Optical saccharides

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. 

Boronic acid-containing polyaniline has also been utilized in diabetes-related research. One such polymer (23) (Fig. 17) has been observed to exhibit a linear near-infrared optical response to saccharides.43 The polymer was prepared by the copolymerization of aniline with 3-aminophenylboronic acid using lOmM (NH4)S208 in 1M HC1. The films were observed to undergo changes in the absorption spectra on addition of saccharides at pH 7.2. 

Figure 15.14 Study of the sample from the Dogon statuette 71.1935.105.169. (a) Optical microphotograph (b) SEM micrograph showing the layer structure ToF SIMS images of (c) proteins, (d) polysaccharides and (e) stearic acid (f) superposition of the distribution of poly saccharides and stearic acid (see colour Plate 9)...

Several, optically pure imino sugars have been synthesised by Fleet25 from simple mono-saccharides in a short, high yield synthetic sequences. The novelty of the presented approach involved an application of benzhydryl protecting group which allowed to avoid epimerisation at C-2 (Fig. 14). 

The thioaldonic phenylhydrazides obtained by reduction of saccharide formazans condense with benzaldehyde to give 1,3,4-thiadi-azolines, characterized by their high optical rotatory power.234,235... 

Fluorescence sensors for saccharides are of particular interest in a practical sense. This is in part due to the inherent sensitivity of the fluorescence technique. Only small amounts of a sensor are required (typically 10-6 M), offsetting the synthetic costs of such sensors. Also, fluorescence spectrometers are widely available and inexpensive. Fluorescence sensors have also found applications in continuous monitoring using an optical fiber and intracellular mapping using confocal microscopy. 

The optical rotations of saccharides are of such great value in the identification of such substances, in following their reactions, and in the proper assignment of configurations, that almost invariably the report on the isolation of a new sugar will include optical rotation data. In the raffinose family, sufficient data have been accumulated that the present writer considers it worth-while to summarize and correlate the available information. The optical rotatory values are listed in Table VI. 

Hudson s rules of isorotation are used for the determination of the configuration at the anomeric centers in oligo- and poly-saccharides and Korytnyk has discussed some extensions of these rules. Reeves has demonstrated that studies of the optical rotation in cuprammonia solution can give valuable information on the types of linkages and also on the conformation of sugar residues in a polysaccharide. Bourne and coworkers have shown that some o- and /S-D-glycosidic linkages display characteristic absorptions in the infrared at 844 and 891 cm, respectively. 

Related optical and fluorescent sensor systems have been widely used. For instance, the fluorescence of the pyrene unit in species (187) is quenched upon saccharide binding to the boron center. Boronic acid groups were also attached to dendrimers and polymers. The benefit of systems containing at least two boronic acid centers, as shown for the luminescent saccharide sensor (187), is that two-point binding can more effectively control saccharide binding. Similar... 

Mention has been made previously of the use of acid form cation exchangers to bring about optical inversion of saccharides. Another important application in the petrochemical industry is the use of hydrogen form macroporous cation exchange resins as a catalyst in the synthesis of various alkoxyalkanes (ethers) by the electrophilic addition of alcohols across carbon-carbon double bonds of alkenes ... 

Pringsheim, E. Terpetschnig, E. Piletsky, S. A. Wolfbeis, O. S. A polyaniline with near-infrared optical response to saccharides. Adv. Mater. 1999, 11, 865-868... 

Schulz and Jacobi opened up a new chapter in the study of the optical properties of oligo- and poly-saccharides by optical rotatory dispersion (o.r.d.) and circular dichroism (c.d.) measurements for amylose and amylo-pectin. 

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