Background of the invention Olanzapine, or 2-methyl-4- [4-methyl-l-piperazinyl]-IOH- thieno [2, 3-b] [1, 5]-benzodiazepine, is a recognised drug acting on the central nervous system and is known, among others, from EP 0454436.

In EP 0454436 there are disclosed processes for olanzapine preparation. One of the known procedures consists in reduction and cyclization reaction of 2- (2-nitroanilino)-5-methylthiophen-3- carbonitrile with stannous chloride SnCl2 in an aqueous-alcoholic solution of hydrogen chloride, followed by a reaction of thus formed 4-amino-2-methyl-1 OH-thieno [2,3-b] [1, 5] -benzodiazepine with N- methylpiperazine in an organic solvent such as anisole, toluene, dimethylformamide or dimethylsulphoxide (DMSO), preferably at a temperature from 100 to 150°C, to produce olanzapine. Another of the known procedures consists in cyclization of 1- { [2- (2- <BR> <BR> <BR> aminoaniline)-5-methylthiophen-3-yl] carbonyl}-4-methylpiperazine, which is in turn obtained from methyl cyanoacetate in a series of laborious steps requiring specific complex reaction conditions, re- actants and reducing agents as well as high-boiling and hard to remove solvents, like toluene, DMF, DMSO, etc.. The reaction yields of the prior-art processes are not high. Further disadvantage

of the prior-art processes is generation of impurities which have to be removed by repeated crystallizations, what has adverse effect on the process efficiency.

The aim of this invention was to develop a new process for olanzapine preparation, which would not require the use of hard- to-remove organic solvents.

Further aim was to develop a new process for olanzapine preparation, which would involve more simple chemical proce- dures, while allowing to obtain high yields of the final product hav- ing satisfactory purity.

To remove the aforementioned deficiencies of the prior art the applicants have developed new processes for olanzapine prepara- tion, wherein N-demethylolanzapine, that is, 2-methyl-4-piperazin- 1-yl-lOH-thieno [2,3-b] [1, 5] benzodiazepine is used as the starting material, which is subjected to N-methylation to form olanzapine.

According to the processes of the invention crude olanzapine is produced which is as pure as the one obtained by prior art proc- esses, in mild conditions with relatively short reaction times and low reaction temperatures. The use of low-volatile solvents and generation of great amounts of impurities is avoided.

N-Demethylolanzapine is a compound known as an olanzap- ine metabolite and is described by Calligaro et al., Biorg. & Med.

Chem. Letters, 1,25-39, (1997), and in the publication of the inter- national patent application WO00/30650. This compound can readily be made by a reaction of the known compound 4-amino-2- methyl-10H-thieno [2, 3-b] [1, 5] benzodiazepine with piperazine as described by Calligaro et aZ., Biorg. & Med. Chem Letters, 1,25-39, (1997).

Detailed description of the invention According to the first aspect of the invention, there is pro- vided a process for the preparation of olanzapine of formula I which comprises N-methylation of 2-methyl-4-piperazin-1-yl-lOH- thieno [2, 3-b] [1, 5] benzodiazepine (N-demethylolanzapine) of formula II

In the first variant of this first aspect of the invention said N-methylation is carried out by reductive N-methylation of N- demethylolanzapine with formaldehyde in the presence of a reduc- ing agent.

In the first embodiment of this first variant a borohydride of a Group I or II metal can be used as said reducing agent and the reaction can be performed in an aqueous medium at a temperature in the range from-10°C to +20°C.

An alkali-metal borohydride may be used, in particular so- dium borohydride. The preferred reaction temperature range is zero to 5°C.

The reductive N-methylation using formaldehyde in the pres- ence of a borohydride is carried out in a simple manner which is as such known in the art. Typically, the reaction is performed in an aqueous solution in the presence of acetic acid and sodium acetate as a buffer. Into the reaction mixture containing N-demethyl-

olanzapine and formaldehyde upon its cooling the borohydride is added portionwise. After completion of the reaction the mixture is made alkaline, thereby the crude olanzapine precipitates and the precipitate is subsequently isolated.

Alternatively, in the second embodiment of this first variant of the process, said reductive N-methylation with formaldehyde can also be carried out using formic acid as said reducing agent.

The N-methylation with formaldehyde in formic acid is gener- ally known as the Eschweiler-Clarke reaction. The procedure is simple and is known in the art as such. In general, for one mole of olanzapine about 1.25 mole of formaldehyde is taken (in a little ex- cess because of formaldehyde volatility) and 2-4 moles of formic acid which serves here also as a solvent in the reaction. Formalde- hyde can also be used in the form of a 35-% formalin. The reaction is carried out in an aqueous solution at the reflux temperature of the reaction mixture. After completion of the reaction, the reaction mixture is allowed to cool thereby crude olanzapine precipitates.

In the third embodiment of this variant first of the process, the said reductive N-methylation with formaldehyde can alterna- tively be carried out by low-or medium-pressure catalytic hydro- genation with hydrogen in the presence of a metal catalyst. As a metal catalyst can be used, for instance, platinum, palladium and nickel catalysts, e. g. Pd/C, Pt/C or Raney's nickel. The catalytic hydrogenation reaction in the presence of metallic catalysts is as such well known in the art and is described in handbooks.

In a second variant of the first aspect of the invention, the said N-methylation is carried out in such a manner that N- demethylolanzapine of formula II is reacted with ethyl formate, op- tionally in the presence of a solvent, and subsequently thus pro- duced 2-methyl-4- (4-formyl-1-piperazinyl)-lOH-thieno [2, 3-b]- [1, 5] benzodiazepine (N-demethyl-N-formylolanzapine) of formula III

is subjected to a reduction.

The said reduction of (N-demethyl-N-formylolanzapine) can be carried out with a Group I or II metal borohydride in an aque- ous medium at a temperature in the range from-10°C to +20°C.

Preferably, an alkali-metal borohydride, in particular sodium borohydride, is used.

A preferred reaction temperature is a temperature in the range from zero to 5°C.

The borohydride reduction can be run similarly as described above for the first variant of the process.

The manner of carrying out the reaction with ethyl formate is simple and known in the art as such. Typically ethyl formate, which also serves as a reaction solvent, is used in considerable ex- cess (about 70 moles of ethyl formate per 1 mole of N-demethyl- olanzapine). The amount of the ethyl formate used can be de- creased by half, if an inert organic solvent, like tetrahydrofuran, is introduced as a co-solvent. The reaction is carried out at the reflux temperature of the reaction medium. On cooling N-demethyl-N- formylolanzapine precipitates from the reaction mixture.

In a third variant of the first aspect of the invention, the said N-methylation is carried out by direct methylation of N- demethylolanzapine with a methylating agent.

Methylating agents typically employed in the art for direct methylation of amines are suitable here. Non-limiting examples are methyl halogenides, dimethyl sulphate, methyl arylsulphonates

and methyl alkylsulphonates. Preferably methyl iodide is used. The procedure of the methylation reaction with methylating agents is generally known in the art as such. The methylation is typically carried out in inert polar solvents like alcohols, e. g. methanol, ethanol, isopropanol, butanol, etc.; ethers, e. g. THF, dioxan; chlo- roform ; aprotic bipolar solvents, e. g. dimethylformamide, dimethyl- sulphoxide, in the presence of an organic base (a tertiary amine) or an inorganic base (like potassium carbonate), at ambient tempera- ture. One mole of the methylating agent is used per one mole of N- demethylolanzapine.

Preferably methyl iodide is used as the methylating agent.

In a second aspect the invention provides a process for the preparation of olanzapine (2-methyl-4- [4-methyl-1-piperazinyl]- 10H-thieno-[2, 3-b] [1, 5] -benzodiazepine), of the structural formula I, which process comprises reduction of 2-methyl-4- (4-formyl-1- piperazinyl)-1 OH-thieno [2, 3-b] [1, 5]-benzodiazepine (N-demethyl-N- formylolanzapine) of formula III

Preferably the N-demethyl-N-formylolanzapine is produced in a reaction of N-demethylolanzapine with ethyl formate, optionally in the presence of a solvent.

Preferably, the said reduction reaction is carried out with a Group I or II metal borohydride as said reducing agent in an aque- ous medium at a temperature in the range from-10°C to +20°C.

Preferably, an alkali-metal borohydride, in particular sodium borohydride, is used.

The preferred reaction temperature is a temperature in the range from 0°C to 5°C.

The reduction with borohydride is conducted using the pro- cedure which as such is known in the art. Typically, the reaction is carried out in an aqueous medium, in the presence of acetic acid and sodium acetate as a buffer. The borohydride is added portion- wise to the cooled reaction mixture containing N-demethyl-N- formylolanzapine. After reaction is complete, the reaction mixture is made alkaline, thereby crude olanzapine precipitates and the precipitate is subsequently isolated.

N-Demethyl-N-formylolanzapine is a new compound, not dis- closed in the prior-art.

Accordingly, in its third aspect the invention provides also a new compound, N-demethylolanzapine derivative, that is 2-methyl- 4- (4-formyl-1-piperazinyl)-1 OH-thieno [2, 3-b] [1,5]-benzodiazepine (N-demethyl-N-formylolanzapine) of formula III:

As stated above, N-demethyl-N-formylolanzapine is useful as an intermediate in the olanzapine preparation. Olanzapine is pre- pared by reduction of N-demethyl-N-formylolanzapine.

In the fourth aspect the invention provides a process for the preparation of 2-methyl-4-(4-formyl-1-piperazinyl)-10H-thieno [2,3- b] [1, 5]-benzodiazepine (N-demethyl-N-formylolanzapine) of formula III,

which process comprises reaction of 2-methyl-4-piperazin-1-yl- 1 OH-thiene- [2, 3-b] [1, 5]-benzodiazepine (N-demethylolanzapine) of formula II

with ethyl formate.

The reaction with ethyl formate is carried out as described above for the second variant of the first aspect of the invention, that is for the preparation of olanzapine by reaction of N-demethyl- olanzapine of formula II with ethyl formate and then reduction.

The invention will be described in more detail with reference to the following, non-limiting examples, which should not be con- strued as the limitation of its scope.

Example 1.

N-Demethylolanzapine Preparation A mixture of 4-amino-2-methyl-lOH-thieno [2,3-b] [1, 5] benzo- diazepine hydrochloride (3 g, 11.3 mmol), piperazine (7 g, 81.4 mmol) in 15 ml of DMSO and 15 ml of toluene was heated to reflux under an inert gas atmosphere, with no access of moisture of the air. The reaction mixture was refluxed for 2 h.

After completion of the reaction the reaction mixture was cooled in an ice-bath and 30 ml of distilled water was added. The mixture was stirred at 5°C for 1 h until completion of the formation of a precipitate. The light-yellow precipitate was filtered off, washed with water and dried in a vacuum desiccator over silica gel. 2. 89 g (yield 85,7%) of N-Demethylolanzapine was obtained; m. p. 144. 5°C.

Example 2 Olanzapine Preparation by Reductive Alkylation of N- Demethylolanzapine with Formaldehyde in the Presence of Sodium Borohydride A mixture of N-demethylolanzapine (10 g, 33.5 mmol), an- hydrous sodium acetate (6.6 g, 80 mmol) (or an equivalent amount of the acetate hydrate), 34 ml glacial acetic acid, 20 ml of 37-% aqueous formalin and 100 ml of distilled water was cooled to 0°C.

Subsequently, sodium borohydride (8.5 g, 0.22 mmol) was added in small portions while maintaining temperature at 0°C and with vigorous stirring. Upon addition of the total amount of the boro- hydride the foaming solution was stirred at a low temperature for 1 h, then it was made alkaline to a pH = ca. 9 with 2N NaOH aq. The light-yellow precipitate produced was filtered off and washed with water. The crude product was dried in a circulating-air oven at ca.

25°C. 10.2 g of olanzapine was obtained with a purity 97% as de-

termined by HPLC (yield: 97,3%).

Example 3 Olanzapine Preparation by Methylation of N-Demethyl- olanzapine with Methyl Iodide N-Demethylolanzapine (2. 8 g, 9.4 mmol), methyl iodide (1.33 g, 9.4 mmol), and potassium carbonate (3.89 g, 28.2 mmol) in 20 ml of methanol were stirred for 8 h at a room temperature. Subse- quently, 20 ml of distilled water were added into the mixture and the whole was cooled in an ice-bath until a light-yellow precipitate was formed. The precipitate was filtered off, washed with water to obtain 1.5 g of olanzapine of a 90% purity as determined by HLPC (yield: 51%).

Example 4 Olanzapine Preparation by Reductive N-Methylation with For- maldehyde in Formic Acid (the Eschweiler-Clarke Reaction) A mixture of 20 ml of 85-% formic acid and 14 ml of an 37-% aqueous formaldehyde was cooled in an ice-bath to 0°C. While cooling N-demethylolanzapine (50 g, 0.168 mol) was added under vigorous stirring. After addition of the amine the mixture was heater to reflux in an oil bath and maintained under reflux for 8 h.

Then the mixture was cooled in an ice-bath and gently made alka- line to a pH = ca. 8 with 2N NaOH aq. The yellow precipitate formed was filtered off, washed with water and dried. Crude olan- zapine was obtained (40 g) of a purity of 95% by HPLC (yield: 76,2%).

Example 5 Preparation of N-demethyl-N-formylolanzapine (i. e. 2-methyl-4- (4-formyl-1-piperazinyl)-1 OH-thieno [2,3-b] [1, 5]-benzodiazepine) A solution of 5 g (16.8 mmol) of N-demethylolanzapine in 100 ml of ethyl formate and 100 ml of tetrahydrofuran was kept under reflux for 20 h. Subsequently, the mixture was cooled in an ice- bath. The pale beige precipitate formed was filtered off and dried in

the air. The product, 2-methyl-4- (4-formyl-1-piperazinyl)-lOH- thieno [2,3-b] [1, 5] -benzodiazepine was obtained in a 4 g quantity (yield : 72,9%). The structure of the compound produced was con- firmed by the NMR and MS analyses.

NMR (CDCls) 8 ppm: 2.32 (d, J = 1.2 Hz, 3H); 3.38-3. 69 (m, 8H); 4.88 (s, 1H); 6.29 (d, J = 1.2 Hz, 1H) ; 6.57-7. 07 (m, 4H); 8.11 (s, 1H), MS: 255 (100%), M-1 = 325 (58%), M = 326 (12%).

Example 6 Preparation of olanzapine by reduction of N-demethyl-N- formylolanzapine A mixture of 2-methyl-4- (4-formyl-1-piperazinyl)-lOH-thieno- [2, 3-b] [1, 5]-benzodiazepine (3 g, 9.2 mmol), sodium acetate (1 g, 12.2 mmol), 15 ml of glacial acetic acid and 15 ml of distilled water was cooled in an ice-bath to 0°C. Under vigorous stirring sodium borohydride (4 g, 9.4 mmol) was added portionwise. The stirring and cooling were continued for about 0.5 h after completion of the borohydride addition. Subsequently, the mixture was made alka- line to a pH = ca. 9 with 2N NaOH aq. The light-yellow precipitate formed was filtered off, washed with water and dried in an air- circulation oven at a temperature of ca. 25°C. Olanzapine was ob- tained (2.5 g) of an 88% purity as determined by HPLC (yield: 86,9%).