Design and synthesis of DNA topoisomerase II inhibitors targeting the proton-transfer process

DNA拓扑异构酶是负责DNA代谢的生物过程的核酶，如复制、转录、重组和有丝分裂时的染色体分离。因此，作为抑制这些酶的主要细胞靶点的化合物是特别感兴趣的，因为这些化合物是有希望的抗癌药物的候选者。我们先前的研究表明，氮杂脱氧鬼臼毒素类似物中的邻苯二酚或邻苯二酚部分在显示拓扑异构酶II(TOPO II)酶抑制中起关键作用，在这一过程中，DNA切割和再密封过程中的质子传输被认为是被邻苯二酮这样的小结构单元所阻断。在本研究项目中，我们致力于合成与氮鬼臼毒素类似物杂化的新型Topo II抑制剂核苷类似物，并对其进行生物学评价。我们的合成包括1，3-二硫烷与手性丁烯内酯的Michael加成反应，相当于核苷的脱氧核糖部分，以及作为关键反应的Silyl-Hilbert-Johnson反应。正如预测的那样，邻苯二酚和邻苯二酚对Topo II有抑制作用，而二甲氧基衍生物则没有活性。除了活性核苷外，还发现几种缺乏胸腺嘧啶碱基的内酯衍生物也抑制Topo II，表明胸腺嘧啶碱基不是Topo II抑制的必要条件。这些内酯衍生物的构效关系表明，在非核苷衍生物的情况下，分子中TBS基团或二硫杂环的存在对于Topo II的抑制是必不可少的。

DNA topoisomerases are nuclear enzymes responsible for biological processes of DNA metabolism such as replication, transcription, recombination and chromosome segregation at mitosis. Therefore, compounds that inhibit these enzymes as the primary cellular target are of special interest since those are promising candidates for anticancer drugs.Our previous studies demonstrated that the ortho-quinone or catechol moiety in aza-deoxypodophyllotoxin analogues plays a critical role in showing topoisomerase II (topo II) enzyme inhibition, in which proton transport during cutting and resealing of DNA is presumed to be blocked by a small structural unit like ortho-quinone. In this research project, we have aimed at the synthesis and biological evaluation of nucleoside analogues as novel topo II inhibitors that are hybrids with aza-podophyllotoxin analogues. Our synthesis contains a Michael addition reaction of 1, 3-dithianes to chiral butenolide, an equivalent to the deoxyribose moiety of a nucleoside, and a Silyl-Hilbert-Johnson reaction as key reactions. As predicted, ortho-quinone and catechol showed topo II inhibition, while dimethoxy derivative was inactive. In addition to the active nucleosides, it was found that several lactone derivatives lacking a thymine base also inhibited topo II, indicating that a thymine base is not requisite to topo II inhibition. Structure-activity relationship of these lactone derivatives showed that the presence of the TBS group or dithiane moiety in the molecule is essential for topo II inhibition in the case of non-nucleoside derivatives.