Pharmacokinetics, Dynamics, and Metabolism-New Chemical Entities, Pfizer Worldwide Research and Development, Cambridge, MA 02139, USA.
Drug Metab Dispos. 2013 Jul;41(7):1375-88. doi: 10.1124/dmd.113.051839. Epub 2013 Apr 22.
The current study examined the bioactivation potential of ghrelin receptor inverse agonists, 1-{2-[2-chloro-4-(2H-1,2,3-triazol-2-yl)benzyl]-2,7-diazaspiro[3.5]nonan-7-yl}-2-(imidazo[2,1-b]thiazol-6-yl)ethanone (1) and 1-{2-[2-chloro-4-(2H-1,2,3-triazol-2-yl)benzyl]-2,7-diazaspiro[3.5]nonan-7-yl}-2-(2-methylimidazo[2,1-b]thiazol-6-yl)ethanone (2), containing a fused imidazo[2,1-b]thiazole motif in the core structure. Both compounds underwent oxidative metabolism in NADPH- and glutathione-supplemented human liver microsomes to yield glutathione conjugates, which was consistent with their bioactivation to reactive species. Mass spectral fragmentation and NMR analysis indicated that the site of attachment of the glutathionyl moiety in the thiol conjugates was on the thiazole ring within the bicycle. Two glutathione conjugates were discerned with the imidazo[2,1-b]thiazole derivative 1. One adduct was derived from the Michael addition of glutathione to a putative S-oxide metabolite of 1, whereas, the second adduct was formed via the reaction of a second glutathione molecule with the initial glutathione-S-oxide adduct. In the case of the 2-methylimidazo[2,1-b]thiazole analog 2, glutathione conjugation occurred via an oxidative desulfation mechanism, possibly involving thiazole ring epoxidation as the rate-limiting step. Additional insights into the mechanism were obtained via ¹⁸O exchange and trapping studies with potassium cyanide. The mechanistic insights into the bioactivation pathways of 1 and 2 allowed the deployment of a rational chemical intervention strategy that involved replacement of the thiazole ring with a 1,2,4-thiadiazole group to yield 2-[2-chloro-4-(2H-1,2,3-triazol-2-yl)benzyl]-2,7-diazaspiro[3.5]nonan-7-yl)-2-(2-methylimidazo[2,1-b][1,3,4]thiadiazol-6-yl)ethanone (3). These structural changes not only abrogated the bioactivation liability but also retained the attractive pharmacological attributes of the prototype agents.
本研究考察了胃饥饿素受体反向激动剂 1-{2-[2-氯-4-(2H-1,2,3-三唑-2-基)苄基]-2,7-二氮杂螺[3.5]壬烷-7-基}-2-(咪唑并[2,1-b]噻唑-6-基)乙酮（1）和 1-{2-[2-氯-4-(2H-1,2,3-三唑-2-基)苄基]-2,7-二氮杂螺[3.5]壬烷-7-基}-2-(2-甲基咪唑并[2,1-b]噻唑-6-基)乙酮（2）的生物活化潜力，这两种化合物在含有融合咪唑并[2,1-b]噻唑基序的核心结构的人肝微粒体中经 NADPH 和谷胱甘肽补充进行氧化代谢，生成谷胱甘肽缀合物，这与它们向反应性物质的生物活化一致。质谱裂解和 NMR 分析表明，硫醇缀合物中谷胱甘肽部分的连接点位于双环中的噻唑环上。咪唑并[2,1-b]噻唑衍生物 1 中发现了两种谷胱甘肽缀合物。一种加合物是谷胱甘肽对 1 的潜在 S-氧化物代谢物的迈克尔加成的产物，而第二种加合物是通过初始谷胱甘肽-S-氧化物加合物与第二个谷胱甘肽分子的反应形成的。对于 2-甲基咪唑并[2,1-b]噻唑类似物 2，谷胱甘肽缀合通过氧化脱硫机制发生，可能涉及噻唑环环氧化作为限速步骤。通过¹⁸O 交换和与氰化钾的捕获研究获得了对生物活化途径的更深入了解。对 1 和 2 的生物活化途径的机制见解使我们能够实施一种合理的化学干预策略，该策略涉及用 1,2,4-噻二唑基团取代噻唑环，生成 2-[2-氯-4-(2H-1,2,3-三唑-2-基)苄基]-2,7-二氮杂螺[3.5]壬烷-7-基）-2-（2-甲基咪唑并[2,1-b][1,3,4]噻二唑-6-基）乙酮（3）。这些结构变化不仅消除了生物活化的责任，而且保留了原型药物的有吸引力的药理学特性。
