Enzymatic processes ring-opening polymerization

PCL - The polycaprolactone is derived from 8-caprolactone by ring-opening polymerization catalyzed by transition metal compounds. Toldwa and Suzuki (Tokiwa and Suzuki, 1977) have reported that PCL can be enzymatically degraded in presence of fungi and the biodegradation process has been discussed by Bastioli (Bastioli, 1998). 

The polymerization of 1 mentioned above should be compared with the enzymatic synthesis of chitin reported by Kobayashi and coworkers, in which an oxazoline derivative of A, A -diacetylchitobiose, the repeating unit of chitin was polymerized in the presence of chitinase enzyme via ring-opening addition process to give an artihcial chitin (Scheme 6) [5]. The method using an enzyme, however, may not enable synthesis of nonnatural-type aminopolysaccharide because the reaction catalyzed by chitinase enzyme is limited to the formation of (1 4)-P-glycosidic linkage. 

Chitin is the most abundant biomacromolecule in the animal field, which is found normally in invertebrates as a structural component. This important polysaccharide was synthesized for the first time by the enzymatic polymerization using chitinase and a chitobiose oxazoline derivative (Scheme 14).131 The latter activated monomer has a distorted structure with an a configuration at Cl, which resembles a transition-state structure of substrate chitin at the active site during a hydrolysis process (Scheme 15).3b 131132 The ring-opening polyaddition of the chitobiose oxazoline derivative was exclusively promoted by chitinase at pH 10.6, where the hydrolytic activity of chitinase was very much lowered. 

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