Subcritical Fluid Chromatography at Sub-Ambient Temperatures for the Chiral Resolution of Ketamine Metabolites with Rapid-Onset Antidepressant Effects.

Robert K Hofstetter,Andreas Link,Lukas Schulig,Simon Kim,Mahmoud Hasan,Felix Potlitz

doi:10.3390/molecules24101927

Abstract

Chiral metabolites of ketamine exerting rapid-onset yet sustained antidepressant effects may be marketed directly in the future, but require chemo- and enantio-selective chromatographic methods for quality assurance and control. The chromatographic behavior of S-/R-ketamine, S-/R-norketamine, S-/R-dehydronorketamine, and (2R,6R)-/(2S,6S)-hydroxynorketamine in supercritical fluid chromatography (SFC) was investigated computationally and experimentally with the aim of identifying problematic pairs of enantiomers and parameters for chiral resolution. Retention on three different polysaccharide-based chiral stationary phases (Lux Amylose-2, i-Amylose-3, and i-Cellulose-5) provided new information on the significance of halogen atoms as halogen bond donors and hydrogen bond acceptors for enantioselectivity, which could be corroborated in silico by molecular docking studies. Modifiers inversely affected enantioselectivity and retention. Methanol yielded lower run times but superior chiral resolution compared to 2-propanol. Lower temperatures than those conventionally screened did not impair phase homogeneity but improved enantioresolution, at no cost to reproducibility. Thus, sub-ambient temperature subcritical fluid chromatography (SubFC), essentially low-temperature HPLC with subcritical CO2, was applied. The optimization of the SubFC method facilitated the chiral separation of ketamine and its metabolites, which was applied in combination with direct injection and online supercritical fluid extraction to determine the purity of pharmaceutical ketamine formulations for proof of concept.

Highlights

IntroductionOn 5 March 2019, ketamine (K) was approved by the FDA for treatment-resistant depression [1].Unique in its mechanism of action and different from monoaminergic modulators, which alleviate depressive systems within 6–8 weeks and in only about 2/3 of patients, K exerts rapid onset (within hours) yet sustained (one week and more) antidepressant effects, even in patients suffering from treatment-refractory depression [2]
On 5 March 2019, ketamine (K) was approved by the FDA for treatment-resistant depression [1].Unique in its mechanism of action and different from monoaminergic modulators, which alleviate depressive systems within 6–8 weeks and in only about 2/3 of patients, K exerts rapid onset yet sustained antidepressant effects, even in patients suffering from treatment-refractory depression [2]
Molecules 2019, 24, 1927 of rac-K lowers suicidal ideation in patients suffering from bipolar depression to a greater degree than midazolam, and demonstrated memory improvement and pre- to post-infusion decrease in serum brain-derived neurotrophic factor (BDNF) as promising biomarkers [3]

Summary

Introduction

On 5 March 2019, ketamine (K) was approved by the FDA for treatment-resistant depression [1].Unique in its mechanism of action and different from monoaminergic modulators, which alleviate depressive systems within 6–8 weeks and in only about 2/3 of patients, K exerts rapid onset (within hours) yet sustained (one week and more) antidepressant effects, even in patients suffering from treatment-refractory depression [2]. Molecules 2019, 24, 1927 of rac-K lowers suicidal ideation in patients suffering from bipolar depression to a greater degree than midazolam (used to address functional unblinding due to dissociative effects associated with verum administration), and demonstrated memory improvement and pre- to post-infusion decrease in serum brain-derived neurotrophic factor (BDNF) as promising biomarkers [3]. Rac-K infusion is known to induce anxiety, which appears to be associated with higher non-responder rates (up to 45%), defined as a less than 50% reduction on the Montgomery–Asberg. On the other hand, increase abuse liability of K, and actual prevalence is not known, the incidence of recreational use among young adults is estimated to be as high as 4.5%, which might include attempts at self-directed therapy [5].

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