Department of Chemistry, Central Michigan University , Mount Pleasant, Michigan 48859, United States.
J Org Chem. 2013 Nov 15;78(22):11221-8. doi: 10.1021/jo401603d. Epub 2013 Nov 6.
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. 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, they were 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 the background level. The synthesized antioxidants, free from copper contamination, demonstrated potent radical scavenging with IC50 values of less than 3 μM in the 2,2-diphenyl-1-picrylhydrazyl (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.
通过微波辅助炔基-叠氮 1,3-偶极环加成反应，使用铜颗粒作为催化剂合成了基于水杨醛和香草醛的抗氧化树枝状大分子。使用 Cu(I) 作为催化剂会导致树枝状大分子中含有铜污染物。为了生产用于生物应用的不含铜的抗氧化树枝状大分子，用铜颗粒替代了 Cu(I)。铜颗粒在室温下和回流条件下（<5%产率）均无效。然而，当在微波辐射下进行树枝状大分子合成时，它们是一种出色的催化剂，在 8 小时内产率高达 94%。用这种方法得到的抗氧化树枝状大分子的 ICP-质量分析显示几乎没有铜污染（9 ppm），与背景水平相同。合成的抗氧化剂不含铜污染，在 2,2-二苯基-1-苦基肼（DPPH）测定中，其 IC50 值小于 3 μM，具有很强的清除自由基能力。相比之下，由 Cu(I) 催化的点击化学合成的树枝状大分子含有大量的铜污染（4800 ppm），并且没有检测到抗氧化活性。
