Synthesis And Biochemistry Of Ascorbic Acid Analogues

我们继续进行6-卤代-6-脱氧抗坏血酸的合成工作，这些类似物已被证明是运输研究的有用工具，由Mark Levine博士合作完成。6-卤代抗坏血酸类似物的还原形式在结构上类似于抗坏血酸，据预测它们将由维生素C转运体SVCT1和SVCT2转运。水中氧化抗坏血酸(DHA)在13C核磁共振波谱溶液中的唯一形式是水合双环半缩酮，它的形成需要C6羟基的存在。这种分子的整体几何构型和多个羟基的存在表明这种结构与葡萄糖的结构相似。这种结构上的相似性在一定程度上导致了近30年前的假说，即DHA和葡萄糖将共享相同的转运机制，这一假说随后在几种促进葡萄糖转运蛋白上得到了验证。当6-溴-6-脱氧-L抗坏血酸被氧化为6-溴-6-脱氧抗坏血酸(BrDHA)时，由于C-6卤代取代了6-OH基团，不能形成水合的双氧环己二缩醛。2，3-二酮内酯，或更可能的水合形式，将代表BrDHA在溶液中的结构。这种化合物在结构上与葡萄糖缺乏相似性，我们预测它不会被谷氨酸运输或结合。 当GLUT1或GLUT3在非洲爪哇卵母细胞中表达时，BrDHA既不转运也不结合。这与表达葡萄糖转运蛋白GLUT1和GLUT3的非洲爪哇卵母细胞对DHA的强劲转运形成了鲜明对比。此外，使用被预测主要由DHA和GLUT转运体介导的激活的人中性粒细胞，6-溴-6-脱氧-L-抗坏血酸的积聚比抗坏血酸的积聚多1%。我们得出结论，6-溴-6-脱氧-L-抗坏血酸是第一个被鉴定为完全专用于SVCTs而不是GLTS的转运底物，并为确定每条途径对抗坏血酸积累的贡献提供了一种新的策略。 我们正在继续合成工作，以制备新的类黄酮类类似物，以研究这些抗坏血酸和葡萄糖转运抑制剂的结构参数。被包含的将是运输蛋白的潜在亲和标记(S)。此外，还将考察类黄酮类化合物的氟代换生物效应。一系列氟化查尔酮已经被制备出来，并将在产生类黄酮结构的条件下进行环化。

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.