Title:
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Novel synthetic lectins for carbohydrate recognition in water
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Carbohydrate recognition in water still remains one of the most challenging tasks for supramolecular
chemists. Despite the challenges, the Davis group has had good success in designing and synthesising
compounds capable of carbohydrate recognition. Within this body of work 6 novel carbohydrate
receptors are reported, based upon the anthracene design shown below. The majority of the reported
receptors displayed good to excellent affinities to all-equatorial carbohydrates.
One of the synthesised receptors, containing methoxy functionality on the anthracene units,
demonstrated remarkably high affinity to maltodextrins, such as maltotriose and maltotetraose
(Chapter 2). The binding affinities displayed towards maltodextrins by this receptor, ~2000 M-1, are
amongst the highest affinities reported for synthetic carbohydrate receptors in water, and they also
are of a similar magnitude to the binding affinities displayed by natural carbohydrate receptors, lectins.
A selection of unsymmetrical receptors were also synthesised, wherein one anthracene moeity was
unsubstituted and the other was substituted with either bromines, methylesters or carboxylic acids
(Chapter 3). These designs were implemented in order to red-shift the receptor's fluorescence
emission wavelength, something they did achieve, however only at the consequence of a reduced
increase in the receptor's fluorescence intensity upon carbohydrate binding.
Of the unsymmetrical receptors synthesised, one, containing a tetracarboxylic acid substituted
anthracene, displayed exceptional binding to all-equatorial carbohydrates, binding D-glucose with a
binding affinity of 186 M-1. This represents the highest binding affinity to glucose reported.
Additionally, the receptor displayed a selectivity of 186:1 for glucose over mannose, a selectivity higher
than many lectins.
One receptor, wherein one anthracene unit was substituted with a naphthalene, displayed no affinity
towards carbohydrates in water (Chapter 4). Such a result, highlighted the importance of hydrophobic
interactions are in achieving carbohydrate recognition in water.
Finally, further investigations into the reported binding of carbohydrates by a porphyrin based system
were carried out (Chapter 6). The results showed tight 1:1 binding between the carbohydrate and the
porphyrin was absent, and instead kinetically slow readjustments of porphyrin aggregates appeared
to be responsible for the change in UV-vis and fluorescence properties of the porphyrin.
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