NEUTRAL NUCLEOTIDE ANALOG PRODRUGS USING KETOL ESTERS

治疗病毒疾病最成功的方法是基于抑制病毒DNA复制。这些抑制剂是核苷类似物，当它们被结合到病毒的DNA中时，可以防止进一步的聚合。核苷实际上是活性5‘-三磷酸代谢物的前体药物，通过细胞或病毒编码的酶催化的三个磷酸化步骤产生。核苷在非磷酸化状态下给药，以促进进入人体细胞。然而，并不是所有的核苷类似物都以同样的效率被磷酸化，其中一些三磷酸是病毒DNA聚合酶的有效抑制剂，当作为核苷使用时，它们是糟糕的抗病毒药物。这可能是由于这些酶的专一性，或者因为这些酶的量不足。如果核苷能够以其单磷酸盐的形式在细胞内传递，从而绕过第一个关键的磷酸化步骤，它们作为抗病毒药物的性能将得到显著改善。这项建议描述了一类独特的活性核苷一磷酸三酯的合成和评价，其中带电的磷酸基团被酮醇基团掩盖。这些以前不为人知的酮醇核苷一磷酸三酯有望具有足够的亲脂性，足以穿透细胞膜，并具有足够的活性，可以在细胞内水解性揭开面纱。通过这种方式，核苷一磷酸可以在细胞内释放出来，在那里它们有望表现出增强的转化为三磷酸。酮醇磷酸三酯对水解性特别敏感。因此，从被屏蔽的核苷酸中去除第一个酮醇基团的胞内反应有望以非酶和区域特异性的方式进行，从而得到核苷一磷酸二酯。生成的双酯的水解可能在酶和非酶途径之间进行分配。这一战略要求将已证实的抗病毒药物以一种新的更活跃的前药形式进行化学包装。如果这一方法成功，将导致病毒感染临床治疗的数量和种类增加。

The most successful approaches to the treatment of viral diseases are based on the inhibition of viral DNA replication. The inhibitors are nucleoside analogs which, when incorporated into the DNA of the virus, prevent further polymerization. The nucleosides are actually prodrugs of the active 5'-triphosphate metabolites produced via a sequence of three phosphorylation steps catalyzed by cellular or virally encoded enzymes. The nucleosides are administered in the non-phosphorylated state to promote transit into human cells. However, not all nucleoside analogs are phosphorylated with the same efficiency, and some, whose triphosphates are potent inhibitors of viral DNA polymerase are poor antiviral agents when administered as the nucleoside. This may be due to the specificity of the kinases, or because of insufficient amounts of these enzymes. If the nucleosides could be delivered intracellularly as their monophosphates, thus bypassing the first critical phosphorylation step, their performance as antivirals would be substantially improved. This proposal describes the synthesis and evaluation of a unique class of activated nucleoside monophosphate triesters in which the charged phosphate moeity is masked with ketol groups. These previously unknown ketol nucleoside monophosphate triesters are expected to be lipophilic enough for cell membrane penetration and reactive enough for hydrolytic unmasking within the cell. In this way, the nucleoside monophosphates can be liberated intracellularly where they are expected to exhibit enhanced conversion to the triphosphate. Ketol phosphate triesters are exceptionally reactive toward hydrolysis. Thus the intracellular hydrolytic removal of the first ketol group from the masked nucleotides is expected to proceed non-enzymatically and regiospecifically to afford nucleoside monophosphate diesters. Hydrolysis of the resulting diester is likely to be partitioned between enzymatic and nonenzymatic hydrolysis pathways. This strategy calls for the chemical packaging of proven antivirals in a new more active prodrug form. If this approach is successful, it will lead to an increase in the number and variety of clinical treatments for viral infections.