Synthesis, Spectroscopic Study and Radical Scavenging Activity of Kaempferol Derivatives: Enhanced Water Solubility and Antioxidant Activity

• Published in: International journal of molecular sciences Vol. 20; no. 4; p. 975
• Main Authors: Deng, Sui-Ping, Yang, Yi-Li, Cheng, Xing-Xing, Li, Wen-Rong, Cai, Ji-Ye
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 23.02.2019; MDPI
• Subjects: antioxidant activity; Antioxidants; Carbon; flavonoid; Flavonoids; Free radicals; Fruits; gallium complex; Hydrogen atoms; Kaempferol; Ligands; Mass spectrometry; Mass spectroscopy; NMR; Nuclear magnetic resonance; Organic chemistry; Scavenging; Sulfonation; Sulfonic acid; Thiazoline; water solubility; gallium complex; flavonoid; kaempferol; water solubility; antioxidant activity
• ISSN: 1422-0067; 1661-6596; 1422-0067
• DOI: 10.3390/ijms20040975

Kaempferol (Kae) is a natural flavonoid with potent antioxidant activity, but its therapeutic use is limited by its low aqueous solubility. Here, a series of Kae derivatives were synthesized to improve Kae dissolution property in water and antioxidant activity. These compounds included sulfonated Kae (Kae-SO₃), gallium (Ga) complexes with Kae (Kae-Ga) and Kae-SO₃ (Kae-SO₃-Ga). The compound structures were characterized by high-resolution mass spectrometry (HRMS), nuclear magnetic resonance (NMR) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and thermal methods (TG/DSC). The results showed that a sulfonic group (-SO₃) was successfully tethered on the C3' of Kae to form Kae-SO₃. And in the metal complexation, 4-CO and 3-OH of the ligand participated in the coordination with Ga(III). The metal-to-ligand ratio 1:2 was suggested for both complexes. Interestingly, Kae-SO₃-Ga was obviously superior to other compounds in terms of overcoming the poor water-solubility of free Kae, and the solubility of Kae-SO₃-Ga was about 300-fold higher than that of Kae-Ga. Furthermore, the evaluation of antioxidant activities in vitro was carried out for Kae derivatives by using α,α-diphenyl-β-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid) diammonium salt (ABTS) free radical scavenging. The results showed that Kae-SO₃-Ga was also optimal for scavenging free radicals in a dose-dependent manner. These data demonstrate that sulfonate kaempferol-gallium complex has a promising future as a potential antioxidant and as a potential therapeutic agent for further biomedical studies.