Tai Akihiro, Iomori Atsuko, Ito Hideyuki
Faculty of Life and Environmental Sciences, Prefectural University of Hiroshima, Shobara, Hiroshima 727-0023, Japan.
Faculty of Life and Environmental Sciences, Prefectural University of Hiroshima, Shobara, Hiroshima 727-0023, Japan.
Bioorg Med Chem. 2017 Oct 15;25(20):5303-5310. doi: 10.1016/j.bmc.2017.07.044. Epub 2017 Jul 28.
2-O-α-d-Glucopyranosyl-l-ascorbic acid (AA-2G) exhibits biological activities after enzymatic hydrolysis to ascorbic acid (AA) by α-glucosidase. We have found that AA-2G per se exerted radical-scavenging activity toward 1,1-diphenyl-2-picrylhydrazyl radical (DPPH radical). The radical-scavenging property of AA-2G was greatly different from that of AA; that is, the reaction rate with DPPH radical of AA-2G was far slower than that of AA, but the long-lasting radical-scavenging ability per one molecule of AA-2G was superior to that of AA. We purified key intermediates for the characteristic radical-scavenging reaction of AA-2G and carried out time-course studies of the radical-scavenging reactions of the intermediates, AA-2G and AA to determine both the reaction rate and stoichiometry of AA-2G with DPPH radical. One mole of AA-2G quenched 2.7mol of DPPH radical over a period of 120min, while one mole of AA quenched 1.9mol of the radical. The high reaction stoichiometry of AA-2G against DPPH radical was associated with adduct formation of AA-2G with DPPH radical. The radical-scavenging reaction mechanism of AA-2G consists of the following three steps: (1) At an early stage of the reaction, AA-2G scavenged DPPH radical to generate AA-2G radical, (2) AA-2G radical immediately reacted with an additional DPPH radical to give two types of AA-2G-DPPH adducts and (3) AA-2G-DPPH adducts slowly quenched the other DPPH radical to generate several reaction products. Our results suggest the practical value of AA-2G, even before being converted into AA, as a beneficial antioxidant in food and cosmetic applications.
2-O-α-D-吡喃葡萄糖基-L-抗坏血酸（AA-2G）在被α-葡萄糖苷酶酶解为抗坏血酸（AA）后具有生物活性。我们发现AA-2G本身对1,1-二苯基-2-苦基肼自由基（DPPH自由基）具有自由基清除活性。AA-2G的自由基清除特性与AA有很大不同；也就是说，AA-2G与DPPH自由基的反应速率远比AA慢，但每一个AA-2G分子的持久自由基清除能力优于AA。我们纯化了AA-2G特征性自由基清除反应的关键中间体，并对中间体、AA-2G和AA的自由基清除反应进行了时间进程研究，以确定AA-2G与DPPH自由基的反应速率和化学计量关系。在120分钟的时间内，1摩尔的AA-2G淬灭了2.7摩尔的DPPH自由基，而1摩尔的AA淬灭了1.9摩尔的该自由基。AA-2G对DPPH自由基的高反应化学计量关系与AA-2G与DPPH自由基形成加合物有关。AA-2G的自由基清除反应机制包括以下三个步骤：（1）在反应早期，AA-2G清除DPPH自由基生成AA-2G自由基，（2）AA-2G自由基立即与另一个DPPH自由基反应生成两种类型的AA-2G-DPPH加合物，（3）AA-2G-DPPH加合物缓慢淬灭另一个DPPH自由基生成几种反应产物。我们的结果表明，即使在转化为AA之前，AA-2G作为食品和化妆品应用中的有益抗氧化剂也具有实际价值。
