Development of the first anti-HIV drug from Japan : 4'-Ethynyl-d4T as the candidate

在合成支链糖核苷的研究中，我们对有机铝试剂对环氧糖核苷的开环反应进行了研究。在一个实例中，用二甲基二氧杂环丙烷（DMDO）氧化4 '，5'-不饱和胸腺嘧啶-核苷。用有机铝试剂对所得环氧化物进行开环，揭示了获得4 '-支链类似物的新途径。作为该研究的结果，合成了各种类型的4 '-碳取代的2'，3 '-二硫代-3'-脱氧-胸苷。在这些化合物中，发现4 ′-乙炔基类似物（4 ′-Ed 4 T）对HIV的抑制活性高于司他夫定（d4 T），司他夫定在临床上用于AIDS的化疗。该化合物（4 ′-Ed 4 T）对各种细胞的毒性比d4 T小得多，并且作为抗HIV剂具有几个有希望的特征：1）不抑制线粒体DNA合成，2）比d4 T更好的人胸苷激酶底物，3）非常耐胸苷磷酸化酶的卡替林，和4） 关于我们 其活性在存在主要突变K103 N的情况下得到改善，K103 N已知为非核苷逆转录酶抑制剂抗性HIV。为了在临床前研究中进一步评估4 ′-Ed 4 T，我们需要适合于其大规模制备的替代合成方法，因为DMDO的使用因其高浓度溶液的不可及性而受挫。发现Pb（OBz）_4与4 ′，5 ′-不饱和胸腺嘧啶核苷反应，在4 ′-位引入了一个苯甲酰氧基离去基团。该底物与Me_3SiO_2Cl（Et）Cl反应后，乙炔基被立体选择性地引入到4 ′-位上。这些反应在几个10克规模进行，我们认为这种方法即使在工业规模也会成功。计划于2007年完成4 '-Ed 4 T的临床前研究，并于2008年开始临床研究。我们还对4'-Ed 4 T的构效关系进行了研究。sp-杂化碳取代基的存在似乎是抗HIV活性所必需的。然而，引入氰基而不是乙炔基降低了抑制活性。用亚甲基取代4 '-Ed 4 T中的呋喃糖氧是完全无效的。另一方面，用硫原子的这种取代允许在一定程度上保留活性。少

During our continuing studies on the synthesis of branched-sugar nucleosides, ring opening of epoxy-sugar nucleosides with organoaluminum reagents was investigated. In one example, 4',5'-unsaturated thymine-nucleoside was oxidized with dimethyldioxirane (DMDO). Ring opening of the resulting epoxide with organoaluminum reagents disclosed a new access to the 4'-branched analogues. As a result of this study, a various types of 4'-carbon-substituted 2',3'-didehydro-3'-deoxy-thymidines were synthesized. Among these compounds, the 4'-ethynyl analogue (4'-Ed4T) was found to have a higher inhibitory activity against HIV than does stavudine (d4T), which is clinically used for chemotherapy of AIDS.This compound (4'-Ed4T) is much less toxic to various cells than d4T and has several promising features as anti-HIV agent : 1) not inhibitory to mitochondrial DNA synthesis, 2) better substrate for human thymidine kinase than d4T, 3) very much resistant to catabolism by thymidine phosphorylase, and 4) … More its activity improves in the presence of a major mutation, K103N, known for nonnucleoside reverse transcriptase inhibitor resistant HIV.To further evaluate 4'-Ed4T in preclinical studies, we were in need of an alternative synthetic method suitable for its large scale preparation, since the use of DMDO is frustrated by inaccessibility of its highly concentrated solution. It was found that the reaction of Pb(OBz)_4 with the previously employed 4',5'-unsaturated thymine-nucleoside allowed to introduce a benzoyloxy leaving group into the 4'-position. Upon reacting this substrate with Me_3SiC≡CAl(Et)Cl, the ethynyl group was introduced stereoselectively to the 4'-position. These reactions were performed in several 10 g-scale, and we assume this approach would be successful even in industrial scale. It is planed that the preclinical studies of 4'-Ed4T will complete in 2007, and its clinical studies will start in 2008.We have also investigated the structure-activity relationship studies of 4'-Ed4T. The presence of sp-hybridized carbon-substituent seems to be essential for the anti-HIV activity. However, introduction of a cyano group instead of the ethynyl group decreased the inhibitory activity. Replacement of the furanose oxygen in 4'-Ed4T with methylene was totally ineffective. On the other hand, such replacement with a sulfur atom allowed to retain the activity to some extent. Less