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The use of enzymes in academic as well as industrial chemical laboratories is now common, and in some cases live organisms are utilized. In this laboratory project, porcine pancreatic lipase (PPL) is used to convert a racemic sample of methyl gamma-hydroxypentanoate into gamma-methyl-gamma-butyrolactone in an effort to demonstrate the ability of enzymes to differentiate between enantiomeric substrates. This project also uses a number of chemical and spectroscopic techniques commonly used by organic and biochemists.
Students are asked to complete two lactonization reactions of racemic methyl gamma-hydroxypentanoate: one is catalyzed by PPL and the other by para-toluenesulfonic acid, which produces a racemic mixture of gamma-methyl-gamma-butyrolactone. Both samples of the gamma-lactone are analyzed by TLC, purified by silica gel column chromatography, and characterized by infrared and 1H-NMR studies. While the sample of g-lactone obtained from the PPL catalyzed reaction is optically active, [alpha]D25° = -13.4° (c = 0.0098, chloroform), the sample from the acid catalyzed reaction is not. Results from 1H-NMR studies of these lactones with a mole equivalent of (R)-(-)-2,2,2-trifluoro-1-(9-anthryl)ethanol show the enantiomeric excess of the optically active lactone to be 37 + 4 % favoring the S-enantiomer.
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