Oxetane moieties are increasingly being used by the pharmaceutical industry as building blocks in drug candidates because of their pronounced ability to improve physicochemical parameters and metabolic stability of drug candidates. The enzymes that catalyze the biotransformation of the oxetane moiety are, however, not well studied. The in vitro metabolism of a spiro oxetane-containing compound AZD1979 [(3-(4-(2-oxa-6-azaspiro[3.3]heptan-6-ylmethyl)phenoxy)azetidin-1-yl)(5-(4-ethoxyphenyl)-1,3,4-oxadiazol-2-yl)methanone] was studied and one of its metabolites, M1, attracted our interest because its formation was NAD(P)H independent. The focus of this work was to elucidate the structure of M1 and to understand the mechanism(s) of its formation. We established that M1 was formed via hydration and ring opening of the oxetanyl moiety of AZD1979. Incubations of AZD1979 using various human liver subcellular fractions revealed that the hydration reaction leading to M1 occurred mainly in the microsomal fraction. The underlying mechanism as a hydration, rather than an oxidation reaction, was supported by the incorporation of (18)O from H2 (18)O into M1. Enzyme kinetics were performed probing the formation of M1 in human liver microsomes. The formation of M1 was substantially inhibited by progabide, a microsomal epoxide hydrolase inhibitor, but not by trans-4-[4-(1-adamantylcarbamoylamino)cyclohexyloxy]benzoic acid, a soluble epoxide hydrolase inhibitor. On the basis of these results, we propose that microsomal epoxide hydrolase catalyzes the formation of M1. The substrate specificity of microsomal epoxide hydrolase should therefore be expanded to include not only epoxides but also the oxetanyl ring system present in AZD1979.

中文翻译：

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螺环氧杂环丁烷的新型微粒体环氧水解酶催化水合的发现。

氧杂环丁烷部分因其改善候选药物的理化参数和代谢稳定性的显着能力而越来越多地被制药业用作候选药物的组成部分。但是，催化氧杂环丁烷部分生物转化的酶尚未得到很好的研究。含螺氧杂环丁烷的化合物AZD1979 [（3-（4-（2-oxa-6-azaspiro [3.3] heptan-6-ylmethyl）phenoxy）azetidin-1-yl）（5-（4- [乙氧基苯基）-1,3,4-恶二唑-2-基）甲酮]的研究及其代谢物之一M1引起了我们的兴趣，因为其形成与NAD（P）H无关。这项工作的重点是阐明M1的结构并了解其形成的机制。我们确定M1是通过水合和AZD1979氧杂环丁烷基部分的开环形成的。使用各种人类肝脏亚细胞组分进行的AZD1979孵育显示，导致M1的水合反应主要发生在微粒体组分中。通过将H2中的（18）O掺入M1中来支持水合而不是氧化反应的潜在机理。进行酶动力学以探测人肝微粒体中M1的形成。M1的形成基本上被微粒体环氧化物水解酶抑制剂普加比德抑制，但未被可溶性环氧化物水解酶抑制剂反式4- [4-（1-金刚烷基氨基甲酰氨基）环己氧基]苯甲酸抑制。基于这些结果，我们建议微粒体环氧化物水解酶催化M1的形成。