Synthesis And Biochemistry Of Ascorbic Acid Analogues

抗坏血酸类似物的合成与生物化学

• 批准号: 7152475
• 负责人: KENNETH L KIRK
• 金额: --
• 依托单位: NATIONAL INSTITUTE OF DIABETES AND DIGESTIVE AND KIDNEY DISEASES
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/7152475
• 关键词: ascorbate; bioaccumulation; biological transport; chemical structure function; chemical synthesis; flavonoids; glucose transport; glucose transporter; membrane transport proteins; nutrition related tag; radiotracer; transport inhibitor; vitamin analog; vitamin metabolism

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.

我们继续进行 6-卤代-6-脱氧抗坏血酸的合成工作，这种类似物已被证明是运输研究的有用工具，由 Mark Levine 博士在一个合作项目中完成。 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，预计它们将由维生素 C 转运蛋白 SVCT1 和 SVCT2 转运。 13C NMR 光谱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。该分子的整体几何形状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，该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-抗坏血酸被氧化为 6-溴-6-脱氧抗坏血酸 (BrDHA) 时，由于 C-6 卤素取代了 6-OH 基团，因此无法形成水合双环半缩酮。 2,3-二酮内酯，或更可能是水合形式，代表了溶液中 BrDHA 的结构。这种化合物缺乏与葡萄糖的结构相似性，我们预测它不会被过量转运或结合。 当 GLUT1 或 GLUT3 在爪蟾卵母细胞中表达时，BrDHA 既不被运输也不结合。这与表达葡萄糖转运蛋白 GLUT1 和 GLUT3 的非洲爪蟾卵母细胞对 DHA 的强劲转运形成鲜明对比。此外，使用活化的人中性粒细胞（预计抗坏血酸积累主要由 DHA 和 GLUT 转运蛋白介导），与抗坏血酸相比，6-溴-6-脱氧-L-抗坏血酸积累量< 1%。我们得出的结论是，6-溴-6-脱氧-L-抗坏血酸是第一个被确定为完全特异性针对 SVCT 而不是 GLUT 的转运底物，并提供了一种新策略来确定每个途径对抗坏血酸积累的贡献。 我们正在继续进行合成工作，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。包括转运蛋白的潜在亲和标记。还将检查氟取代对类黄酮的生物作用的影响。一系列氟化查耳酮已被制备，并将在产生类黄酮结构的条件下环化。