Enantioselective Syntheses of (S)-Ketamine and (S)-Norketamine

Automatic monitoring and on-line chiral separation of chiral drug synthesis

Chiral synthesis of single chiral drugs offers high efficiency, controllable costs, and excellent enantioselectivity, making it crucial in the pharmaceutical industry. A significant number of studies on chiral drug synthesis primarily focuses on the design and synthesis of innovative chiral catalysts and ligands with extremely high selectivity, as well as the development of new methods and strategies. Nonetheless, the on-line monitoring of chiral drug synthesis and its underlying mechanisms remain obscure. The principal challenge lies in the diverse synthesis pathways and intricate mechanisms of chiral drugs, with numerous intermediates and by-products. To tackle this issue, employing the chiral drug omeprazole as a breakthrough, we design and establish a reliable and stable analytical method to monitor the synthesis process. By integrating electrokinetic chromatography technology with automatic sequence injection, the chiral synthesis of omeprazole can be comprehensively tracked and monitored throughout its entire process. During the chiral drug synthesis process, all compounds, containing all reagents and products (omeprazole sulfide, R-omeprazole, S-omeprazole, iodobenzene and iodobenzene diacetate) are efficiently separated and simultaneously detected through a single run. The method shows a high resolution greater than 1.2, a wide linear range with a detection limit as low as 0.008 μM, as well as exceptional repeatability in sequence analysis. Therefore, the proposed method has demonstrated significant value in the analysis of chiral drug synthesis and holds potential for extensive application in the industrial production of chiral compound synthesis.

Is there a risk of esketamine misuse in clinical practice?

In 2019, intranasal esketamine gained approval as a promising therapy for those individuals grappling with treatment-resistant depression. Both clinical trials and real-world studies have underscored its efficacy in alleviating and remitting depressive symptoms, with sustained benefits observed for nearly 4.5 years. As the S-enantiomer of ketamine, esketamine's dosing guidelines and strict medical supervision stem from prior research on ketamine's use in depression and history as a recreational drug. Despite initial concerns, long-term clinical studies have not documented instances of abuse, misuse, addiction or withdrawal, and the same was found in case reports or subsamples of high-risk populations with comorbidities such as substance use disorder or alcohol use disorder. Esketamine has proven to be safe and well tolerated without fostering new-onset substance use in vulnerable groups. Real-world studies reinforced these observations, reporting no adverse events (AEs) related to pharmacological interactions of esketamine with any other substance, and no new-onset drug or alcohol misuse, craving, misuse or diversion of use. Reports of esketamine craving remain rare, with only one case report documented in 2022. Most drug-related AEs reported in pharmacovigilance databases are those identified in the product's technical data sheet and with known reported frequency. More importantly, no register of illicit acquisition of esketamine or its tampering for obtaining ketamine or other altered products was found in our search. Overall, our review confirms esketamine's safety across diverse patient populations, reassuring its responsible use and the scarcity of reports of abuse or misuse since its introduction to the market.

A Concise Synthesis of (2R,6R)-Hydroxynorketamine

A concise synthesis of (2R,6R)-hydroxynorketamine was accomplished in eight steps, starting from commercially available materials. This synthesis features a cerium chloride-enhanced Stork-Danheiser reaction, an asymmetric reduction of ketone by the Corey-Bakshi-Shibata reaction, a signature Overman rearrangement, and a facial selective dihydroxylation of an electronically deficient olefin by RuCl3/NaIO4. The overall yield is 7.3% with 94.5% ee.

Effect of intraoperative injection of esketamine on postoperative analgesia and postoperative rehabilitation after cesarean section

BACKGROUND

Following cesarean section, a significant number of women encounter moderate to severe pain. Inadequate management of acute pain post-cesarean section can have far-reaching implications, adversely impacting maternal emotional well-being, daily activities, breastfeeding, and neonatal care. It may also impede maternal organ function recovery, leading to escalated opioid usage, heightened risk of postpartum depression, and the development of chronic postoperative pain. Both the Chinese Enhanced Recovery After Surgery (ERAS) guidelines and the American ERAS Society guidelines consistently advocate for the adoption of multimodal analgesia protocols in post-cesarean section pain management. Esketamine, functioning as an antagonist of the N-Methyl-D-Aspartate receptor, has been validated for pain management in surgical patients and has exhibited effectiveness in depression treatment. Research has suggested that incorporating esketamine into postoperative pain management via pain pumps can lead to improvements in short-term depression and pain outcomes. This study aims to assess the efficacy and safety of administering a single dose of esketamine during cesarean section.

AIM

To investigate the effect of intraoperative injection of esketamine on postoperative analgesia and postoperative rehabilitation after cesarean section.

METHODS

A total of 315 women undergoing elective cesarean section under combined spinal-epidural anesthesia were randomized into three groups: low-dose esketamine (0.15 mg/kg), high-dose esketamine (0.25 mg/kg), and control (saline). Postoperative Visual Analog Scale (VAS) scores were recorded at 6 hours, 12 hours, 24 hours, and 48 hours. Edinburgh Postnatal Depression Scale (EPDS) scores were noted on 2 days, 7 days and 42 days. Ramsay sedation scores were assessed at specified intervals post-injection. Postoperative adverse reactions were also recorded.

RESULTS

Low-dose group and high-dose group compared to control group, had significantly lower postoperative VAS pain scores at 6 hours 12 hours, and 24 hours (P < 0.05), with reduced analgesic usage (P < 0.05). EPDS scores and postpartum depression rates were significantly lower on 2 days and 7 days (P < 0.05). No significant differences in first exhaust and defecation times were observed (P > 0.05), but ambulation times were shorter (P < 0.05). Ramsay scores were higher at 5 minutes, 15 minutes, and upon room exit (P < 0.05). Low-dose group and high-dose group had higher incidences of hallucination, lethargy, and diplopia within 2 hours (P < 0.05), and with low-dose group had lower incidences of hallucination, lethargy, and diplopia than high-dose group (P < 0.05).

CONCLUSION

Esketamine enhances analgesia and postpartum recovery; a 0.15 mg/kg dose is optimal for cesarean sections, balancing efficacy with minimized adverse effects.

Characterization of 17 unknown ketamine manufacturing by-product impurities by UHPLC-QTOF-MS

This study initially reported the selection and characterization of 17 unknown impurities attributed to the manufacture process of ketamine. A total of 150 seized ketamine samples were investigated through ultra-high-performance liquid chromatography-quadrupole-time of flight (UHPLC-Q-TOF). Seventeen characteristic impurities were selected in accordance with four criteria: The compound was detected in over 10% of all 150 seized ketamine samples, the compound had at least one nitrogen, the unsaturation of the compound was more than 5, and the compound was stable in the dilution solvent solution for 48 h. The accurate masses of the protonated molecules and product ions of the target impurities were obtained based on the full scan mode and the product ion mode of Q-TOF, respectively. Lastly, the possible structures of the above impurities were tentatively elucidated in accordance with the synthetic route of ketamine, protonated molecules, and MS2 product ions. All 17 impurities had the same skeleton of deschloroketamine (DCK), but were substituted with additional chlorine, hydroxyl, methyl, cyclohexane, and o-chlorophenyl cyclopentyl ketone substituents. Under the electrospray ionization (ESI), the above impurities showed similar characteristic fragment ions through the dissociation of the CH3NH2, C2H6NH, H2O, CO, C2H4O, C4H6, and C2H2 moieties. The above impurities have been routinely used for the profiling analysis of seized ketamine samples in the National Narcotics Laboratory of China and employed to establish the tactical intelligence for law enforcement agencies.

New materials used for the synthesis of 2-chlorophenyl cyclopentyl ketone seized from an illicit ketamine manufacturing unit

Ketamine deemed as a psychoactive substance has gained popularity for recreational use owing to its hallucinogenic and dissociative effects. Understanding the synthetic processes of ketamine can provide essential clues for law enforcement officers against illicit ketamine manufacturing. In this case report, a chemical company was being monitored by law enforcement officers due to its importation of precursors and materials that could be used for the synthesis of illicit drugs. After materials and products seized from this chemical company were employed for analyses using gas chromatography-mass spectrometry, liquid chromatography-high-resolution mass spectrometry, and nuclear magnetic resonance analyses, ketamine, hydroxylamine, 2-chlorophenyl cyclopentyl ketone, and cyclopentanone p-toluenesulfonylhydrazone were identified. In addition, a novel process for the synthesis of ketamine precursor 2-chlorophenyl cyclopentyl ketone from cyclopentanone p-toluenesulfonylhydrazone and 2-chlorobenzaldehyde was validated. This is the first report to uncover this novel process for the synthesis of 2-chlorophenyl cyclopentyl ketone and can be used to increase awareness among law enforcement officers and forensic practitioners about these novel starting materials for the synthesis of ketamine.

Synthesis of anti-depressant molecules via metal-catalyzed reactions: a review

Depression is one of the most mutilating conditions in the world today. It has been difficult to make advancements toward better, more effective therapies since the introduction of antidepressant medicines in the late 1950s. One important field of medicinal chemistry is the synthesis of antidepressant molecules through metal-catalyzed procedures. The important role that different transition metals, including iron, nickel, ruthenium, and others, serve as catalysts in the synthesis of antidepressants is examined in this review. Key structural motifs included in antidepressant drugs such as tricyclic antidepressants (TCAs), selective serotonin reuptake inhibitors (SSRIs), and others can be synthesized in a variety of effective ways using metal-catalyzed steps. This review examines current developments in the catalytic synthesis of antidepressants and their potential application over the previous thirteen years.

A new process of ketamine synthesis from 2-(2-chlorophenyl)-2-nitrocyclohexanone proposed by analyzing drug materials and chemicals seized in Taiwan

Because of its hallucinogenic and dissociative effects, ketamine is often abused for recreational purposes. Thus, the seizure of ketamine manufacturing units is crucial for preventing drug abuse. The precursors popularly used for ketamine synthesis include 1-[(2-chlorophenyl)(methylimino)methyl]cyclopentanol hydrochloride and 2-(2-chlorophenyl)-2-nitrocyclohexanone (2-CPNCH). Herein, we report a case of the seizure of a ketamine manufacturing unit by law enforcement officers. The seized materials were sent to our laboratory for confirmation. We found that 2-CPNCH was used as the precursor. Using zinc powder and formic acid, 2-CPNCH was reduced to norketamine. Through the Eschweiler-Clarke reaction, norketamine was reacted with formaldehyde and formic acid to synthesize ketamine; the advantages of this process are a short duration of reaction and the requirement of small amounts of chemicals. We further identified an impurity (N-methyl ketamine), which was used as a marker to validate this new process of ketamine synthesis. To the best of our knowledge, this study is the first to report illegal ketamine synthesis through the Eschweiler-Clarke reaction when using 2-CPNCH as the precursor. Our findings inform law enforcement officers and forensic practitioners about this new process of ketamine synthesis.

Three Birds, One Excipient: Development of an Improved pH, Isotonic, and Buffered Ketamine Formulation for Subcutaneous Injection

Subcutaneous (SC) ketamine has been found to be effective in pain management, though reports of injection site irritation and sterile abscesses exist with currently available ketamine HCl formulations. Such adverse SC reactions are commonly associated with low pH, high osmolality and/or high injection volumes. An optimal SC formulation of ketamine would thus have a pH and osmolality close to physiological levels, without compromising on concentration and, thus, injection volume. Such a formulation should also be buffered to maintain the pH at the acceptable level for extended time periods. As many of these physicochemical properties are interrelated, achieving these aims represented a significant challenge in formulation development. We describe the development of a novel Captisol^®-based formulation strategy to achieve an elevated pH, isosmotic and buffered formulation of ketamine (hence, three birds, one excipient) without compromising on concentration. This strategy has the potential to be readily adapted to other amine-based APIs.

Recent advances in artificial enzyme cascades for the production of value-added chemicals

Enzyme cascades are efficient tools to perform multi-step synthesis in one-pot in a green and sustainable manner, enabling non-natural synthesis of valuable chemicals from easily available substrates by artificially combining two or more enzymes. Bioproduction of many high-value chemicals such as chiral and highly functionalised molecules have been achieved by developing new enzyme cascades. This review summarizes recent advances on engineering and application of enzyme cascades to produce high-value chemicals (alcohols, aldehydes, ketones, amines, carboxylic acids, etc) from simple starting materials. While 2-step enzyme cascades are developed for versatile enantioselective synthesis, multi-step enzyme cascades are engineered to functionalise basic chemicals, such as styrenes, cyclic alkanes, and aromatic compounds. New cascade reactions have also been developed for producing valuable chemicals from bio-based substrates, such as ʟ-phenylalanine, and renewable feedstocks such as glucose and glycerol. The challenges in current process and future outlooks in the development of enzyme cascades are also addressed.

Process for (S)-Ketamine and (S)-Norketamine via Resolution Combined with Racemization

A concise, recyclable, and efficient process is presented for the preparation of (S)-ketamine (esketamine, (S)-1a) via classic resolution combined with the recycling of the undesired isomer. With commercially available ketone 2 as the starting material, this procedure features three steps including (1) an unique hydroxylation-ring expansion rearrangement, (2) mild amination via methanesulfonate, and (3) chiral separation using L-(+)-tartaric acid. The three simple steps are all performed in mild conditions and (S)-1a tartrate is obtained in 99.5% ee without recrystallization. Subsequently, racemization of the unwanted (R)-1a remained in resolution mother liquor was performed in the presence of a Lewis acid in quantitative yield with >99.0% chemical purity. This original and economical process afforded esketamine in 67.4% (28.9% without racemization) overall yield with two times recycling of the mother liquor without column purification. In addition, this procedure can also be applied to the preparation of (S)-norketamine, which is a safer potential antidepressant.

Stereospecific Overman Rearrangement of Substituted Cyclic Vinyl Bromides: Access to Fully Substituted α-Amino Ketones

A versatile thermal Overman rearrangement of enantioenriched, cyclic allylic alcohols providing tertiary allylic amines has been developed. The vinyl bromide used to control enantioselectivity in a preceding CBS reduction is utilized as a synthetic handle for the preparation of tertiary α-amino ketones and related derivatives in an asymmetric fashion.