2- chiral saccharides

Thiourea functions were used to attach chiral saccharide units to the molecule of calix[4]arene [72]. The complexation properties of these molecules toward chiral anions have not yet been examined. However, in the preliminary complexation studies (XH NMR titrations in DMSO-d6) the affinity toward acetate and AT-Ac-L-alaninate was observed. 

Fig. 21 Schematic illustration of a predominantly one-handed helix induction in 64 by hydrogen bonded complex formation with a chiral saccharide 65...

We have thus established that thiocarbonyl dienophiles on chiral saccharide carriers can be used for the synthesis of optically active thiopyran derivatives including 5-thiopyranoses. 

To construct helical columns several studies have used a different strategy where the core structure is dissymmetric. Saturated mesogens that are derived from chiral saccharides [80,81] and inositols [82] have a core that is chiral and are substituted with hydrocarbon chains. These materials stack into columnar structures but do not show any macroscopic manifestation of the core chirality. This is likely due to poor chiral information transfer from members of the stack. 

Postigo et al. developed novel UV-induced iodoperfluoroallg lation reactions of electron-rich and -deficient alkenes with C4F9I in water.Allyl benzoate derivatives in THF, 1,4-dioxane, or 2-propanol upon 305 nm irradiation afforded the solvent-adducts. A chiral saccharide ester of 1,4-naphthalenedicarboxylic acid acted as a sensitizer for the enantio-differentiating photocyclization of 5,5-diphenyl-4-penten-l-ol (174) to (175) in solvents and solvent mixtures, including near-critical/super-critical carbon dioxide. ... 

The asymmetric induction of chiral saccharide substituents was more effective in the cyclodimerization of cyclohexene 47. Trans-anti-trans dimer 48 was obtained in low enantioselectivity (2.1% ee) at 25°C, but in much higher enantioselectivity (68% ee) at -78°C in pentane with the chiral sensitizer (-)-50 (Scheme 16) this represents the highest ee value reported for an enantiodilferentiating-photosensitized cyclodimerization. 

Danishefsky et al. were probably the first to observe that lanthanide complexes can catalyze the cycloaddition reaction of aldehydes with activated dienes [24]. The reaction of benzaldehyde la with activated conjugated dienes such as 2d was found to be catalyzed by Eu(hfc)3 16 giving up to 58% ee (Scheme 4.16). The ee of the cycloaddition products for other substrates was in the range 20-40% with 1 mol% loading of 16. Catalyst 16 has also been used for diastereoselective cycloaddition reactions using chiral 0-menthoxy-activated dienes derived from (-)-menthol, giving up to 84% de [24b,c] it has also been used for the synthesis of optically pure saccharides. 

Competitive binding studies have shown that 164 and 166 are suitable for the detection of glucose at physiological levels [253-255]. Diboronate 165 is capable of chiral recognition of monosaccharides and gave the best chiral recognition for fructose when tested with a series of different saccharides [255]. 

Among the peculiar features of 2-bromoamides there are the following i) possibility of substitution at the tertiary C-Br (RCO2H, RR NH, or a saccharide, as the nucleophiles) ii) chiral stability and stereochemical control at the secondary C-Br atom (RR NH, ROH or a saccharide as the nucleophiles) iii) the presence of bromine allows cyclic voltammetry and electroreduction at controlled potential both of starting compounds and relevant intermediates iv) the Ca polarity can be reversed upon electroreduction, and the resulting Ca enolate forms a C-C bond (CO2 as the electrophile). 

In designing siderophore mimics, solubility and molecular recognition are key issues. A saccharide can provide a chiral... 

Deuterated and tritiated tin hydrides have been used to prepare deuterated saccharides93 and tritiated steroids46 from alkyl bromides, (equations 68 and 69). It is important to note that isomerization has occurred at the chiral reaction centre in the saccharide reaction (equation 68). For the steroid, the tin hydride reaction is regiospecific, i.e. it only reacts at the more reactive bromide rather than the less reactive chloride site and does not react with the keto group, the hydroxyl group or the acetal group. 

Besides a chiral remote induction for glycosidation, other glycosidic sugar-fused lactones have been also directly used as saccharidic delivery synthons. 

Both steric and electronic factors are used for chiral recognition of saccharides by the R and S forms of S-3. A difference in PET efficiency is created by the asymmetric immobilization of the amine groups relative to the binaphthyl moiety upon 1 1 complexation of saccharides by d- or L-isomers. For instance, D-fructose is recognized by the R form of S-2 with a large fluorescence enhancement. 

Carbohydrates are configurationally stable, easily available in enantiopure forms from the chiral pool, and they show a high density of chiral information per molecular unit. Their polyfunctionality and structural diversity fadhtate their tailor-made modification, derivatization, and structural optimization for a broad spectrum of synthetic applications. While derivatives of various saccharides have already been utilized as versatile starting materials and building blocks for chiral auxiliaries, ligands, and reagents [330] their obvious role as precursors for the... 

Work by Irie et al. on the control of intermolecular chiral l,l -binapthyl fluorescence quenching by chiral amines [66] and the use of 1,1 -binaphthyl in the recognition of chiral amines by Cram [67] were the inspiration behind the design of 26 (R or S). Chiral recognition of saccharides by 26 (R or S)... 

Chiral guanidinium-based ligands have also been used for recognition of diastereomeric salts of saccharides [45]. Some promising ligands with guani-dinium structure have not been studied yet [46], and some of them have been used as catalysts for the nitroaldol reaction [47] and Michael addition to a,P-unsaturated ketones [48]. 

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