6740-87-0

An improved synthesis of (S)-ketamine (esketamine) has been developed, which was cost-effective, and the undesired isomer could be recovered by racemization. Critical process parameters of each step were identified as well as the process-related impurities. The formation mechanisms and control strategies of most impurities were first discussed. Moreover, the (S)-ketamine tartrate is a dihydrate, which was disclosed for the first time. The practicable racemization catalyzed by aluminum chloride was carried out in quantitative yield with 99% purity. The ICH-grade quality (S)-ketamine hydrochloride was obtained in 51.1% overall yield (14.0% without racemization) by chiral resolution with three times recycling of the mother liquors. The robust process of esketamine could be industrially scalable.

The first detailed description of the Lewis acid-catalyzed racemization of (R)-ketamine is reported. A process for racemization of the undesired (R)-ketamine enantiomer produced from the resolution for preparing the NMDA receptor antagonist (S)-ketamine was developed in quantitative yield with 99% chemical purity in the presence of a Lewis acid at 150 °C. Varying degrees of racemization were observed in the presence of various frequently used Lewis acids separately, and the catalytic efficiencies were arranged as follows: MgCl2 ≈ AlCl3 > FeCl3 > ZnCl2 > BF3 > CaCl2. The racemized ketamine was subsequently resolved using l-(+)-tartaric acid to obtain (S)-ketamine in 41% yield with 99.5% ee. Such a concise and cost-efficient approach for the racemization can be industrially useful to recycle the waste (R)-ketamine enantiomer into the resolution process to obtain (S)-ketamine.

The invention relates to the compounds or its pharmaceutical acceptable polymorphs, solvates, enantiomers, stereoisomers and hydrates thereof. The pharmaceutical compositions comprising an effective amount of compounds of formula I, formula II and formula III and the methods for the treatment of neurological diseases may be formulated for oral, buccal, rectal, topical, transdermal, transmucosal, lozenge, spray, intravenous, oral solution, nasal spray, oral solution, suspension, oral spray, buccal mucosal layer tablet, parenteral administration, syrup, or injection. Such compositions may be used to treatment of neurological diseases.

The invention provides a method for synthesizing a compound of formula (I) wherein each R independently represents an optionally substituted aryl, heteroaryl, alkyl, perfluoroalkyl, cycloalkyl, alkoxy, aryloxy, acyl, carboxyl, hydroxyl, halogen, amino, nitro, cyano, sulfo or sulfhydryl group, in ortho, meta or para position to the cycloalkylamine moiety; R1 and R2 each independently represents a hydrogen atom, a lower alkyl group or a cycloalkyl group; R3 represents a hydrogen group, substituted aryl, heteroaryl, alkyl, perfluoroalkyl, cycloalkyl, alkoxy, aryloxy group; Y represents an oxygen atom, a sulfur atom, a NH group, a NR4 group or a CH2 group; R4 represents a hydrogen atom or an alkyl, aryl or a heteroaryl group; and n and m each independently represents an integer from 1 to 5; or a pharmaceutically acceptable salt thereof; or a precursor thereof; wherein the method comprises one or more of the following steps: (a) reacting a compound of formula (II): (II) wherein R, R3, Y, n and m are as defined above in relation to the compound of formula (I) with an oxygenating agent, a first additive and a second additive in a solvent in a fluidic network or in a batch process under thermal and/or photochemical conditions to form a compound of formula (III): (III) wherein R, R3, Y, n and m are as defined above in relation to the compound of formula (I), (b) reacting a compound of formula (III) with a nitrogen containing nucleophile in the presence of a third additive and/or a solvent in the fluidic network or in a batch process under thermal conditions to form a compound of formula (IV): (IV) wherein R, R1, R2, R3, Y, n and m are as defined above in relation to the compound of formula (I); and/or (c) reacting a compound of formula (IV) in a fluidic network or in a batch process, optionally in the presence of a fourth 20 additive, under thermal conditions to form a compound of formula (I); wherein one or more of steps (a), (b) and/or (c) is carried out in a fluidic network that comprises micro- and/or meso-channels having an internal dimension of from 100 μm to 2000 μm.

A robust three-step continuous flow procedure is presented for the efficient and sustainable preparation of active pharmaceutical ingredient ketamine. The procedure relies on the main assets of continuous flow processing, starts from commercially available chemicals, utilizes low toxicity reagents and a FDA class 3 solvent under intensified conditions. The procedure features a unique hydroxylation step with molecular oxygen, a fast imination relying on triisopropyl borate and a thermolysis employing Montmorillonite K10 as a heterogeneous catalyst, all three steps being performed in ethanol. The three individual steps can be run independently or can be concatenated, thus providing a compact yet efficient setup for the production of ketamine. The scalability of the critical hydroxylation step was assessed in a commercial pilot continuous flow reactor. The process can also be adapted for the preparation of ketamine analogs. A thorough computational study on the backbone rearrangement of the cyclopentylphenylketone scaffold under thermal stress rationalizes the experimental selectivity and the various experimental observations reported herein.