ENZYME-ANALOG-BUILT POLYMERS .27. RACEMIC-RESOLUTION OF FREE SUGARS WITH MACROPOROUS POLYMERS PREPARED BY MOLECULAR IMPRINTING - SELECTIVITY DEPENDENCE ON THE ARRANGEMENT OF FUNCTIONAL-GROUPS VERSUS SPATIAL REQUIREMENTS

A molecular imprinting procedure was adopted to prepare highly cross-linked polymers for racemic resolution of free sugars. This is the first example illustrating a racemic resolution of free sugars on a support. For this purpose beta-D-fructopyranose 2,3:4,5-bis-O-((4-vinylphenyl)boronate) 2 and alpha-D-galactopyranose 1,2:3,4-bis-O-((4-vinylphenyl)boronate) 3, easily prepared from their parent free sugars in a single step, were copolymerized with a large amount of cross-linking agent. After splitting off the respective templates these polymers were used for racemic resolution of the racemates of the templates with separation factors alpha as high as alpha = 2.36 in the batch procedures. Surprisingly, polymers prepared from 2 preferably absorb D-fructose from D,L-fructose, but L-galactose from D,L-galactose. Similarly, polymers prepared from 3 preferably absorb D-galactose but L-fructose from the corresponding racemates. From these results and similar studies carried out with mannose derivatives, important conclusions can be drawn with regard to the separation mechanism on polymers prepared by molecular imprinting with templates. The influence of the arrangement of functional groups within the cavities versus the spatial requirements (shape selectivity) on selectivity is discussed in detail. In the examples presented here, the orientation of the functional groups inside the cavity is the dominating factor; shape selectivity is only of secondary importance. These findings offer new possibilities for the construction of selective adsorbents and enzyme-analogue-built catalysts.