Synthesis, Characterization, and Antiradical Activity of 6-Hydroxygenistein
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SYNTHESIS, CHARACTERIZATION, AND ANTIRADICAL ACTIVITY OF 6-HYDROXYGENISTEIN
Jin Shao,1,2 Tong Zhao,1,3 Hui-Ping Ma,1 Zheng-Ping Jia,1,2 and Lin-Lin Jing1*
A convergent synthesis route of 6-hydroxygenistein (6-OHG) was reported, starting from cheap and readily available biochanin A, via methylation, bromination, methoxylation, and demethylation. The structure of the products was confirmed by MS, IR, 1H NMR, and 13C NMR analysis. The antiradical activity of 6-OHG was determined using six different methods, namely, DPPH assay, ABTS assay, nitric oxide assay, superoxide assay, reducing power assay, and phosphomolybdenum assay using ascorbic acid (VC) as positive control. The results show that 6-OHG possesses similar or greater antiradical activity than VC. In conclusion, 6-OHG can be useful as an antioxidant agent. Keywords: genistein, 6-hydroxygenistein, synthesis, antiradical activity. Genistein is biosynthetically the simplest isoflavonoid compound of the Leguminosae [1] and exhibits a wide range of biological activities, such as antidiabetic effect [2], neuroprotective effect [3], antioxidant [4], anti-cancer [5], and antimicrobial activity [6]. However, there are some drawbacks, such as low fat solubility, low water solubility [7], low bioavailability [8], and multiple targets, which significantly limit its clinical and therapeutic applications. In order to obtain more pharmacologically active and more selective drugs with less adverse reactions for clinical use, many studies have been performed on the synthesis of genistein derivatives. Genistein derivatives are mainly modified by glycosylation, alkylation, esterification, and hydroxylation [9, 10]. Among those mentioned above, hydroxylation, an ordinary modification of isoflavones which happens in nature, can produce more complicated isoflavones with stronger bioactivity than their precursors. For example, 3′-hydroxygenistein was demonstrated to be a potent melanogenesis inhibitor from the biotransformation of genistein by recombinant Pichia pastoris [11]. In structure–activity relationships, the functions of the isoflavones are influenced by the number and position of hydroxyl groups in the chemical structures. In addition, the bioactivity can be enhanced by growing number of phenolic hydroxyl groups. 6-Hydroxygenistein (1, 6-OHG, 4′,5,6,7-tetrahydroxyisoflavone), which has three consecutive hydrogen groups in the A ring, may exhibit strong antioxidant activity. Previous studies have reported that 6-OHG can be isolated from fermented soybean or microbial fermentation broth feeding with soybean meal. But these methods have some disadvantages, including high enzyme requirements, low yield, and complicated process [11, 12]. In addition, the chemical synthesis methods to access 1 are rare. Therefore, new practical and economical methods for the synthesis of 1 are required to be developed. The purpose of this study was to synthesize and evaluate the antiradical activity of 1. As shown in Scheme 1, 6-OHG was synthesized via four steps using biochanin A as raw mater
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