Stereoselective depolymerization of chiral polyesters

Enzymes precisely structured chiral active pockets can achieve highly selective recognition of chirality in small molecules as well as macromolecule, enabling asymmetric transformation. Inspired by enzymic catalysis, the design of synthetic catalysts has enabled diverse asymmetric reactions of small molecules. However, stereoselective transformations of macromolecules catalyzed by synthetic catalysts remain unexplored. This work establishes a significant advancement in the field by demonstrating chiral recognition and conversion of polymers using synthetic catalysts. Employing the representative chiral polymer polylactic acid (PLA) as a model substrate, a specially designed catalyst BisSalen-Al with confined chiral cavity facilitated the stereoselective depolymerization of PLA into chiral lactide (LA) monomers. In depth exploration of the relationship between catalyst structure and stereoselectivity revealed the chiral recognition mechanism of polymer stereochemistry and catalyst chiral cavity matching. This work provides a strategy for the stereoselective conversion of chiral polymers and significantly advances the expansion of asymmetric catalysis into macromolecular systems. Lactide is enantiomeric, and depolymerization of poly(lactic acid) (PLA) with mixed chirality typically produces a racemic mixture. Here, the authors use a chiral Aluminium catalyst for the stereoselective depolymerization of PLLA and PDLA towards chiral lactide with high optical purity.