters a = b = 103.98, c = 256.53 Å. The structure was solved by molecular replacement using the structure of Mesorhizobium loti L-ribulose 3-epimerase (MlL-RE), which has 41% sequence identity, as a search model. A hexagonal crystal contained two molecules in the asymmetric unit, and AgD-AE formed a homotetramer with twofold symmetry. The overall structure of AgD-AE was more similar to that of MlL-RE than to the known structures of D-psicose (alternative name D-allulose) 3-epimerases (D-PEs or D-AEs), although AgD-AE and MlL-RE have different substrate specificities. Both AgD-AE and MlL-RE have long helices in the C-terminal region that would contribute to the stability of the homotetramer. AgD-AE showed higher enzymatic activity for L-ribulose than D-allulose; however, AgD-AE is stable and is a unique useful enzyme for the production of D-allulose from D-fructose.

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 4 C 1 (or 1 C 4) 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)].

The equilibrium tautomeric composition in aqueous solution of 6-deoxy-L-psicose and 1-deoxy-D-tagatose was elucidated by means of 13C NMR spectroscopy at 15–50 °C. The molar absorption coefficient ...

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.

Das seltene Vorkommen und die Kosten der Herstellung von L-Zuckern und anderen seltenen Zuckern haben die volle Ausschopfung ihres biologischen Potenzials bisher verhindert; zum Beispiel D-Psicose, erst seit kurzem verfugbar, ist schon als wichtiges neues Nahrungsmittel anerkannt. Hier stellen wir die preiswerte Synthese von 99.4 % reiner L-Glucose aus D-Glucose vor, die keinerlei Aufbereitung von Zwischen- oder Endprodukten, abgesehen von der Extraktion in und dem Entfernen von Losungsmitteln, benotigt. Durch einfache Umkristallisation wird die Reinheit auf >99.8 % erhoht.

A gene encoding L-ribulose 3-epimerase (L-RE) from Mesorhizobium loti, an important enzyme for rare sugar production by the Izumoring strategy, was cloned and overexpressed. The enzyme showed highest activity toward L-ribulose (230 U/mg) among keto-pentoses and keto-hexoses. This is the first report on a ketose 3-epimerase showing highest activity toward keto-pentose. The optimum enzyme reaction conditions for L-RE were determined to be sodium phosphate buffer (pH 8.0) at 60 °C. The enzyme showed of higher maximum reaction a rate (416 U/mg) and catalytic efficiency (43 M(-1) min(-1)) for L-ribulose than other known ketose 3-epimerases. It was able to produce L-xylulose efficiently from ribitol in two-step reactions. In the end, 7.2 g of L-xylulose was obtained from 20 g of ribitol via L-ribulose at a yield of 36%.

External control of gene expression is crucial in synthetic biology and biotechnology research and applications, and is commonly achieved using inducible promoter systems. The E. coli rhamnose-inducible rhaBAD promoter has properties superior to more commonly used inducible expression systems, but is marred by transient expression caused by degradation of the native inducer, l-rhamnose. To address this problem, 35 analogues of l-rhamnose were screened for induction of the rhaBAD promoter, but no strong inducers were identified. In the native configuration, an inducer must bind and activate two transcriptional activators, RhaR and RhaS. Therefore, the expression system was reconfigured to decouple the rhaBAD promoter from the native rhaSR regulatory cascade so that candidate inducers need only activate the terminal transcription factor RhaS. Rescreening the 35 compounds using the modified rhaBAD expression system revealed several promising inducers. These were characterized further to determine the strength, kinetics, and concentration-dependence of induction; whether the inducer was used as a carbon source by E. coli; and the modality (distribution) of induction among populations of cells. l-Mannose was found to be the most useful orthogonal inducer, providing an even greater range of induction than the native inducer l-rhamnose, and crucially, allowing sustained induction instead of transient induction. These findings address the key limitation of the rhaBAD expression system and suggest it may now be the most suitable system for many applications.

In the search for alternative non‐metabolizable inducers in the l ‐rhamnose promoter system, the synthesis of fifteen 6‐deoxyhexoses from l ‐rhamnose demonstrates the value of synergy between biotechnology and chemistry. The readily available 2,3‐acetonide of rhamnonolactone allows inversion of configuration at C4 and/or C5 of rhamnose to give 6‐deoxy‐d ‐allose, 6‐deoxy‐d ‐gulose and 6‐deoxy‐l ‐talose. Highly crystalline 3,5‐benzylidene rhamnonolactone gives easy access to l ‐quinovose (6‐deoxy‐l ‐glucose), l ‐olivose and rhamnose analogue with C2 azido, amino and acetamido substituents. Electrophilic fluorination of rhamnal gives a mixture of 2‐deoxy‐2‐fluoro‐l ‐rhamnose and 2‐deoxy‐2‐fluoro‐l ‐quinovose. Biotechnology provides access to 6‐deoxy‐l ‐altrose and 1‐deoxy‐l ‐fructose.

2-Deoxy- d -glucitol and 2-deoxy- d -allitol, both prepared as crystalline polyols from d -erythronolactone, are oxidized by Gluconobacter thailandicus NBRC 3254 to 5-deoxy- d - threo -hexulose [5-deoxy- d -fructose = 5-deoxy- l -sorbose] and 5-deoxy- d - erythro -hexulose [5-deoxy- l -psicose = 5-deoxy- d -tagatose], respectively. d -Tagatose-3-epimerase (DTE) equilibrates 5-deoxy- d -fructose to 5-deoxy- d -psicose and 5-deoxy- l -psicose to 5-deoxy- l -fructose, providing substrates for the preparation of all eight d - and l -5-deoxy aldohexoses by aldose isomerases. This combination of chemical and biotechnological methods allows a concise approach to the synthesis of all twelve 5-deoxy hexoses and further demonstrates the range of deoxy sugar substrates on which DTE is active. NMR studies show that 5-deoxy- d -fructose exists solely as the β-pyranose form whereas both pyranoses of 5-deoxy- d -fructose [α:β. 22:78] are observed. [For the sake of clarity, all ketoses in this Letter are shown in blue, alditols in red and aldoses in purple.]

Crystal structures were obtained for the two C2 epimeric azido-γ-lactones 2-azido-2-deoxy-3,5:6,7-di-O-isopropylidene-D-glycero-D-ido-heptono-1,4-lactone and 2-azido-2-deoxy-3,5:6,7-di-O-isopropylidene-D-glycero-D-gulo-heptono-1,4-lactone prepared from kinetic and thermodynamic azide displacements of a triflate derived from D-glucoheptonolactone. Azido-γ-lactones are very useful intermediates in the synthesis of iminosugars and polyhydroxylated amino acids. In this study two epimeric azido-heptitols allow biotechnological transformations via Izumoring techniques to 8 of the 16 possible homonojirimycin analogues, 5 of which were isolated pure because of the lack of stereoselectivity of the final reductive amination. A side-by-side glycosidase inhibition profile of 11 of the possible 16 HNJ stereoisomers derived from D-glucose and D-mannose is presented.

1-Deoxy-d-tagatose was produced by the hydrogenation of 6-deoxy-l-galactose (l-fucose) to l-fucitol followed by oxidation with Enterobacter agglomerans 221e; a similar sequence on d-fucose afforded 6-deoxy-d-tagatose. Thus, the polylol dehydrogenase recognizes the d-galacto-configuration of both d-fucitol and l-fucitol. The procedures were conducted in water and show the power of green, environmentally friendly biotechnology in the preparation of new monosaccharides with a potential for novel bioactive properties. 6-Deoxy-d-tagatose was also synthesized from d-tagatose via the efficient formation of 1,2:3,4-di-O-isopropylidene-α-d-tagatofuranose; a difficult final removal of protecting groups by acid makes the biotechnological route more attractive. © 2008 Elsevier Ltd. All rights reserved.

Although there are 32 6-azidoheptitols, there are only 16 homonojirimycin (HNJ) stereoisomers. Two epimeric azidoalditols derived from d-mannose allow the synthesis in water of eight stereoisomers of HNJ.

The Kiliani synthesis on the 4 readily accessible ketohexoses ( d -fructose, d -tagatose, l -sorbose, d -psicose) allows access to 4 diastereomeric 2-C-methyl-aldohexoses (2-C-methyl- d -mannose, 2-C-methyl- d -talose, 2-C-methyl- l -gulose, 2-C-methyl- d -allose) and 4 diastereomeric 2-C-methyl-alditols (2-C-methyl- d -mannitol, 2-C-methyl- d -talitol, 2-C-methyl- l -gulitol, 2-C-methyl- d -allitol). Microbial oxidation of 2-C-methyl- d -mannitol and 2-C-methyl- l -gulitol gave 5-C-methyl- d -fructose; microbial oxidation of 2-C-methyl- d -talitol afforded 5-C-methyl- d -psicose, whereas 2-C-methyl- d -allitol formed 5-C-methyl- l -psicose. Both enantiomers of 5-C-methyl-fructose were equilibrated by d -tagatose-3-epimerase (DTE) with both enantiomers of 5-C-methyl-psicose. These transformations demonstrate that polyol dehydrogenases and DTE act on branched synthetic sugars. Full NMR analyses show that 5-C-methyl- d -fructose is present as the β-pyranose and β-furanose forms in a ratio of 90:10; all pyranose and furanose forms of 5-C-methyl- d -psicose are present in solution. The combination of chemical and biological procedures allows the environmentally friendly generation of a new family of branched monosaccharides.

Ring closure of a 3,5-di-O-triflate derived from d-altrose with benzylamine allowed the formation of both monocyclic and bicyclic azetidine analogues of swainsonine.

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 a3T4(orE4) 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).

Acinetobacter sp. L-ribose isomerase (L-RI) catalyzes a reversible isomerization reaction between L-ribose and L-ribulose. To date, information on L-RI remains limited and its amino-acid sequence shows no similarity to those of any known enzymes. Here, recombinant His-tagged L-RI was successfully overexpressed, purified and crystallized. Crystals of His-tagged L-RI were obtained by the hanging-drop vapour-diffusion method at room temperature as two crystal forms which belonged to the monoclinic space group C2, with unit-cell parameters a = 96.60, b = 105.89, c = 71.83 Å, β = 118.16°, and the orthorhombic space group F222, with unit-cell parameters a = 96.44, b = 106.26, c = 117.83 Å. Diffraction data were collected to 3.1 and 2.2 Å resolution, respectively.

The L-rhamnose isomerase gene (rhi) of Mesorhizobium loti was cloned and expressed in Escherichia coli, and then characterized. The enzyme exhibited activity with respect to various aldoses, including D-allose and L-talose. Application of it in L-talose production from galactitol was achieved by a two-step reaction, indicating that it can be utilized in the large-scale production of L-talose.

The efficient isomerization of l-rhamnose [the only cheaply available deoxy hexose] to 1-deoxy-l-psicose, 1-deoxy-d-psicose, 1-deoxy-l-fructose, 1-deoxy-d-fructose, 1-deoxy-l-tagatose, 6-deoxy-l-psicose, 6-deoxy-d-psicose, 6-deoxy-l-fructose, 6-deoxy-d-fructose, and 6-deoxy-l-tagatose is described. The conversion of rhamnose to ten of the sixteen 1- and 6-deoxyketohexoses is accomplished in water in three steps. The range of substrates for d-tagatose-3-epimerase (DTE) is extended to 1- and 6-deoxyketoses. An authentic sample of 6-deoxy-d-psicose is prepared from d-psicose. © 2009 Elsevier Ltd. All rights reserved.

The scarcity and expense of access to L-sugars and other rare sugars have prevented the exploitation of their biological potential; for example D-psicose, only recently available, has been recognized as an important new food. Here we give the definitive and cheap synthesis of 99.4% pure L-glucose from D-glucose which requires purification of neither intermediates nor final product other than extraction into and removal of solvents; a simple crystallization will raise the purity to >99.8%.

Microbial oxidation of 2-C-methyl-d-ribitol and 2-C-methyl-d-arabinitol by Gluconobacter thailandicus NBRC 3254 produces 4-C-methyl-l-ribulose and 4-C-methyl-d-ribulose, respectively. Further, 4-C-methyl-l-ribulose and 4-C-methyl-d-ribulose were equilibrated by d-tagatose-3-epimerase (DTE) with 4-C-methyl-l-xylulose and 4-C-methyl-d-xylulose, respectively. These transformations demonstrate that polyol dehydrogenase and DTE act on branched synthetic sugars. The green preparation of all of the stereoisomers of 4-C-methyl pentuloses illustrates the ability of biotechnology to generate novel branched monosaccharides. © 2008 Elsevier Ltd. All rights reserved.

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 a2C5(or5C2) 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 theaaxis. The columns are linked by other O—H...O hydrogen bonds between D- and L-fructose molecules, forming a three-dimensional network.

We biosynthesized 6-deoxy- l -talose, 6-deoxy- l -sorbose, 6-deoxy- l -gulose, and 6-deoxy- l -idose, which rarely exist in nature, from l -fucose by coupling and sequential enzymatic reactions. The first product, 6-deoxy- l -talose, was directly produced from l -fucose by the coupling reactions of immobilized d -arabinose isomerase and immobilized l -rhamnose isomerase. In one-pot reactions, the equilibrium ratio of l -fucose, l -fuculose, and 6-deoxy- l -talose was 80:9:11. In contrast, 6-deoxy- l -sorbose, 6-deoxy- l -gulose, and 6-deoxy- l -idose were produced from l -fucose by sequential enzymatic reactions. d -Arabinose isomerase converted l -fucose into l -fuculose with a ratio of 88:12. Purified l -fuculose was further epimerized into 6-deoxy- l -sorbose by d -allulose 3-epimerase with a ratio of 40:60. Finally, purified 6-deoxy- l -sorbose was isomerized into both 6-deoxy- l -gulose with an equilibrium ratio of 40:60 by l -ribose isomerase, and 6-deoxy- l -idose with an equilibrium ratio of 73:27 by d -glucose isomerase. Based on the amount of l -fucose used, the production yields of 6-deoxy- l -talose, 6-deoxy- l -sorbose, 6-deoxy- l -gulose, and 6-deoxy- l -idose were 7.1%, 14%, 2%, and 2.4%, respectively.

Addition of human milk oligosaccharides (HMO) to baby foods may protect infants from disease. As many simple HMOs are fucosylated this is likely to increase the demand for L-fucose as a synthetic building block. Any chemical synthesis must be cheap to compete with a biotechnological process. Acetonide is the only protecting group we have used in this new synthesis of L-fucose from vitamin C in 27% overall yield (purification by recrystallization; no chromatography required in the entire sequence).

Sucrose phosphorylase (SPase) from Leuconostoc mesenteroides exhibited activity towards eight ketohexoses, which behaved as D-glucosyl acceptors, and α-D-glucose-1-phosphate (G1P), which behaved as a donor. All eight of these ketohexoses were subsequently transformed into the corresponding d-glucosyl-ketohexoses. Of the eight ketohexoses evaluated in the current study, d-allulose behaved as the best substrate for SPase, and the resulting d-glucosyl-d-alluloside product was found to be a non-reducing sugar with a specific optical rotation of [α]D(20) + 74.36°. D-Glucosyl-D-alluloside was identified as α-D-glucopyranosyl-(1→2)-β-D-allulofuranoside by NMR analysis. D-Glucosyl-D-alluloside exhibited an inhibitory activity towards an invertase from yeast with a Km value of 50 mM, where it behaved as a competitive inhibitor with a Ki value of 9.2 mM. D-Glucosyl-D-alluloside was also successfully produced from sucrose using SPase and D-tagatose 3-epimerase. This process also allowed for the production of G1P from sucrose and d-allulose from D-fructose, which suggested that this method could be used to prepare d-glucosyl-d-alluloside without the need for expensive reagents such as G1P and d-allulose.

6-Deoxy-l-glucose, 6-deoxy-l-altrose, and 6-deoxy-l-allose were produced from l-rhamnose with an immobilized enzyme that was partially purified (IE) and an immobilized Escherichia coli recombinant treated with toluene (TT). 6-Deoxy-l-psicose was produced from l-rhamnose by a combination of l-rhamnose isomerase (TT-PsLRhI) and d-tagatose 3-epimerase (TT-PcDTE). The purified 6-deoxy-l-psicose was isomerized to 6-deoxy-l-altrose and 6-deoxy-l-allose with l-arabinose isomerase (TT-EaLAI) and l-ribose isomerase (TT-AcLRI), respectively, and then was epimerized to l-rhamnulose with immobilized d-tagatose 3-epimerase (IE-PcDTE). Following purification, l-rhamnulose was converted to 6-deoxy-l-glucose with d-arabinose isomerase (TT-BpDAI). The equilibrium ratios of 6-deoxy-l-psicose:6-deoxy-l-altrose, 6-deoxy-l-psicose:6-deoxy-l-allose, and l-rhamnulose:6-deoxy-l-glucose were 60:40, 40:60, and 27:73, respectively. The production yields of 6-deoxy-l-glucose, 6-deoxy-l-altrose, and 6-deoxy-l-allose from l-rhamnose were 5.4, 14.6, and 25.1%, respectively. These results indicate that the aldose isomerases used in this study acted on 6-deoxy aldohexoses.

l-Ribose, a pentose, is not known to exist in nature. Although organisms typically do not have a metabolic pathway that uses l-ribose as a carbon source, prokaryotes use various sugars as carbon sources for survival. Acinetobacter sp. DL-28 has been shown to express the novel enzyme, l-ribose isomerase (AcL-RbI), which catalyzes reversible isomerization between l-ribose and l-ribulose. AcL-RbI showed the highest activity to l-ribose, followed by d-lyxose with 47% activity, and had no significant amino acid sequence similarity to structure-known proteins, except for weak homology with the d-lyxose isomerases from Escherichia coli O157 : H7 (18%) and Bacillus subtilis strain (19%). Thus, AcL-RbI is expected to have the unique three-dimensional structure to recognize l-ribose as its ideal substrate. The X-ray structures of AcL-RbI in complexes with substrates were determined. AcL-RbI had a cupin-type β-barrel structure, and the catalytic site was found between two large β-sheets with a bound metal ion. The catalytic site structures clearly showed that AcL-RbI adopted a cis-enediol intermediate mechanism for the isomerization reaction using two glutamate residues (Glu113 and Glu204) as acid/base catalysts. In its crystal form, AcL-RbI formed a unique homotetramer with many substrate sub-binding sites, which likely facilitated capture of the substrate. Database The atomic coordinates and structure factors of AcL-RbI/l-ribose, AcL-RbI/l-ribulose, AcL-RbI/ribitol, E204Q/l-ribose and E204Q/l-ribulose have been deposited in the Protein Data Bank under accession codes, 4Q0P, 4Q0Q, 4Q0S, 4Q0U and 4Q0V. Structured digital abstract • AcL-RbI and AcL-RbI bind by x-ray crystallography (View interaction).

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 a2C5(or5C2) 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 thebaxis. 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].

Only D-allose, among various rare monosaccharides tested, induced resistance to Xanthomonas oryzae pv. oryzae in susceptible rice leaves with defence responses: reactive oxygen species, lesion mimic formation, and PR-protein gene expression. These responses were suppressed by ascorbic acid or diphenylene iodonium. Transgenic rice plants overexpressing OsrbohC, encoding NADPH oxidase, were enhanced in sensitivity to D-allose. D-Allose-mediated defence responses were suppressed by the presence of a hexokinase inhibitor. 6-Deoxy-D-allose, a structural derivative of D-allose unable to be phosphorylated, did not confer resistance. Transgenic rice plants expressing Escherichia coli AlsK encoding D-allose kinase to increase D-allose 6-phosphate synthesis were more sensitive to D-allose, but E. coli AlsI encoding D-allose 6-phosphate isomerase expression to decrease D-allose 6-phosphate reduced sensitivity. A D-glucose 6-phosphate dehydrogenase-defective mutant was also less sensitive, and OsG6PDH1 complementation restored full sensitivity. These results reveal that a monosaccharide, D-allose, induces rice resistance to X. oryzae pv. oryzae by activating NADPH oxidase through the activity of D-glucose 6-phosphate dehydrogenase, initiated by hexokinase-mediated conversion of D-allose to D-allose 6-phosphate, and treatment with D-allose might prove to be useful for reducing disease development in rice.