title: Copper-granule-catalyzed microwave-assisted click synthesis of polyphenol dendrimers.
abstract: 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.
authors.affiliation: Department of Chemistry, Central Michigan University , Mount Pleasant, Michigan 48859, United States.
authors.forename: Choon Young
authors.initials: CY
authors.lastname: Lee
authors.forename: Rich
authors.initials: R
authors.lastname: Held
authors.forename: Ajit
authors.initials: A
authors.lastname: Sharma
authors.forename: Rom
authors.initials: R
authors.lastname: Baral
authors.forename: Cyprien
authors.initials: C
authors.lastname: Nanah
authors.forename: Dan
authors.initials: D
authors.lastname: Dumas
authors.forename: Shannon
authors.initials: S
authors.lastname: Jenkins
authors.forename: Samik
authors.initials: S
authors.lastname: Upadhaya
authors.forename: Wenjun
authors.initials: W
authors.lastname: Du
mesh_terms: D000480:Alkynes / Q000737:chemistry; D000975:Antioxidants / Q000138:chemical synthesis / Q000737:chemistry; D001386:Azides / Q000737:chemistry; D002384:Catalysis; D057930:Click Chemistry; D003300:Copper / Q000737:chemistry*; D003500:Cyclization; D050091:Dendrimers / Q000138:chemical synthesis* / Q000737:chemistry; D008872:Microwaves; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D059808:Polyphenols / Q000138:chemical synthesis* / Q000737:chemistry
chemical_list: D000480:Alkynes; D000975:Antioxidants; D001386:Azides; D050091:Dendrimers; D009942:Organometallic Compounds; D059808:Polyphenols; D003300:Copper