Process for the preparation of an intermediate useful for the synthesis of voclosporin

Abstract

The invention relates to a process for the preparation of an intermediate useful for the synthesis of voclosporin, an immunosuppressant active ingredient inhibitor of calcineurin.

Description

[0001] PROCESS FOR THE PREPARATION OF AN INTERMEDIATE USEFUL FOR

[0002] THE SYNTHESIS OF VOCLOSPORIN

[0003] The invention relates to a process for the preparation of an intermediate useful for the synthesis of voclosporin.

[0004] Background of the invention

[0005] Voclosporin (formula 1), is an immunosuppressant active ingredient inhibitor of calcineurin obtained through derivatizazion of cyclosporine (formula 2); due to such a derivatization, the inhibitory ability of the calcineurin and the metabolic stability of voclosporin are higher than those of cyclosporine.

[0006] Voclosporin is approved in Europe and in the United States under the trademark Lupkynis™, and it is used in combination with mycophenolate mofetil in the treatment of glomerulonephritis caused by systemic lupus erythematosus, also known as lupus nephritis; furthermore, voclosporin is used as drug candidate in clinical trials relating to pathologies such as focal segmental glomerulosclerosis, psoriasis, dry-eye syndrome, non- infective uveitis, keratoconjuntivitis sicca, or patients subjected to kidney transplant.

[0007] Processes for the preparation of voclosporin are disclosed in WO 2003 / 033526, WO 2003 / 033527 and WO 2004 / 89960 and said processes involve at least a step of formation or introduction of a carbon-carbon double bond by Wittig reaction, Peterson olefination or by the use of phospho- or titan-allyls.

[0008]

[0009] The aldehyde of formula 3 represents a key intermediate in the above processes and it is obtained by ozonolysis of the compound of formula 4; such procedure, although commonly used in industrial processes, shows several limitations such as the compatibility with a narrow number of solvents and the employment on a scale of the order of hundreds of grams. Moreover, the eventual development of undesired peroxide species is particularly disadvantageous, both for security reasons due to the explosivity of such species, and for the related formation of undesired by-products.

[0010] Considering the utility and the interest in voclosporin, it is necessary to develop alternative methods of synthesis of such compound and, in particular, of its intermediates / precursors.

[0011] Description of the invention

[0012] The Applicant developed a process for the preparation of the aldehyde of formula 3 comprising the conversion of a compound of formula 4 to a diol of formula 5 followed by the isolation and oxidation of the diol of formula 5

[0013]

[0014] In the compounds of formula 3-5 and in the carboxylic acid 6 mentioned below, the R group is selected from acetyl, chloroacetyl, trifluoroacetyl, pivaloyl, benzoyl; preferably, R is acetyl.

[0015] The diol of formula 5 is obtained by dihydroxylation of the compound of formula 4 using a metal catalyst containing a metal selected from the group consisting of: Ru, Yb, Ce, Mn, Fe, Pd, and Os; preferably, using a catalyst selected from an osmate salt, encapsulated osmium, supported osmium. In addition to the metal catalysts expressly mentioned as preferred, the catalysts mentioned in Von Willingh G., “Recent Advancements in the Development of Osmium Catalysts for Various Oxidation Reactions: A New Era?,” Comments on Inorganic Chemistry 2021 and Achard T. et al., European Journal of Organic Chemistry 2021, 2021 (6), 877-896 can be used. By “isolation of the diol of formula 5” the separation of such compound from the reaction mixture is meant and, in particular, the separation from any unreacted metal catalyst. According to a particularly preferred embodiment, the process according to the invention involves the use of an osmate salt, preferably K2OsO4· 2 H2O, Na2OsO4·2H2O.

[0016] The isolation of the diol of formula 5 is carried out by solvent extraction with a solvent selected from dichloromethane, butanol, ethyl acetate, tetrahydrofuran, methyl tetrahydrofuran, diethyl ether, methyl tert-butyl ether, toluene and mixtures thereof.

[0017] The aldehyde 3 is obtained by treatment of the diol of formula 5 with an oxidizing agent selected from NaIO4, IBX, Dess-Martin periodinane, KMnO4, Pb(OAc)4, CrO3, MnO2, pyridinium chlorochromate; preferably, the oxidizing agent is selected from NaIO4, IBX and Dess-Martin periodinane.

[0018] More in detail, the process for the preparation of the compound of formula 3 comprises the following steps: a. dissolving a compound of formula 4 in a mixture of an organic solvent SI and water to give a solution A; b. adding a metal catalyst to the solution A to give a solution B and stirring the solution B until conversion of the compound of formula 4 into the corresponding diol of formula 5; c. extracting the solution B with an organic solvent S2 to give an organic phase and an aqueous phase; d. adding an aqueous solution of an oxidizing agent to the organic phase to give a solution C and stirring the solution until conversion of the diol of formula 5 into the corresponding aldehyde of formula 3; e. extracting the solution C with an organic solvent S3 to give an organic phase and an aqueous phase; f. isolating the aldehyde of formula 3 from the organic phase obtained in step e.

[0019] Typically, in step a. the solvent S1 a mixture of water and of an organica solvent selected from methanol, ethanol, propanol, isopropanol, acetone, acetonitrile, dichloromethane, dimethylformamide, dimethyl sulfoxide, ethyl acetate, hexamethylphosphoramide, pyridine, tetrahydrofuran, and mixtures thereof; preferably the organic solvent is selected from acetone, acetonitrile, ethyl acetate, and tetrahydrofuran; more preferably, the solvent SI is a mixture of acetonitrile and water. Typically, the ratio between the organic solvent and water is comprised between 10:1 and 1:3; preferably, between 7: 1 and 1:1; more preferably, the ratio is 5: 1. In a particularly preferred aspect, in step a. the compound of formula 4 is dissolved in a mixture acetonitrile: water 5:1.

[0020] Typically, in step b. the metal catalyst is selected from the catalysts containing a metal selected from the group consisting of: Ru, Yb, Ce, Mn, Fe, Pd, and Os; preferably, the catalyst is selected from an osmate salt, encapsulated osmium, supported osmium; more preferably, the catalyst is an osmate salt selected from K2OsO4· 2 H2O and Na2OsO4· 2 H2O; more preferably, K2OsO4· 2 H2O. When in step b. K2OSO4· 2 H2O or Na2OsO4· 2 H2O are used, a co-oxidizing agent selected from the group consisting of N-methylmorpholine N- oxide, H2O2, triethylamine N-oxide, KMnO4is also added,; such co-oxidizing agent is needed to restore the metal catalyst, allowing to use it effectively in a catalytic amount. The ratio between the equivalents of the compound of formula 4 and the metal catalyst is comprised in the range5:0.001; preferably, in the range 3:0.005; more preferably, in the range 1:0.01. The use of an osmate salt, in particular K2OsO4· 2 H2O or Na2OsO4· 2 H2O, is particularly preferred on industrial scale as it avoids the use of OsO4, which implies issues connected to high costs, toxicity, volatility and impossibility of a reuse.

[0021] Typically, the solvent S2 used in step c. is selected from dichloromethane, butanol, ethyl acetate, tetrahydrofuran, methyl tetrahydrofuran, diethyl ether, methyl tert-butyl ether, toluene and mixtures thereof; preferably, dichloromethane, butanol, methyl tert- butyl ether; more preferably, dichloromethane. Furthermore, the organic phase obtained in step c. can be optionally washed with an aqueous solution containing a reducing agent, preferably, with an aqueous solution of sodium thiosulphate, sodium metabisulfite, ascorbic acid in order to eliminate possible residues of the catalyst.

[0022] The organic phase obtained in step c. can be concentrated by distillation under vacuum to obtain a volume equal to two thirds compared to the initial volume; preferably, to a half compared to the initial volume; more preferably, to a third compared to the initial volume, thereafter, before adding the aqueous solution of the oxidizing agent of step d., a dilution with 5 - 10 volumes of a solvent selected from acetone, acetonitrile, dichloromethane, dimethylformamide, dimethyl sulfoxide, ethyl acetate and mixture thereof, preferably, acetonitrile can be carried out. The oxidizing agent used in step d. can be selected from NaICO4, IBX, Dess-Martin periodinane, KMnO4, Pb(OAc)4, CrO3, MnO2, pyridinium chlorochromate; preferably, NaICO,4IBX, and Dess-Martin periodinane.

[0023] Verified the disappearing of the diol 5 from the solution C, using any one of the methods known by one skilled in the art, an aqueous solution containing a reducing agent selected from sodium thiosulphate, sodium metabisulfite, ascorbic acid can be added to the solution C; preferably, Na2S2C>3 in order to remove any residue of the oxidizing agent.

[0024] Typically, in step e. the organic solvent S3 is selected from pentane, hexane, cyclohexane, benzene, toluene, tetrahydrofuran, methyl tetrahydrofuran, diethyl ether, methyl tert-butyl ether and dichloromethane; preferably, hexane, toluene, tetrahydrofuran, diethyl ether and mixture thereof; more preferably, toluene. Furthermore, the organic phase obtained in step e. is preferably concentrated by distillation under vacuum to obtain a volume equal to two thirds compared to the initial volume, more preferably to half with respect to the initial volume; even more preferably, to a third with respect to the initial volume.

[0025] Typically, in step f., the isolation of the aldehyde 3 is carried out adding an organic solvent S4 selected from pentane, hexane, cyclohexane, cyclopentane, heptane, methyl tert- butyl ether, diethyl ether and mixtures thereof; preferably, cyclohexane or heptane; more preferably, heptane. Such an addition causes the precipitation of the aldehyde 3 in a crystalline form, referred to as form V; the X-RPD spectrum of the crystalline form V of aldehyde 3 shows a crystalline structure and comprises distinctive reflections, expressed as angles 2θ° and with relative intensity higher than or equal to 5%, approximately equal to: 8.0 - 8.7 - 10.08 - 11.4 - 11.8 - 12.9 - 14.5 - 16.1 - 16.5 - 17.2 - 18.0 - 18.2 - 18.5 - 18-9 - 19.8 - 20.2 - 21.7 - 25.7 (± 0.2). More in detail, the X-RPD spectrum of the form V shows a crystalline structure and comprises distinctive reflections, expressed as angles 29° and with relative intensity higher than 1%, approximately equal to: 6.0 - 8.0 - 8.7 - 10.08 - 11.4 - 11.8 - 12.0 - 12.9 - 14.5 - 16.1 - 16.5 - 17.2 - 18.0 - 18.2 - 18.5 - 18-9 - 19.8 - 20.2 - 21.7 - 22.0 - 23.6 - 24.1 - 24.6 - 25.7 - 26.3 - 28.4 - 29.3 - 30.3 - 31.4 - 31.7 - 32.8 - 34.5 - 35.5 - 35.8 - 38.3 (± 0.2). Even more in detail, the X-RPD spectrum of the form V shows a crystalline structure and comprises distinctive reflections, expressed as angles 29°, approximately equal to: 6.0 - 8.0 -8.7 — 10.08 - 11.4 — 11.8 - 12.0 — 12.9 — 14.5 - 16.1 - 16.5 - 17.2 - 18.0 - 18.2 - 18.5 - 18 - 9 -19.8 - 20.2 - 21.7 - 22.0 - 23.6 - 24.1 - 24.6 - 25.7 -26.3 - 28.4 - 29.3 - 30.3 - 31.4 - 31.7 - 32.8 - 34.5 -35.5 -35.8- 38.3 - 42.6 (± 0.2). The X-RPD spectrum of the crystalline form V of the aldehyde 3 is set in Figure 1.

[0026] The crystalline form V, compared to the amorphous form of the aldehyde 3, is particularly advantageous since, having less impurities, prevents the formation of undesired byproducts.

[0027] The process of the invention allows to obtain the aldehyde of formula 3 in two steps, i.e. by the conversion of the compound of formula 4 into diol of formula 5, followed by the isolation and conversion of the latter into the aldehyde of formula 3 by oxidative cleavage; such process is particularly advantageous, for example compared to the known processes, since it provides the aldehyde of formula 3 with high yield and purity. In particular, the process of the invention allows to obtain an aldehyde of formula 3 with an amount of the corresponding carboxylic acid of formula 6 less than 1%; preferably, less than 0.5%, 0.2%, 0.1%, 0.05%, 0.02%. The amount of impurities is measured by HPLC analysis according to the method described in the “Materials and methods” section.

[0028]

[0029] The extraction carried out in step c. allows to separate the diol of formula 5 from any unreacted metal catalyst; such separation step is particularly advantageous since the eventual presence of the metal catalyst in the following steps could promote the oxidation of the aldehyde of formula 3 into the carboxylic acid of formula 6. In fact, when the conversion of the compound of formula 4 into the compound of formula 3 is carried out in a single step treating the compound of formula 4 with OSO4and NaIO4, the carboxylic acid of formula 6 is usually obtained in an amount comprised between 5-15%; the presence of such impurity in such an high amount is critical, as it affects notably the reaction yield. The content of the carboxylic acid of formula 6 obtained by the oxidation of the compound of formula 4 in a single step and according to the process object of the invention is set in Table 1:

[0030] Table 1

[0031] Furthermore, as it is not possible to separate the aldehyde of formula 3 from the carboxylic acid of formula 6 through a simple precipitation or crystallization, in order to purify the aldehyde of formula 3, it would be necessary to use alternative purification methods, such as column chromatography, which could make the process longer and labor intensive and cause a further loss of the product of interest. Experimental

[0032] Materials and methods

[0033] The diffraction pattern was recorded using a Bruker D2-Phaser diffractometer with the following parameters:

[0034] Anodic tube: Cu

[0035] Voltage generator (kV): 30

[0036] Electricity generator (mA): 10

[0037] Wavelength λ1and λ2(Å): 1.54056, 1.54439

[0038] Intensity ratio (λ2 / λ1): 0.500

[0039] Spinner: off

[0040] Angolar range ( 2θ°): 2.00 - 50.00

[0041] Step size ( 2θ°): 0.020

[0042] Time for step (sec): 3.0

[0043] The HPLC analyses were carried out by a HPLC apparatus consisting of a quaternary pump, a thermostated autosampler, a column compart and a 2998 PDA detector, using a 150 mm x 4.6 mm 2.5 μm Xselect CSH Fluoro-phenyl column, the solvents A 1% of a solution of 0.2M HCOONH4 / 99% water + 0.1% HCOOH and B 1% of a solution of 0.2M HCOONH4 / 99% CH3CN + 0.1% HCOOH as mobile phase.

[0044] Example 1 - Method of preparation of the aldehyde of formula 3

[0045] 65.0 g of acetyl cyclosporine A (formula 4, R = acetyl) (52.2 mmol, 1.0 eq.) were dissolved in a CH3CN:H2O 5:1 mixture (390 mL) at room temperature. Subsequently 194 mg of K2OsO4·H2O (0.52 mmol, 0.01 eq.) were added and the mixture was kept under stirring for half an hour. At the end, 6.4 g of N-methylmorpholine N-oxide (54.8 mmol, 1.05 eq.) were added and the final mixture was heated at 30 °C. After the complete conversion of the starting material into the corresponding diol 5, the mixture was cooled to room temperature and diluted with water (260 mL) and CH2CI2(162 mL). The two phases were separated and the organic phase was subsequently washed twice with water (260 mL x 2) and concentrated under reduced pressure to 130 mL. The residue was diluted with CH3CN (520 mL, 8 volumes) and heated at 30 °C. 22.5 g of NalO4(105.1 mmol, 2.0 eq.) dissolved in water (130 mL, 2 volumes) were added under stirring. After the complete conversion of the diol 5 into the corresponding aldehyde 3, the mixture was cooled to 20 °C and quenched with 12.41 g of Na2S2O3(78.6 mmol, 1.5 eq.), dissolved in water (260 mL), keeping the temperature constant. The final mixture was extracted with toluene (195 mL) and the two phases were separated. The organic layer was washed with water (260 mL) and brine (260 mL). The final solution was concentrated to 130 mL and the product was precipitated by adding 260 mL of heptane. The suspension was filtered and the solid washed once with heptane (65 mL). The solid was dried at 50 °C under vacuum for 16 hours to afford a white solid (53.9 g, yield = 83%, typical purity A% HPLC 96-98%).

[0046] Example 2 - Method of preparation of the aldehyde of formula 3

[0047] Synthesis of the aldehyde

[0048] 1.5 g of acetyl cyclosporine (1.2 mmol, 1.0 eq.) was dissolved in 9 mL of an acetonitrile: water mixture (5:1). Subsequently, 200 mg of encapsulated osmium (osmium tetroxide encapsulated within a crosslinked polyurea porous matrix, trademark “Os EnCat® 40” (0.3 mmol / g Os, 0.06 mmol, 0.05 eq.) were added and the suspension was heated at 45 °C. Subsequently, 280 mg of NMO (2.4 mmol, 2.0 eq.) was added portionwise.

[0049] After complete conversion of the starting material, the mixture was filtered and 4.5 mL of toluene and 4.5 mL of a 10% aqueous solution of sodium metabisulfite were added. The mixture was left under stirring for 16 hours. Subsequently, the phases were separated and the organic phase was distilled and diluted with 7.5 mL of acetonitrile. 385 mg of NaIO4(1.8 mmol, 1.5 eq.) dissolved in 1.5 mL of water was added and the mixture was heated at 30 °C. After complete conversion of the intermediate to the desired product, the mixture was cooled at 20 °C and quenched with 285 mg of Na2S2O3(1.8 mmol, 1.5 eq.), dissolved in 6 mL of water, keeping the temperature constant. After separation of the phases, the organic phase was further washed with water and the final solution was concentrated to 3 mL. The product was precipitated by adding 6 mL of heptane. The suspension was filtered and the solid washed once with 1.5 mL of heptane. The solid was dried at 50 °C under vacuum for 16 hours to afford a white solid (1.2 g, yield = 79%, typical purity A% HPLC ≥ 90%). Example 3 (comparative) - Method of preparation of the aldehyde of formula 3 5.58 g of acetyl cyclosporine A (formula 4, R = acetyl) (4.48 mmol, 1.0 eq.) was suspended in a CH3CN:H2O 1:1 mixture (55.8 mL + 55.8 mL) and heated at 30 °C. Subsequently, 50 mg of K2OsO4· 2 H2O (0.13 mmol, 0.03 eq.) was added and the mixture was kept under stirring for half an hour. Finally, 2.01 g of NaIO4(9.42 mmol, 2.1 eq.), was added in three portions. At complete conversion, the reaction mixture was cooled at room temperature and quenched with 7.09 g of Na2S2O3(44.86 mmol, 10.0 eq.), dissolved in water (20 mL), keeping the temperature constant. The final reaction mixture was extracted with methyl tetrahydrofuran (Me-THF) (110 mL) and the two phases separated. The aqueous phase was extracted again with Me-THF (110 mL) and the combined organic phases were concentrated to 100 mL. The product was precipitated by adding 500 mL of heptane. The suspension was filtered and the solid (aldehyde 3) was washed twice with heptane (2 x 25 mL). The solid was dried at 50 °C under vacuum for 16 hours to afford a white solid.

Claims

CLAIMS1. A process for the preparation of the aldehyde of formula 3 by conversion of a compound of formula 4 to a diol of formula 5followed by isolation and oxidation of the diol of formula 5wherein R is selected from the group consisting of acetyl, chloroacetyl, trifluoroacetyl, pivaloyl, benzoyl.

2. The process according to claim 1, wherein the diol of formula 5 is obtained by using a metal catalyst containing a metal selected from the group consisting of: Ru, Yb, Ce, Mn, Fe, Pd, and Os.

3. The process according to claim 2, wherein the metal catalyst is selected from an osmate salt, encapsulated osmium, supported osmium.

4. The process according to claim 3, wherein the metal catalyst is K2OsO4· 2 H2O orNa2OsO4· 2 H2O.

5. The process according to claim 1, wherein the isolation of the diol of formula 5 is carried out by solvent extraction, which solvent is selected from dichloromethane, butanol, ethyl acetate, tetrahydrofuran, methyl tetrahydrofuran, diethyl ether, methyl tert-butyl ether, toluene, and mixtures thereof.

6. The process according to claim 1, wherein the oxidation of the diol of formula 5 is carried out using an aqueous solution of an oxidizing agent selected from NalO4, IBX, Dess-Martin periodinane, KMnO4, Pb(OAc)4, CrO3, MnO2, pyridinium chlorochromate.

7. The process according to any one of the preceding claims, comprising a. dissolving a compound of formula 4 in a mixture of an organic solvent SI and water to give a solution A; b. adding a metal catalyst to the solution A to give a solution B and stirring of the solution B until conversion of the compound of formula 4 to a corresponding diol of formula 5; c. extracting the solution B with an organic solvent S2 to give an organic phase and an aqueous phase; d. adding the organic phase of an aqueous solution of an oxidizing agent to give a solution C and stirring of the solution until conversion of the diol of formula 5 to the corresponding aldehyde of formula 3; e. extraction of the solution C with an organic solvent S3 to give an organic phase and an aqueous phase; f. isolation of the aldehyde of formula 3 from the organic phase obtained in step e.

8. The process according to claim 7, wherein in step b. a co-oxidant agent selected from the group consisting of N-methylmorpholine N-oxide, H2O2, triethylamine N- oxide, KMnO4 is used.

9. The process according to claim 7, wherein the organic phase obtained in step c. and the solution C are treated with an aqueous solution containing a reducing agent selected from sodium thiosulphate, sodium metabisulfite, ascorbic acid.

10. The process according to claim 7, wherein the isolation of the aldehyde 3 of step f. is carried out by adding an organic solvent S4 selected from pentane, hexane, cyclohexane, cyclopentane, heptane, methyl tert-butyl ether, diethyl ether, and mixtures thereof to the organic phase obtained from step e.

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