In the search for a radioactive form of the peptidomimetic renin inhibitor, ditekiren, with a metabolically suitable radiolabel for conducting drug disposition studies, we prepared [3H]ditekiren with tritium labels in the N-methyl-histidine moiety and in the leu-val alcohol transition-state insert. [His-3H]ditekiren was obtained by first introducing two iodine substituents into the N-methyl-histidine moiety of the parent drug, followed by catalytic hydrodehalogenation with tritium gas. Administration of this labeled drug to monkeys, however, resulted in prolonged retention of radioactivity in the test animals, even though little or no tritiated water was detected in urine. This suggested in vivo production of a labeled fragment from the drug, e.g., N-methyl-[3H]histidine, which became incorporated into the endogenous amino acid pool. These results, together with similar earlier findings after administration of [3H]ditekiren labeled in the proline moiety of the drug, led us to synthesize [3H]ditekiren labeled in the “unnatural” leu-val alcohol (LVA) portion of the molecule. [LVA-3H]ditekiren was obtained by first oxidizing the parent drug to produce an LVA-keto analog, which was then reduced with sodium borotritide to give a mixture of tritium labeled ditekiren and its LVA-epimer. The two epimeric labeled materials were separated and purified by means of preparative high performance liquid chromatography (HPLC). The tritium label in [LVA-3H]ditekiren was found to be metabolically suitable for conducting drug disposition studies, with no liability for tritiated water production or prolonged retention of radioactivity in tissues of test animals.
在寻找放射性形式的肽模仿雷尼酶
抑制剂ditekiren时,我们准备了在N-甲基组
氨酸部分和亮
氨酸-缬
氨酸醇过渡态插入位点上带有氚标记的[3H]ditekiren。通过首次向母药的N-甲基组
氨酸部分引入两个
碘取代基,然后用氚气进行催化脱卤化反应,获得了[His-3H]ditekiren。然而,将该标记药物给猴子施用后,尽管在尿液中几乎没有检测到氚标记
水,但实验动物体内的放射性物质却长期保留。这表明药物在体内产生了一个标记片段,例如N-甲基-[3H]组
氨酸,这个片段被纳入内源性
氨基酸池中。这些结果,加上之前在给药[3H]ditekiren(标记在药物的脯
氨酸部分)后的类似发现,促使我们合成标记在分子“非天然”亮
氨酸-缬
氨酸醇部分的[3H]ditekiren。通过首先氧化母药以产生LVA-
酮类似物,然后用氢化
硼钠还原,最终得到混合的氚标记ditekiren及其LVA-对映体,获得了[LVA-3H]ditekiren。这两种对映体标记材料通过制备型高效
液相色谱(HPLC)分离和纯化。[LVA-3H]ditekiren中的氚标记被发现适合用于药物分布研究,没有氚标记
水产生的风险或在实验动物组织中放射性物质的长期滞留。