Integrating Urea-based Units into Porphyrinic Covalent Organic Framework for Efficient Artemisinin Photosynthesis

Abstract

Artemisinin and its derivatives are the most efficacious treatment for malaria, and the artificial synthesis of artemisinin supplies a promising method to satisfy market demand. However, conventional artemisinin preparation via homogeneous photo/acid-catalytic reactions usually suffers from the difficulty in recycling the photo/acid-catalysts and treating waste acid. Consequently, it is still highly urgent for developing environment-friendly and effective artificial preparation methods for artemisinin. Herein, a dual-function covalent organic framework (COF), named Urea-COF, has been synthesized from the condensation of meso-tetra(p-formylphenyl)porphyrin with 1,3-bis(4-aminophenyl)urea. Urea-COF exhibits a high surface area of 1732 m2 g-1 with a large pore size of 3.1 nm, enabling a fast mass transport and high accessibility of urea groups. The urea groups as hydrogen bond donor catalytic sites bind strongly to the carboxylic acid to release H+, thereby increasing the acidity of the carboxylic acid. This, in combination with the exceptional capacity of porphyrin macrocycles to generate singlet oxygen, endows Urea-COF with excellent heterogeneous photocatalytic activity towards tandem semisynthesis of artemisinin from dihydroartemisinic acid in a high conversion rate (99%) and yield (71%) without additional acid, superior to all the thus far reported homogeneous and heterogeneous photocatalytic systems.