Poly(3-hydroxybutyrate)-depolymerase from Pseudomonas lemoignei: catalysis of esterifications in organic media

Lipase catalysis in nonaqueous media is recognized as a powerful tool in organic and more recently polymer synthesis. Even though none of the currently known polyhydroxyalkanoate (PHA) depolymerases have lipase activity, they do have a catalytic center that resembles that of lipases. Motivated by the above, the potential of using the poly(3-hydroxybutyrate), PHB, depolymerase from Psuedomonas lemoignei in organic media to catalyze ester-forming reactions was investigated. The effect of different organic solvents (benzene-d(6), cyclohexane-d(12), and acetonitrile-d(3)) on the activity of the PHB-depolymerase toward propylation of L-lactide was studied. A significant difference in the catalytic rate was observed as a function of solvent polarity. The selectivity of the PHB-depolymerase (P. lemoignei) to catalyze the propylation of a series of different lactones including epsilon-caprolactone, delta-butyrolactone, gamma-butyrolactone, and D, L, meso, and racemic lactides has been studied with the PHB-depolymerase (P. lemoignei) in organic solvents. Important differences in the reactivity of these lactones, as well as selective hydrolysis of stereochemically different linear lactic acid dimers, were observed. Moreover, the ability of the PHB-depolymerase to catalyze the solventless polymerization of epsilon-caprolactone and trimethylene carbonate was investigated.