Lipase‐catalyzed ring‐opening polymerization of morpholine‐2,5‐dione derivatives: A novel route to the synthesis of poly(ester amide)s

The enzymatic ring‐opening polymerization of 6‐membered cyclic depsipeptides, 3(S)‐isopropyl‐morpholine‐2,5‐dione, 3(R)‐isopropyl‐morpholine‐2,5‐dione, 3(R,S)‐isopropyl‐morpholine‐2,5‐dione, (3S, 6R,S)‐3‐isopropyl‐6‐methyl‐morpholine‐2,5‐dione, 3(S)‐isobutyl‐morpholine‐2,5‐dione, 3(S)‐sec‐butyl‐morpholine‐2,5‐dione, 6(S)‐methyl‐morpholine‐2,5‐dione and 6(R,S)‐methyl‐morpholine‐2,5‐dione in the bulk, was investigated by using the lipase PPL as a catalyst. In the absence of the enzyme, the monomers were recovered, indicating that the present polymerization proceeds through enzymatic catalysis. During the polymerization of morpholine‐2,5‐diones racemization of both the amino acid and the S‐lactic acid moiety takes place. Enzymatic polymerization produces polydepsipeptides with a carboxylic acid group at one end and a hydroxyl group at the other one.