Process for preparing (15a,16a,17B)-estra-1,3,5(10)-triene-3,15,16,17-tetrol (Estetrol) monohydrate

Abstract

The present invention relates to a process for preparing (15α,16α,17β)-estra-1,3,5(10)-triene- 3,15,16,17-tetrol monohydrate, also known as Estetrol monohydrate, having formula (I).

Description

[0001] PROCESS FOR PREPARING (15a,16a,17p)-ESTRA-l,3,5(10)-TRIENE-3,15,16,17- TETROL (ESTETROL) MONOHYDRATE

[0002] FIELD OF THE INVENTION

[0003] The present invention refers to the field of processes for the synthesis of active ingredients for pharmaceutical use (API), and in particular to a process for preparing on an industrial scale the compound (15a,16a,17P)-estra-l,3,5(10)-triene-3,15,16,17-tetrol monohydrate, also known as Estetrol monohydrate.

[0004] STATE OF THE ART

[0005] Estetrol is an active ingredient with pharmacological activity that makes it useful for Hormone Replacement Therapy (HRT), in female contraception, or in the therapy of autoimmune dysfunctions linked to hormonal imbalances. The compound is a natural product isolated from human urine and has been known for years; it has been described for the first time in the article “Synthesis of epimeric 15-hydroxyestriols, new and potential metabolites of estradiol”, J. Fishman et al., JOC Vol. 33, No. 8, August 1968, p. 3133-3135 (compound la of the figure at page 3133).

[0006] The structural formula of Estetrol is reported below:

[0007] Estetrol

[0008] The positions 15, 16 and 17 of the steroidal skeleton (highlighted in the above reported formula) each bear one hydroxyl radical that, as indicated in the structural formula above, has a defined spatial arrangement, namely, the hydroxy groups in positions 15 and 16 have a configuration while the hydroxy group in position 17 has P configuration.

[0009] The content of impurities below a set limit in an active ingredient is a compulsory requirement to allow the use thereof in pharmaceutical preparations; the limits accepted by international guidelines for pharmaceutical substances are 0.1% for unknown ones and 0.15% for identified ones. The capability to meet these limits is thus a fundamental characteristic for defining an industrially applicable process. Any process, regardless of the yield, providing an API with an impurity content that does not respect the above limits is not industrially useful since the resulting API cannot be granted a marketing authorization by the relevant authorities (EMA, FDA, and so on).

[0010] In the case of Estetrol, the scientific and patent literature has so far concentrated on processes directed to producing the compound in high yield, such to be suitable for an industrial application, and with the high purity necessary for pharmaceutical products; in particular, one of the objects of the industrial processes is to avoid the presence of the isomer 15p, 16p, 17p of the compound, having the structural formula shown below, from which Estetrol must be purified to be used in pharmaceutical preparations:

[0011] Patent application WO 2004 / 041839 A2 (page 6, lines 5-10) describes a process for obtaining Estetrol the purity of which can reach 99%, with the sum of the single impurities not exceeding 1%.

[0012] Subsequent applications relating to the production of Estetrol are, for example, WO 2012 / 164096 Al, WO 2013 / 034780 Al, WO 2013 / 050553 Al, WO 2015 / 040051 Al, WO 2015-086643 Al, and WO 2021 / 044302 Al; WO 2015 / 040051 Al, for instance, shows in the examples the achievement of a ratio Estetrol / isomer 15p, 16p, 17p up to 99: 1.

[0013] Other requirements of the pharmaceutical industry are connected with the stability and processability of the compounds of interest.

[0014] Active molecules may be more stable when provided in the form of salts, complexes or solvates, from which the molecule can be easily released in metabolic conditions; besides, active molecules are almost invariably formulated with excipients to produce administrable compositions, in which the excipients perform different functions such as controlling the release rate of the active component, masking unpleasant taste, bringing the dosage unit to handleable weight and volume, and so on.

[0015] One useful form of Estetrol is the monohydrate, that is, a solvate of the compound with water in a 1 : 1 stoichiometric ratio; Estetrol monohydrate can be represented as follows:

[0016] The patent publications above refer to the process of synthesis of Estetrol and salts or solvates of the compound are mentioned in passing, such as in WO 2015-086643 Al, or not mentioned at all; none of said publications reports a reproducible method for the preparation of Estetrol monohydrate on an industrial level and with the necessary purity level.

[0017] Patent application WO 2021 / 058716 Al, in the name of the present Applicant, describes a method for producing Estetrol monohydrate, which consists in dissolving anhydrous Estetrol in an organic solvent miscible with water, mixing the resulting solution with water, eliminating the organic solvent by distillation obtaining a suspension, maintaining the suspension under stirring, and then filtering, washing and finally drying the solid under reduced pressure. The method of WO 2021 / 058716 Al is reliable and consistently provides Estetrol monohydrate of quality and purity suitable for the intended application, but involves the use of organic solvents that need to be distilled off and then recovered, adding time and costs to the whole process; besides, the greatest care must be used to ascertain that solvent is completely eliminated and not included in the final dosage units.

[0018] It is an object of the present invention to provide a process for the preparation of Estetrol monohydrate that is suitable for industrial application, providing the compound in pharmaceutical quality, while avoiding the use of organic solvents.

[0019] SUMMARY OF THE INVENTION

[0020] The object of the present invention is to provide an industrially applicable process of preparation of Estetrol monohydrate, without having to resort to purification techniques.

[0021] The invention relates to a process for the transformation of Estetrol into Estetrol monohydrate:

[0022] Estetrol Estetrol monohydrate by contacting anhydrous Estetrol with pure water, either in liquid or vapour form. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figures 1 and 2 show the DRX diffractograms of Estetrol monohydrate obtainable with the first embodiment of the process of the invention, under different conditions;

[0024] Figure 3 shows the DRX diffractogram of Estetrol monohydrate obtainable with the second embodiment of the process of the invention.

[0025] DETAILED DESCRIPTION OF THE INVENTION

[0026] The invention relates to a method for the preparation of Estetrol monohydrate starting from anhydrous Estetrol.

[0027] Anhydrous Estetrol may be produced according to any of the processes known from the prior art; one preferred method is the one comprising steps A) to D) of WO 2021 / 058716 Al. Anhydrous Estetrol can be employed both in crystalline form and in amorphous form.

[0028] By “pure water”, in the present description and in the claims, it is intended distilled water.

[0029] In a first embodiment, the invention consists in a process comprising contacting anhydrous Estetrol with pure water, according to the following steps: a) preparing and stirring a suspension of anhydrous Estetrol in water for at least 5 minutes, obtaining a suspension of Estetrol monohydrate; b) filtering the suspension of Estetrol monohydrate obtained in step a) to produce wet Estetrol monohydrate; c) drying the wet Estetrol monohydrate of step b) obtaining Estetrol monohydrate.

[0030] The stirring of step a) is carried out at a temperature between 5 and 90 °C, preferably between 15 and 35 °C.

[0031] The inventors have studied the evolution in time of the transformation from anhydrous Estetrol to Estetrol monohydrate, by preparing slurries of the anhydrous compound in water, sampling the slurry at different times, drying the sample and analysing it by XRPD; an example of the results obtained is represented by the different diffractograms in Figure 1. The analyses show that the signals corresponding to anhydrous Estetrol disappear after just a few minutes of stirring in water, rapidly converting into Estetrol monohydrate.

[0032] The drying of step c) is carried out at a pressure, lower than 800 mbar, preferably lower than 500 mbar, and more preferably lower than 250 mbar, at a temperature between 15 and 50 °C, preferably between 15 and 35 °C.

[0033] In the second embodiment, the invention consists in a process for transforming anhydrous Estetrol into Estetrol monohydrate by a simple conditioning procedure, said process comprising a first step d) of exposing powders of anhydrous Estetrol for at least 24 hours to an atmosphere with at least 75% relative humidity (RH) at a temperature between 20 and 25 °C, and a second step e) of recovering the powders of Estetrol monohydrate.

[0034] At the end of step d), the transformation is complete and powders of Estetrol monohydrate can be simply recovered in step e), ready for use in pharmaceutical formulations, without further processing.

[0035] Step d) is preferably carried out with an atmosphere with a RH of at least 90% and, independently from the RH, preferably for at least 36 hours.

[0036] The invention will be further illustrated by the examples that follow.

[0037] EXPERIMENTAL INSTRUMENTS, METHODS AND CONDITIONS

[0038] HPLC:

[0039] Agilent Model 1260 Infinity chromatography system; UV Detector MODEL G1315C

[0040] DAD VL+

[0041] Method HPLC:

[0042] Chromatographic conditions:

[0043] - Column: Supelco discovery C18 150x4.6 mm, 5pm

[0044] - Flow: 1 ml / min

[0045] - Detector: UV 280 nm

[0046] - Injection volume: 25 pl

[0047] - Temperature: 22 °C

[0048] - Mobile phase A: 4.29 g / L solution of CH3COONH4 in water / methanol / acetonitrile 90 / 6 / 4

[0049] - Mobile phase B: 38.6 g / L solution of CH3COONH4 in water / methanol / acetonitrile 10 / 54 / 36

[0050] XPRD:

[0051] XRPD analyses were performed using a Bruker D2 Phaser (2nd edition) powder diffractometer operating in Bragg-Brentano geometry, equipped with a rotating multisampler and linear SSD type detector (Lynxeye). The X-ray source was an X-ray tube with a copper anode operated at 30 KV and 10 mA. For the analysis the X radiation having a wavelength corresponding to the average Ka of copper ( = 1.54184 A) was used. The Kp radiation was filtered through a nickel filter.

[0052] “Zero background” silicon sample holders with a flat surface were used on which the sample was spread to form a thin layer. During the analysis the sample holder was rotated at a speed of 60 rpm.

[0053] Scanning was performed in the 4-40° 29 range with 0.016° 29 increments and an acquisition time of 1.0 s for each increment.

[0054] The diffractograms were processed using the Bruker DIFFRAC.EVA software.

[0055] NOTES

[0056] The water used in the experimental descriptions is to be understood as pure water unless otherwise indicated.

[0057] EXAMPLE 1

[0058] This example refers to the first embodiment of the process of the invention, hydration of anhydrous Estetrol by slurry in water.

[0059] 3.0 g of pure crystalline anhydrous Estetrol were placed in a 100 mL flask.

[0060] Pure water (30 mL, 10 V / w) was added, and the mixture was stirred using a mechanical stirrer at 20-25 °C.

[0061] Slurry samples were taken after 5 min, 1 h, and 4.5 h.

[0062] The samples were filtered under vacuum, dried over the filter for 10 min and analysed by XRPD.

[0063] The results of the XRPD tests are reported in Figs. 1 and 2.

[0064] In Fig. 1, the lower diffractogram, indicated as time zero (t = 0 h) refers to the starting anhydrous Estetrol, the three intermediate diffractograms refer to the samples taken at the indicated times, while the upper diffractogram has been obtained with a sample of pure Estetrol monohydrate prepared according to the process described in WO 2021 / 058716 Al, and has been added as reference.

[0065] Fig. 2 is an enlargement on the vertical axis of the two diffractograms at t = 0 h and t = 4.5 h of Fig. 1, that allows an easier check of the disappearance of peaks of anhydrous Estetrol and of the appearance of peaks of Estetrol monohydrate.

[0066] The final sample, after 4.5 h of slurry, was Estetrol monohydrate (white crystals, HPLC purity = 100%). The XRPD peak list is reported in Table 1 below:

[0067] Table 1

[0068] The list of peaks in Table 1 corresponds, with the usual approximation of ± 0.2°, to the data reported in WO 2021 / 058716 Al for Estetrol monohydrate.

[0069] EXAMPLE 2

[0070] This example refers to the second embodiment of the process of the invention, hydration of anhydrous Estetrol in a 100% RH chamber.

[0071] 3.0 g of pure anhydrous Estetrol were placed in a crystallizer as a thin layer. The crystallizer was put in a glass desiccator filled at the bottom with water at 20 < T <

[0072] 25 °C.

[0073] Small samples of powders were collected after 3.5 h, 7 h, 24 h, 48 h and analysed by XRPD. The obtained diffractograms are reproduced in Fig. 3, in which the diffractogram at time zero (t = 0 h) refers to anhydrous Estetrol, the upper diffractogram, added as reference, has been obtained with a sample of pure Estetrol monohydrate prepared according to the process described in WO 2021 / 058716 Al, and the four intermediate diffractograms have been recorded on the samples obtained after the indicated treatment times.

[0074] The final sample, after 48 h of exposure to wet atmosphere, was Estetrol monohydrate (white crystals, HPLC purity = 100%). The XRPD peak list is reported in Table 2 below:

[0075] Table 2

[0076] The list of peaks in Table 2 corresponds, with the usual approximation of ± 0.2°, to the data reported in WO 2021 / 058716 Al for Estetrol monohydrate.

Claims

CLAIMS1. Process for the transformation of Estetrol into Estetrol monohydrate:Estetrol Estetrol monohydrate which comprises contacting anhydrous Estetrol with pure water, either in liquid or vapour form.

2. Process according to claim 1, in which anhydrous Estetrol is contacted with pure water in liquid form, comprising the following steps: a) preparing and stirring a suspension of anhydrous Estetrol in water for at least 5 minutes, obtaining a suspension of Estetrol monohydrate; b) filtering the suspension of Estetrol monohydrate obtained in step a) to produce wet Estetrol monohydrate; c) drying the wet Estetrol monohydrate of step b) obtaining Estetrol monohydrate.

3. Process according to claim 2, in which step a) is carried out at a temperature between 5 and 90 °C.

4. Process according to claim 3, in which step a) is carried out at a temperature between preferably between 15 and 35 °C.

5. Process according to any one of claims 2 to 4, in which step c) is carried out at a pressure lower than 800 mbar.

6. Process according to claim 5, in which step c) is carried out at a pressure lower than 500 mbar.

7. Process according to claim 6, in which step c) is carried out at a pressure lower than 250mbar.

8. Process according to any one of claims 2 to 7, wherein step c) is carried out at a temperature between 15 and 50 °C.

9. Process according to claim 8, in which step c) is carried out at a temperature between 15 and 35 °C.

10. Process according to claim 1, in which anhydrous Estetrol is contacted with pure water in vapour form, comprising the following steps: d) exposing powders of anhydrous Estetrol for at least 24 hours to an atmosphere with at least 75% relative humidity (RH) at a temperature between 20 and 25 °C; e) recovering Estetrol monohydrate obtained in step d).

11. Process according to claim 10, in which step d) is carried out with an atmosphere with a RH of at least 90%.

12. Process according to claim 10 or 11, in which step d) is carried out for at least 36 hours.

Images