Synthesis Of Sugars Research Articles

Biocatalytic Aldol Addition of Simple Aliphatic Nucleophiles to Hydroxyaldehydes.

Asymmetric aldol addition of simple aldehydes and ketones to electrophiles is a cornerstone reaction for the synthesis of unusual sugars and chiral building blocks. We investigated d-fructose-6-phosphate aldolase from E. coli (FSA) D6X variants as catalysts for the aldol additions of ethanal and nonfunctionalized linear and cyclic aliphatic ketones as nucleophiles to nonphosphorylated hydroxyaldehydes. Thus, addition of propanone, cyclobutanone, cyclopentanone, or ethanal to 3-hydroxypropanal or (S)- or (R)-3-hydroxybutanal catalyzed by FSA D6H and D6Q variants furnished rare deoxysugars in 8–77% isolated yields with high stereoselectivity (97:3 dr and >95% ee).

The modulation of various physiochemical changes in Bruguiera cylindrica (L.) Blume affected by high concentrations of NaCl

Bruguiera cylindrica is a major mangrove species in the tropical mangrove ecosystems and it grows in a wide range of salinities without any special features for the excretion of excess salt. Therefore, the adaptation of this mangrove to salinity could be at the physiological and biochemical level. The 3-month-old healthy plantlets of B. cylindrica, raised from propagules were treated with 0 mM, 400 mM, 500 mM and 600 mM NaCl for 20 days under hydroponic culture conditions provided with full strength Hoagland medium. The modulation of various physiochemical changes in B. cylindrica, such as chlorophyll a fluorescence, total chlorophyll content, dry weight, fresh weight and water content, Na+ accumulation, oxidation and antioxidation (enzymatic and non-enzymatic) features were studied. Total chlorophyll content showed very minute decrease at 500 mM and 600 mM NaCl treatment for 20 days and the water content percentage was decreased both in leaf and root tissues with increasing concentration. A significant increase of Na+ content of plants from 84.505 mM/plant dry weight in the absence of NaCl to 543.38 mM/plant dry weight in plants treated with 600 mM NaCl was recorded. The malondialdehyde and the metabolites content associated with stress tolerance (amino acid, total phenols and proline) showed an increasing pattern with increasing NaCl concentration as compared to the control in both leaf and root tissues but the increase recorded in plantlets subjected to 500 mM was much less, indicating the tolerance potential of this species towards 500 mM NaCl. The significant decrease of sugar content was found only in 600 mM NaCl on 20 days of treatment, showing that the process of sugar synthesis was negatively affected but the same process remains less affected at 500 mM NaCl. A slight reduction in ascorbate and glutathione content and very less increase in carotenoid content were observed at 500 mM and 600 mM NaCl stress. Antioxidant enzymes (APX, GPX, SOD and CAT) showed an enhanced activity in all the treatments and the increased activity was more significant in 600 mM treated plants. The result establishes that B. cylindrica tolerates high NaCl concentration, to the extent of 500 mM NaCl without any major inhibition on photosynthesis and metabolite accumulation. Understanding the modulation of various physiological and biochemical changes of B. cylindrica at high levels of NaCl will help us to know the physiochemical basis of tolerance strategy of this species towards high NaCl.

First protection-free protocol for synthesis of 1-deoxy sugars through glycosyl dithiocarbamate intermediates

A practical two-step synthetic process for 1-deoxy sugars has been established. The process consists of the direct introduction of a dimethyldithiocarbamate group into the anomeric center of unprotected sugars and subsequent hydrogenation in the AIBN-H3PO2-NaHCO3 system. No protecting groups are needed to synthesize 1-deoxy monosaccharides and 1-deoxy disaccharides.

In silico analyses of protein glycosylating genes in the helminth Fasciola hepatica (liver fluke) predict protein-linked glycan simplicity and reveal temporally-dynamic expression profiles

Glycoproteins secreted by helminth parasites are immunogenic and represent appealing components of vaccine preparations. Our poor knowledge of the pathways that mediate protein glycosylation in parasitic flatworms hinders our understanding of how proteins are synthesised and modified, and our ability to target these pathways for parasite control. Here we provide the first detailed description of genes associated with protein glycosylation in a parasitic flatworm, focusing on the genome of the liver fluke (Fasciola hepatica), which is a globally important trematode parasite of humans and their livestock. Using 190 human sequences as search queries against currently available F. hepatica genomes, we identified 149 orthologues with putative roles in sugar uptake or nucleotide sugar synthesis, and an array of glycosyltransferase and glycosidase activities required for protein N- and O-glycosylation. We found appreciable duplication within these orthologues, describing just 87 non-redundant genes when paralogues were excluded. F. hepatica lacks many of the enzymes required to produce complex N- and O-linked glycans, which explains the genomic basis for the structurally simple glycans described by F. hepatica glycomic datasets, and predicts pervasive structural simplicity in the wider glycome. These data provide a foundation for functional genomic interrogation of these pathways with the view towards novel parasite intervention strategies.

The influence of low temperature and diapause phase on sugar and polyol content in the European corn borer Ostrinia nubilalis (Hbn.)

The European corn borer (ECB, Ostrinia nubilalis Hbn.) is a major pest in temperate regions of Europe and North America. Fifth instar ECB larvae enter diapause before winter and gradually develop cold hardiness. Here we investigated the combined influence of diapause phase and low temperature on sugar and polyol content in ECB larvae. Larvae in mid-diapause or diapause termination were acclimated at 5 °C, −3°C or −16 °C, and sugar and polyol content was measured using GC–MS. Control GC–MS measurements were conducted on untreated non-diapausing larvae. We detected differences in polyol (glycerol, sorbitol, myo-inositol) and sugar (trehalose, fructose, glucose) levels in diapausing versus non-diapausing larvae. Glycerol and trehalose were the most abundant of all analyzed cryoprotective compounds in diapausing larvae. Exposure of diapausing larvae to decreasing temperatures induced changes in polyol and sugar levels that depended on the phase of diapause. In mid-diapause larvae, decreasing temperatures induced a significant increase in glycerol and a decrease in sorbitol and myo-inositol. In larvae at diapause termination, polyol content was lower and less influenced by decreasing temperatures. In contrast, sugar levels were lower in larvae at mid-diapause versus diapause termination. Exposure of larvae to −16 °C induced a significant increase in the levels of all detected sugars. In particular, glucose levels were significantly higher in larvae at diapause termination following exposure to −16 °C. We propose that this shift toward sugar synthesis following low temperature exposure in larvae at diapause termination is a consequence of NADPH dependent polyol synthesis, and may be a mechanism for preservation of carbon reserves needed for post-diapause development.

Chemoenzymatic Synthesis of Unnatural Nucleotide Sugars for Enzymatic Bioorthogonal Labeling

In recent years, the development of the enzymatic bioorthogonal labeling strategy has offered exciting possibilities in the probing of structure-defined glycan epitopes. This strategy takes advantage of relaxed donor specificity and strict acceptor specificity of glycosyltransferases to label target glycan epitopes with bioorthogonal reactive groups carried by unnatural nucleotide sugars in vitro. The subsequent covalent conjugation by bioorthogonal chemical reactions with either fluorescent or affinity tags allows further visualization, quantification, or enrichment of target glycan epitopes. However, the application and development of the enzymatic labeling strategy have been hindered due to the limited availability of unnatural nucleotide sugars. Herein, a platform that combines chemical synthesis and enzymatic synthesis for the facile preparation of unnatural nucleotide sugars modified with diverse bioorthogonal reactive groups is described. By this platform, a total of 25 UDP-GlcNAc and UDP-GalNAc de...

Sugar content and expression of sugar metabolism-related gene in strawberry fruits from various cultivars

Strawberry (Fragaria × ananassa) is a globallycultivated and popular fruit crop, prized for its flavor and nutritional value. Sweetness, a key determinant of fruit quality, depends on the sugar composition and concentration. We selected eight strawberry cultivars based on the fruit soluble solids content to represent high and low sugar content groups. The average soluble solid content was 13.6 °Brix (Okmae, Geumsil, Aram, and Maehyang) and 2.9 °Brix (Missionary, Camino Real, Portola, and Gilgyung53), for the high and low sugar content groups, respectively. Sucrose was the main sugar in the cultivars with high sugar content, whereas fructose was the main component in the low sugar content cultivars. Fruit starch concentration ranged from 3.247±0.056 to 3.850±0.055 g/100g, with a 12% higher concentration in the high sugar content cultivars. Additionally, we identified 41 sugar metabolism-related genes in Fragaria × ananassa and analyzed the relationship between their transcripts and the sugar accumulation in fruit. FaGPT1, FaTMT1, FaHXK1, FaPHS1, FaINVA-3, and FacxINV2-1 were highly expressed in the high sugar content cultivars, while FapGlcT, FaTMT2-1, FaPHS2-1, FaSUSY1-1, and FaSUSY1-2 were highly expressed in the low sugar content cultivars. In general, a greater number of genes encoding sugar transporters or involved in sugar synthesis were highly expressed in the high sugar content cultivars. Contrarily, genes involved in sugar degradation were preferentially transcribed in the low sugar content cultivars. Although gene expression was not perfectly proportional to sugar content or concentration, our analysis of the genes involved in sugar metabolism and accumulation in strawberries provides a framework for further studies and for the subsequent engineering of sugar metabolism to enhance fruit quality.

Relationship Between Carbon Mobilization and Root Growth Measured by Carbon-11 Tracer in Arabidopsis Starch Mutants

Experiments designed to quantify the physiological and metabolic status of Arabidopsis thaliana seedlings across their photoperiod used wild-type (Col-0) and genotypes deficient in starch biosynthesis (adg1-1, pgm-1) and in starch degradation (sex1-1) in combination with radioactive 11CO2 tracer. Measurements of root allocation and root exudation of 11C-photosynthates were conducted at 1 and 8 h into a 10-h photoperiod. Additionally, bioassays conducted on leaflets provided a measure of ‘new’ carbon partitioning (as 11C) into structural and non-structural carbohydrates. As expected, starch biosynthesis increased across the photoperiod for Col-0 controls. This increase was correlated with systematic decreases in soluble sugar synthesis and sink allocation across the photoperiod. We showed that this was a causal effect, which could be eliminated in the adg1-1 and pgm-1 mutants that were deficient in starch biosynthesis. Furthermore, these genotypes exhibited systematically higher levels of soluble sugars and sink allocation relative to Col-0 and sex1-1, which resulted in very different root growth traits including (i) increased root area balanced by shorter primary roots; (ii) increased number of lateral roots; and (iii) decreased root gravitropism. These differences in growth traits were correlated with higher observed levels of root auxin in these genotypes and to lower starch levels in their root tips. In a broader context, we find that carbon storage in the aboveground tissues can strongly influence root growth and root architecture belowground.

A Novel Method for the Pentosan Analysis Present in Jute Biomass and Its Conversion into Sugar Monomers Using Acidic Ionic Liquid.

Recently, ionic liquids (ILs) are used for biomass valorization into valuable chemicals because of their remarkable properties such as thermal stability, lower vapor pressure, non-flammability, higher heat capacity, and tunable solubility and acidity. Here, we demonstrate a method for the synthesis of C5 sugars (xylose and arabinose) from the pentosan present in jute biomass in a one-pot process by utilizing a catalytic amount of Brønsted acidic 1-methyl-3-(3-sulfopropyl)-imidazolium hydrogen sulfate IL. The acidic IL is synthesized in the lab and characterized using NMR spectroscopic techniques for understanding its purity. The various properties of BAIL are measured such as acid strength, thermal and hydrothermal stability, which showed that the catalyst is stable at a higher temperature (250 °C) and possesses very high acid strength (Ho 1.57). The acidic IL converts over 90% of pentosan into sugars and furfural. Hence, the presenting method in this study can also be employed for the evaluation of pentosan concentration in other kinds of lignocellulosic biomass.

Effects of IPT or NDGA Application on ABA Metabolism and Maturation in Grape Berries

The effects of isoprothiolane (IPT: a fungicide used to control rice blast) and nordihydroguaiaretic acid (NDGA: an inhibitor of the phytohormone abscisic acid (ABA) biosynthesis) on the maturation of “Shine Muscat” grape berries were investigated. The results showed that IPT and NDGA retarded chlorophyll degradation in the berry skin. Transcriptional profiling revealed that 2218 genes in the grapes treated with IPT and 2270 genes in those treated with NDGA were differentially expressed compared to the untreated control grapes at 70 days after full bloom (DAFB). IPT or NDGA application regulated the expression of genes involved in ABA, auxin, and ethylene metabolism. MapMan analysis and qRT-PCR validation showed that the expression levels of VvNCED1, VvCYP707A1, VvAAO4, and VvGEM-like genes in the ABA metabolic pathway were negatively regulated by IPT and NDGA treatment at 70 DAFB. Moreover, IPT and NDGA treatment inhibited glucose accumulation via the VvSUS, VvAI, VvHT genes in the sugar metabolic pathway. In addition, IPT and NDGA treatment delayed (E)-2-hexenal and hexanol productions, and down-regulated aroma metabolic pathway genes such as VvLOX, VvADH, VvGPPS, and VvTPS. These results suggest that IPT and NDGA influence chlorophyll degradation, ABA accumulation, and sugar and aroma volatile syntheses in the maturation process.

Facile and Stereo-Selective Synthesis of UDP-α-D-xylose and UDP-β-L-arabinose Using UDP-Sugar Pyrophosphorylase.

A novel synthesis of nucleotide sugars was conducted to prepare UDP-α-D-xylose and UDP-β-L-arabinose without utilizing protection strategies or advanced purification techniques. Sugar-1-phosphates of D-xylose and L-arabinose were synthesized from their β-glycosylsulfonylhydrazides and evaluated as substrates for recombinant UDP-sugar pyrophosphorylases from Arabidopsis thaliana or Bifidobacterium infantis to furnish the biologically active nucleotide. The facile, three-step procedure takes advantage of substrate diversity available through chemical synthesis followed by the selectivity of enzyme catalysis. This approach increases the substrate scope of enzymatic preparation and expands access to stereopure nucleotide sugars on preparative scale. Increased production of both sugars has implications for glycoengineering and glycan production using glycosyltransferases.

Augmenting the Calvin\u2013Benson\u2013Bassham cycle by a synthetic malyl-CoA-glycerate carbon fixation pathway

The Calvin–Benson–Bassham (CBB) cycle is presumably evolved for optimal synthesis of C3 sugars, but not for the production of C2 metabolite acetyl-CoA. The carbon loss in producing acetyl-CoA from decarboxylation of C3 sugar limits the maximum carbon yield of photosynthesis. Here we design a synthetic malyl-CoA-glycerate (MCG) pathway to augment the CBB cycle for efficient acetyl-CoA synthesis. This pathway converts a C3 metabolite to two acetyl-CoA by fixation of one additional CO2 equivalent, or assimilates glyoxylate, a photorespiration intermediate, to produce acetyl-CoA without net carbon loss. We first functionally demonstrate the design of the MCG pathway in vitro and in Escherichia coli. We then implement the pathway in a photosynthetic organism Synechococcus elongates PCC7942, and show that it increases the intracellular acetyl-CoA pool and enhances bicarbonate assimilation by roughly 2-fold. This work provides a strategy to improve carbon fixation efficiency in photosynthetic organisms.

Substrate scope of a dehydrogenase from Sphingomonas species A1 and its potential application in the synthesis of rare sugars and sugar derivatives.

SummaryRare sugars and sugar derivatives that can be obtained from abundant sugars are of great interest to biochemical and pharmaceutical research. Here, we describe the substrate scope of a short‐chain dehydrogenase/reductase from Sphingomonas species A1 (SpsADH) in the oxidation of aldonates and polyols. The resulting products are rare uronic acids and rare sugars respectively. We provide insight into the substrate recognition of SpsADH using kinetic analyses, which show that the configuration of the hydroxyl groups adjacent to the oxidized carbon is crucial for substrate recognition. Furthermore, the specificity is demonstrated by the oxidation of d‐sorbitol leading to l‐gulose as sole product instead of a mixture of d‐glucose and l‐gulose. Finally, we applied the enzyme to the synthesis of l‐gulose from d‐sorbitol in an in vitro system using a NADH oxidase for cofactor recycling. This study shows the usefulness of exploring the substrate scope of enzymes to find new enzymatic reaction pathways from renewable resources to value‐added compounds.

A kinetic model of sugar metabolism in peach fruit reveals a functional hypothesis of a markedly low fructose‐to‐glucose ratio phenotype

The concentrations of sugars in fruit vary with fruit development, environment and genotype. In general, there were weak correlations between the variations in sugar concentrations and the activities of enzymes directly related with the synthesis or degradation of sugars. This finding suggests that the relationships between enzyme activities and metabolites are often non-linear and are difficult to assess. To simulate the concentrations of sucrose, glucose, fructose and sorbitol during the development of peach fruit, a kinetic model of sugar metabolism was developed by taking advantage of recent profiling data. Cell compartmentation (cytosol and vacuole) was described explicitly, and data-driven enzyme activities were used to parameterize equations. The model correctly accounts for both annual and genotypic variations, which were observed in 10 genotypes derived from an interspecific cross. They provided important information on the mechanisms underlying the specification of phenotypic differences. In particular, the model supports the hypothesis that a difference in fructokinase affinity could be responsible for a low fructose-to-glucose ratio phenotype, which was observed in the studied population.

Synthesis of Branched-Chain Sugars with a DHAP-Dependent Aldolase: Ketones are Electrophile Substrates of Rhamnulose-1-phosphate Aldolases.

Dihydroxyacetone phosphate (DHAP)-dependent rhamnulose aldolases display an unprecedented versatility for ketones as electrophile substrates. We selected and characterized a rhamnulose aldolase from Bacteroides thetaiotaomicron (RhuABthet) to provide a proof of concept. DHAP was added as a nucleophile to several α-hydroxylated ketones used as electrophiles. This aldol addition was stereoselective and produced branched-chain monosaccharide adducts with a tertiary alcohol moiety. Several aldols were readily obtained in good to excellent yields (from 76 to 95 %). These results contradict the general view that aldehydes are the only electrophile substrates for DHAP-dependent aldolases and provide a new C-C bond-forming enzyme for stereoselective synthesis of tertiary alcohols.

Synthesis of O-Amino Sugars and Nucleosides.

Nucleic acids and carbohydrates are essential biomolecules involved in numerous biological and pathological processes. Development of multifunctional building blocks based on nucleosides and sugars is in high demand for the generation of novel oligonucleotide mimics and glycoconjugates for biomedical applications. Recently, aminooxyl-functionalized compounds have attracted increasing research interest because of their easy derivatization through oxime ligation or N-oxyamide formation reactions. Various biological applications have been reported for O-amino carbohydrate- and nucleoside-derived compounds. Here, we report our efforts in the design and synthesis of glyco-, glycosyl, nucleoside- and nucleo-aminooxy acid derivatives from readily available sugars and amino acids, and their use for the generation of N-oxyamide-linked oligosaccharides, glycopeptides, glycolipids, oligonucleosides and nucleopeptides as novel glycoconjugates or oligonucleotide mimics. Delicate and key points in the synthesis will be emphasized.

Compatible solutes and metabolites accumulation does not explain partial desiccation tolerance in Hymenoglossum cruentum and Hymenophyllum dentatum (Hymenophyllaceae) two filmy ferns with contrasting vertical distribution

Hymenoglossum cruentum (Cav.) Presl. and Hymenophyllum dentatum (Cav.) are poikilohydric partial desiccation tolerant (PDT) epiphytic filmy ferns with contrasting vertical distributions. H. cruentum is restricted to trunk base (ground to 1 m), and H. dentatum is more generalist growing from the ground up to 9 m in the host. Vertical distribution has been related to interspecific differences to cope with greater desiccating conditions such as low humidity and high irradiance. PDT plants exhibit a series of mechanisms that allow them to better tolerate severe dehydration that include the accumulation of compatible solutes, and the de novo synthesis of proteins and free sugars that are thought to protect cellular structure during cycles of desiccation-rehydration. Therefore, interspecific differences in the capacity to accumulate compatible solutes and metabolites during desiccation-rehydration may explain differences in vertical distribution between these two “filmy fern” species. The contents of proline, glycine betaine, soluble sugars, total proteins, and pigments of the photosynthetic system were evaluated during a cycle of desiccation-rehydration in H. cruentum and H. dentatum. The latter exhibited a more rapid desiccation-rehydration cycle in contrast to the former. Soluble sugars, proline, and pigment contents decreased in the dehydrated state. The two filmy ferns did not exhibit a major accumulation of proline (lower than 8 μmol g−1 DW) or glycine betaine (lower than 4 mg g−1 DW) which contrasts with other higher plants exposed to water deficit. Both species exhibited an elevated sugar concentration in the hydrated state, which decreased during desiccation by approximately 2.5-fold. These results differ from previous studies on other desiccation tolerant higher-plants but agree with results from bryophytes. We concluded that accumulation of conventional compatible solutes of higher plants is not part of the dehydration induced mechanisms conferring desiccation tolerance in filmy ferns, and do not explain interspecific differences in vertical distribution of the two species. Therefore, partial desiccation tolerance of filmy ferns probably relies on preformed structural rather than induced biochemical mechanisms, suggesting similarities of Hymenophyllaceae (primitive ferns) with bryophytes.

Synthesis of novel sugar or azasugar modified anthra[1,2-d] imidazole-6,11-dione derivatives and biological evaluation

A series of novel, sugar or azasugar modified anthra[1,2-d] imidazole-6,11-dione derivatives, with different side chain were synthesized, using the synthetic route of imidazole cyclization reaction of 1,2-diaminoanthraquinone with various sugar (azasugar)-derived aldehydes, and imidazole cyclization reaction of 1,2-diaminoanthraquinone with chloroacetic acid and then followed by the nucleophilic substitution of N-alkylamino azasugar. Their biological activities against HIV-RT and cytotoxic activities against A549, Hela and MCF-7 cells were preliminary evaluated, most compounds showed similar HIV-RT inhibition to the control drug (AZT).

Acinetobacter baumannii isolate BAL_212 from Vietnam produces the K57 capsular polysaccharide containing a rarely occurring amino sugar N-acetylviosamine.

The structures of capsular polysaccharides (CPSs) produced by different Acinetobacter baumannii strains have proven to be invaluable in confirming the role of specific genes in the synthesis of rare sugars through the correlation of genetic content at the CPS biosynthesis locus with sugars found in corresponding CPS structures. A module of four genes (rmlA, rmlB, vioA and vioB) was identified in the KL57 capsule biosynthesis gene cluster of A. baumannii isolate BAL_212 from Vietnam. These genes were predicted to direct the synthesis of 4-acetamido-4,6-dideoxy-d-glucose (N-acetylviosamine, d-Qui4NAc) and the K57 CPS was found to contain this monosaccharide. The K57 structure was determined and, in addition to d-Qui4NAc, included three N-acetylgalactosamine residues in the main chain, with a single glucose side branch. The KL57 gene cluster has not been found in any other A. baumannii genomes, but the rmlA-rmlB-vioA-vioB module is present in the KL119 gene cluster that would likely produce a d-Qui4NAc-containing CPS.

Utilization of Lignocellulosic Biomass via Novel Sustainable Process.

In this review, we show novel methods for utilizing lignocellulosic biomass, polysaccharides, and lignin. Firstly, the simultaneous enzymatic saccharification and comminution (SESC) of plant materials is described as an extraction method for lignocellulosic biomass that does not require toxic reagents or organic solvents. Secondly, we demonstrate the material utilization of non-deteriorated lignocellulosic biomass extracted by SESC, such as for sugar and ethanol synthesis, and as a heatproof filler. Finally, we exhibit the use of a functional monomer (e.g., in disinfection chemicals, cesium chelation, and building blocks for polymers), 2-pyrone-4,6-dicarboxylic acid, derived from lignin via metabolic degradation.