Methods for the preparation of nitric oxide-donating prostaglandin analogs

Abstract

The present invention relates to a compound of formula (I): TIFF2024509051000034.tif58161 This invention relates to a process for preparing 6-(nitrooxy)hexanoic acid-(1S,2E)-3-[(1R,2R,3S,5R)-2-[(2Z)-7-(ethylamino)-7-oxo-2-hepten-1-yl]-3,5-dihydroxycyclopentyl]-1-(2-phenylethyl)-2-propen-1-yl ester of According to the present invention, compound (I) can be efficiently prepared in high purity by coupling bimatoprost in its boronate-protected form with 6-(nitrooxy)hexanoyl chloride, followed by removal of the boronate protecting group. The present invention also relates to a process for the preparation of 6-(nitrooxy)hexanoic acid having an HPLC purity of 99% or more and containing 6-{[6-(nitrooxy)hexanoyl]oxy}hexanoic acid (compound (IXa)) in an amount of 0.2% or less.

Description

[Technical Field]

[0001] The present invention relates to a process suitable for the large-scale preparation of 6-(nitrooxy)hexanoic acid-(1S,2E)-3-[(1R,2R,3S,5R)-2-[(2Z)-7-(ethylamino)-7-oxo-2-hepten-1-yl]-3,5-dihydroxycyclopentyl]-1-(2-phenylethyl)-2-propen-1-yl ester of formula (I), which makes it possible to obtain said product with high chemical purity. The present invention also describes the preparation of 6-(nitrooxy)hexanoic acid (VIIIa), a key intermediate in said synthesis, in high purity. [Background technology]

[0002] Formula (I): [ka] 6-(Nitrooxy)hexanoic acid-(1S,2E)-3-[(1R,2R,3S,5R)-2-[(2Z)-7-(ethylamino)-7-oxo-2-hepten-1-yl]-3,5-dihydroxycyclopentyl]-1-(2-phenylethyl)-2-propen-1-yl ester is a prostaglandin analogue that has been shown to be effective as an IOP-lowering agent (Impagnatiello F, Toris CB, Batugo M, Prasanna G, Borghi V, Bastia E, Ongini E, Krauss AHP; Invest Ophthalmol Vis Sci. 2015; 56:6558-64).

[0003] In the first Phase 3 clinical trial, which began in June 2020, two eye drops containing Compound (I) as the active pharmaceutical ingredient (0.065% and 0.1%) are being evaluated for the reduction of intraocular pressure (IOP) in patients with open-angle glaucoma or ocular hypertension.

[0004] Over the past few years, various regulatory authorities have emphasized purity requirements and the identification of impurities in active pharmaceutical ingredients (APIs). Currently, impurities are any organic substances other than pharmaceutical ingredients that may affect the efficacy and safety of pharmaceutical products. Therefore, the identification and quantification of each impurity, especially those with structural alerts for mutagenicity, has become an essential regulatory requirement. Additionally, because APIs are intended for pharmaceutical use, the reagents, solvents, catalysts, etc. that can be used in the synthesis of APIs are limited to those acceptable to the pharmaceutical industry.

[0005] 6-(Nitrooxy)hexanoic acid-(1S,2E)-3-[(1R,2R,3S,5R)-2-[(2Z)-7-(ethylamino)-7-oxo-2-hepten-1-yl]-3,5-dihydroxycyclopentyl]-1-(2-phenylethyl)-2-propen-1-yl ester (I) is an oil, and its large-scale purification is difficult due to the inability of compound (I) to crystallize. Therefore, the presence of impurities is a significant problem for large-scale production.

[0006] From the prior art preparation process of compound (I), the main impurity is a compound of formula (V): [ka] 15-(6-chlorohexanoyl) ester of bimatoprost (when a nitration step is performed at the end of the synthesis, as disclosed in WO 2009 / 136281), or a by-product of the nitration step in the preparation of the intermediate 6-(nitrooxy)hexanoic acid (VIIIa) (6-{[6-(nitrooxy)hexanoyl]oxy}hexanoic acid ester of bimatoprost (VII): [ka] (which results in the formation of

[0007] Therefore, control of the purity of the reagents and the reaction conditions is an important requirement for obtaining Compound (I) with pharmaceutically acceptable purity.

[0008] Methods for preparing compounds of formula (I) are disclosed in WO 2009 / 136281.

[0009] WO 2009 / 136281 discloses the synthesis of compound (I) and, in general, the preparation of 15-alkyl nitrate esters of bimatoprost.

[0010] WO 2009 / 136281 describes bimatoprost in boronate-protected form (II): [ka] is reacted with 6-bromohexanoyl chloride to give a compound of formula (III): [ka] (Example B-1) discloses the synthesis of the compound of formula (I) by providing the 15-(6-bromohexanoyl) ester of bimatoprost in a boronate-protected form, which is converted to the nitrate derivative with silver nitrate in acetonitrile, deprotected, and purified by reverse-phase chromatography to yield the compound of formula (I).

[0011] The major drawbacks of the above synthesis are the use of more than equimolar amounts of 6-bromohexanoyl chloride in the esterification reaction, which presents a structural alert for possible mutagenicity, and the use of silver nitrate in the final step, which generates large amounts of silver salts in the wastewater. Another major drawback of this method is the generation of impurities and by-products, such as those of formula (IV): [ka] 15-(6-bromohexanoyl) ester of bimatoprost, and a compound of formula (V): [ka] The formation of 15-(6-chlorohexanoyl) ester of bimatoprost, etc., which are difficult to remove even after multiple purification steps because their chromatographic polarity, lipophilicity and / or solubility are similar to those of compound (I).

[0012] Furthermore, compound (V) is predicted to be positive for in vitro bacterial mutagenicity based on both statistical and technical rule-based methods as required by regulatory agencies. Compound (IV) also contains a halogenated chain, which is recognized as a structural alert for potential genotoxicity. Removal of these impurities requires repeated purification steps, which further reduces yield and increases the cost of preparing compound (I) on a commercial scale.

[0013] According to the method disclosed in WO 2009 / 136281, the 15-(6-bromohexanoyl) ester of bimatoprost (IV) is an impurity resulting from the incomplete reaction of compound (III) with silver nitrate (after removal of the boronate protection).

[0014] The 15-(6-chlorohexanoyl) ester of bimatoprost (V) is a by-product formed during the esterification reaction by halogen exchange reaction between the bromine atom of the 15-(6-bromohexanoyl) ester of bimatoprost in boronate-protected form (III) and the free chlorine anion of 4-dimethylaminopyridine hydrochloride. The 15-(6-chlorohexanoyl) ester of bimatoprost in boronate-protected form (VI): [ka] does not react with silver nitrate to produce compound (V) after removal of the protecting group.

[0015] WO 2009 / 136281 also discloses an alternative method for preparing bimatoprost derivatives, which are 15-acylalkylnitrates (Examples N-1 and O-1). The synthesis involves reacting boronate-protected bimatoprost (II) with a nitrate ester-alkylcarboxylic acid chloride in the presence of resin-supported 4-dimethylaminopyridine (DMAP) (PS-DMAP), followed by removal of the boronate protecting group and purification using silica gel chromatography.

[0016] The above method avoids the use of 6-bromohexanoyl chloride and the removal of silver salts from the final product. However, this method presents another major drawback: the use of resin-supported 4-dimethylaminopyridine, which makes the method unsuitable and expensive for commercial scale-up. Furthermore, the nitrate ester-alkylcarboxylic acid chloride is added in large excess relative to the compound of formula (II) in two successive steps; in fact, the alkylcarboxylic acid chloride is added in about 2 to 4 equivalents.

[0017] WO 2009 / 136281 also discloses another method (Example Q1) for preparing a 15-acylalkylnitrate bimatoprost derivative, which is obtained by esterification of boronate-protected bimatoprost (II) with an excess of nitrate-alkyl-(p-nitrophenyl)-carboxylate in the presence of 4-dimethylaminopyridine.

[0018] The chromatographic removal of unreacted nitrate-alkyl-(p-nitrophenyl)-carboxylate and the by-product p-nitrophenol (formed in equimolar amounts with the compound of formula (I)) is a major drawback of this method.

[0019] WO 2016 / 155906 discloses 15-nitrooxy derivatives of fluprostenol and reports the synthesis of 15-nitrooxy-hexyl ester of fluprostenol isopropyl ester, which was prepared by reacting boronate-protected fluprostenol isopropyl ester with (4-nitrophenyl)-6-nitrooxyhexanoate in the presence of excess 4-dimethylaminopyridine.

[0020] As reported above, the removal of unreacted nitrate-alkyl-(p-nitrophenyl)-carboxylate and, in particular, the removal of the p-nitrophenol by-product by chromatographic methods are major drawbacks of this method.

[0021] WO 2019 / 162149 discloses a method for preparing 6-(nitrooxy)hexanoic acid-(1S,2E)-3-[(1R,2R,3S,5R)-2-[(2Z)-7-(ethylamino)-7-oxo-2-hepten-1-yl]-3,5-dihydroxycyclopentyl]-1-(2-phenylethyl)-2-propen-1-yl ester (I). Compound (I) is prepared by coupling bimatoprost in a boronate-protected form with 6-(nitrooxy)hexanoyl chloride, followed by removal of the boronate protecting group. The crude compound (I) is purified by column chromatography.

[0022] 6-(Nitrooxy)hexanoyl chloride is synthesized from 6-(nitrooxy)hexanoic acid, which is prepared by the ring-opening reaction of ε-caprolactone and subsequent nitration of the alkali salt of 6-hydroxyhexanoic acid using a mixture of HNO3 and H2SO4 in dichloromethane. 6-(Nitrooxy)hexanoic acid is used without purification to prepare the corresponding acyl chloride, and crude 6-(nitrooxy)hexanoyl chloride is also used without purification.

[0023] Experiments conducted by the present inventors have shown that compound (I) prepared using the method of WO 2019 / 162149 contains about 0.1% to 0.4% of an impurity of formula (VII): [ka] It was shown to contain the 6-{[6-(nitrooxy)hexanoyl]oxy}hexanoic acid ester of bimatoprost.

[0024] Compounds (I) and (VII) have similar polarities, and therefore separation of the two compounds requires cumbersome column purification to remove the impurity (VII), thereby reducing the yield of the final product.

[0025] Therefore, there is a need to develop an industrially viable process for the preparation of highly pure 6-(nitrooxy)hexanoic acid-(1S,2E)-3-[(1R,2R,3S,5R)-2-[(2Z)-7-(ethylamino)-7-oxo-2-hepten-1-yl]-3,5-dihydroxycyclopentyl]-1-(2-phenylethyl)-2-propen-1-yl ester (I) in high yield.

[0026] In the method of WO 2019 / 162149, a compound of formula (VIIIb): [ka] The crude 6-(nitrooxy)hexanoyl chloride of formula (IXb) is a dimer impurity. [ka] It was observed that an impurity of formula (VII) was formed during the coupling step because the compound (VII) contains 6-[6-nitrooxyhexanoyl]oxy}hexanoyl chloride, which also reacts with the boronate-protected form of bimatoprost (II), resulting in the formation of compound (I) with the 6-{[6-(nitrooxy)hexanoyl]oxy}hexanoic acid ester of bimatoprost (VII) after removal of the boronate protection.

[0027] 6-[6-nitrooxyhexanoyl]oxy}hexanoyl chloride of formula (IXb) is a by-product from the crude mixture of the nitration step; in fact, the nitration of alkali metal 6-hydroxyhexanoic acid with a mixture of nitric acid and sulfuric acid gives 6-(nitrooxy)hexanoic acid (VIIIa): [ka] and the dimeric impurity 6-{[6-(nitrooxy)hexanoyl]oxy}hexanoic acid (IXa): [ka] This results in the formation of

[0028] Experiments showed that the nitration mixture contained more than 80% of compound (VIIIa) and about 5% to about 9% of compound (IXa).

[0029] Compounds (VIIIa) and (IXa) are both reacted with a chlorinating agent to give a mixture containing 6-(nitrooxy)hexanoyl chloride (VIIIb) and the dimeric impurity 6-[6-nitrooxyhexanoyl]oxy}hexanoyl chloride (IXb). According to the method of WO 2019 / 162149, this crude mixture is reacted with compound (II) without further purification.

[0030] It was surprisingly found that adding water, instead of saturated aqueous NaCl (brine) as described in WO 2019 / 162149, during the quenching of the nitration reaction of alkali salt of 6-hydroxyhexanoic acid to control the formation of impurity (VII) resulted in a crude nitration mixture containing a reduced amount of the dimeric impurity 6-{[6-(nitrooxy)hexanoyl]oxy}hexanoic acid (IXa). Specifically, this improvement in the workup of the nitration step produced a crude nitration mixture containing 99.2% (a / a%) of 6-(nitrooxy)hexanoic acid (VIIIa) and 0.15% (a / a%) of the dimeric impurity 6-{[6-(nitrooxy)hexanoyl]oxy}hexanoic acid (IXa). Compounds (VIIIa) and (IXa) were identified and quantified by appropriate UHPLC analysis.

[0031] The addition of water at the end of the nitration reaction is believed to allow for more rapid dissolution of inorganic salts and better separation of the organic phase containing 6-(nitrooxy)hexanoic acid (VIIIa) from the acidic aqueous phase containing unreacted HNO3 / H2SO4, relative to the commonly used addition of saturated aqueous NaCl (brine). This improved workup of the nitration reaction results in the reduction / inhibition of side reactions that lead to the formation of the by-product 6-{[6-(nitrooxy)hexanoyl]oxy}hexanoic acid (IXa).

[0032] Additionally, another advantage of this modification of the nitration process is the reduction in the volume of organic solvent used in the work-up of the reaction, which allows for the process to be scaled up by at least three-fold.

[0033] Accordingly, the present invention provides 6-(nitrooxy)hexanoic acid-(1S,2E)-3-[(1R,2R,3S,5R)-2-[(2Z)-7-(ethylamino)-7-oxo-2-hepten-1-yl]-3,5-dihydroxycyclopentyl]-1-(2-phenylethyl)-2-propen-1-yl ester (I) (less than 0.05% (measured as a / a % by HPLC) of the impurity 6-{[6-(nitrooxy)hexanoyl]oxy}hexanoic acid ester of bimatoprost (VII): [ka] The present invention provides an improved method suitable for large-scale production of a compound containing

[0034] A key advantage of the process of the present invention is that it is highly efficient in reducing the level of impurity (VII) while providing good yields of compound (I), providing an advantageous alternative to other processes that could theoretically achieve the same level of reduction in impurity (VII), but which must include an additional purification step of the 6-(nitrooxy)hexanoic acid intermediate.

[0035] Since 6-(nitrooxy)hexanoic acid is a liquid, and both 6-(nitrooxy)hexanoic acid (VIIIa) and 6-{[6-(nitrooxy)hexanoyl]oxy}hexanoic acid (IXa) are polar compounds, purification of large amounts of 6-(nitrooxy)hexanoic acid (VIIIa) for industrial-scale preparation cannot be easily carried out.

[0036] Furthermore, the present invention provides 6-{[6-(nitrooxy)hexanoyl]oxy}hexanoic acid (IXa): [ka] 6-(nitrooxy)hexanoic acid (VIIIa) containing 0.2% or less of: [ka] The present invention relates to a method for the industrial synthesis of Description of the Invention

[0037] The present invention relates to a compound of formula (I): [ka] 1. A process for the preparation of 6-(nitrooxy)hexanoic acid-(1S,2E)-3-[(1R,2R,3S,5R)-2-[(2Z)-7-(ethylamino)-7-oxo-2-hepten-1-yl]-3,5-dihydroxycyclopentyl]-1-(2-phenylethyl)-2-propen-1-yl ester, comprising the following steps A) and B): Step A) Perform the following steps 1a) to 6a): 1a) ε-caprolactone: [ka] with an inorganic base selected from KOH, NaOH and LiOH in a solvent selected from methanol, ethanol or isopropanol at a temperature between 20° C. and the reflux temperature of the solvent to obtain a compound of formula (X): [ka] (wherein M is K, Na or Li) obtaining 6-hydroxyhexanoate of the compound; 2a) Purifying the 6-hydroxyhexanoate of formula (X) obtained in step 1a), comprising the steps of: i) purifying the 6-hydroxyhexanoate of formula (X) obtained in step 1a; i. adding methyl tert-butyl ether to the reaction mixture of step 1a) in a volume ratio of methyl tert-butyl ether / reaction mixture of 2:1; ii. filtering the solids; iii. Slurrying the solid with a mixture of methyl tert-butyl ether, methanol (in a ratio of 3:1 to 5:1) and water (0.3 to 1 moles of water per mole of ε-caprolactone); iv. isolating the 6-hydroxyhexanoate salt of formula (X) as a solid. a process comprising: 3a) reacting 6-hydroxyhexanoate with a mixture of fuming HNO3 and concentrated H2SO4 in dichloromethane at a temperature ranging from 0°C to 10°C; 4a) working up the reaction of step 3a) by adding water to the nitration mixture of step 3a) while maintaining the temperature between 0°C and 5°C; 5a) The organic phase is separated, dried over sodium sulfate, and the solvent is then evaporated to give crude 6-(nitrooxy)hexanoic acid (VIIIa): [ka] obtaining the 6a) reacting crude 6-(nitrooxy)hexanoic acid (VIIIa) with a chlorinating agent in dichloromethane to give crude 6-(nitrooxy)hexanoyl chloride (VIIIb) Preparation of 6-(nitrooxy)hexanoyl chloride (VIIIb) by Step B) Following steps 1b)~4b): 1b) Bimatoprost is reacted with butylboronic acid in methyl tert-butyl ether at a temperature of about 40° C. to give compound (II): [ka] obtaining the 2b) Compound (II) is reacted with crude 6-(nitrooxy)hexanoyl chloride (VIIIb) from step 6a) in the presence of free 4-dimethylaminopyridine in an aprotic organic solvent to give compound (XI): [ka] obtaining the 3b) removing the boronate protecting group to obtain the crude compound of formula (I); 4b) Purifying the crude compound (I) by column chromatography Preparation of 6-(nitrooxy)hexanoic acid-(1S,2E)-3-[(1R,2R,3S,5R)-2-[(2Z)-7-(ethylamino)-7-oxo-2-hepten-1-yl]-3,5-dihydroxycyclopentyl]-1-(2-phenylethyl)-2-propen-1-yl ester by Including, The crude nitration mixture of step 5a) contains 6-(nitrooxy)hexanoic acid (VIIIa) in an amount of 99% or more and 6-{[6-(nitrooxy)hexanoyl]oxy]hexanoic acid (IXa) in an amount of 0.2% or less.

[0038] The 6-(nitrooxy)hexanoic acid (1S,2E)-3-[(1R,2R,3S,5R)-2-[(2Z)-7-(ethylamino)-7-oxo-2-hepten-1-yl]-3,5-dihydroxycyclopentyl]-1-(2-phenylethyl)-2-propen-1-yl ester (I) prepared according to the method of the present invention has a chemical purity of 99% or more and contains less than 0.05% of the impurity 6-{[6-(nitrooxy)hexanoyl]oxy}hexanoic acid ester of bimatoprost (VII). The compound contains about 0.11% of the impurity 15-(6-chlorohexanoyl) ester of bimatoprost (V). The compound is identified and quantified by HPLC analysis, and the amount of the compound is expressed as area percentage (a / a%), where 0.05% is the detection limit of HPLC.

[0039] In step 1a), the ring-opening reaction of ε-caprolactone is preferably carried out in methanol in the presence of potassium hydroxide at a temperature between 20°C and reflux. During workup of the reaction mixture of step 1a), the solid from step 2a)-ii is slurried in a mixture containing methyl tert-butyl ether, methanol (at a ratio of 3:1 to 5:1), and water (0.3 to 1 mole of water per mole of ε-caprolactone) (step 2a)-iii), thereby purifying potassium 6-hydroxyhexanoate. The potassium 6-hydroxyhexanoate is obtained as a solid.

[0040] The crude nitration mixture of step 5a) contains 6-(nitrooxy)hexanoic acid (VIIIa) in an amount of more than 99% and 6-{[6-(nitrooxy)hexanoyl]oxy}hexanoic acid (IXa) in an amount of less than 0.2%. The chemical yield of 6-(nitrooxy)hexanoic acid (VIIIa) is 80-85%. The chemical purity was assessed by analytical UHPLC.

[0041] The preferred chlorinating agent used in step 6a) is oxalyl chloride.

[0042] Step 2b) is carried out at a temperature ranging from 0°C to 25°C, preferably in an aprotic organic solvent selected from methyl tert-butyl ether, N,N-dimethylformamide, or dichloromethane. Most preferably, the organic solvent is methyl tert-butyl ether. "Free" 4-dimethylaminopyridine (DMAP) means that DMAP is not bound to the resin. The molar ratio of compound (II) to 6-(nitrooxy)hexanoyl chloride (VIIIb) is preferably in the range of 1:1.4 to 1:1.6.

[0043] The molar ratio of compound (II) to 4-dimethylaminopyridine is preferably in the range of 1:2.0 to 1:2.4.

[0044] In step 3b), removal of the boronate protecting group is preferably carried out using methanol at a temperature between 17°C and 25°C.

[0045] A preferred process for preparing compounds of formula (I) comprises the following steps A and B shown in Scheme 1: Process A 1a) reacting ε-caprolactone with potassium hydroxide in methanol at a temperature between 20° C. and the reflux temperature of methanol, preferably at the reflux temperature of methanol; and 2a) A step of purifying the potassium 6-hydroxyhexanoate obtained in step 1a), comprising the steps of: i) purifying the potassium 6-hydroxyhexanoate obtained in step 1a; i. adding methyl tert-butyl ether (MTBE) to the reaction mixture of step 1a) in a 2:1 MTBE / methanol ratio; ii. Filtering the solids iii. Slurrying the solid in a mixture of methyl tert-butyl ether, methanol (in a ratio of 3:1 to 5:1) and water (0.3 to 1 moles of water per mole of ε-caprolactone). iv. Isolating 6-hydroxyhexanoic acid potassium salt as a solid. a process comprising: 3a) adding 6-hydroxyhexanoic acid potassium salt (formula (X), M=K) to a mixture of fuming HNO3 and concentrated H2SO4 in dichloromethane at a temperature of about 0°C to 10°C, vigorously stirring the reaction mixture at a temperature of 0°C to 5°C, and monitoring the reaction progress (until 99.9% conversion is achieved); 4a) carefully adding water to the nitration mixture while maintaining the temperature between 0°C and 5°C; 5a) separating the organic phase, drying the organic phase over sodium sulfate, and then distilling off the solvent to obtain crude 6-(nitrooxy)hexanoic acid (VIIIa) containing 99% or more of 6-(nitrooxy)hexanoic acid (VIIIa) and 0.2% or less (equal to less than) the by-product 6-{[6-(nitrooxy)hexanoyl]oxy}hexanoic acid (IXa); 6a) reacting crude 6-(nitrooxy)hexanoic acid with oxalyl chloride to give 6-(nitrooxy)hexanoyl chloride (VIIIb), which is used without further purification in step B of this process. Process B 1b) reacting bimatoprost with butylboronic acid (1.1-1.8 equivalents) in methyl tert-butyl ether (MTBE) at a temperature of about 40°C, followed by azeotropic distillation to remove water, to obtain bimatoprost boronate (II); 2b) reacting bimatoprost boronate (II) with crude 6-(nitrooxy)hexanoyl chloride (VIIIb) (1.4 to 1.6 equivalents) obtained in step 6a) in the presence of 4-dimethylaminopyridine (2.0 to 2.4 equivalents) in methyl tert-butyl ether at a temperature ranging from 0°C to 20±3°C to obtain (1S,2E)-3-{(6R,7R)-3-butyl-7[(2Z)-7-(ethylamino)-7-oxohept-2-en-1-yl]-2,4-dioxa-3-borabicyclo[3.2.1]oct-6-yl}-1-(2-phenylethyl)-prop-2-en-1-yl-6-(nitrooxy)hexanoate (XI); 3b) reacting (1S,2E)-3-{(6R,7R)-3-butyl-7[(2Z)-7-(ethylamino)-7-oxohept-2-en-1-yl]-2,4-dioxa-3-borabicyclo[3.2.1]oct-6-yl}-1-(2-phenylethyl)-prop-2-en-1-yl-6-(nitrooxy)hexanoate (XI) with methanol at room temperature to remove the protecting group and obtain crude 6-(nitrooxy)hexanoic acid-(1S,2E)-3-[(1R,2R,3S,5R)-2-[(2Z)-7-(ethylamino)-7-oxo-2-hepten-1-yl]-3,5-dihydroxycyclopentyl]-1-(2-phenylethyl)-2-propen-1-yl ester (I); 4b) purifying the crude compound (I) by high performance silica gel chromatography using methylene chloride / methanol as the mobile phase to obtain 6-(nitrooxy)hexanoic acid-(1S,2E)-3-[(1R,2R,3S,5R)-2-[(2Z)-7-(ethylamino)-7-oxo-2-hepten-1-yl]-3,5-dihydroxycyclopentyl]-1-(2-phenylethyl)-2-propen-1-yl ester (I). Includes:

[0046] Quantitative HPLC analysis of the isolated compound (I) after chromatographic purification showed that it had a chemical purity of greater than 99% and contained approximately 0.11% of the 15-(6-chlorohexanoyl) ester of bimatoprost (V) and less than 0.05%, the detection limit of HPLC, of ​​the 6-{[6-(nitrooxy)hexanoyl]oxy}hexanoic acid ester of bimatoprost (VII). [ka]

[0047] Another object of the present invention is a pharmaceutical formulation containing 6-(nitrooxy)hexanoic acid-(1S,2E)-3-[(1R,2R,3S,5R)-2-[(2Z)-7-(ethylamino)-7-oxo-2-hepten-1-yl]-3,5-dihydroxycyclopentyl]-1-(2-phenylethyl)-2-propen-1-yl ester of formula I and at least one pharmaceutically acceptable excipient, wherein the 6-(nitrooxy)hexanoic acid-(1S,2E)-3-[(1R,2R,3S,5R)-2-[(2Z)

[0023] The bimatoprost ester (compound (VII)) is a dimeric impurity of 15-(6-chlorohexanoyl) ester of bimatoprost (compound (VII)) in an amount of about 0.11%.

[0048] In this application, the quantitative determination of compounds expressed as percentage % is determined by HPLC analysis (a / a%). [Example]

[0049] All synthetic steps described below were carried out under a nitrogen atmosphere.

[0050] Example 1 Synthesis of 6-(nitrooxy)hexanoic acid-(1S,2E)-3-[(1R,2R,3S,5R)-2-[(2Z)-7-(ethylamino)-7-oxo-2-hepten-1-yl]-3,5-dihydroxycyclopentyl]-1-(2-phenylethyl)-2-propen-1-yl ester (compound (I))

[0051] Synthesis of 6-(nitrooxy)hexanoyl chloride (compound (VIIIb)) Step 1a) and Step 2a): Synthesis of 6-hydroxyhexanoic acid potassium salt (compound (X)) A solution of potassium hydroxide (141.12 g, equivalent to 122.8 g of pure material) in methanol (1250 mL) was prepared under cooling at 15°C to 20°C and added to a solution of ε-caprolactone (250.0 g) in methanol (675 mL) at 5°C to 37°C within 0.25 hours. The mixture was stirred at 20°C to 63°C for 18 hours. The solvent was then concentrated to a volume of approximately 675 mL, and methyl tert-butyl ether (1250 mL) was added at approximately 57°C. The reaction mixture was stirred at room temperature for 48 hours, and the solid was isolated by filtration to give 380.9 g of crude 6-hydroxyhexanoic acid potassium salt. The crude material was reslurried in MTBE (1475 mL), methanol (375 mL), and water (19.7 mL) at 22±3°C for 8 hours and filtered. The solid was reslurried in methyl tert-butyl ether (500 mL), filtered again, and then dried under vacuum at 50° C. for 12 hours to give 354.7 g (93.2% yield) of 6-hydroxyhexanoic acid potassium salt with a purity of 98%. Melting point: 208° C.

[0052] Step 3a) to Step 5a): Synthesis of 6-(nitrooxy)hexanoic acid (compound (VIIIa)) Fuming HNO3 (485.5 g, 4.6 equiv.) was added to concentrated H2SO4 (553.0 g, 3.1 equiv.) over 30 minutes at a temperature between 0 and 5 °C, followed by the addition of dichloromethane (5820 mL) over 23 minutes at a temperature between 0 and 5 °C. 6-Hydroxyhexanoic acid potassium salt (306.09 g, 1 equiv.) was added in small portions over 35 minutes at a temperature below 5 °C. The mixture was stirred at 0 and 5 °C for 2 hours to complete the reaction. 1 Monitoring by H-NMR showed a conversion of 99.9%. Water (2.9 L) was added within 20 min while maintaining the temperature between 0°C and 5°C. The organic layer was decanted, dried over sodium sulfate, and concentrated under vacuum to give 318.4 g (94.8% yield) of 6-(nitrooxy)hexanoic acid having an HPLC purity of 99.2% and a content of 6-{[6-(nitrooxy)hexanoyl]oxy}hexanoic acid (compound (IXa)) of 0.15%.

[0053] Step 6a): Synthesis of 6-(nitrooxy)hexanoyl chloride (compound (VIIIb)) 6-(Nitrooxy)hexanoic acid (270.8 g, 1 equiv.) was dissolved in dichloromethane (1220 mL) and cooled to 0-5°C under nitrogen. N,N-dimethylformamide (1.6 mL) and oxalyl chloride (198.2 g) were then added within 30 min at 0-5°C. The reaction mixture was stirred at 0-5°C for 1 h and then at 15-20°C for 4 h. The reaction mixture was then concentrated under vacuum at a temperature below 40°C and coevaporated with dichloromethane to give 6-(nitrooxy)hexanoyl chloride (323.9 g, 99.6% yield, titration with AgNO3 = 92.0%).

[0054] Step 1b): Synthesis of (Z)-7-[(1S,5R,6R,7R)-3-butyl-6-[((E,3S)-3-hydroxy-5-phenyl-pent-1-enyl]-2,4-dioxa-3-borabicyclo[3.2.1]-octan-7-yl]-N-ethyl-hept-5-enamide (compound (II)) Bimatoprost (249.0 g, 1 eq.) was suspended in methyl tert-butyl ether (4 L) and butylboronic acid (69.0 g, 1.13 eq.) was added. The mixture was heated to 40° C. for 1 hour. The reaction was continued until a conversion of >97% was achieved. 1 It was monitored by H-NMR.

[0055] The reaction mixture was cooled to about 20° C., filtered, and rinsed with methyl tert-butyl ether (250 mL). The mixture was concentrated by azeotropic distillation under vacuum at a temperature of about 40° C. Rinsing with methyl tert-butyl ether, azeotropic distillation was continued until the water content of (Z)-7-[(1S,5R,6R,7R)-3-butyl-6-[((E,3S)-3-hydroxy-5-phenyl-pent-1-enyl]-2,4-dioxa-3-borabicyclo[3.2.1]-octan-7-yl]-N-ethyl-hept-5-enamide (Compound (II)) was 0.25% or less.

[0056] (Z)-7-[(1S,5R,6R,7R)-3-butyl-6-[((E,3S)-3-hydroxy-5-phenyl-pent-1-enyl]-2,4-dioxa-3-borabicyclo[3.2.1]-octan-7-yl]-N-ethyl-hept-5-enamide was isolated as crude material in quantitative yield (313.1 g, corresponding to 298.6 g of pure material).

[0057] Step 2b): Synthesis of (1S,2E)-3-{(6R,7R)-3-butyl-7[(2Z)-7-(ethylamino)-7-oxohept-2-en-1-yl]-2,4-dioxa-3-borabicyclo[3.2.1]-oct-6-yl}-1-(2-phenylethyl)-prop-2-en-1-yl-6-(nitrooxy)hexanoate (compound (XI)) (Z)-7-[(1S,5R,6R,7R)-3-butyl-6-[((E,3S)-3-hydroxy-5-phenyl-pent-1-enyl]-2,4-dioxa-3-borabicyclo[3.2.1]-octan-7-yl]-N-ethyl-hept-5-enamide (Compound (II)) (313.1 g, 1 equivalent) was dissolved in methyl tert-butyl ether (4.27 L) under nitrogen and cooled to 0°C-5°C. 4-Dimethylaminopyridine (4-dimethylaminopyridine) was added. To the reaction mixture was added 162.7 g (2.27 equivalents) of 6-(nitrooxy)hexanoyl chloride (compound (VIIIb)) (172.1 g, 1.5 equivalents) in 600 mL of methyl tert-butyl ether. The mixture was stirred at 0°C to 5°C for 2.5 hours and then at 15°C to 20°C for 16.5 hours. The reaction mixture was then cooled to 0°C to 5°C, and deionized water was added at a maximum temperature of 10°C within 20 minutes.

[0058] The mixture was stirred for 5 minutes. The aqueous layer was separated and discarded. The organic layer was washed with 1N hydrochloric acid solution, then deionized water, and finally with brine. The organic layer was dried over sodium sulfate and concentrated under vacuum to give (1S,2E)-3-{(6R,7R)-3-butyl-7-[(2Z)-7-(ethylamino)-7-oxohept-2-en-1-yl]-2,4-dioxa-3-borabicyclo[3.2.1]-oct-6-yl}-1-(2-phenylethyl)-prop-2-en-1-yl-6-(nitrooxy)hexanoate (compound (XI)) (402.9 g, 94.9% yield).

[0059] Step 3b) and Step 4b): Synthesis of 6-(nitrooxy)hexanoic acid-(1S,2E)-3-[(1R,2R,3S,5R)-2-[(2Z)-7-(ethylamino)-7-oxo-2-hepten-1-yl]-3,5-dihydroxycyclopentyl]-1-(2-phenylethyl)-2-propen-1-yl ester (compound (I)) (1S,2E)-3-{(6R,7R)-3-butyl-7-[(2Z)-7-(ethylamino)-7-oxohept-2-en-1-yl]-2,4-dioxa-3-borabicyclo[3.2.1]-oct-6-yl}-1-(2-phenylethyl)-prop-2-en-1-yl-6-(nitrooxy)hexanoate (compound (XI)) (396 g, crude, 1 equivalent) was dissolved in methanol (4.20 L), and the resulting solution was stirred at room temperature for 24 hours to complete the reaction. 1 The reaction mixture was monitored by H-NMR. Methanol was then removed under reduced pressure at 35-40°C. The residue was dissolved in methanol, stirred for 14 hours, and evaporated under reduced pressure at 35-40°C. The residue was dissolved in methyl tert-butyl ether and washed with deionized water and then brine. The organic layer was dried over sodium sulfate and concentrated under reduced pressure at a temperature below 40°C to give crude 6-(nitrooxy)hexanoic acid-(1S,2E)-3-[(1R,2R,3S,5R)-2-[(2Z)-7-(ethylamino)-7-oxo-2-hepten-1-yl]-3,5-dihydroxycyclopentyl]-1-(2-phenylethyl)-2-propen-1-yl ester (352.3 g, 96.5% yield).

[0060] The residue was divided into three equal portions (approximately 107 g each) and purified by chromatography on a Biotage Isolera LS system using dichloromethane / methanol (100:0 to 95:5 v / v gradient) as the eluent on a high-performance silica gel column (SNAP Ultra column, 1500 g silica). Fractions were monitored by TLC and UHPLC. The fractions were concentrated under vacuum at temperatures below 50 °C to give compound (I) as an oil (242.5 g, 90.3% yield).

[0061] 6-(Nitrooxy)hexanoic acid-(1S,2E)-3-[(1R,2R,3S,5R)-2-[(2Z)-7-(ethylamino)-7-oxo-2-hepten-1-yl]-3,5-dihydroxycyclopentyl]-1-(2-phenylethyl)-2-propen-1-yl ester (Compound (I)) was dissolved in ethanol, treated with activated carbon for 30 minutes, filtered, and the solvent was evaporated under vacuum at a temperature below 50° C. Compound (I) was isolated as an oil (212.7 g, 92.4% yield). The purity of 6-(nitrooxy)hexanoic acid-(1S,2E)-3-[(1R,2R,3S,5R)-2-[(2Z)-7-(ethylamino)-7-oxo-2-hepten-1-yl]-3,5-dihydroxycyclopentyl]-1-(2-phenylethyl)-2-propen-1-yl ester (compound (I)) was 99.89% (assessed by UHPLC), the content of 15-(6-chlorohexanoyl) ester of bimatoprost (compound (V)) was 0.11%, and the content of dimeric impurity ester of bimatoprost with 6-{[6-(nitrooxy)hexanoyl]oxy}hexanoic acid (compound (VII)) was less than 0.05%.

[0062] Example 2 (Comparative Example) The syntheses reported below were carried out according to the methods disclosed in WO 2019 / 162149.

[0063] Synthesis of 6-(nitrooxy)hexanoic acid-(1S,2E)-3-[(1R,2R,3S,5R)-2-[(2Z)-7-(ethylamino)-7-oxo-2-hepten-1-yl]-3,5-dihydroxycyclopentyl]-1-(2-phenylethyl)-2-propen-1-yl ester (I)

[0064] Synthesis of 6-(nitrooxy)hexanoyl chloride (VIIIb) Synthesis of 6-hydroxyhexanoic acid potassium salt (compound (X)) A solution of 90% potassium hydroxide (89.7 g) in methanol (830 mL) was prepared under cooling at 10-20°C. 165.2 g (1 equivalent) of ε-caprolactone and 415 mL of methanol were added to a 4 L three-necked round-bottom flask. The mixture was stirred until dissolved. Next, a solution of potassium hydroxide in methanol was added within 25 minutes at 0-30°C. The mixture was stirred at 15-20°C for 20 hours. The reaction mixture was concentrated under vacuum (at a temperature below 40°C) to give crude 6-hydroxyhexanoic acid potassium salt. The crude solid was suspended in methyl tert-butyl ether (830 mL) at 15-20°C for 2 hours, filtered through a pore 3 filter, washed with methyl tert-butyl ether (2 x 165 mL), and dried under vacuum at 35°C to give 6-hydroxyhexanoic acid potassium salt (228.1 g, 98.3% HCl assay) as a white powder in 92.7% yield.

[0065] Synthesis of 6-(nitrooxy)hexanoic acid (VIIIa) To control the reaction temperature and shorten the addition time of the nitration mixture, the nitration reaction was carried out on a scale of approximately 100 g. The reaction was carried out twice. The nitration mixture was quenched by adding saturated aqueous sodium chloride (brine). The results of two separate nitration reactions are reported in Table 1.

[0066] Nitration 1: A 6 L glass reactor was charged with concentrated sulfuric acid (200.9 g) under nitrogen and cooled to 0-5°C. Fuming HNO3 (187.9 g) was carefully added dropwise over 20 minutes at 0-10°C. Dichloromethane (2.23 L) was then added and the reaction mixture was stirred for 45 minutes. 6-Hydroxyhexanoic acid potassium salt (110.1 g, 1 equivalent) was added in small portions over 30 minutes at a temperature between -5°C and 5°C. The mixture was stirred at a temperature between -5°C and 5°C for 2.5 hours, then at 20°C overnight, to complete the reaction. 1Monitoring by H-NMR showed 99.6% conversion. Saturated aqueous sodium chloride solution (315.3 g in 1.0 L) was carefully added within 25 minutes at a temperature below 10°C. Precipitation of a large amount of inorganic salts was observed. Carefully transferring the reaction mixture to a separatory funnel, taking care not to transfer inorganic salts. The organic layer was decanted, dried over sodium sulfate, and concentrated under vacuum (at a temperature below 40°C) to give crude 6-(nitrooxy)hexanoic acid (105.4 g, 85.2%). HPLC purity = 83.7% (with 8.8% of 6-{[6-(nitrooxy)hexanoyl]oxy]hexanoic acid (Compound (IXa))).

[0067] Nitration 2: The reaction was carried out using 109.97 g of potassium 6-hydroxyhexanoate to give 101.6 g (82%) of crude 6-(nitrooxy)hexanoic acid (VIIIa) with an HPLC purity of 89.7% and an amount of 6-{[6-(nitrooxy)hexanoyl]oxy}hexanoic acid (compound (IXa)) of 5.8%.

[0068] The two batches were combined and carried on to the following step without further purification.

[0069] Synthesis of 6-(nitrooxy)hexanoyl chloride (VIIIb) 6-(Nitrooxy)hexanoic acid (193 g) was dissolved in dichloromethane (870 mL). The resulting cloudy solution was filtered through a glass fiberglass tube washed with dichloromethane (130 mL). The clear solution was analyzed by Karl Fischer analysis (water content = 0.018%). The solution was cooled to 0-5°C under nitrogen. N,N-dimethylformamide (1.2 mL) and oxalyl chloride (141.4 g) were then added at 0-5°C within 30 min. The reaction mixture was stirred at 0-5°C for 1 h and at 15-20°C for 14 h. TLC monitoring indicated a complete reaction. The mixture was concentrated under vacuum (temperature below 40°C) and coevaporated with dichloromethane (4 × 870 mL) to give 6-(nitrooxy)hexanoyl chloride (212.4 g) in 91.9% yield.

[0070] Preparation of (Z)-7-[(1S,5R,6R,7R)-3-butyl-6-[((E,3S)-3-hydroxy-5-phenyl-pent-1-enyl]-2,4-dioxa-3-borabicyclo[3.2.1]-octan-7-yl]-N-ethyl-hept-5-enamide (compound (II)) Methyl tert-butyl ether (3900 mL, 14 vol) was placed in a flask. Bimatoprost (249.1 g, 1 eq) was added, and the apparatus was rinsed with methyl tert-butyl ether (250 mL, 1 vol). Butylboronic acid (70.66 g, 69.2 g neat, 1.13 eq) was added in one portion to the resulting suspension, and the apparatus was rinsed with methyl tert-butyl ether (250 mL, 1 vol). The mixture was heated to 40° C. for 2 hours. The reaction was run until >97% conversion was achieved. 1 H-NMR was used for monitoring.

[0071] The reaction mixture was cooled to 20-25°C, clarified on a glass filter, and washed with methyl tert-butyl ether (250 mL, 1 volume). The filtrate was concentrated under vacuum by azeotropic distillation at a temperature of about 40°C. Rinsing with methyl tert-butyl ether, azeotropic distillation was continued until the water content of (Z)-7-[(1S,5R,6R,7R)-3-butyl-6-[((E,3S)-3-hydroxy-5-phenyl-pent-1-enyl]-2,4-dioxa-3-borabicyclo[3.2.1]-octan-7-yl]-N-ethyl-hepta-5-enamide (Compound (II)) was 0.2%. Compound (II) was obtained. 1 Residual MTBE was determined by H-NMR analysis.

[0072] (Z)-7-[(1S,5R,6R,7R)-3-butyl-6-[((E,3S)-3-hydroxy-5-phenyl-pent-1-enyl]-2,4-dioxa-3-borabicyclo[3.2.1]-octan-7-yl]-N-ethyl-hept-5-enamide (compound (II)) was obtained in quantitative yield (386.7 g of crude material (unmodified)).

[0073] Preparation of (1S,2E)-3-{(6R,7R)-3-butyl-7-[(2Z)-7-(ethylamino)-7-oxohept-2-en-1-yl]-2,4-dioxa-3-borabicyclo[3.2.1]-oct-6-yl}-1-(2-phenylethyl)-prop-2-en-1-yl-6-(nitrooxy)hexanoate (XI) Methyl tert-butyl ether (4100 mL, 11.6 vol) was placed in a 4 L three-neck round-bottom flask under nitrogen. (Z)-7-[(1S,5R,6R,7R)-3-butyl-6-[((E,3S)-3-hydroxy-5-phenyl-pent-1-enyl]-2,4-dioxa-3-borabicyclo[3.2.1]-octan-7-yl]-N-ethyl-hept-5-enamide (Compound (II)) (378 g, crude, 1 equiv.) was added, and the flask was rinsed with methyl tert-butyl ether (510 mL, 1.44 vol.). The resulting solution was cooled to 0 °C–5 °C.

[0074] 4-Dimethylaminopyridine (177.5 g, 2.27 equiv.) was added in one portion. A solution of 6-(nitrooxy)hexanoyl chloride (204.4 g, equivalent to 188 g of pure water, 1.5 equiv.) in methyl tert-butyl ether (650 mL, 1.84 vol.) was added dropwise within 45 min at 0°C to 5°C. The addition funnel was rinsed with methyl tert-butyl ether (40 mL, 0.12 vol.). After stirring for 2 h at 0°C to 5°C, the mixture was stirred for 17.5 h at 15°C to 20°C. HPLC monitoring indicated 99.0% conversion. Deionized water (1730 mL, 4.89 vol.) was added within 9 min at a maximum temperature of 25°C.

[0075] The mixture was decanted. The aqueous layer was analyzed and discarded. The organic layer was washed with 1 M aqueous hydrochloric acid. The aqueous layer was analyzed and discarded. The organic layer was washed first with deionized water (1351 mL, 5 vol) and then with saturated sodium chloride solution (3 x 1177 mL, 3 x 4.25 vol). The aqueous layer (pH = 4 after the final wash) was analyzed and discarded. The organic layer was dried over sodium sulfate (240 g, 86.8% w / w), washed with methyl tert-butyl ether (616 mL, 2 volumes), and concentrated under vacuum to give (1S,2E)-3-{(6R,7R)-3-butyl-7[(2Z)-7-(ethylamino)-7-oxohept-2-en-1-yl]-2,4-dioxa-3-borabicyclo[3.2.1]-oct-6-yl}-1-(2-phenylethyl)-prop-2-en-1-yl-6-(nitrooxy)hexanoate (compound (XI)) in quantitative yield (417.4 g, corresponding to 322.1 g of pure product, 85.8% yield as pure product).

[0076] Synthesis of 6-(nitrooxy)hexanoic acid-(1S,2E)-3-[(1R,2R,3S,5R)-2-[(2Z)-7-(ethylamino)-7-oxo-2-hepten-1-yl]-3,5-dihydroxycyclopentyl]-1-(2-phenylethyl)-2-propen-1-yl ester (I) (crude compound) (1S,2E)-3-{(6R,7R)-3-butyl-7-[(2Z)-7-(ethylamino)-7-oxohept-2-en-1-yl]-2,4-dioxa-3-borabicyclo[3.2.1]-oct-6-yl}-1-(2-phenylethyl)-prop-2-en-1-yl-6-(nitrooxy)hexanoate (compound (XI)) (407.3 g, crude, 1 equivalent) was dissolved in methanol (3550 mL, 8.9 volumes). The resulting solution was placed in a flask, and the apparatus was rinsed with methanol (1140 mL, 2.8 volumes). The mixture was stirred at 15 °C to 25 °C for 15 hours to complete the reaction. 1The reaction mixture was monitored by H-NMR. Methanol was then removed under vacuum at 35-40°C. Methanol (3550 mL, 8.8 vol) was added and the solution was transferred to a reactor. The reaction was stirred at 20-22°C for 16 hours. IPC was performed by NMR, which showed the reaction was complete. The reaction mixture was concentrated under vacuum at a temperature below 40°C. The residue was dissolved in methyl tert-butyl ether (4350 mL, 10.85 vol). The resulting solution was washed with deionized water (2190 mL). The aqueous layer (pH = 7) was discarded. The organic layer was washed with sodium chloride solution (2 x 1930 mL, 2 x 4.8 vol). The aqueous layer was discarded. The organic layer was dried over sodium sulfate (395 g, 1 equivalent w / w), washed with methyl tert-butyl ether (790 mL, 2 volumes) and concentrated under vacuum at a temperature below 40° C. to give crude 6-(nitrooxy)hexanoic acid-(1S,2E)-3-[(1R,2R,3S,5R)-2-[(2Z)-7-(ethylamino)-7-oxo-2-hepten-1-yl]-3,5-dihydroxycyclopentyl]-1-(2-phenylethyl)-2-propen-1-yl ester (Compound (I)) (367.1 g, 98.3% yield) having an HPLC purity of 80.4%.

[0077] The mixture was purified on a Combiflash using a silica gel column (750 g × 6, 10.34 vol) and dichloromethane / methanol (with a gradient from 100:0 to 95:5) as eluent. Fractions were monitored by TLC and analyzed by HPLC (% area). The fractions were concentrated under vacuum at temperatures below 50 °C to give 206 g of 6-(nitrooxy)hexanoic acid-(1S,2E)-3-[(1R,2R,3S,5R)-2-[(2Z)-7-(ethylamino)-7-oxo-2-hepten-1-yl]-3,5-dihydroxycyclopentyl]-1-(2-phenylethyl)-2-propen-1-yl ester (Compound (I)), which was placed in a 4 L three-neck round-bottom flask, dissolved in absolute ethanol (2100 mL, 10 vol). Activated carbon (21 g, 10% w / w) was added, and the mixture was stirred at 20 °C to 25 °C for 0.5 h. The activated carbon was filtered and washed with absolute ethanol (210 mL, 1 vol). The filtrate was concentrated under industrial vacuum at 45 °C to 50 °C for 4 h, then under high vacuum at 45 °C to 50 °C for 8 h. In DMSO-d6 1 Monitoring by 1 H-NMR showed no residual solvent.

[0078] 6-(Nitrooxy)hexanoic acid-(1S,2E)-3-[(1R,2R,3S,5R)-2-[(2Z)-7-(ethylamino)-7-oxo-2-hepten-1-yl]-3,5-dihydroxycyclopentyl]-1-(2-phenylethyl)-2-propen-1-yl ester (192.9 g) was obtained in an overall yield of 62% from compound (II). The HPLC purity was 99.13%. [Table 1] [Table 2]

[0079] Table 1 reports the results of quantitative analysis and chemical yields of 6-(nitrooxy)hexanoic acid (VIIIa) prepared according to the nitration reaction of the present invention and the method disclosed in WO 2019 / 162149. The results show that adding water during the workup of the nitration reaction of alkali salt of 6-hydroxyhexanoic acid instead of the saturated aqueous NaCl solution (brine) described in WO 2019 / 162149 resulted in a crude nitration mixture containing nearly pure compound (VIIIa) (99.2% (a / a%) purity) and a reduced amount of the dimeric impurity 6-{[6-(nitrooxy)hexanoyl]oxy}hexanoic acid (IXa) (0.15% a / a%). Compound (VIIIa) was also obtained in a high chemical yield, such as 99%. The use of the crude nitration mixture of step 5a makes it possible to obtain the final product 6-(nitrooxy)hexanoic acid-(1S,2E)-3-[(1R,2R,3S,5R)-2-[(2Z)-7-(ethylamino)-7-oxo-2-hepten-1-yl]-3,5-dihydroxycyclopentyl]-1-(2-phenylethyl)-2-propen-1-yl ester (I) containing less than 0.05% of the impurity 6-{[6-(nitrooxy)hexanoyl]oxy}hexanoic acid ester of bimatoprost (VII). Indeed, the results in Table 2, which reports the quantitative analysis of Compound (I) and major impurities prepared according to the method of the present invention (Example 1) and the method disclosed in WO 2019 / 162149 (Example 2—Comparative), demonstrate that the method of the present invention provides Compound (I) containing less than the detection limit of 0.05% of the "dimeric impurity" ester of bimatoprost with 6-{[6-(nitrooxy)hexanoyl]oxy}hexanoic acid (Compound (VII)) and 0.11% of the 15-(6-chlorohexanoyl) ester of bimatoprost (Compound (V)). Prior art methods yield Compound (I) with lower chemical purity, containing 0.1% to 0.4% of Compound (VII). The results demonstrate that the method of the present invention represents an improved method that is easily transferable to industrial scale.

Claims

1. Formula (I): 【Chemical 1】 1. A process for the preparation of 6-(nitrooxy)hexanoic acid (1S,2E)-3-[(1R,2R,3S,5R)-2-[(2Z)-7-(ethylamino)-7-oxo-2-hepten-1-yl]-3,5-dihydroxycyclopentyl]-1-(2-phenylethyl)-2-propen-1-yl ester of the formula (I), comprising the following steps A) and B): Step A) The following steps 1a) to 6a): 1a) ε-caprolactone: 【Chemistry 2】 with an inorganic base selected from KOH, NaOH and LiOH in a solvent selected from methanol, ethanol or isopropanol at a temperature between 20° C. and the reflux temperature of the solvent to obtain a compound of formula (X): 【Chemistry 3】 (Wherein, M is K, Na or Li) obtaining a 6-hydroxyhexanoate salt of 2a) Purifying the 6-hydroxyhexanoate of formula (X) obtained in step 1a), comprising the steps of: i) preparing a 6-hydroxyhexanoate salt of formula (X) from the following compounds i) to iv) i. adding methyl tert-butyl ether to the reaction mixture of step 1a) in a volume ratio of methyl tert-butyl ether / reaction mixture of 2:1; ii. Filtering the solids iii. Slurrying the solid with a mixture of methyl tert-butyl ether and methanol in a volume ratio of 3:1 to 5:1 and water in an amount of 0.3 to 1 mole of water per mole of ε-caprolactone. iv. Isolating the 6-hydroxyhexanoate of formula (X) as a solid. a process comprising: 3a) 6-hydroxyhexanoate is reacted with fuming HNO in dichloromethane at a temperature ranging from 0°C to 10°C. ３ and deep H ２ SO ４ reacting the mixture with a mixture of 4a) adding water to the nitration mixture of step 3a) while maintaining the temperature between 0°C and 5°C; 5a) The organic phase was separated, dried over sodium sulfate, and the solvent was evaporated to give crude 6-(nitrooxy)hexanoic acid (VIIIa): 【Chemistry 4】 obtaining 6a) Reacting crude 6-(nitrooxy)hexanoic acid (VIIIa) with a chlorinating agent in dichloromethane to give crude 6-(nitrooxy)hexanoyl chloride (VIIIb). Preparation of 6-(nitrooxy)hexanoyl chloride (VIIIb) according to: Step B) The following steps 1b) to 4b): 1b) Bimatoprost is reacted with butylboronic acid in methyl tert-butyl ether at a temperature of 40° C. to give compound (II): 【Chemistry 5】 obtaining 2b) Reacting compound (II) with crude 6-(nitrooxy)hexanoyl chloride (VIIIb) from step 6a) in the presence of free 4-dimethylaminopyridine in an aprotic organic solvent to give compound (XI): 【Chemistry 6】 obtaining 3b) removing the boronate protecting group to obtain the crude compound of formula (I); 4b) Purifying the crude compound of formula (I) by column chromatography Preparation of 6-(nitrooxy)hexanoic acid (1S,2E)-3-[(1R,2R,3S,5R)-2-[(2Z)-7-(ethylamino)-7-oxo-2-hepten-1-yl]-3,5-dihydroxycyclopentyl]-1-(2-phenylethyl)-2-propen-1-yl ester (I) A method comprising:

2. 2. The process according to claim 1, wherein in step 1a), the inorganic base is KOH, the solvent is methanol, and the reaction is carried out at the reflux temperature of methanol.

3. In step 3a), 6-hydroxyhexanoic acid potassium salt is reacted with fuming HNO in dichloromethane. ３ and dark H ２ SO ４ at a temperature of 0°C to 10°C, and the reaction mixture is vigorously stirred at a temperature of 0°C to 5°C for 60±15 minutes.

4. The process according to any one of claims 1 to 3, wherein in step 6a) the chlorinating agent is oxalyl chloride.

5. 5. The process according to any one of claims 1 to 4, wherein in step 2b) the aprotic solvent is methyl tert-butyl ether at a temperature ranging from 0°C to 20±3°C.

6. The method according to any one of claims 1 to 5, wherein in step 2b), the molar ratio of compound (II) to 4-dimethylaminopyridine is 1:2.0 to 1:2.

4.

7. The process according to any one of claims 1 to 6, wherein in step 3b), the solvent used in the reaction is methanol and the reaction is carried out at room temperature.

8. The process according to any one of claims 1 to 7, wherein in step 4b) the crude compound of formula (I) is purified using high performance silica gel chromatography and methylene chloride / methanol as the mobile phase.

9. 1. A process for the synthesis of 6-(nitrooxy)hexanoic acid, comprising: 1a) ε-caprolactone: 【Chemistry 7】 with KOH in methanol at the reflux temperature of the methanol; 2a)-i. adding methyl tert-butyl ether to the reaction mixture of step 1a) in a volume ratio of methyl tert-butyl ether / reaction mixture of 2:1; 2a)-ii. Filtration of solid 6-hydroxyhexanoic acid potassium salt; 2a)-iii. Slurrying the solid with a mixture of methyl tert-butyl ether and methanol in a volume ratio of 3:1 to 5:1 and water in an amount of 0.3 to 1 mole of water per mole of ε-caprolactone; 2a)-iv. isolating 6-hydroxyhexanoic acid potassium salt as a solid; 3a) The 6-hydroxyhexanoic acid potassium salt of step 2a) is reacted with fuming HNO in dichloromethane at a temperature ranging from 0°C to 10°C. ３ and deep H ２ SO ４ and vigorously stirring the reaction mixture at a temperature of 0°C to 5°C; 4a) adding water to the nitration mixture of step 3a) while maintaining the temperature between 0°C and 5°C; 5a) separating the organic phase, drying the organic phase with sodium sulfate, and distilling off the solvent to obtain 6-(nitrooxy)hexanoic acid characterized by a chemical purity of 99% or more and a content of 6-{[6-(nitrooxy)hexanoyl]oxy}hexanoic acid of 0.2% or less. A method comprising:

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