Lipase-catalyzed transformation of unnatural-type poly(3-hydroxybutanoate) into reactive cyclic oligomer

Unnatural-type syndiotactic and atactic poly[(R,S)-3-hydroxybutanoate]s [P(3HB)s] were enzymatically transformed into a reactive cyclic 3HB oligomer of molecular weight ca. 500 in an organic solvent, such as toluene, using immobilized lipase from Candida antarctica at 40°C for 24 h. It was confirmed that similar results were obtained for both syndiotactic and atactic P(3BHB)s. On the other hand, the acidic degradation of these polymers using a protonic acid, such as p-toluenesulfonic acid, exclusively produced the linear 3HB oligimer instead of the cyclic oligomer. The formation of the cyclic oligomer was regarded as the characteristic feature of the lipase-catalyzed degradation in organic media. The cyclic oligomer obtained readily reacted with alcohol as a nucleophile, and using lipase, to produce the alkyl ester of the 3HB oligomer.