Synthesis And Biochemistry Of Ascorbic Acid Analogues

我们继续我们的合成工作与6-卤代-6-脱氧抗坏血酸，类似物已被证明是有用的工具，运输研究，在一个合作项目中完成的博士。6-卤代抗坏血酸类似物的还原形式在结构上与抗坏血酸相似，并且预测它们将由维生素C转运蛋白SVCT 1和SVCT 2转运。通过13C NMR光谱法溶液检测到的氧化抗坏血酸（DHA）在水溶液中的唯一形式是水合双环半缩酮，其形成需要C6羟基的存在。该分子的整体几何结构和多个羟基的存在表明该结构与葡萄糖的结构相似。这种结构相似性在一定程度上导致了近30年前的假设，即DHA和葡萄糖具有相同的转运机制，这一假设随后在几种易化葡萄糖转运蛋白中得到了验证。当6-溴-6-脱氧-L-抗坏血酸被氧化成6-溴-6-脱氧抗坏血酸（BrDHA）时，由于C-6卤素已经取代了6-OH基团，因此不能形成水合双环半缩酮。2，3-二酮内酯，或更可能的水合形式，将代表溶液中BrDHA的结构。这种化合物与葡萄糖缺乏结构相似性，我们预测它不会被GLUT转运或结合。 当GLUT 1或GLUT 3在爪蟾卵母细胞中表达时，BrDHA既不被转运也不被结合。这与表达葡萄糖转运蛋白GLUT 1和GLUT 3的爪蟾卵母细胞对DHA的稳健转运形成对比。此外，使用活化的人嗜中性粒细胞，预测其具有主要由DHA和GLUT转运蛋白介导的抗坏血酸盐蓄积，与抗坏血酸相比，6-溴-6-脱氧-L-抗坏血酸蓄积<蓄积的1%。我们的结论是，6-溴-6-脱氧-L-抗坏血酸是第一个运输基板确定为完全特定的SVCT，但不是GLUT，并提供了一个新的策略，以确定每个途径的抗坏血酸积累的贡献。 我们正在继续合成工作，以制备新的类黄酮类似物，以研究这些抗坏血酸和葡萄糖转运抑制剂的结构参数。将包含转运蛋白的潜在亲和标记。并探讨了氟取代对黄酮类化合物生物活性的影响。已经制备了一系列氟化查耳酮，并将在产生类黄酮结构的条件下环化。

We have continued our synthetic work with 6-halo-6-deoxyacorbic acids, analogues that have proven to be useful tools for transport studies, done in a collaborative project by Dr. Mark Levine. The reduced forms of the 6-halo ascorbic acid analogs are structurally similar to ascorbic acid, and it was predicted they would be transported by the vitamin C transporters SVCT1 and SVCT2. The only form of oxidized ascorbic acid (DHA) in aqueous detected by 13C NMR spectroscopy solution is a hydrated bicyclic hemiketal, formation of which requires the presence of the C6 hydroxyl group. The overall geometry of this molecule and the presence of multiple hydroxyl groups has suggested a similarity of this structure to that of glucose. This structural similarity in part led to the hypothesis nearly 30 years ago that DHA and glucose would share the same transport mechanisms, a hypothesis that was subsequently verified for several facilitated glucose transporters. When 6-bromo-6-deoxy-L-ascorbic acid is oxidized to 6-bromo-6-deoxyacorbic acid (BrDHA), the hydrated bicylcic hemiketal cannot form since the C-6 halogen has replaced the 6-OH group. The 2,3-diketolactone, or more likely the hydrated form, would represent the structure of BrDHA in solution. This compound lacks structural similarity to glucose, and we predicted that it would not be transported or bound by GLUTs. When GLUT1 or GLUT3 were expressed in Xenopus oocytes, BrDHA was neither transported nor bound. This contrasted to robust transport of DHA by Xenopus oocytes expressing glucose transporters GLUT1 and GLUT3. In addition, using activated human neutrophils, predicted to have ascorbate accumulation mediated predominantly by DHA and GLUT transporters, 6-bromo-6-deoxy-L-ascorbic acid accumulation was < 1% of accumulation compared to ascorbic acid. We conclude that 6-bromo-6-deoxy-L-ascorbic acid is the first transport substrate identified as completely specific for SVCTs, but not GLUTs, and provides a new strategy to determine the contribution of each pathway to ascorbate accumulation. We are continuing synthetic work to prepare new flavonoid analogues to study sturtural parameters of these inhibitors of ascorbate and glucose transport. Inculded will be potential affinity labels for the transport protein(s). Effects of fluorine substitution biolgical begavior of the flavonoids also will be examined. A series of fluorinated chalcones have been prepared and will be cyclized under conditions that produce the flavonoid structures.