WO2015057043A1

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Publication number: WO2015057043A1
Application number: PCT/LV2014/000010
Authority: WO
Inventors: Ivars Kalvins; Jurijs PONOMARJOVS; Larisa VARACEVA; Aleksandrs Cernobrovijs; Antons Lebedevs
Original assignee: Latvian Institute Of Organic Synthesis
Priority date: 2013-10-14
Filing date: 2014-10-03
Publication date: 2015-04-23
Also published as: LV14985B; LV14985A; GB2535004B; GB201522674D0; GB2535004A

Abstract

Improvements in the preparation process of 3-(4-amino-1-oxo-1,3-dihydro-2H- isoindol-2-yl)piperidine-2,6-dione (Ienalidomide), wherein the intermediate 2-methyl- 3-nitrobenzoic acid methyl ester is brominatcd with N-bromosuccinimide in methyl acetate and the end product is obtained from 3-(4-nitro-l-oxo-l,3-dihydro- 2H-isoindol-2-yl)piperidine-2,6-dione by reducing with iron and ammonium chloride reducing system.

Description

A PROCESS FOR THE PREPARATION OF LENALIDOMIDE

TECHNICAL FIELD

[0001] The invention relates to a process for the preparation of pharmacologically active substance. In particular, the invention relates to the preparation process of anticancer agent lenalidomide (I).

BACKGROUND ART

[0002] Lenalidomide or (RS)-3-(4-amino-l-oxo-l,3-dihydro-2H-isoindol-2-yl)- piperidine-2,6-dione (I) is an immunomodulator designed for the various types of melanomas and certain myelodysplastic syndrome subtypes causing anemia [1].

[0003] The main steps in the preparation process of lenalidomide (I) are bromination of 2-methyl-3 -nitrobenzoic acid methyl ester (II) to yield 2-(bromomethyl)-3- nitrobenzoic acid methyl ester (III) and reduction of nitro group of 3-(4-nitro-l-oxo- 1 ,3-dihydro-2H-isoindol-2-yl)piperidine-2,6-dione (IV).

[0004] Known methods of obtaining the intermediate (III) of lenalidomide involve bromination by the free-radical mechanism, which usually occurs at temperatures between 90 to 140°C, using bromine source (bromine or N-bromosuccinimide) and a radical initiator (benzoyl peroxide [1, 2], 2,2'-azobisizobutyronitrile [3, 21]), light [4] or a combination of radical initiator and light [5].

For successful reaction it is necessary to use inert chlorine-containing solvents such as carbon tetrachloride, chlorobenzene, dichlorobenzene, dichlormethane,

dichloroefhane, chloroform.

It is known that these solvents are hazardous to health and environment, also their price is higher than that of the chlorine-free solvents, as well as their use requires additional expenses on disposal and environmental pollution control.

[0005] The most convient precursor for the preparation of lenalidomide is 3-(4-nitro- l-oxo-l,3-dihydro-2H-isoindol-2-yl)piperidine-2,6-dione (IV). The most common conditions for the conversion of the starting material is reduction of a nitro group by catalytic hydro enation [6-15, 23].

[0006] The catalytic hydrogenation requires the use of transition metal catalysts (Pd/C, Pt0₂) and hydrogen as a reductant. This raises the product's overall cost due to necessarity to install specialized hydrogenation equipment and safety devices for the work with the explosive gases. Also it is requred to control the impurity level of transition metals in the final product. During the reaction, products of partial reduction of nitro group, as well as diproportionation products of intermediate nitrozo compounds, are formed. Product purification from the structurally related byproducts is a very complex process, which adversely affects product yield and raises the expenses of the process.

[0007] Other known non-catalytic process for the preparation of lenalidomide is reduction of nitro compound (IV) with an iron in hydrochloric acid, thus obtaining a lenalidomide hydrochloride (V), which is further treated with the aqueous ammonia yielding the desired product lenalidomide base (I) [20]. [0008] 3-(4-Nitro- 1 -oxo- 1 ,3-dihydro-2H-isoindol-2-yl)piperidine-2,6-dione (IV) might be obtained by different methods and routes. In publications [22, 23], as well as in patents [ 16-19] the intermediate (IV) is obtained by cyclization of 2- (bromomethyl)-3-nitrobenzoic acid methyl ester (III) and 3-aminopiperidine-2,6- dione V).

[0009] Another synthetic path is described in the patent [11] for the synthesis of precursor (IV) by using different glutamine and glutamic acid derivatives (VI): their reaction with 2-(bromomefhyl)-3-nitrobenzoic acid methyl ester (III) yielded compounds (VII), which were cyclized to provide lenalidomide intermediate (IV). Hence, lenalidomide can be obtained as fast as in four steps starting from the 2- meth l-3-nitrobenzoic acid methyl ester (II).

R = OH, OMe, NH₂

[0010] Another route, that is much longer and less beneficial, is described in patent [8]. This synthetic route involves cyclization of the 2-(bromomethyl)-3-nitrobenzoic acid methyl ester (III) and the reduction of nitro group, thereby obtaining 4- aminoisoindoline- 1 -one (VIII). After the protection of amino group and alkylation of the amide with 2-bromoglutaric acid derivatives compound (IX) is obtained, which is cyclized and upon cleavage of the protecting group, yielded lenalidomide (I). One of the most suitable protecting groups used in such reactions, as well as it is described in the patent [8], is benzyloxycarbonyl group (Cbz), which usually is removed by catalytic hydrogenation.

R = OH, OMe, NH₂; PG - protecting group (Cbz or other)

[0011] As follows from the previous schemes, 2-(bromomethyl)-3-nitrobenzoic acid methyl ester (III) is a key intermediate in the overall synthetic scheme of lenalidomide (I) regardless of the synthetic route.

Considering that this compound is synthesized at the early stages of the process, it has to be synthesized in bulk quantities, which requires using of a large amount of halogen-containing solvent. It makes the overall lenalidomide production process pricier by increasing the costs of solvents and disposal. The aforementioned requires the search of other synthetic methods that could make the process cheaper and environmentally cleaner, thus making the end product - lenalidomide - more accessible to cancer patients.

[0012] If lenalidomide is obtained by hydrogenation of 3-(4-nitro-l-oxo-l,3-dihydro- 2H-isoindol-2-yl)piperidine-2,6-dione (IV) in the presence of transition metals, it usually contains a significant amount of partial hydrogenation and nitroso

intermediate disproportionation products as well as residual amounts of transition metals. In order to obtain a pharmaceutical grade product it should be recrystallized several times, or converted in the form of a salt, purified, and then converted into a base. The most challenging task is to remove metal impurities, because their acceptable levels in the final product are counted in parts per million. [0013] In the case of reduction of 3-(4-nitro-l-oxo-l ,3-dihydro-2H-isoindol-2-yl)- piperidine-2,6-dione (IV) with iron in hydrochloric acid, lenalidomide hydrochloride is obtained, which is soluble in water and it is problematic to separate it from iron salts. In this case, in order to obtain lenalidomide in a base form it is necessary to neutralize the hydrochloride with a stronger base, but this process is problematic due to a large amount of iron hydroxide, which formed during neutralization process. All previously mentioned additional purification procedures reduce the product yield and increase the cost of the technological process.

SOLUTION OF PROBLEM

[0014] We unexpectedly found, that the known lenalidomide preparation process can be improved with new routes of obtaining 2-(bromomethyl)-3-nitrobenzoic acid methyl ester (III) and the final product.

[0015] 2-(Bromomethyl)-3-nitrobenzoic acid methyl ester (III) can be obtained from the 2-methyl-3-nitrobenzoic acid methyl ester (II) using halogen-free solvent - methyl acetate. This newly developed method has several advantages: the process takes place at a relatively low temperature (57°C) and the product obtained in almost quantitative yield, high purity, and without additional purification (98% by HPLC). Considering that 2-(bromomethyl)-3-nitrobenzoic acid methyl ester (III) is indispensable raw material for the synthesis of lenalidomide, this method allows to achieve a significant reduction in use of environmentally harmful solvents in the process, as well as it avoids safety measures associated with their use and disposal, thus reducing the total cost of the lenalidomide synthesis. Methyl acetate has limited citations as a solvent for radical bromination reaction.

[0016] Also, we found that the final product - lenalidomide - can be obtained by the reduction of 3-(4-nitro-l-oxo-l,3-dmydro-2H-isoindol-2-yl)piperidine-2,6-dione (IV) with ammonium chloride and iron. It is remarkable that lenalidomide (I) can be obtained by this method with very low impurity content (-2% by HPLC). Moreover, it is obtained in the base form, that is impossible when using metal-acid system.

Advantage of the invention is a low cost (iron and ammonium chloride are cheap and easy to store), short reaction time (4 hours) and high efficiency (high yields of a product, purity of the raw product ~98%). Cycle opening side reactions are not typical for this method. By using a simple recrystalization it is possible to obtain

pharmaceutical rade product with a total yield of around 80%.

[0017] Example 1

Preparation of 2-(bromomethyl)-3-nitrobenzoic acid methyl ester (III).

2-Methyl-3-nitrobenzoic acid methyl ester (100.0 g, 0.51 mol) is loaded in a reactor equipped with reflux condenser and mechanical stirrer, then N-bromosuccinimide (134.0 g, 0.75 mol) and methyl acetate (1.0 L) are added. 2,2'-Azobisisobutyronitrile (8.4 g, 0.05 mol) is added to the resulting suspension which then is refluxed and stirred for 18 hours (the reaction temperature is 57 °C). Next, the reaction mixture is cooled, washed with 10% Na₂S0₃ aq. solution, then with 10% NaCl aq. solution. The organic layer is filtered and evaporated and to obtain orange-yellow oil. A mixture of isopropyl alcohol and water (2:1, 90 mL) is added to the product immediately after evaporation, and the mixture is stirred at room temperature, that results in the crystallization of the product. The precipitate is filtered and dried for 6 hours at 50- 55°C in vacuum (10-20 mbar). Yield 138.0 g (98%), pale yellow crystals, purity 98% (by HPLC).

[0018] Example 2

Preparation of lenalidomide (I).

Ammonium chloride (95.6 g, 1.76 mol) is dissolved in water (580 mL). After that, 3- (4-nitro-l-oxo-l,3-dihydro-2H-isoindol-2-yl)piperidine-2,6-dione (65.0 g, 0.22 mol) and ethanol (2,9 L) are added. The reaction mixture is heated to 60°C and iron powder (49.0 g, 0.88 mol) is added with stirring. The reaction mixture is stirred at 80°C for 4 hours, then filtered hot; the precipitate washed twice with hot ethanol-water mixture (50 mL water + 150 mL ethanol). The filtrate is evaporated, water (200 mL) is added to dry residue, and the mixture is stirred for 30 min. The precipitated product is filtered off and washed twice with water (50 mL). The raw product is boiled for 2.5 hours in a mixture of ethanol (900 mL) and water (600 mL), then activated charcoal (6 g) is added, and the mixture is boiled for 1 hour more. The hot mixture is filtered, the filtrate is allowed to crystallize at temperature 0-5°C, and the precipitated product is filtered off. Obtained product is dried for 6 hours at 60°C under 15-20 mbar pressure. Yield 47.6 g (84%), pale yellow substance, purity 99.8% (by HPLC).

[0019] If necessary, the product can be recrystallized from water, methanol, acetone or other solvents to obtain the required polymorph.

[0020] All methods can be realized in industrial production, yielding important pharmaceutically active substance for treating various types of cancer by cost- effective and environmentally-friendly production methods.

CITATION LIST

PATENT LITERATURE

1. US2003/139451 Al, 2003

2. WO2010/56344 Al, 2010

3. US2010/10060 A1. 2010

4. US6335/349 B 1, 2002

5. US5534481 Al, 1996

6. US6335/349 B 1, 2002

7. WO2009/114601 A2, 2009

8. WO2010/139266 A1. 2010

9. WO2010/56384 Al, 2010

10. WO2011/50962 Al, 2011

11. WO2011/27326 A1. 2011

12. WO2011/69608 A1. 2011

13. US2011/237802 A1. 2011

14. US2011/223157 Al, 2011

15. US2012/71509 A1. 2012

16. WO2010/100476A2, 2010

17. WO2011/27326A1. 2011

18. WO2011/111053A1, 2011

19. US2012/71509A1. 2012

20. WO2010/61209 Al, 2010

NON-PATENT LITERATURE

21. Bioorg. Med. Chem. Lett., 14, 81 (2004).

22. Bioorg. Med. Chem. Lett., 9, 1625 (1999).

23. Bioorg. Med. Chem. Lett., 3, 1019 (2011).

Claims

1. A process for the preparation of 3-(4-amino- 1 -oxo- 1 ,3-dihydro-2H-isoindol-2- yl)piperidine-2,6-dione (lenalidomide), involving bromination of 2-methyl- 3-nitrobenzoic acid methyl ester, reaction of the obtained 2-(bromomethyl)- 3-nitrobenzoic acid methyl ester with 3-aminopiperidine-2,6-dione, and reduction of obtained 3-(4-nitro-l-oxo-l,3-dihydro-2H-isoindol-

2- yl)piperidine-2,6-dione to 3-(4-amino-l-oxo-l,3-dihydro-2H-isoindol-2-yl)- piperidine-2,6-dione, characterized by that the bromination of 2-methyl-

3- nitrobenzoic acid methyl ester is performed with N-bromosuccinimide in methyl acetate and the reduction of 3-(4-nitro-l-oxo-l,3-dihydro-2H-isoindol-

2- yl)piperidine-2,6-dione is performed with an iron and ammonium chloride reducing system.

2. A process according to claim 1, wherein bromination of 2-methyl-3- nitrobenzoic acid methyl ester is performed at the boiling point of methyl acetate in the presence of radical formation initiator - 2,2'- azobisisobutyronitrile.

3. A process according to claim 1, wherein the solvent in the reduction phase of

3- (4-nitro-l-oxo-l,3-dihydro-2H-isoindol-2-yl)piperidine-2,6-dione is methanol, ethanol, 2-propanol, 1-butanol or water; more preferable - mixture of ethanol and water.