Investigation of the Effects of Hydrogen Bonding on the Enantiomeric Excess of Pig Liver Esterase Hydrolysis Products

Pig Liver Esterase (PLE) is an effective enzyme used in the Masterson Research Group due to its ability to hydrolyze only one ester in a malonic diester. PLE is employed for creating chiral molecules for the synthesis of unnatural amino acid precursors. Previous research in the group found that malonic half esters with hydrogen bonding capable substrates yielded varying degrees of enantiomeric excess, and non-hydrogen bonding substrates yielded racemic mixtures.1,2 The compounds synthesized contained substrates consisting of thiophene rings in the second and third position, and these molecules act as a control for the other research done in the group. Due to sulfurs inability to hydrogen bond, it was suspected that the synthesized compounds would be racemic.3 However, this was not the case. The hydrolysis product from Figure 3 had an enantiomeric excess of 43%, and the hydrolysis product from Figure 9 gave an enantiomeric excess of 8.6% These results question the initial hypothesis that a thiophene-substituted malonic half ester would be racemic. This could be caused by the size of the sulfur atom sterically hindering one enantiomer, but the exact reason is unknown. Further research will need to be conducted to determine the cause of the discrepancy