Examples using carbohydrates

An illustrative example of carbohydrate-protein recognition has been reported by Chen and coworkers [192] using a C18-mucin mimic polymer that interacts hydro-phobically with SWCNTs. This biohybrid is able to specifically recognize the lectin Hdixpomatia agglutinin (Figure 1.15 A). Galactose-modified CNTs are able to capture... 

When comparing these results with those previously obtained using carbohydrate-based vinyl ethers as chiral dienophiles, this improved facial diastereoselectivity to heterodienes under similar conditions is noteworthy.81 The efficient chiral transfer in the second example might mostly be attributed to the specific architecture of the l,2 5,6-di-0-isopropylidene-a-D-glucofuranose moiety.Those findings open the way to develop well-defined spiro-carbohydrate templates towards improved auxiliaries for chirality transfer in a wide range of syntheses. 

In polymer applications derivatives of oils and fats, such as epoxides, polyols and dimerizations products based on unsaturated fatty acids, are used as plastic additives or components for composites or polymers like polyamides and polyurethanes. In the lubricant sector oleochemically-based fatty acid esters have proved to be powerful alternatives to conventional mineral oil products. For home and personal care applications a wide range of products, such as surfactants, emulsifiers, emollients and waxes, based on vegetable oil derivatives has provided extraordinary performance benefits to the end-customer. Selected products, such as the anionic surfactant fatty alcohol sulfate have been investigated thoroughly with regard to their environmental impact compared with petrochemical based products by life-cycle analysis. Other product examples include carbohydrate-based surfactants as well as oleochemical based emulsifiers, waxes and emollients. 

Carbohydrates have found widespread use as chiral auxiliaries in asymmetric Diels-Al-der reactions156. A recent example is a study conducted by Ferreira and colleagues157 who used carbohydrate based chiral auxiliaries in the Lewis acid catalyzed Diels-Alder reactions of their acrylate esters 235 with cyclopentadiene (equation 66). Some representative results of their findings, including the ratios of products 236 and 237, have been summarized in Table 9. The formation of 236 as the main product when diethylaluminum chloride was used in dichloromethane (entry 3) was considered to be the result of an equilibrium between a bidentate and monodentate catalyst-dienophile complex. The bidentate complex would, upon attack by the diene, lead to 236, whereas the monodentate complex would afford 236 and 237 in approximately equal amounts. The reversal of selectivity on changing the solvent from dichloromethane to toluene (entry 2 vs 3) remained unexplained by the authors. 

Many aspects of the chemistry of carbohydrates are not specihc to this class of compounds, but are merely examples of the simple chemical reactions we have already met. Therefore, against usual practice, we have not attempted a full treatment of carbohydrate chemistry and biochemistry in this chapter. We want to avoid giving the impression that the reactions described here are something special to this group of compounds. Instead, we have deliberately used carbohydrates as examples of reactions in earlier chapters, and you will find suitable cross-references. 

AUylic systems are interesting substrates for the investigation of new methods of C-C bond formation. Some of these methods have been adapted to the carbohydrate field. Enopyrano-sides are often crystalline compounds readily available, for example, using Ferrier rearrangement of tri-0-acetyl glycals with alcohols or its variants with carbon nucleophiles. 

Organometallic methods, with the possible exception of those involving the stoichiometric generation of enolates and other stabilized carbanionic species 140], have seldom been used in carbohydrate chemistry for the synthesis of cyclohexane and cyclopentane derivatives. The present discussion will not cover these areas. The earliest of the examples using a catalytic transition metal appears in the work of Trost and Runge [41], who reported the Pd-catalyzed transformation of the mannose-derived intermediate 22 to the functionalized cyclopentane 23 in 98% yield (Scheme 10). Under a different set of conditions, the same substrate gives a cycloheptenone 24. Other related reactions are the catalytic versions of the Ferrier protocol for the conversion of methylene sugars to cyclohexanones (see Chap. 26) [40,42,43]. 

Comminution also may be used to examine the stability of dispersed phases such as oil droplets. Depending on the viscosity of the product one simply mixes it or breaks it up in a solvent (usually water but, for example, use fresh soybean oil for chocolate), a buffer or the appropriate dyes (below). For instance, we mix easily dispersible foods (cream cheese, ice cream mix or tablespreads) with dyes on slides in a ratio of about 1 1 before examination. Where the dye is a diachrome (that is, highly colored) or is fluorescent in the absence of the substrate (for example, Acridine Orange) some attempt must be made to remove excess, uncomplexed dye molecules which might confound the interpretation. This can be done by reduction of the dye concentration or by making the preparation thinner. The advantage of these simple techniques is that a battery of microchemical tests to identify protein, lipid and carbohydrate can be completed on multiple samples in a very short time period. 

These are (1) The chiral substrate approach. This approach involves using chiral precursors that transfer their chirality to the final cyclopentenone. This implies the synthesis of chiral substrates, which has generally been made from classic chiral pools. Examples include carbohydrate derivatives like 40 that give 41 with variable yields depending on the substitution pattern. 41 is transformed into cyclopenta[c]pyrane 42, which is the skeleton of iri-doids [93]. In another example epichlorhydrin (43) is used to construct chiral enyne 44 which gives cyclopentenone 45 [94] (Scheme 14). 

QCM has been used extensively in the areas of DNA hybridization, protein adsorption studies, immunological systems and also in the areas of protein-protein and protein-carbohydrate interaction [24]. Examples prepared using carbohydrate SAMs to function as lectin biosensors are known since initially it was shown... 

Several examples of carbohydrates whose structure and/or conformation have been found using proton-proton vicinal couplings are listed in Table 5.3. 

Multifunctional carbohydrate derivatives have been used widely as chiral synthons [240], and they have more recently found application as chiral auxiliaries [241], In this chapter, examples of carbohydrates in which an alcohol functional group is the point of attachment to the reagent wall be presented. Alkylations of ester etiolates of the D-allofiiranose derivative 1.47 or of the diacetoneghicose... 

The pharmaceutical impact of carbohydrate-based therapeutics can also be seen in the agents now under evaluation in pre-clini-cal and clinical development. For example, synthetic carbohydrate chains, modeled on tumor cell antigens but modified to stimulate an immune response, are being used to develop novel cancer vaccines. 

In this article we provide a broad overview of the application of radical methods in carbohydrate chemistry, including typical examples classified by the type of bond formed. The factors controlling the stereoselectivity of inter- and intramolecular C-C bond formation are now well understood and have been exploited in the synthesis of C-glycosides [2]. Intramolecular C C bond formation using carbohydrate-based chiral templates also provides a powerful route to branched-chain sugars [3] and carbocycles [4]. Finally, we include synthetically useful processes involving key carbon-heteroatom and C-H bond formation. 

Given the dynamics of the supramolecular system described, one could go a step further and transgress the confinements of molecular constitution. It should be just as possible to use carbohydrates, steroids, terpenes or even nonbiogenic substance classes - dendrimers, for example - in place of the peptides. Through the addition of conjugates of different types of constitution, the transition from one type to another could be studied in a quasi-continuous way, opening up a further, new option for the determination of structure—activity relationships. 

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