POLYCONDENSATION OF ALPHA-HYDROXY ACIDS BY ENZYMES OR PEG-MODIFIED ENZYMES IN ORGANIC MEDIA

In order to provide biodegradable poly(hydroxy acid)s by a simple proc ess, fundamental studies on the polycondensation of alpha-hydroxy acid s by enzymes and polyethylene glycol (PEG)-modified enzymes in organic media were carried out. The oligomer formation by unmodified hog live r esterase proceeded well using glycolic acid as a substrate in cycloh exanone. Lipase from Aspergillus niger gave the best result for the po lycondensation of glycolic acid among the unmodified enzymes used. The effects of the PEG-modification of enzyme on the polycondensation of alpha-hydroxy acids are also discussed. When the enzyme modified with a small amount of low-molecular-weight PEG was used, the conversion by polycondensation was relatively high. In particular, by using ethyl g lycolate as a substrate, which allows an ester exchange reaction, and 1,4-dioxane as a solvent, polycondensation by PEG-modified enzyme proc eeded effectively to give the pentamer of poly(glycolic acid).