Optically Active β-Methyl-δ-Valerolactone: Biosynthesis and Polymerization

Abstract

Chemo-enzymatic pathways were developed to prepare optically enriched (+)-β-methyl-δ-valerolactone and (−)-β-methyl-δ-valerolactone. Anhydromevalonolactone, synthesized by the acid-catalyzed dehydration of bioderived mevalonate, was transformed to (+)-β-methyl-δ-valerolactone with 76% ee and 69% conversion using the mutant enoate reductase, YqjM(C26D, I69T). With the same substrate but a different enoate reductase (OYE2), we obtained the other enantiomer ((−)-β-methyl-δ-valerolactone) with higher selectivity and yield (96% ee and a 92% conversion). The enzyme-docking program LibDock was used to help explain the origin of the divergent enatntioselectivity of the two reductases, and complementary in vitro experiments were used to determine the turnover number and Michaelis constant for each. Finally, the effect of the enantiopurity of the β-methyl-δ-valerolactone monomer on the properties of the corresponding polyester was investigated. Like atactic poly((±)-β-methyl-δ-valerolactone), the isotactic polymer was determined to be amorphous with a low softening temperature (−52 °C).