Procedure for the preparation of racemic derivatives of 1,5-diaryl-3-trifluoromethyl-delta2-pyrazolines

Abstract

Procedure for preparation of compounds with the general formula 1, which include the racemic mixtures (±)-1, and the enantiomerically pure compounds (−)-1 and (+)-1, wherein R1 and R3, like or different, represent an atom of hydrogen, chlorine, fluorine, a methyl, trifluoromethyl or methoxy group; R2 represents an atom of hydrogen, chlorine, fluorine, a methyl, trifluoromethyl, methoxy, trifluoromethoxy, methylsulphonyl or aminosulphonyl group; R4 represents an atom of hydrogen, chlorine, fluorine, a methyl, trifluoromethyl, methoxy, trifluoromethoxy, methylsulphonyl or aminosulphonyl group, with the condition that one of the substituents R2 or R4 is a methylsulphonyl or aminosulphonyl group; which involves obtaining the racemic mixture with the general formula (±)-1 by reacting an (E)-1,1,1-trifluoro-4-aryl-3-buten-2-one with a phenylhydrazine, followed by a treatment with chlorosulphonic acid, or by reacting with chlorosulphonic acid followed by a reaction with sodium hydroxide and, finally, with thionyl chloride. The product obtained by either of these methods is made to react with ammonium carbonate or ammonia, or with sodium sulphite and methyl iodide or methyl sulphate. In addition, to obtain the enantiomerically pure compounds with the general formula 1 by resolving the racemic mixture with the general formula (±)-1, a reaction is effected with optically active ephedrine, followed by formation of the sodium salt of each enantiomer, reaction with thionyl chloride and ammonium carbonate or ammonia, or instead with thionyl chloride followed by sodium sulphite and methyl iodide or methyl sulphate to thereby obtain separately the enantiomerically pure compounds with the general formulae (−)-1 and (+)-1.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a new, commercially useful procedure for the preparation of compounds having the general formula 1, which includes the racemic mixture (±)—1, and the enantiomerically pure compounds (−)-1 and (+)-1. BACKGROUND OF THE INVENTION [0002] Our patent WO 9962884 describes new derivatives of A2-pyrazolines, also known as 4,5-dihydro-1H-pyrazoles, which inhibit the enzyme cyclooxygenase-2, with application in human and / or veterinary medicine as anti-inflammatories and in other diseases in which cyclooxygenase-2 is involved, and which present a low or zero gastric and renal toxicity, so that they are anti-inflammatories with a greater safety profile. Certain racemic mixtures (±)-1, and the enantiomerically pure stereoisomers (−)-1 and (+)-1 described in said patent are currently in a clinical investigation stage. The aforementioned Patent describes the preparation of (±)-1 by reaction of (E)-1,1,1-trifluoro-4-aryl-3-buten-2-one w...

AI Technical Summary

Benefits of technology

[0011] It also provides an industrial application method for obtaining the enantiomerically pure stereoisomers (+)-1 and (−)-1.0. One pair of enantiomers can be resolved by various methods, with conversion to diastereoisomeric salts and their separation by fractioned crystallisation being the most commonly used. Once the diastereoiseomeric salts have been obtained and separated the enantiomers (acids or bases) can be easily liberated, and the chiral acid or base recovered, so that this simple and inexpensive method has been widely used for industrial applications. If the racemic compound contains an amine group in its structure it is possible to form diastereoisomeric salts with an optically active acid, and it the racemic compound contains an acid group it is possible to form diastereoisomeric salts with an optically active base. Since the compound 1 lacks any acid or basic groups strong enough to form diastereoisomeric salts the present invention develops a procedure which is described schematically below (Schematic 1) for obtaining the racemic mixture (±)-1 and the enantiomerically pure compounds (−)-1 and (+)-1.

[0013] The compound (−)-8 is synthesised, in accordance with the present invention, by the method described below with the schematic indicating certain preferred conditions. The third stage involves the resolution of the racemic mixture (±)-6 into its two enantiomers, using as a resolution agent (+)-ephedrine. Ephedrine is an excellent resolving agent, as both enantiomers can be used in the resolution, they are available in a high enantiomeric concentration, are commercially available and are easily recoverable and crystallisable. The compound (+)-8 is prepared by the same synthesis path as in the previous case, changing only the ephedrine enantiomer in the resolution process (step 3). Synthesis of the racemic compound (±)-8 is performed in the same manner, skipping the steps related to resolution, that is, directly by reaction of the acid chloride with ammonium or ammonium carbonate.

Problems solved by technology

This method has the disadvantage of using successive recrystallisations in both the process of formation of sodium sulphonate (between 3 and 7 recrystallisations), and in the process of formation and separation of the mixture of diastereoisomeric salts (between 4 and 7 recrystallisations), which results in a considerable reduction of the yield.

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