Ketamine is a chiral drug used for various clinical purposes but often misused. It is metabolized to norketamine, an active chiral metabolite. Both substances have been detected in environmental matrices, but studies about their enantioselective toxic effects are scarce. In the present study, the enantiomers of ketamine and norketamine were separated by a semipreparative enantioselective liquid chromatography method, and their toxicity was investigated in different aquatic organisms. The enantioseparation was achieved using a homemade semipreparative chiral column. Optimized conditions allowed the recovery of compounds with enantiomeric purity higher than 99%, except for (R)-ketamine (97%). The absolute configuration of the enantiomers was achieved by experimental electronic circular dichroism (ECD). The ecotoxicity assays were performed with the microcrustacean Daphnia magna and the protozoan Tetrahymena thermophila using Toxkit MicroBioTests. Different concentrations were tested (0.1–10 000 µg/L) to include environmental levels (~0.5–~100 µg/L), for racemates (R,S) and the isolated enantiomers (R or S) of ketamine and norketamine. No toxicity was observed in either organism at environmental levels. However, at greater concentrations, (R,S)-ketamine presented higher mortality for D. magna compared with its metabolite (R,S)-norketamine (85 and 20%, respectively), and the (S)-ketamine enantiomer showed higher toxicity than the (R)-ketamine enantiomer. In addition, (S)-ketamine also presented higher growth inhibition than (R)-ketamine for T. thermophila at the highest concentrations (5000 and 10 000 µg/L). Contrary to D. magna, growth inhibition was observed for both enantiomers of norketamine and in the same magnitude order of the (S)-ketamine enantiomer. The results showed that the 2 organisms had different susceptibilities to norketamine and that the toxicity of ketamine at high concentrations is enantioselective for both organisms. Environ Toxicol Chem 2022;41:569–579. © 2020 SETAC

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氯胺酮和去甲氯胺酮：对映拆分和对映选择性水生生态毒性研究

氯胺酮是一种手性药物，用于各种临床用途，但经常被滥用。它被代谢成去甲氯胺酮，一种活性手性代谢物。这两种物质都已在环境基质中检测到，但关于它们的对映选择性毒性作用的研究很少。在本研究中，氯胺酮和去甲氯胺酮的对映体通过半制备对映选择性液相色谱法分离，并研究了它们在不同水生生物中的毒性。使用自制的半制备手性柱实现对映体分离。优化的条件允许对映体纯度高于 99% 的化合物的回收率，除了 ( R)-氯胺酮 (97%)。对映体的绝对构型是通过实验电子圆二色性 (ECD) 实现的。使用 Toxkit MicroBioTests对微型甲壳动物Daphnia magna和原生动物嗜热四膜虫进行生态毒性测定。测试了不同浓度 (0.1–10 000 µg/L)，包括环境水平 (~0.5–~100 µg/L)，氯胺酮和去甲氯胺酮的外消旋体 ( R , S ) 和分离的对映异构体 ( R或S )。在环境水平的任何一种生物体中均未观察到毒性。然而，在更高的浓度下，( R,S )-氯胺酮对D. magna表现出更高的死亡率与其代谢物 ( R,S )-去甲氯胺酮 (分别为 85% 和 20%) 相比，( S )-氯胺酮对映体的毒性高于 ( R )-氯胺酮对映体。此外，在最高浓度（5000 和 10 000 µg/L）下，( S )-氯胺酮对嗜热木霉的生长抑制作用也高于 ( R )-氯胺酮。与D. magna不同的是，对去甲氯胺酮的两种对映异构体都观察到生长抑制，并且与 ( S ) 的数量级相同。)-氯胺酮对映异构体。结果表明，两种生物体对去甲氯胺酮的敏感性不同，高浓度氯胺酮的毒性对两种生物体具有对映选择性。环境毒物化学2022；41：569–579。© 2020 SETAC