Synthesis of immobilized poly-D-leucine

The /V-carboxyanhydridc was placed in a 250 mL round-bottomed flask equipped with a magnetic stirrer bar, under nitrogen. Dry tetrahydrofuran (llOmL) was then added followed by crasx-linked aminomethylpolystyrene. The mixture was stirred for 4 days. 

The solution was filtered, diethyl ether (50 mL) was added to the solid and collected on the filter. The solid was left to soak in the diethyl ether for 30 minutes before removing the solvent by aid of a water aspirator. This procedure of soaking the solid on the filter was repeated with acetone distilled water (1 1), acetone-distilled water (4 1), acetone (2 x 50 mL), ethyl acetate (50 mL) and petroleum ether (50 mL). 

The white solid was placed under high vacuum overnight to give immobilized poly-D-leucine (4.4 g) as a white powder. 

The quality of the catalyst can be determined by performing an asymmetric epoxidation reaction on chalcone according to the following procedure. The activity of the polymer was considered satisfactory if it provided the epoxy-chalcone in 85% yield and 95% of enantiomeric excess, with a reaction time between 10 and 40 minutes. 

In a lOmL round-bottomed flask equipped with a magnetic stirrer bar were placed tetrahydrofuran (0.8 mL) and immobilized poly-D-leucine (100 mg). (7 )-Benzylidene acetophenone (50 mg), l,8-diazabicyclo[5.4.0] undec-7-ene (90 mg), and urea-hydrogen peroxide (27 mg) were added to the mixture. The thick white reaction mixture was stirred vigorously for 30 minutes. 

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