Poly(β-malic acid): obtaining high molecular weights by improvement of the synthesis route

Abstract

Poly(β-malic acid), PMLA, was first synthesized with the aim of being used as a macromolecular prodrug. However, this biodegradable polymer is now the parent compound of a large family functional polymers, copolymers and polystereoisomers. The requirement for high molecular weight polymers for a series of temporary therapeutic or specific applications needs to be conducted to examine the different steps of the synthesis route starting from either racemic or chiral aspartic acid. Drastic purifications of the intermediate products and of the β-substituted-β-lactone used as monomer has allowed the synthesis of polymers with high molecular weights, in a reproducible manner. In the case of racemic poly(β-malic acid benzyl ester), a precursor of PMLA, it is now possible to prepare polymers with a M SEC superior to 150 000 (polystyrene standards). The specific catalytic hydrogenolysis of the lateral benzyl protecting groups can be carried out and leads to the corresponding PMLA with long molecular chains, which are necessary for certain applications in vivo. The results have been extended to different racemic and optically active derivatives of this poly(3-hydroxy aci) ester type. Consequently, reproducible characteristics of the corresponding polymeric materials can be obtained.