Target analogue imprinted polymers with affinity for folic acid and related compounds

Two approaches to synthesize molecularly imprinted polymers with affinity f or folic acid and other substituted pteridines have been compared. In the f irst approach, the folic acid analogue methotrexate was used as template an d functional monomers capable of generating selective binding sites were se arched in a miniaturized screening system based on binding assessment in th e batch mode. Highest selectivity was seen using 2-vinylpyridine as functio nal monomer, which was confirmed in the chromatographic mode for a batch sy nthesized on a gram scale. However, the retentivity and selectivity of this phase were insufficient for anticipated applications. In a second approach , using methacrylic acid as the functional monomer organic soluble inhibito rs for the enzyme dihydrofolate reductase; wars used to develop sites compl ementary toward the pteridine substructure. This resulted in materials show ing enhanced selectivity for substituted pteridines when evaluated by HPLC. Thus, methotrexate and leucovorine were selectively retained in mobile pha ses of either low or high aqueous content, thus showing the typical bimodal retention behavior of previously reported MIPs. In organic mobile-phase sy stems, the inhibitor used as template had an influence on the retentivity a nd selectivity of the MIP. The polymer imprinted with trimethoprim retained all folic acid analogues strongly and showed the highest selectivity among the MIPs in an organic mobile-phase system. This was supported by Scatchar d analysis resulting in biphasic plots and a quantitative yield of high-ene rgy binding sites. All templates were shown to associate strongly with MAA in CDCl3 the strength of association correlating roughly with the template basicity and the selectivity observed in chromatography. Nonparallel comple xation-induced shifts indicated formation of 1:2 template monomer complexes at concentrations corresponding to those of the prepolymerization solution s.