Large acceleration of a-chymotrypsin-catalyzed dipeptide formation by 18-crown-6 in organic solvents

The effects of 18-crown-6 on the synthesis of peptides catalyzed by α-chymotrypsin are reported. Lyophilization of the enzyme in the presence of 50 equivalents of 18-crown-6 results in a 425-fold enhanced activity when the reaction between the 2-chloroethylester of N-acetyl-L-phenylalanine and L-phenylalaninamide is carried out in acetonitrile. Addition of crown ether renders the dipeptide synthesis in nonaqueous solvents catalyzed by α-chymotrypsin possible on a preparative scale. The acceleration is observed in different solvents and for various peptide precursors