4-Nitrophenyl chloroformate activation of poly-α,β-[N-(2-hydroxyethyl)-d,l- aspartamide] and poly-α,β-[N-(2,3- dihydroxypropyl)-d,l-aspartamide

Abstract

Poly-α,β-[N-(2-hydroxyethyl)-d,l-aspartamide] (PHEA) and poly-α,β-[N-(2,3-dihydroxypropyl)-d,l- aspartamide] (PDHPA) are suitable as macromolecular drug carriers. In order to introduce amine- containing drug moieties onto these polymers, partial conversion of the hydroxyl side groups is required. This paper describes the 4-nitrophenyl chloroformate activation of PHEA and PDHPA. It is shown that, during the course of the activation of PHEA, only linear aromatic carbonate structures were formed. However, during the activation reaction of PDHPA, conversion of 4-nitrophenyl carbonates into cyclic carbonate structures could be observed. The relative amount of the two types of carbonate moieties could be controlled by addition of the appropriate catalyst. During the activation reaction of both polymers, the total content of carbonate groups could, for a given set of reaction conditions, be controlled by the amount of chloroformate added. The 4-nitrophenyl carbonate groups easily reacted with amines. However, the conversion of the cyclic carbonate moieties into urethane-bound derivatives was only possible with highly reactive amines. This could be an interesting property for the introduction of different types of amine- containing derivatives onto the polymer backbone. The results of this study demonstrate the feasibility of the described activation methods to prepare macromolecular prodrugs.