Synthesis and Properties of 5,7-dimethylated anthocyanins: Focusing on peonidin-3-O-glucoside and
Jun Hu1, Guangkai Wu2, Xinman Zhan3
1School of Chemical Engineering and Light Industry, Guangdong Provincial Key Laboratory of Plant Resources Biorefinery, Guangdong University of Technology, Guangzhou 510632, China; Department of Food Science and Engineering, Institute of Food Safety and Nutrition, Guangdong Engineering Technology Center of Food Safety Molecular Rapid Detection, Jinan University, Guangzhou 510632, China.
Abstract:
This study developed an efficient chemical synthesis method for 5,7-dimethylated anthocyanins (Pn3GdM and Pt3GdM) to improve the poor liposolubility and instability of anthocyanins. The synthesis involved selective methylation of the A ring using a total synthesis approach and methoxy protection mediated by dimethyl sulfate. Structural and purity characterization by HPLC, NMR, and HRMS confirmed the feasibility of the strategy, yielding products with purities exceeding 95 %. The hydrophobicity of the methylated anthocyanins was significantly enhanced, as evidenced by increased logP values: Pn3G from -0.118 to -0.026 and Pt3G from -0.806 to -0.194, while maintaining water solubility. Additionally, the photostability of Pn3G was notably improved. Comparative analyses revealed that B-ring substituents had a greater impact on antioxidant activity, color, and pH stability. These results demonstrate that A-ring methylation is a promising strategy to enhance the solubility and stability of anthocyanins, offering potential for broader applications in food industries.
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