Structure-activity Relationships for α-Glucosidase Inhibition of Baicalein, 5,6,7-Trihydroxyflavone: the Effect of A-Ring Substitution
作者:Hong GAO、Tetsuo NISHIOKA、Jun Kawabata、Takanori KASAI
DOI:10.1271/bbb.68.369
日期:2004.1
In order to estimate the effects of the A-ring hydroxyl group of baicalein (5,6,7-trihydroxyflavone, 1) on rat intestinal α-glucosidase inhibition, flavone, monohydroxyflavones, dihydroxyflavones, and methylated derivatives of 5,6,7-trihydroxyflavone were used for the structure-activity relationship (SAR) study. The importance of the 6-hydroxyl group of baicalein was validated for an exertion of the activity. And also, the tested flavones which lacked a hydroxyl substituent on any of positions 5, 6, or 7, showed no activity. Hence, the 5,6,7-trihydroxyflavone structure was concluded to be crucial for the potent inhibitory activity. In addition, an introduction of electron-withdrawing or electron-donating groups at position 8 of baicalein led to a dramatic decrease for activity, except for 8-fluoro-5,6,7-trihydroxyflavone, which carried a less bulky substituent on position 8. Hence, this result suggested that a sterically bulky substituent on C-8 of baicalein was detrimental for the activity regardless of its electronic nature. Through examining the inhibitory mechanism of baicalein against rat intestinal α-glucosidase, it was suggested to be a mixed type inhibition.
为了估计黄芩(5,6,7-三羟基黄酮,1)的A环羟基对大鼠肠α-葡萄糖苷酶抑制的影响,采用了黄酮、单羟基黄酮、二羟基黄酮及5,6,7-三羟基黄酮的甲基化衍生物进行结构-活性关系(SAR)研究。验证了黄芩的6-羟基对该活性的发挥的重要性。此外,测试的黄酮若在5、6或7位上缺乏羟基取代基,则显示无活性。因此,得出5,6,7-三羟基黄酮结构对强抑制活性至关重要的结论。此外,在黄芩的8位引入电子吸引或电子给体基团会使活性急剧降低,唯独8-氟-5,6,7-三羟基黄酮因其在8位上带有体积较小的取代基而例外。因此,该结果表明,黄芩C-8上的空间庞大取代基无论其电子性质如何,对活性都是不利的。通过研究黄芩对大鼠肠α-葡萄糖苷酶的抑制机制,建议其为混合型抑制。