Synthesis of S-linked carbohydrate analogues via a Ferrier reaction

In this work, the synthetic utility of the Ferrier reaction to access S-linked disaccharides and S-linked glycoamino acids has been probed. Significantly, entry to a range of 1,4- and 1,6-S-linked disaccharides has been achieved using glycals derived from glucose and galactose, and sulfur containing coupling partners derived from methyl α-d-glucopyranoside. Access to S-linked glycoamino acids and glycopeptides has also been achieved using protected cysteine and homocysteine coupling partners within the Ferrier reaction. Functionalisation of the Ferrier products, for example, via dihydroxylation using OsO4 or amino acid coupling, and deprotection of the targets have also been achieved. In this way, entry to materials of interest as mimics of biologically interesting disaccharides and glycopeptides has been realised, including targets derived from rare sugars such as talopyranose and gulopyranose.

Rapid synthesis of carbohydrate derivatives, including mimetics of c-linked disaccharides and c-Linked aza disaccharides, using the Hetero-Diels−Alder Reaction

In this work we demonstrate the value of performing a Hetero Diels-Alder reaction (HDAR) between Danishefsky’s diene and a range of aldehydes or imines, under microwave irradiation. By using a range of aldehydes and imines, including those derived from carbohydrates, access to functionalised 2,3-dihydro-4H-pyran-4-ones or 2,3-dihydro-4-pyridinones in good to excellent synthetic yields is possible. A particular strength of the methodology is its ability to access mimetics of C-linked disaccharides and C-linked aza disaccharides, targets of current therapeutic interest, in a rapid, convenient and diastereoselective manner. The effect of high pressure on the HDARs involving carbohydrate derived aldehydes and imines is also explored, with enhancement in yields occurring for the aldehyde substrates. Finally, HDARs using carbohydrate derived ketones, enones and enals are described under a range of conditions. Optimum results were obtained under high pressure conditions, with highly functionalized carbohydrate derivatives being afforded, in good yields, in this way.

Synthetic entry to functionalised morpholines and [1,4]-oxazepanes via reductive amination reactions of carbohydrate derived dialdehydes

The rapid synthesis of functionalised morpholines and [1,4]-oxazepanes displaying up to three stereocentres, by reductive amination reactions between carbohydrate derived dialdehydes and a range of amines, is described. (C) 2004 Elsevier Ltd. All rights reserved.

Synthesis of fused cyclic systems containing medium-sized rings through tandem ROM-RCM of norbornene derivatives embedded in a carbohydrate template

A general approach for the synthesis of fused cyclic systems containing medium-sized rings (7-9) has been developed. The key steps involve a diastereoface-selective Diels-Alder reaction of the dienophiles 4a-d attached to a furanosugar with cyclopentadiene and ring opening (ROM)-ring closing metathesis (RCM) of the resulting norbornene derivatives 10a-d and 11a-d. Diels-Alder reaction of the dienophiles 4a-d with cyclopentadiene in the absence of a catalyst produced 10a-d as the major product arising through addition of the diene to the unhindered Si-face. The most interesting and new aspect of the Diels-Alder reaction of these dienophiles is the accessibility of the Re-face that was blocked by the alkenyl chains under Lewis acid catalysis producing the diastereoisomers 11a-d exclusively. The reversal of facial selectivity from an uncatalyzed reaction to a catalyzed one is unprecedented. The observed stereochemical dichotomy is attributed to rotation of the enone moiety along the or bond linking the sugar moiety during formation of the chelate 13. This makes the Re-face of the enone moiety in 4a-d unhindered. Diels-Alder reaction of the carbocyclic analogue 15 under Lewis acid catalysis produced a 1: 1 mixture of the adducts 16 and 17 confirming the participation of sugar ring oxygen in chelate formation. Finally ROM-RCM of 10a-d and 11a-d with Grubbs' catalyst afforded the cis-syn-cis and cis-anti-cis bicyclo-annulated sugars 21a-d and 23a-d, respectively, containing 7-9 membered rings.

Application of the asymmetric hetero Diels-Alder reaction for synthesising carbohydrate derivatives and glycosidase inhibitors

This review provides a discussion of recent developments in the asymmetric hetero Diels-Alder reaction (AHDAR), with particular emphasis on the synthesis of carbohydrates, their derivatives, and inhibitors of carbohydrate processing enzymes.

Carbohydrate-based therapeutics

In recent years there has been a resurgence of interest in the biological roles of carbohydrates and as a result it is now known that carbohydrates are involved in a vast array of disease processes. This review summarises progress in the development of carbohydrate-based therapeutics that involve: inhibition of carbohydrate-lectin interactions; immunisation, using monoclonal antibodies for carbohydrate antigens; inhibition of enzymes that synthesise disease-associated carbohydrates; replacement of carbohydrate-processing enzymes; targeting of drugs to specific disease cells via carbohydrate-lectin interactions; carbohydrate based anti-thrombotic agents.

Carbohydrate preference, acid tolerance and bile tolerance in five strains of Bifidobacterium

Aims: To assess the suitability of bifidobacteria for inclusion in synbiotic products on the basis of carbohydrate preference, acid and bile tolerance. Methods and Results: Five strains of Bifidobacterium were analysed for their carbohydrate preference from 12 substrates. Maximum growth rates were used to compare substrate preferences. Galacto-oligosaccharides and isomalto-oligosaccharides were well utilized by all the test species. Most bacteria tested could also utilize at least one type of fructan molecule. To determine transit tolerance of potentially probiotic bifidobacteria, acid and bile resistance was tested. A wide range acid resistance was found. Bile tolerance also varied. Conclusions: GOS and IMO were generally well utilized by the tested species. Other substrates were used to different degrees by the different species. Most bifidobacteria are poorly resistant to strongly acidic conditions with the exception of Bifidobacterium lactis Bb12. Bile tolerances were widely variable and it was shown that caution should be exercised when using colorimetric methods to assess bile tolerance. Significance and Impact of Study: The study allows the comparison of the properties of bifidobacteria, allowing a cost effective screen for the best species for use in synbiotic products to allow better survival and efficacy.

Modulation of anti-pathogenic activity in canine-derived Lactobacillus species by carbohydrate growth substrate

Aims: To investigate the effect of various carbon sources on the production of extracellular antagonistic compounds against two Escherichia coli strains and Salmonella enterica serotype Typhimurium by three canine-derived lactobacilli strains. Methods and Materials: Cell-free preparations, pH neutralized, were used in antibiotic disc experiments as an initial screening. The bacteria/carbohydrate combinations that showed inhibition of the growth of those pathogens, were further investigated in batch co-culture experiments. The cell-free supernatants of the cultures, that decreased the population number of the pathogens in the co-culture experiments to log CFU ml(-1) less than or equal to 4, were tested for inhibition of the pathogens in pure cultures at neutral and acidic pH. Conclusions: The results showed that the substrate seems to affect the production of antimicrobial compounds and this effect could not just be ascribed to the ability of the bacteria to grow in the various carbon sources. L. mucosae, L. acidophilus and L. reuteri, when grown in sugar mixtures consisting of alpha-glucosides (Degree of Polymerization (DP) 1-4) could produce antimicrobial compounds active against all three pathogens in vitro. This effect could not be attributed to a single ingredient of those sugar mixtures and was synergistic. This inhibition had a dose-response characteristic and was more active at acidic pH. Significance and Impact of the Study: Knowledge of the effect that the carbon source has on the production of antimicrobial compounds by gut-associated lactobacilli allows the rational design of prebiotic/probiotic combinations to combat gastrointestinal pathogens.

Carbohydrate-based anti-adhesive inhibition of Vibrio cholerae toxin binding to GM1-OS immobilized into artificial planar lipid membranes

We have studied 'food grade' sialyloligosaccharides (SOS) as anti-adhesive drugs or receptor analogues, since the terminal sialic acid residue has already been shown to contribute significantly to the adhesion and pathogenesis of the Vibrio cholerae toxin (Ctx). GM1-oligosaccharide (GM1-OS) was immobilized into a supporting POPC lipid bilayer onto a surface plasmon resonance (SPR) chip, and the interaction between uninhibited Ctx and GM1-OS-POPC was measured. SOS inhibited 94.7% of the Ctx binding to GM1-OS-POPC at 10 mg/mL. The SOS EC50 value of 5.521 mg/mL is high compared with 0.2811 mu g/mL (182.5 pM or 1.825 x 10(-10) M) for GM1-OS. The commercially available sialyloligosaccharide (SOS) mixture Sunsial E (R) is impure, containing one monosialylated and two disialylated oligosaccharides in the ratio 9.6%. 6.5% and 17.5%, respectively, and 66.4% protein. However, these inexpensive food-grade molecules are derived from egg yolk and could be used to fortify conventional food additives, by way of emulsifiers, sweeteners and/or preservatives. The work further supports our hypothesis that SOS could be a promising natural anti-adhesive glycomimetic against Ctx and prevent subsequent onset of disease. (C) 2009 Elsevier Ltd. All rights reserved

Carbohydrate preferences of Bifidobacterium species isolated from the human gut

The growth of nine species of Bifidobacterium on media containing glucose, xylose, xylooligosaccharides (XOS), xylan or fructooligosaccharides (FOS) as the sole carbon source were compared in pure culture. The bifidobacteria differed in fermentation profiles when tested on different carbohydrates. All species grew to their highest final optical density (OD) on a glucose containing medium, with the exception of B. catenulatum which demonstrated a preference for xylose over glucose, and XOS over FOS. B. bifidum grew to the highest OD on XOS compared to xylose suggesting a specific transport system for the oligosaccharide over the monomer. This is consistent with a lack of β-xylosidase activity present in the culture medium. Lactate, formate and acetate levels were determined and the ratios of these metabolites altered between and within species growing on different carbohydrates. In general, high lactate production correlated with low formate production and low lactate concentrations were obtained at higher levels of formate. Bifidobacteria may alter their metabolic pathways based upon the carbohydrates that are available for their use.

Successful manipulation of the quality and quantity of fat and carbohydrate consumed by free-living individuals using a food exchange model

Our objective in this study was to develop and implement an effective intervention strategy to manipulate the amount and composition of dietary fat and carbohydrate (CHO) in free-living individuals in the RISCK study. The study was a randomized, controlled dietary intervention study that was conducted in 720 participants identified as higher risk for or with metabolic syndrome. All followed a 4-wk run-in reference diet [high saturated fatty acids (SF)/high glycemic index (GI)]. Volunteers were randomized to continue this diet for a further 24 wk or to I of 4 isoenergetic prescriptions [high monounsaturated fatty acids (MUFA)/high GI; high MUFA/low GI; low fat (LF)/high GI; and LF/low GI]. We developed a food exchange model to implement each diet. Dietary records and plasma phospholipid fatty acids were used to assess the effectiveness of the intervention strategy. Reported fat intake from the LF diets was significantly reduced to 28% of energy (%E) compared with 38% E from the HM and LF diets. SF intake was successfully decreased in the HM and LF diets was similar to 10% E compared with 17% E in the reference diet (P = 0.001). Dietary MUFA in the HIM diets was similar to 17% E, significantly higher than in the reference (12% E) and LF diets (10% E) (P = 0.001). Changes in plasma phospholipid fatty acids provided further evidence for the successful manipulation of fat intake. The GI of the HGI and LGI arms differed by similar to 9 points (P = 0.001). The food exchange model provided an effective dietary strategy for the design and implementation across multiple sites of 5 experimental diets with specific targets for the proportion of fat and CHO. J. Nutr. 139: 1534-1540, 2009.

Carbohydrate-based micelle clusters which enhance hydrophobic drug bioavailability by up to 1 order of magnitude

Amphiphilic chitosan-based polymers (M-w < 20 kDa) self-assemble in aqueous media at low micromolar concentrations to give previously unknown micellar clusters of 100-300 nm in size. Micellar clusters comprise smaller 10-30 nm aggregates, and the nanopolarity/drug incorporation efficiency of their hydrophobic domains can be tailored by varying the degree of lipidic derivatization and molecular weight of the carbohydrate. The extent of drug incorporation by these novel micellar clusters is 1 order of magnitude higher than is seen with triblock copolymers, with molar polymer/drug ratios of 1:48 to 1:67. On intravenous injection, the pharmacodynamic activity of a carbohydrate propofol formulation is increased by 1 order of magnitude when compared to a commercial emulsion formulation, and on topical ocular application of a carbohydrate prednisolone formulation, initial drug aqueous humor levels are similar to those found with a 10-fold dose of prednisolone suspension.

Effect of changing the amount and type of fat and carbohydrate on insulin sensitivity and cardiovascular risk: the RISCK (Reading, Imperial, Surrey, Cambridge, and Kings) trial

Background: Insulin sensitivity (Si) is improved by weight loss and exercise, but the effects of the replacement of saturated fatty acids (SFAs) with monounsaturated fatty acids (MUFAs) or carbohydrates of high glycemic index (HGI) or low glycemic index (LGI) are uncertain. Objective: We conducted a dietary intervention trial to study these effects in participants at risk of developing metabolic syndrome. Design: We conducted a 5-center, parallel design, randomized controlled trial [RISCK (Reading, Imperial, Surrey, Cambridge, and Kings)]. The primary and secondary outcomes were changes in Si (measured by using an intravenous glucose tolerance test) and cardiovascular risk factors. Measurements were made after 4 wk of a high-SFA and HGI (HS/HGI) diet and after a 24-wk intervention with HS/HGI (reference), high-MUFA and HGI (HM/HGI), HM and LGI (HM/LGI), low-fat and HGI (LF/HGI), and LF and LGI (LF/LGI) diets. Results: We analyzed data for 548 of 720 participants who were randomly assigned to treatment. The median Si was 2.7 × 10−4 mL · μU−1 · min−1 (interquartile range: 2.0, 4.2 × 10−4 mL · μU−1 · min−1), and unadjusted mean percentage changes (95% CIs) after 24 wk treatment (P = 0.13) were as follows: for the HS/HGI group, −4% (−12.7%, 5.3%); for the HM/HGI group, 2.1% (−5.8%, 10.7%); for the HM/LGI group, −3.5% (−10.6%, 4.3%); for the LF/HGI group, −8.6% (−15.4%, −1.1%); and for the LF/LGI group, 9.9% (2.4%, 18.0%). Total cholesterol (TC), LDL cholesterol, and apolipoprotein B concentrations decreased with SFA reduction. Decreases in TC and LDL-cholesterol concentrations were greater with LGI. Fat reduction lowered HDL cholesterol and apolipoprotein A1 and B concentrations. Conclusions: This study did not support the hypothesis that isoenergetic replacement of SFAs with MUFAs or carbohydrates has a favorable effect on Si. Lowering GI enhanced reductions in TC and LDL-cholesterol concentrations in subjects, with tentative evidence of improvements in Si in the LF-treatment group. This trial was registered at clinicaltrials.gov as ISRCTN29111298.