Cross-Reference to Related Applications

[0001] This application claims the benefit of priority of US Provisional Application No. 63/255,947, filed October 14, 2021, which is incorporated by reference herein in its entirety for any purpose.

Technical Field

[0002] The present disclosure provides a novel monohydrate salt form of denatonium acetate. More particularly, the present novel salt form and crystalline hydrate form is useful for the treatment and prevention of diseases and conditions. In particular, such diseases and conditions include metabolic syndrome, obesity, NASH, glycemic control/diabetes, Prader Willi Syndrome and IBD (intestinal bowel disease).

Background

[0003] Denatonium acetate is a salt mentioned in US2015/0252305 (“The bittering agent is preferably a denatonium salt or a derivative thereof. In one aspect, the bittering agent is a denatonium salt selected from the group consisting of denatonium chloride, denatonium citrate, denatonium saccharide, denatonium carbonate, denatonium acetate, denatonium benzoate, and mixtures thereof. In one aspect, the liquid composition comprises a first denatonium salt and the film comprises a second denatonium salt that is different than the first denatonium salt.”). However, it appears denatonium acetate was never synthesized but listed only as a theoretical salt of many with denatonium as the cation. Later, a group of patent applications, assigned to Aardvark Therapeutics, Inc., described denatonium acetate as a pharmaceutical composition and included a synthesis process for synthesizing denatonium acetate from lidocaine. See, e.g., W02021/062061. That synthesis process produces denatonium acetate, anhydrous (DAA). However, it was subsequently determined that DAA was insufficiently stable and was not suitable for use as an API (active pharmaceutical ingredient) as there are FDA regulatory requirements for stability of active pharmaceutical ingredients that DAA did not meet. Therefore, there is a need in the art for a more stable salt form of denatonium acetate (DA). Denatonium acetate is known to be useful for treating various conditions such as metabolic syndrome, obesity, and hyperglycemia. See, e.g., WO2021/133908. Summary

[0004] The present disclosure is based on the discovery that DAA is unstable and degrades under at least some conditions. DAA was hydrated and recrystallized into a stable salt, i.e., denatonium acetate monohydrate (DAM). The present disclosure provides a novel denatonium acetate monohydrate salt and crystalline forms thereof. The denatonium acetate monohydrate salt and crystalline forms can provide advantages in the preparation of denatonium acetate, such as greater stability, handling and dosing. In particular, DAM can exhibit improved physical and chemical stability to stress, high temperatures and humidity, e.g., relative to DAA.

[0005] The present disclosure provides a denatonium acetate monohydrate salt of structural formula 1 :

• H ₂ O.

Preferably, the salt is a crystalline monohydrate. The salt may be characterized by an X-ray powder diffraction (XRPD) spectrum substantially as shown in Fig. 5 A or Fig. 5B.

[0006] The present disclosure further provides a pharmaceutical composition comprising a therapeutically effective amount of the denatonium acetate monohydrate crystalline salt in association with one or more pharmaceutically acceptable carriers. The one or more pharmaceutically acceptable carriers may comprise a biocompatible polymer. The biocompatible polymer may be cellulose. The one or more pharmaceutically acceptable carriers may comprise a saccharide. The saccharide may be a sugar alcohol. The sugar alcohol may be mannitol. The one or more pharmaceutically acceptable carriers may comprise talc. The one or more pharmaceutically acceptable carriers comprise an organic acid. The organic acid may be acetic acid. The pharmaceutical composition may be formulated for oral administration. The pharmaceutical composition may comprise solid granules.

[0007] And the present disclosure provides a process for preparing denatonium acetate monohydrate crystalline salt comprising the steps of contacting an equivalent of DAA (denatonium acetate, anhydrous) with a lower alkyl isobutyl ketone, such as methyl isobutyl ketone, and water such that the water concentration is above 10 weight percent, recovering the resultant solid phase, and removing the solid therefrom. The present disclosure provides a process for preparing a denatonium acetate monohydrate salt described herein comprising contacting anhydrous denatonium acetate with a lower alkyl isobutyl ketone and water, resulting in formation of a solid phase comprising denatonium acetate monohydrate. The lower alkyl isobutyl ketone may be methyl isobutyl ketone or ethyl isobutyl ketone. Contacting the anhydrous denatonium acetate with a lower alkyl isobutyl ketone and water forms a composition in which the water concentration is above 10 weight percent. The denatonium acetate monohydrate is a crystalline monohydrate. The crystalline monohydrate may be characterized by an X-ray powder diffraction (XRPD) spectrum substantially as shown in Fig. 5A or Fig. 5B.

Brief Description of the Figure

[0008] Figure 1 shows a synthesis process for making DAM from DAA.

[0009] Figure 2 shows a form diagram showing the relationship between the polymorph patterns found for DAM.

[0010] Figure 3 shows an overlay diffractogram of DAM of Pattern 1 (lower trace) and Pattern 2 (upper trace).

[0011] Figure 4 shows an overlay diffractogram of DAM of Pattern 1 (lower trace) and Pattern 5 in red (upper trace).

[0012] Figure 5A shows a diffractogram of DAM of Pattern 1.

[0013] Figure 5B shows an enlarged version of the region of the diffractogram of DAM of Pattern 1 from 0 to approximately 5500 counts.

Detailed Description

[0014] A process for synthesizing DAM begins with Lidocaine base to make Denatonium Hydroxide and then DAA.

Step 1 : Synthesis of Denatonium Hydroxide from Lidocaine

[0015] To a reflux apparatus add 25 g of lidocaine, 60 ml of water, and 17.5 g of benzyl chloride with stirring and heating in 70-90 °C. The solution needs to be heated and stirred in the before given value for 24h, the solution needs to be cooled down to 30 °C. The unreacted reagents are removed with 3x 10 mL of toluene. With stirring dissolve 65 g of sodium hydroxide into 65 mL of cold water and add it to the aqueous solution with stirring over the course of 3 h. Filter the mixture, wash with some water and dry in open air. Recrystallize in hot chloroform or hot ethanol.

Step 2: Preparation of Denatonium Acetate, anhydrous (DAA) from Denatonium Hydroxide.

[0016] To a reflux apparatus 10 g of denatonium hydroxide (MW: 342.475 g/mol, 0.029 mol), 20 mL of acetone, and 2 g of acetic acid glacial (0.033 mol) dissolved in 15 mL of acetone is added, the mixture is stirred and heated to 35 °C for 3 h. Then evaporated to dryness and recrystallized in hot acetone.

[0017] The DAA degraded and it was found that DAA degraded to either (A) lidocaine and benzyl acetate or it degraded to (B) 2-(diethylamino)-3 -phenyl -N-(2, 6- dimethylphenylpropionamide. Therefore, DAA required a low temperature to be used as an intermediate. For Step 3, DAA was maintained in an organic layer and was distilled under vacuum until the temperature reached 65-67 °C at <150 torr. Methyl isobutyl ketone was added and refluxed under vacuum to remove water via azeotropic distillation to form DAM. DAM was crystalized by adding isopropyl alcohol. Residual salts were removed. The mixture was distilled under vacuum. Next, methyl isobutyl ketone was added and then water. In some embodiments, a lower alkyl isobutyl ketone is used in place of methyl isobutyl ketone. In some embodiments, the lower alkyl is a C1-3 alkyl. In some embodiments, the lower alkyl is methyl or ethyl. The temperature was lowered to <10 °C. The remaining solid was isolated and washed with methyl isobutyl ketone to produce the final DAM (denatonium acetate monohydrate).

[0018] The present disclosure provides crystalline denatonium acetate monohydrate. In some embodiments, the crystalline denatonium acetate monohydrate is characterized by an X-ray powder diffraction (XRPD) spectrum substantially as shown in Fig. 5A or Fig. 5B.

[0019] In some embodiments, a pharmaceutical composition is provided comprising denatonium acetate monohydrate and a pharmaceutically acceptable carrier. The pharmaceutically acceptable carrier may comprise, e.g., a biocompatible polymer such as cellulose and/or a saccharide, e.g., a sugar alcohol such as mannitol. In some embodiments, the pharmaceutically acceptable carrier comprises talc. In some embodiments, the pharmaceutical acceptable carrier comprises talc, a cellulose and a saccharide. In some embodiments, the pharmaceutical composition is an oral formulation. In some embodiments, the pharmaceutical composition (e.g., an oral formulation) is a sustained release cellulosic and mannitol excipient formulation. In some embodiments, the pharmaceutically acceptable carrier comprises an organic acid, such as acetic acid, which may be present in combination with any of the foregoing components or combinations of components. The pharmaceutical composition may be formulated for oral administration. The pharmaceutical composition may comprise solid granules.

Example 1

[0020] This example describes the characterization of a batch of Denatonium acetate monohydrate (DAM) and polymorph screening studies carried out with the material. DAM was highly crystalline with an XRPD Pattern designated as Pattern 1 (Fig. 5A; enlarged version in Fig. 5B).

[0021] Gravimetric Vapor Sorption (GVS) experiments and storage under stress conditions performed on DAM show that the material was very hygroscopic at relative humidity (RH) levels above 80%. It was observed to deliquesce at 96% RH after 5 days. It also lost mass when taken to relative humidity levels of less than 10%. A sample of DAM kept at 0% RH converted to Pattern 5. This pattern is metastable and converted to Pattern 1 under ambient laboratory conditions within a few hours.

[0022] DAM was thermally unstable when heated to 150 °C (just beyond the melt) in the DSC showing only ca. 54.9% of input material remaining by UPLC analysis.

[0023] Attempts to prepare amorphous material by lyophilization from a range of solvents, by fast evaporation or anti-solvent precipitation did not yield amorphous material. Pattern 1, as supplied, was used as input material for the polymorph screening studies using 48 solvents, as well as the solvent/anti- solvent screening studies. During all the investigations into DAM there were 4 additional XRPD Patterns found.

[0024] Pattern 2 was obtained from the attempted preparation of amorphous material by lyophilization of a solution of DAM in t-butanol. After storage for 7 weeks in a closed vial it was observed to have converted to Pattern 1.

[0025] Pattern 3 (from evaporation of a solution of DAM in ethyl formate) was found to be a mixture of acetate and formate salts of denatonium based upon the ^T H NMR and is therefore not a pattern representative of denatonium acetate alone.

[0026] Pattern 4 was obtained from the polymorph screen by evaporation of a solution of DAM in 2-m ethoxy ethanol. A sample reanalyzed by XRPD after storage in a closed vial for 6 weeks shows conversion to Pattern 1.

[0027] Pattern 5 was obtained by storage of DAM at 0% RH, drying in vacuo at room temperature or heating to 120 °C in the DSC and crash cooling. It was observed to readily convert to Pattern 1 on standing on the XRPD disc under ambient lab conditions after 4 hours. A form diagram showing the relationship between the patterns found can be seen in Figure 2.

[0028] A summary of the initial characterization of DAM is provided in Table 1.

Table 1

0029] Particle size distribution was measured and showed a bimodal distribution with a D90 of ca. 65 pm. ES+ mass spectrum of DAM shows a M+ ion of 325.4 consistent with the quaternary component. The sample was highly crystalline. Thermal analysis of DAM by Differential Scanning Calorimetry (DSC) at 10 °C/min showed a broad shallow endothermic event between 44-124 °C, a broad endothermic event of onset 135 °C consistent with a possible melt and further endothermic events between 149-206 °C. Thermogravimetric analysis (TGA) at 10 °C/min showed mass losses of 4.3% over 40-153 °C, 12.3% over 154- 192 °C, 7.8% over 193-220 °C followed by further mass losses.

[0030] Several Gravimetric Vapor Sorption (GVS) experiments were carried out to investigate the behavior of DAM over a range of different relative humidity levels. A GVS experiment (GVS 1) over the relative humidity range (40-90-0-90-0-40%) showed DAM to be very hygroscopic with a 23% mass increase over the 0-90% relative humidity range (second sorption cycle). Most of the mass increase was observed to take place above 80% RH. It is worth noting that the experiment did not reach equilibrium at the highest humidity stages (even with a method allowing for a maximum of 24 hours at each stage if equilibrium is not reached) and so the mass increase of 23% was likely to be an under estimate of the hygroscopicity.

[0031] A GVS experiment (GVS 2) with DAM (DAM, lot:ED21356-001-001-00) to investigate the behavior of the material at levels of relative humidity up to 80% was performed. This experiment used a similar method to GVS 1 without the steps involving 90% RH where the large mass changes were observed and equilibrium was not reached. GVS 2 over the relative humidity range (40-80-0-80-0-40%) starting with a sorption cycle showed an increase in mass of 2.1% (over 0-80% relative humidity in the second sorption cycle) with most of this mass change (+1.4%) taking place between 0-10% RH. The material remained as a free-flowing powder after the experiment and XRPD analysis showed a diffractogram consistent with Pattern 1.

[0032] A further GVS experiment (GVS 3) with DAM over the relative humidity range (40- 0-80-0-80-0-40%) was performed to investigate whether there was a significant difference in behavior if the sample had not been exposed to high (80%) RH before the start of the 0-80% RH sorption cycle. This experiment (GVS 3) starting with a desorption cycle showed an increase in mass of 2% (over 0-80% relative humidity in both the first and second sorption cycles). This was the same for both sorption cycles in the experiment and comparable with the result of 2.1% obtained in GVS 2. Most of the mass change (1.3 - 1.4% increase) occurred between 0-10% RH. The material remained as a free-flowing powder after the experiment and XRPD analysis showed a diffractogram consistent with Pattern 1.

[0033] The GVS experiments and storage under stress conditions carried out with DAM show that the material is very hygroscopic at relative humidity levels above 80%. It showed a mass increase of 1.4% between 0-10% RH and 2.1% between 0-80% RH (in GVS 2) and 23% (in GVS 1) between 0-90% RH. It was observed to deliquesce after storage at 96% RH after 5 days. It also loses mass when taken to relative humidity levels of less than 10%.

[0034] After the observation that DAM lost mass when taken from 10% RH to 0% RH in the GVS experiments described above, a portion of DAM was placed in an open vial and kept at 0% RH in the GVS instrument for 2 days. It was then removed from the instrument and a portion immediately analyzed by XRPD. It showed a diffractogram consistent with Pattern 5. Reanalysis of the sample after standing on the disc for 4 hours under ambient laboratory conditions showed conversion to Pattern 1.

[0035] The GVS and storage under stress conditions experiments carried out with DAM show that the material is very hygroscopic at relative humidity levels above 80%. It also loses mass when taken to relative humidity levels of less than 10%. A sample of DAM kept at 0% RH converted to Pattern 5, however this Pattern is metastable and converts to Pattern 1 under ambient laboratory conditions within a few hours.

[0036] A series of additional DSC experiments were carried out to further investigate the thermal behavior of DAM. A sample of DAM (5 mg) was heated in the DSC at 10 °C/min to 150 °C and then cooled to 30 °C. After the experiment the pan was removed from the instrument, the pan opened and the material (DAM, lot:ED21356-003-001-00) was investigated to check for signs of degradation. UPLC shows significant signs of degradation with only ca. 54.9% of input material remaining. The ^X H NMR also shows evidence of substantial degradation.

[0037] A sample of DAM (4.55 mg) was heated in the DSC at 10 °C/min to 120 °C, held at 120 °C for 2 minutes and then cooled to 30 °C. After the experiment the pan was removed from the instrument, the pan opened and the material was investigated to check for signs of degradation. UPLC and ¹ H NMR showed no significant signs of degradation.

[0038] The DSC experiments carried out with DAM show that the material is thermally unstable when heated to 150 °C showing significant decomposition by NMR and UPLC. No significant chemical degradation was observed when the sample was heated briefly to 120 °C, however a change in XRPD diffractogram from Pattern 1 to Pattern 5 was observed. The material reverted to Pattern 1 after standing at room temperature overnight. Pattern 5 is metastable and converts to Pattern 1 under ambient laboratory conditions after standing overnight on the XRPD disc. A summary of the initial and further characterization of DAM is provided in Table 2.

Table 2

[0039] A portion of DAM (8 mg) was completely dissolved in t-butanol (0.5 mL) and then placed in dry ice to freeze. The frozen sample was lyophilized on the freeze dryer until all the solvent was removed. The resulting solid material (DAM, lot:ED21356-005-001-01) was analyzed by XRPD. It was not amorphous and showed a different pattern to the input. This was designated as Pattern 2. Figure 3 shows an overlay diffractogram of DAM of Pattern 1 in black and Pattern 2 in red. The sample of Pattern 2 was reanalyzed by XRPD after storage in a closed vial for 7 weeks and showed a diffractogram consistent with Pattern 1.

[0040] A portion of DAM (10.9 mg), was dried at room temperature overnight in vacuo, to give a solid ED21356-004-001-00. It was analyzed by XRPD and was found not to be amorphous. It showed diffraction peaks consistent with crystalline material. It showed a pattern quite similar to Pattern 1 with an extra peak at 18° 29 and some other small differences as shown in the overlay in Figure 4. This was assigned as Pattern 5.

[0041] Attempts to prepare amorphous DAM by drying in vacuo, fast evaporation from DCM, anti-solvent precipitation or freeze drying from water, 1,4-dioxane/water (1 : 1), MeCN/water (1 : 1) or t-Butanol under the conditions of these studies did not give amorphous material. Crystalline material consistent with Pattern 1 was obtained from fast evaporation from DCM or freeze drying from water, 1,4-dioxane/water (1 : 1) or MeCN/water (1 : 1). The rapid addition of a concentrated solution of DAM in DCM to heptane resulted in precipitation. Analysis of the solid by XRPD showed diffraction peaks of DAM Pattern 1. In the case of freeze drying from t-BuOH a new Pattern, designated Pattern 2, was isolated. This was found to have converted to Pattern 1 after storage in a closed vial after 7 weeks.

[0042] Drying of a sample of DAM in vacuo at room temperature gave Pattern 5. This was found to have converted to Pattern 1 after storage in a closed vial after 6 weeks.

[0043] Attempts were made to crystallize the API (DAM) from a wide range of solvent systems to try to generate new crystalline forms. DAM was used as input material for these screening studies and solvents chosen were mainly ICH class II and III with a range of different properties as shown in Table 3 below.

Table 3

[0044] Portions of crystalline DAM (each ca. 10 mg) were treated with solvents until it a solution formed, or until 1 mL had been added. The resultant samples were refrigerated (solutions) or shaken at room temperature (suspensions) for several days. The samples that had initially formed solutions were examined for signs of solid formation after refrigeration. If solid material had formed, it was analyzed by XRPD. If no solid had formed the vials were uncapped and the solutions evaporated, and solid residues analyzed by XRPD. For samples which had initially formed suspensions - if solid was still present it was analyzed by XRPD. The supernatant from the suspension was filtered and then the filtrates were then treated as the solutions above. In some experiments further solid was obtained from evaporation of the filtrates and was analyzed by XRPD where the quantity of material allowed.

[0045] The results are summarized in Table 4and Table 5 below. Table 4 (experiments 1-24)

[0046] Most of the experiments with the first 24 solvents gave solid material giving XRPD diffractograms consistent with Pattern 1. Ethyl formate gave a new pattern (designated Pattern 3) and formic acid gave a syrup after evaporation of the experiment. Further data collected for Pattern 3 suggested it was a mixture of formate and acetate salts of denatonium. [0047] Experiments 25-48 gave solid material with XRPD diffractograms consistent with Pattern 1 from nearly all the solvents. Three samples remained as solutions even after evaporation for six weeks. A new pattern, designated as Pattern 4, was obtained from 2- methoxy ethanol.

Table 5 (experiments 25-48)

[0048] Pattern 2 was obtained from the attempted preparation of amorphous material by lyophilization of a solution of DAM in t-butanol to give DAM, lot:ED21356-005-001-01. Characterization data is summarized in Table 6 below.

Table 6 DAM Pattern 2

DAM in ethyl formate. ^X H NMR analysis shows a reduced peak for acetate and an additional peak for formate. This would be consistent with a mixture of formate and acetate salts of denatonium. Characterization data is summarized in Table 7 below.

Table 7 DAM 7 Pattern 3

[0050] Pattern 4 was obtained from the polymorph screen by evaporation of a solution of DAM in 2-m ethoxy ethanol. A sample reanalyzed by XRPD after storage in a closed vial for 6 weeks shows conversion to Pattern 1. Characterization data is summarized below in Table 8.

Table 8 DAM Pattern 4

[0051] Pattern 5 was obtained by storage of DAM (Pattern 1) at 0% RH, drying in vacuo at room temperature or heating to 120 °C in the DSC and crash cooling. Pattern 5 converted to Pattern 1 after standing on XRPD disc under ambient lab conditions for 4 hours. A sample left overnight on XRPD disc under ambient lab conditions was also found to convert to Pattern 1. A sample stored in a closed vial for 6 weeks had also converted to Pattern 1. A summary of the characterization data for the samples of Pattern 5 can be found in Table 9.

Table 9 DAM Pattern 5

0052] DAM was highly crystalline with an XRPD Pattern designated as Pattern 1. During the investigations into DAM there were 4 additional XRPD Patterns found. One of these (Pattern 3) was found to be a mixture of denatonium acetate and formate salts based upon the ^T H NMR and is therefore not a pattern representative of denatonium acetate alone. Pattern 2 was obtained from the attempted preparation of amorphous material by lyophilization of a solution of DAM in t-butanol. After storage for 7 weeks in a closed vial it was observed to have converted to Pattern 1. Pattern 4 was obtained from the polymorph screen by evaporation of a solution of DAM in 2-m ethoxy ethanol. A sample reanalyzed by XRPD after storage in a closed vial for 6 weeks showed conversion to Pattern 1. Pattern 5 was obtained by storage of DAM (Pattern 1) at 0% RH, drying in vacuo at room temperature or heating to 120 °C in the DSC and crash cooling. It was observed to readily convert to Pattern 1 on standing on the XRPD disc under ambient lab conditions after 4 hours.