Copper Granule-Catalyzed Microwave-Assisted Click Synthesis of Polyphenol Dendrimers

摘要

Syringaldehyde and vanillin-based antioxidant dendrimers were synthesized via microwave-assisted alkyne-azide 1,3-dipolar cycloaddition using copper granules as a catalyst. The use of Cu(I) as a catalyst resulted in copper contaminated dendrimers. In order to produce copper-free antioxidant dendrimers for biological applications, Cu(I) was substituted with copper granules. Copper granules were ineffective at both room temperature and under reflux conditions (< 5% yield). However, it was an excellent catalyst when dendrimer synthesis was performed under microwave irradiation, giving yields up to 94% within 8 h. ICP-mass analysis of the antioxidant dendrimers obtained with this method showed virtually no copper contamination (9 ppm), which was the same as background level. The synthesized antioxidants, free from copper contamination, demonstrated potent radical scavenging with IC50 values of less than 3 µM in the DPPH assay. In comparison, dendrimers synthesized from Cu(I)-catalyzed Click chemistry showed a high level of copper contamination (4800 ppm) and no detectable antioxidant activity.