Possible applications of chiral-core dendrimers

The first example of the use of a chiral-core dendrimer as enantioselective receptor in molecular recognition processes was reported by Diederich (see Fig. 4.70). This dendrimer, designated as a dendrocleff, acts as enantioselective receptor for monosaccharides. It bears a central axially chiral 9,9 -spirobi[9H-fluorene] unit which is linked via two 2,6-bis(carbonylamino)pyridine spacer groups, each in 2,2 position, with triethylene glycol monomethyl ether dendrons [14b]. Both 

1H-NMR studies and analysis of sensor responses in the CD spectrum - after addition of sugar as guest to the dendrocleft host - show that the ability of this dendritic host to enantioselectively recognise monosaccharides decreases with increasing generation number of the dendron surrounding the chiral core unit. 

In contrast, the diastereoselectivity of the dendritic host increases. This indicates that on shielding of the chiral core unit with sterically more demanding dendrons in higher-generation dendroclefts the monosaccharide guests are no longer bound in the immediate vicinity of the chiral core unit instead, a less specific host/guest interaction takes place with the dendrimer scaffold. 

The prototype of a first fluorescence sensor for enantioselective recognition of chiral amino alcohols was synthesised by Pu et al. by linking phenylacetylene dendrons to an axially chiral binaphthol core unit (see Fig. 4.71) [14c, d, 25], 

Such chiral luminescent dendrimers, whose fluorescence is quenched significantly more strongly by one enantiomer of a chiral guest molecule than by its mirror-image counterpart, would be of interest for rapid determination of the 

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