FIELD OF THE INVENTION

The invention relates to a process for preparing an N-acylethanolamide derivative.

BACKGROUND OF THE INVENTION

N-acylethanolamides, such as those described in WO 2018/071679, are widely recognized as potentially useful therapeutic compounds, and have been extensively studied in particular for their analgesic and/or anti-inflammatory effects.

The compound of formula (I): disclosed as compound 1-16 in WO 2018/071679 is known to be a prodrug of the endogenous bioactive lipid, palmitoylethanolamide (PEA), and is currently in development as a non-opiate treatment for inflammatory or neuropathic pain syndromes.

There is a need to provide alternative, and ideally improved, processes for preparing the compound of formula (I).

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a process for preparing a compound of formula (I): which comprises: reacting a compound of formula (II):

(NO-

DETAILED DESCRIPTION OF THE INVENTION

The process of the invention has a number of advantages. For example, the process of the invention contains less steps than the process for making the compound of formula (I) described in WO 2018/071679. In addition, the process of the invention utilises widely available and low cost starting materials and reagents. Furthermore, the process of the invention facilitates the use of ICH Class 2/3 solvents and avoids the need for precious metal catalysis steps, which is both complex and costly. Furthermore, the route is capable of being undertaken in a batch process due to the stabillity of intermediates. Finally, the process of the invention achieves a series of regioselective esterifications with high selectivity and a surprising low level of transesterification, avoiding a requirement for often burdensome chromatographic purification.

In one embodiment, the process comprises reacting the compound of formula (II) or a suitable salt thereof, with the compound of formula (III) in the presence of a suitable solvent, such as dichloromethane, acetonitrile, tetrahydrofuran (THF) or Methyl-THF. In a further embodiment, the process additionally comprises a coupling agent, such as 1-(3- dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDCI) or propanephosphonic acid anhydride (T3P). In a yet further embodiment, the process comprises reacting the compound of formula (II) and the compound of formula (III) in the presence of a catalyst, such as an acylation catalyst, in particular 4-(dimethylamino)pyridine (DMAP). In one embodiment, the process additionally comprises a purification step.

It will be appreciated that the compound of formula (I) may be purified by any conventional purification procedures. Suitable examples of purification include crystallisation from a suitable solvent, such as a heptane solution. In a further embodiment the compound of formula (I) may be purified by precipitation in a suitable solvent, such as precipitation in water from solution in DMSO.

In a particular embodiment, the process of the invention comprises the experimental procedure described in Example 1 - Procedure A herein.

In an alternative particular embodiment, the process of the invention comprises the experimental procedure described in Example 1 - Procedure B herein.

The compound of formula (II) may be prepared in accordance with Scheme 1 below:

Scheme 1

Step (i) typically comprises reacting the compound of formula (IV) with vinyl butyrate in the presence of a suitable solvent, such as dichloromethane, MTBE, THF, DMSO or acetonitrile. Step (i) also typically comprises an appropriate catalyst, such as an enzyme. Control of the reaction temperature and timing has surprisingly been shown to provide regioselectivity. Residual vinyl butyrate and butyric acid formed in the course of the reaction may be reduced by azetropic distillation with a solvent such as toluene. Detailed methodology for step (i) may be found herein in Description 1 - Procedures A and B.

Step (ii) typically comprises reacting the compound of formula (V) with succinic anhydride in the presence of a suitable base, such as pyridine and a suitable catalyst, such as an acylation catalyst, in particular 4-(dimethylamino)pyridine (DMAP). Surprisingly, it has been found to be possible to extract the triester into an aqueous base solution to effect a purification, without causing ester hydrolysis. Detailed methodology for step (ii) may be found herein in Description 2 - Procedures A and B.

The compound of formula (III) is commercially available as palmitoylethanolamide (PEA) (Sigma Product Code: P0359).

According to a further aspect of the invention, there is provided a process for preparing the compound of formula (II) as defined herein, which comprises reacting a compound of formula (V) with succinic anhydride.

In one embodiment of this aspect of the invention, the process comprises reacting the compound of formula (V) with succinic anhydride in the presence of a suitable base, such as pyridine.

In a further embodiment of this aspect of the invention, the process comprises reacting the compound of formula (V) with succinic anhydride in the presence of a suitable catalyst, such as an acylation catalyst, in particular 4-(dimethylamino)pyridine (DMAP).

According to a further aspect of the invention, there is provided a process for preparing the compound of formula (V) as defined herein, which comprises reacting a compound of formula (IV) with vinyl butyrate.

In one embodiment of this aspect of the invention, the process comprises reacting the compound of formula (IV) with vinyl butyrate in the presence of a suitable solvent, such as dichloromethane, methyl tert-butyl ether (MTBE), acetonitrile and tetrahydrofuran (THF).

The invention will now be described with reference to the following non-limiting examples:

Abbreviations DCM Dichloromethane DMAP 4-Dimethylaminopyridine DMSO Dimethylsulfoxide

EDCI 1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride IPAC Isopropyl acetate

PEA Palmitoyl ethanolamide MTBE Methyl tert-butyl ether MeCN Acetonitrile THF Tetrahydrofuran MeTHF 2-Methyltetrahydrofuran

T3P Propanephosphonic acid anhydride

Description 1 : 2-Hydroxypropane-1,3-diyl dibutyrate (Compound of Formula (V)) - Procedure A

A 1 L glass jacketed reactor was equipped with a paddle agitator, baffle, temperature probe, and blanketed in nitrogen. It was charged with glycerol (10.4 g, 0.113 mol. 1.00 eq), DCM (52 ml_ anhydrous grade) and vinyl butyrate (35.8 ml_, 0.283 mol, 2.5 eq. (SAFC, ³99.0% GC, stabilized with 20 ppm hydroquinone). The mixture was cooled to 0 °C and Novozym 435 (5.98 g, Ex Novozym Bx. LC200289) added as a single portion (T 0 °C -> 2 °C).

Agitation was introduced to mobilise the mixture. Stirring continued for 19 hr (0 °C) then \ filtered. The filtrate was concentrated by rotary evaporation (water bath 36 °C, vacuum 200->5 mbar) to give the title compound as a cloudy oil (21.8 g, 83% yield uncorrected for purity). ¹ H NMR (Bruker, 400.1 MHz, CDCh): 4.15-4.00 (series of m, 5H); 2.27 (m, 4H); 1.60 (m, 4H); 0.89 (t, 6H).

¹³ C NMR (100.6 MHz, CDCh): 173.7; 68.4; 65.0; 36.0; 18.4; 13.6. Description 1 : 2-Hydroxypropane-1,3-diyl dibutyrate (Compound of Formula (V)) - Procedure B

A 100 L double jacketed reactor equipped with a thermoregulator, and 3 x 4 bladed pitched blade turbine stirrer, was charged with Novozym 435 (1.6 kg, 0.29 wt. %) under nitrogen. MTBE (21.6 L) was charged and the mixture agitated at 100 rpm to form a slurry. The mixture was cooled to 0-10 °C. Separate feeds of glycerol (4.3 L) in DMSO (4.3 L) solution and of vinyl butyrate (18.6 L) were added simultaneously over not less than 30 minutes. The reactor was connected to an aqueous scrubber network. An exotherm was observed so the addition was temporarily paused midway for 10 min to allow reaction to remain within temperature parameters. 500 ml_ MTBE and 500 ml DMSO washes of the vinyl butyrate and Glycerol addition vessels respectively, were added once primary addition was completed. 3h after complete addition, water (25 L) was charged onto a filter and the reactor contents discharged onto the filter, together with 3 x 5 L MTBE rinses of the reaction vessel. The filterates were returned to the reaction vessel, water (27 L) charged, the mixture stirred for 10 minutes then the layers allowed to separate. The organic phase was washed with brine (8.8 L) followed by separation. The organic phase was concentrated to approximately 4 volumes and filtered through 0.7 micron glass microfibre and the line washed with further MTBE (8 L). The MTBE was evaporated under vacuum and residual water removed by azeotroping with toluene under vacuum (3 x approx 10 L) at 40 °C to afford the title compound as a yellow oil (13.74 kg), consistent spectroscopically with material produced by Description 1 - Procedure A.

Description 2: 4-((1,3-Bis(butyryloxy)propan-2-yl)oxy)-4-oxobutanoic acid (Compound of Formula (II)) - Procedure A

A 100 mL round bottom flask fitted with thermometer and magnetic stirrer bar was charged with the compound of formula (V) which may be prepared as described in Description 1 - Procedure A (9.10 g, 0.039 mmol, 1.00 eq, (estimated 92% pure, containing approximately 8% glycerol 1 ,2,3-tributyrl ester impurity), pyridine (27 mL, 3 vol), DMAP (0.237 g, 0.002 mol, 0.05 eq.), then succinic anhydride (3.99 g 0.040 mol, 1.02 eq.) added. The mixture was heated to 45-50 °C for 18 hr. The reaction was cooled to 20 °C and the pale yellow liquid diluted with IPAC (80 mL) and washed 5 times with HCI (1 N, 60 mL). The organic phase was further washed with sodium bicarbonate (50 mL, 5%) and brine (sat, 50 mL) then concentrated by rotary evaporation and dried under 10 mbar vacuum to give the title compound as a crude product as a pale oil 10.81 g

¹ H NMR (400.1 MHz, CDCh): 5.21 (m, 1H); 4.24 (dd, 2H); 4.09 (dd, 2H); 2.60 (m, 4H); 2.23 (t, 4H); 1.57 (m, 4H); 0.87 (t, 6H). ¹³ C NMR (100.6 MHz, CDCh): 177.3; 173.2; 171.2; 69.6; 61.9; 35.9; 28.8; 28.7; 18.3; 13.6.

Description 2: 4-((1,3-Bis(butyryloxy)propan-2-yl)oxy)-4-oxobutanoic acid (Compound of Formula (II)) - Procedure B The compound of formula (V) (which may be prepared as described in Description 1 - Procedure B) (11.50 kg, -81% purity), pyridine (11.2 L), DMAP (0.25 kg) and succinic anhydride (5.25 kg) were charged into a 100 L reactor and warmed to 45-50 °C over 1 hr and held at that temperature for 16 hr. The reaction mixture was diluted with IPAC and quenched with HCI (2 M, 32 L) and re-dosed with HCI (2 M, 3 L x 2), until pH = 4 then stirred at room temperature for 1 hr. The aqueous phase was removed and the organic layer treated with 20% aq KHCO ₃ (32 L) over 30 minutes, retaining the temperature of the mixture below 30 °C. The vessel was stirred for 15 minutes and the phases allowed to separate then the organic phase was removed and the aqueous retained. Aqueous HCI (2M, 32 L), was charged over 30 minutes retaining the temperature below 30 °C. The mixture was stirred for a further 15 minutes then the phases allowed to separate and the lower aqueous phase discarded. IPAC (32 L) was added and the mixture stirred for 5 minutes then aqueous HCI (2M, 16 L) was charged, the mixture stirred for a further 15 minutes, then the phases separated and the organic phase concentrated to 1 volume in two portions at 70 mbar at 40 °C. The mixture was filtered through a 0.7 micron microfibre filter, washed with IPAC and the filtrate evaporated to the title compound (II) (11.7 kg) as an oil, consistent spectroscopically with that produced by Description 2 - Procedure A.

Example 1 : 1,3-Bis(butyryloxy)propan-2-yl (2-palmitamidoethyl) succinate (Compound of Formula (I)) - Procedure A

A 200 mL PolyBLOCK flask fitted with thermocouple and magnetically driven agitator was charged with the compound of formula (II) which may be prepared as described in Description 2 - Procedure A (3.000 g crude, 2.622 g contained based on Q-NMR assay 87% w/w, 7.88 mmol, 1.00 eq.) dissolved in DCM (30 mL, 10 vol). DMAP (0.193 g, 1.58 mmol,

0.2 eq.), then PEA (2.363 g, 7.88 mmol, 1.00 eq., Ex. TCI) were added. The mixture was stirred for 5 minutes. EDCI (1.469 g, 9.47 mmol, 1.20 eq.) was added and the mixture stirred at 25 °C for 19 hr. The mixture was diluted with DCM (10 mL), then sequentially washed with HCI (1 N, 50 mL), water (50 mL) and brine (50 mL). The DCM solution was concentrated to a waxy solid.

A portion of the crude title compound was recrystallized. Heptane added (93 L, 25 vol) and warmed to 45 °C then cooled to 20 °C over 3 hr. The resulting slurry was aged for 18 hr, filtered and the cake washed with heptane (23 mL, 5 vol). The material was dried under vacuum. The NMR showed the material to be consistent with a known sample of the title compound.

Example 1 : 1,3-E3is(butyryloxy)propan-2-yl (2-palmitamidoethyl) succinate (Compound of Formula (I)) - Procedure A

A 100 L reactor under a nitrogen atmosphere was charged with the compound of formula (II) which may be prepared as described in Description 2 - Procedure B (4 kg), acetonitrile (23.6 L) added and the mixture stirred. DMAP (252 g) was added followed by palmitoylethanolamide (3.2 kg). EDCI (2.5 kg) was added followed by further acetonitrile (8.4 L). The mixture was heated to between 40 and 45 °C for over 30 minutes and held at this temperature for 1 h with stirring. The reaction was cooled to 20-25 °C, water (8.4 L) and MTBE (32 L) added and the mixture stirred for 10 minutes. The phases were separated and the organic layer washed with 10% aq. KHCO ₃ (8.4 L) then brine (20 L), The organic phase was concentrated in vacuo to around 2 volumes then MTBE (approx. 13 L) added to achieve 8 volumes total. The solution was filtered through 0.7 micron microfibre and the filter washed with further MTBE (14 L). The solution was evaporated at 40 °C under vaccum to give (I) (6.26 kg), consistent with material produced in Example 1 - Procedure A.

A 10 g portion of the crude title compound was recrystallized. The sample as dissoved in four volumes of DMSO at 50 °C This was cooled to RT then added to four volumes of water maintaining the temperature at 25 °C. The suspension was filtered and washed with further water (1 vol) then the residue aseotroped with MTBE to remove residual water and the solid dried under vacuum.