Diels-alder "click" cycloadditions: a tool for synthesis of macromolecules

Abstract

Diels-Alder reaction is a well known [4+2] cycloaddition reaction between a diene and a dienophile. The fact that Diels-Alder reaction takes place even at room temperature without use of any other reagents and catalysts and formed products are obtained in good purity and yields makes this reaction a widely used method in synthetic organic chemistry. These properties had lead to classification of Diels-Alder reaction among ‘click’ reactions. In this study, this reaction is employed in order to synthesize unsymmetrical dendrons. Synthesis of unsymmetrical dendrons allows formation of dendrimers which can be furnished with more than one functional group and a structure like this, allows formation of targeted drug carrying macromolecules by attachment of targeting groups and drug molecules. The methodology employed in this research serves as a demonstration for efficient synthesis of segment block dendrimers. The strategy is mainly based on synthesis of three generations of furan functionalized Fréchet type dendrons and synthesis of maleimide functionalized poly (ester) dendrons which are then brought together with Diels-Alder reaction to yield unsymmetrical dendrimers in good yields. The formed dendrimers were further investigated for their stereochemical composition. Moreover the thermo reversible nature of the formed products was also demonstrated. As an extension of this project, surface of biodegradable poly (ester) dendrons with a maleimide core were furnished with alkyne moieties at their peripheries. These bifunctional macromolecules enable orthogonal functionalization and hence allow attachment of different molecules to the core and surface in a selective and efficient manner.