Boronic acids saccharides

One of the clearest pieces of evidence for the reversibility of some covalent interactions came from the work of Gunther Wulff at the University of Dusseldorf, Germany [172], He used imprinted polymers of o-aminomethyl phenylboronic acids as chromatographic stationary phases for the separation of saccharides. Older studies [173] also point to the reversible nature of the boronic acid-saccharide interaction. The pioneering studies of fluorescent transduction of this phenomenon by Czarnik and Yoon [174] (Ohio State University), Aoyama et al. [175] (Kyushu University, Japan), and Shinkai et al. [176] (Kyushu University, Japan) have been reviewed previously [9], Our concern in this review is particularly with the systems that clearly involve PET. Czarnik and Yoon s 93 [177] which interacts with catechol derivatives to produce 94 also belongs here. It... 

LOCHMCller AND HILL Boronic Acid-Saccharide Compkxation... 

The use of boronic acids in the development of fluorescent sensors for saccharides is a comparatively new field (Scheme 3). Following the first report by Yoon and Czamik" o-glucose selectivity was achieved in 1994 by James et al. A year later, this was followed up by enan-tioselective saccharide recognition. The intervening years have seen the field grow to the point where hundreds of publications now report on boronic acid-saccharide recog-... 

Photoinduced electron transfer (PET) has been wielded as a tool of choice in fluorescent sensor design for protons and metal ions. Design of fluorescent sensors for neutral organic species presents a harsher challenge due to the lack of electronic changes upon inclusion. The design of a fluorescent sensor based on the boronic acid saccharide interaction has been difficult due to the lack of sufficient electronic changes found in either the boronic acid moiety or in the saccharide moiety. Furthermore, facile boronic... 

To attain this purpose one must manipulate two boronic acids in an appropriate spatial position to achieve successful two-point interrogation of a specific saccharide guest. In these systems it is known that only when two boronic acids are intramolecularly bridged by a saccharide, resultant saccharide-containing macrocycles become CD-active. In order to arrange two boronic-acid-appended porphyrins in an appropriate spatial position a )U-oxo dimer (15) of porphinatoiron(III) (14) would have a great potential the jU-oxo dimer is stable in basic aqueous solution where the boronic acid-saccharide complex is also stable. Furthermore, the distance between two... 

Another possible transcription method is to use chiral metal complexes. Tris[2,2 -bipyridine(bpy)]-metal complexes have inherent A vs. A chirality. It occurred to us that two pyridine rings may be asymmetrically oriented by a boronic acid-saccharide interaction and the metal complexes thus formed may contain an excess... 

The final point to be considered in boronic acid - saccharide binding is the predisposition of boronic acids to interact with different kinds of diols. The stability constants (K) between various polyols and boronic acids were first quantified by Lorand and Edwards and it is the case that the trends established now appear inherent in all monoboronic acids. ... 

As discussed in Section 3.2 the formation of a boronic acid-saccharide complex acidifies the boron atom, making the resultant boronic ester more acidic than the initial uncomplexed boronic acid. In this instance, a of 8.8 was reported for the neutral 2-anthrylboronic acid, and a p a of 5.9 was reported for the 2-anthrylboronic acid complex formed in saturated fructose solution. Exploiting this phenomenon, the system was bulfered to a pH of 7.4, a value between the corresponding pA a and pKj values reported. With this constraint in place, a high-fluorescence emission intensity was observed from the uncomplexed boronic acid (pH < pKf). However, imder these buffered conditions, addition of a saccharide to the solution formed the boronic ester, lowering the acidity of the boronic species below the pH of the solution pKf < pH). As a direct result, the boronate anion was generated inducing the decrease in fluorescence observed on addition of saccharide. 

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