WO2012020417A1

WO2012020417A1 - Process for the preparation of estradiol and its derivatives

Info

Publication number: WO2012020417A1
Application number: PCT/IN2010/000528
Authority: WO
Inventors: Ramana Kondepati Venkata; Pandurang Bhujbal Sandeep; Venkat Raman Jayaraman
Original assignee: Reliance Life Sciences Pvt. Ltd.
Priority date: 2010-08-10
Filing date: 2010-08-10
Publication date: 2012-02-16

Abstract

The present invention provides a process for the preparation of a compound of formula I wherein R₁ represents a hydrogen atom, halogen atom, cyano group, hydroxyl group, straight or branched C₁-C₁₀ alkyl group, straight or branched C₂-C₁₀ alkenyl group or C₆- C₁₀ aryl group; or a -OR₂, -O(CO)R₂, or -R₂-OH group, wherein R₂ is a straight or branched Ci-C6 alkyl group or a straight or branched C₂-C₆ alkenyl group, which process comprises treating a compound of formula II wherein R₁ is as defined above, with a compound of formula III M(BH₄) III wherein M is a monovalent metal ion, in a solvent at a temperature of from -10 to 10°C.

Description

TITLE:

PROCESS FOR THE PREPARATION OF ESTRADIOL AND ITS DERIVATIVES

TECHNICAL FIELD

The present invention relates to a process for reducing steroidal ketones. In particular, the present invention relates to an efficient process for reducing estrone and its derivatives to Estradiol and its derivatives.

BACKGROUND

Estradiol (estra-1, 3, 5(10)-triene-3, Πβ-diol or 17 -Estradiol) is a steroidal sex hormone and is the major estrogen in humans. Estradiol has not only a critical impact on^' reproductive and sexual functioning, but also affects other organs including bone structure. Estradiol and its derivatives are commonly administered in hormone replacement therapy regimens and are also indicated in treating climacteric complaints and the treatment of osteoporosis. Estradiol has the following structure:

17P-Estradiol

The epimer of estradiol, referred to as 17a-Estradiol, has the following structure.

17a-Estradiol This epimer is less potent than the 17β form. In certain cell lines, the 17a form has been found to be only one tenth as potent as the 17β form (see, for example, Edwards DP & McGuire WL,. Endocrinology, 1980, Vol. 107, 884-891).

Estradiol is known to form several crystal structures. The most stable form of estradiol is estradiol hemihydrate. Two anhydrous structures have also been reported in the literature. Estradiol also forms solvates with organic solvents such as methanol and ethanol.

A common synthetic preparation of Estradiol reported in the art is the reduction of estrone (3 -Hydroxyestra-l, 3, 5(10)-trien-17-one) to the 17-hydroxy equivalent (estradiol). Reducing agents used in the prior art include Raney Nickel, Alumiminum isopropoxide, lithium aluminum hydride, sodium borohydride and catalytic reduction using Na.

US patent 2,623,886 describes a method of reducing of Estrone using methanolic sodium borohydride at room temperature. However this process involves high volumes of solvent and yields up to 2% of 17a-Estradiol.

The reduction of Estrone described in the prior art has mainly resulted in a mixture of the 17a and 17β forms. Repeated solvent recrystallisations and chromatography techniques have been employed to yield 17P-Estradiol with high purity.

The prior art processes also result in incomplete conversion of Estrone to Estradiol'. Due to their structural similarity and similar properties, the separation of Estrone and Estradiol is also a challenge.

There is therefore a need for a process that results in efficient conversion of Estrone and its derivatives to 17P-Estradiol and its derivatives, substantially free of Estrone and 17a- Estradiol impurities.

It has now been surprisingly found that 17p-Estradiol and its derivatives can be prepared by a new process that avoids many of the problems described in the prior art. Furthermore, an increase both in yield and purity of the 17β product can be achieved. In contrast to the processes described in the prior art,-the process of the present invention involves reducing, estrone and its derivatives in a specific temperature range using a borohydride.

Reduction of Estrone to . I 7P-Estradiol is advantageously performed at low temperature. This low temperature is thought to favour the kinetic 17β product over the thermodynamic 17a product. Reduction to 17β is faster than reduction to 17a, so a lower temperature favours reduction to the 17β product.

Further, it has surprisingly been found that an almost complete conversion of estradiol to the 17β product is achieved if the reduction is carried out first at a low temperature, followed by a maintenance step at a higher temperature. This two-step process has the advantages both of a very high yield of Estradiol and also of a very high purity of the 17β product.

SUMMARY OF THE INVENTION

The present invention therefore provides a process for the preparation of a compound of formula I

Formula I

wherein Ri represents a hydrogen atom, halogen atom, cyano group, hydroxyl group, straight or branched -Cio alkyl group, straight or branched C₂-C₁₀ alkenyl group or C₆- C₁₀ aryl group; or a -OR₂, -0(CO)R₂, or -R₂-OH group, wherein R₂ is a straight or branched C -C alkyl group or a straight or branched C₂-C₆ alkenyl group, which process comprises treating a compound of formula II

Formula II

wherein R is as defined above, with a compound of formula III

M(BH₄) Formula III

wherein M is a monovalent metal ion, in a solvent at a temperature of from -10 to 10°C.

Also provided is a compound of formula (I) obtained by the process of the present invention as defined above.

Also provided is a compound of formula (I), which is substantially free of a compound of formula (IV)

Formula IV

DETAILED DESCRIPTION OF THE INVENTION

Scheme 1 below shows an embodiment of the process of the invention, in which the compound of formula (I) is β-Estradiol.

Estrone β-Estradiol As used herein, the term "Estradiol" refers to 17p-Estradiol including all polymorphs, solvates, esters and salts thereof, for example, Estradiol hemihydrate.

Some compounds of the present invention may exhibit polymorphism. The scope of the present inyention includes all polymorphic forms of the compounds according to the invention, which forms the further aspect of the invention. It is to be understood that the present invention encompasses all polymorphic forms or mixtures thereof which form or forms possess properties useful in the treatment of the conditions for which they are indicated.

As used herein, the term halogen atom refers to chlorine, fluorine, bromine or iodine atoms typically a fluorine, chlorine or bromine atom, most preferably chlorine or fluorine. The term halo when used as a prefix has the same meaning.

As used herein, the term Cj-Cio alkyl includes both saturated straight chain and branched alkyl groups. Examples of Ci-Cio alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, hexyl, heptyl, octyl, nonyl and decyl. Typically, the Ci- Cio alkyl group is a C_1-6 alkyl group, more preferably a Ci_-4 alkyl group.

As used herein, the term C₂-C₁₀ alkenyl refers to groups containing one or more carbon- carbon double bonds, which group may be straight or branched. Typically, the C₂-C₁₀ alkenyl group is a C₂-C₆ alkenyl group, preferably a C₂-C₄ alkenyl group. Most typically, the C₂-C₁₀ alkenyl group is a vinyl, allyl or crotyl group, most preferably an ally! group.

As used herein, the term C6-C₁₀ aryl refers to a 6-10 membered aromatic carbocyclic group. It may be monocyclic or polycyclic, for instance monocyclic or bicyclic. Examples of a C₆-Cio aryl group include phenyl and naphthyl. Phenyl is preferred.

As used herein, the term C]-C₆ alcohol means a compound of formula R-OH, wherein R is a Ci_-6 alkyl group as defined herein. Examples of a Cj-C₆ alcohol include methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, s-butanol, t-butanol, pentanol and hexanol , Typically, the Ci-C₆ alcohol is a C 1.4 alcohol, preferably a C1-2 alcohol. Generally, the C]-C₆ alcohol is, methanol or ethanol, preferably methanol.

Typically, R] is a hydrogen atom or a group -OR₂.

Typically, a group -OR₂ is a methoxy, ethoxy, propoxy, isopropoxy, butyloxy, pentyloxy or hexyloxy group. Preferably, a group -OR₂ is a methoxy or ethoxy group, more preferably a methoxy group.

Preferably, Rl is a hydrogen atom.

Typically, M is a monovalent metal ion of a Group I metal. For example, M is Li, K, Na or Rb. Preferably, M is Na or K, more preferably Na.

Typically, the process of the invention is a process for producing a compound of formula' I, as defined herein, wherein less than 2%, preferably less than 1%, more preferably less than 0.7% of compound of formula IV, as defined herein, is produced. ,

Typically, the process of the invention is a process for producing a compound of formula I, as defined herein, in a purity of higher than 98%, preferably higher than 99%, more preferably higher than about 99.4%.

Typically, the process of the invention is conducted at a temperature of from -10 to less than 0°C, preferably from -10 to -3°C, more preferably from -10 to -5°C, most preferably from -7 to -5°C.

Typically, the solvent used in the process of the present invention is an aqueous organic : solvent, preferably an aqueous C_1-6 alcohol. Generally, the solvent used in the process of the present invention comprises methanol. Preferably, the solvent is aqueous methanol or ethanol, more preferably aqueous methanol. Typically, the process of the present invention is conducted . under alkaline conditions. Methods of achieving alkaline conditions will be well known to the skilled person. Alkaline conditions are suitably achieved using an aqueous alkali. Suitable examples of an aqueous alkali include an aqueous solution of a compound of formula M(OH), wherein M is as defined above. .

Most preferably, the solvent used in the process of the present invention is alkaline aqueous C]_-6 alcohol, typically alkaline aqueous methanol.

Typically, the ratio of compound of formula (III) to compound of formula (II) is from 0.5:1 to 6.5: 1 , preferably from 0.5: 1 to 2.5:1, more preferably from 0.5: 1 to 0.8:1.

Typically, the compound of formula (III) is present as an alkaline solution in a solvent, as defined herein.

In the process of the present invention, the reaction mixture is typically maintained at the required temperature for a period of from 1 to 4 hours, preferably 1.5 to 2.5 hours, more preferably about 2 hours.

In one aspect, the process of the present invention comprises:

(i) preparing an alkaline solution of a compound of formula (II), as defined above; and

(ii) adding to the alkaline solution prepared in step (i) an alkaline solution of a compound , of formula (III), as defined in claim 1, and maintaining the resulting reaction mixture at a temperature as defined above.

Typically, step (i) comprises adding aqueous alkali to a solution of a compound of formula (II) in a solvent.:

Alternatively, step (i) comprises preparing a solution of a compound of formula (II), as defined above, in a solvent arid adding the thus obtained solution to an aqueous alkali. The aqueous alkali is typically as defined above. Preferably, the aqueous alkali is aqueous sodium hydroxide.

Typically, in step (ii), the alkaline solution of a compound of formula (III) is added to the alkaline solution of a compound of formula (II) over a period of 1 to 4 hours, preferably 1.5 to 2.5 hours.

Compounds of formula (III) are typically commercially available or can be prepared by known methods.

Compounds of formula (II), where Ri is a hydrogen atom, i.e. estrone, are commercially available.

Compounds of formula (II), where R_\ is not a hydrogen atom are commercially available, or may be prepared by known methods, for example as described in WO-A-06013196, the entirety of which is incorporated herein by reference.

Typically, after the reaction has proceeded substantially to completion, the temperature of the reaction mixture is maintained at a temperature of from 0 to 10°C, typically at 5 tolO°C, preferably at 8 tolO°C, more preferably at about 10°C. The chosen temperature is typically maintained for a period of from 0.5 to 1.5 hours, preferably 0.8 to 1.2 hours, more preferably for about 1 hour. Generally, HPLC is used to determine that the reaction has proceeded substantially to completion.

In one embodiment, after the reaction has proceeded substantially to completion, the reaction mixture is maintained at a temperature of from 0 to 10°C for a period of from 0.5 to 1.5 hours.

In a particularly preferred embodiment, the invention provides a process for the preparation of a compound of formula I, as defined herein, which process comprises the sequential steps of: , (a) treating a compound of formula II, as defined herein, with a compound of formula III, as defined herein, at a temperature of from -10 to less than 0 °C for a period of from 1 to 4 hours; and

(b) after the reaction has proceeded substantially to completion, maintaining the reaction mixture at a temperature of from 0 to 10°C for a period of from 0.5 to 1.5 hours.

Typically, the temperature employed in step (a) is from -10 to -3°C, preferably from -10 to -5°C, more preferably from -7 to -5°C.

Typically, the temperature employed in step (b) is from 5 tol0°C, preferably from 8 tol0°C, more preferably about 10°C.

Typically, the period of time employed in step (a) is from 1.5 to 2.5 hours, preferably about 2 hours.

Typically, the period of time employed in step (b) is from 0.8 to 1.2 hours, preferably about 1 hour

As used herein, the term "substantially to completion" means that generally greater than 70%, preferably greater than 75%, more preferably greater than about 80% of the Estrone or Estrone derivative has been reduced to estradiol or estradiol derivative.

Typically, completion of the reaction is monitored by HPLC.

Typically, after the reaction has proceeded substantially to completion, the compound of formula (I) is isolated. Typically, isolation of the compound of formula I is effected by acidifying the reaction mixture (for example, so that the pH = 2) with dilute aqueous acid (for example, dilute HC1), stirring at room temperature and recovering the crude product by filtration. The filtered product is typically washed free of acid and dried. When the compound of formula (I) is 17 β -Estradiol, the overall yield of crude product is typically quantitative, for example 99% or higher. The crude Estradiol typically has a purity greater than' 99%, for example 99.14%). The crude Estradiol typically has less than 0.65%) 17a-estradiol as impurity, for example 0.64%).

Typically, the crude product is recrystallised from aqueous isopropyl alcohol.

When the compound of formula (I) is 17p-Estradiol, the overall yield of recrystallised product is . typically 82 to 85%, for example, 82.2%. The purity of the recrystallised product is typically 99.5% or greater, preferably 99.75%> or greater, for example 99.8%. The recrystallised estradiol typically has less than 0.075% 17a-estradiol as impurity, for example 0.07%.

A compound of formula (I) substantially free of a compound of formula (IV). typically contains less than 0.65% compound of formula (IV), preferably less than 0.3%, more preferably less than 0.1%, even more preferably less than 0.075%), for example 0.7% of compound of formula (IV).

As mentioned above, the process of the present invention typically takes place under alkaline conditions. The reaction goes to completion under alkaline conditions and the best results are observed when an alkaline sodium borohydride solution is used.

As mentioned above, a methanol solvent is preferred. Thus, reductions were carried out using a variety of solvents such as methanol, THF, alkaline THF and alkaline Methanol. It was found that the best results were obtained with alkaline methanol.

The reaction time was varied from 4- 16 hours and it was observed that estrone was reduced efficiently within 4 hours. The . effect of the temperature of the reaction is critical in determining the amounts of the 17a- and 17β- forms of estradiol produced. To this end, reactions were carried out at temperature from -10 to 55°C. It was observed that when the reduction was carried out at -10 to -5°C and the reaction mixture was then maintained at 0-10°C, 17P-estradiol was obtained in an amount of approximately 99%.

As mentioned above, the crude product is typically recrystallised from aqueous isopropyl alcohol. Thus, recrystallisation of crude 17 -estradiol were carried out using various solvents such as methanol, Isopropyl alcohol and 5% aqueous solutions of these solvents. It was observed that 5% aqueous isopropyl alcohol was effective in increasing the purity of crude estradiol from 99% to 99.84% without greatly compromising the yields.

EXAMPLES

The following examples are included to demonstrate preferred embodiments of ^"the invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques discovered by the inventor to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.

Although specific starting materials and reagents are depicted in the Scheme illustrated in the above scheme 1, suitable substitutions can be easily bemade to provide a variety of estradiol derivatives. Conventional methods and/or techniques of separation and purification known to one of ordinary skill in the art can be used to isolate & purify the compounds of the present invention. Such techniques will be well known to one of ordinary skill in the art and may include, for example, all types of chromatography (high pressure liquid chromatography (HPLC), column chromatography using common adsorbents such as silica gel, and thin-layer chromatography), recrystallization, and differential (i.e., liquid-liquid) extraction techniques. The following examples illustrate the embodiments of the present invention. It is to be understood, however, that the embodiments of the invention are not limited to the specific details of these Examples, as other variations thereof will be known, or apparent in light of the instant disclosure, to one of ordinary skill in the art.

a) All operations carried out at room or ambient temperature were in the range of 18- 25 degree Centigrade unless otherwise specified.

b) The course of the reaction was monitored by thin layer chromatography (TLC) and >. reaction times are given for illustration only. ,

c) Melting points are uncorrected, the melting points are given for the. materials prepared as described, polymorphism may result in isolation of materials with . different melting points in some preparations.

d) The structure and purity^' of all final products were assured by the following techniques: TLC, NMR (nuclear magnetic resonance) spectroscopy, mass spectroscopy and microanalysis.

e) When given, NMR data is in the form of delta (δ) values for major diagnostic protons given in parts per million (ppm) relative to tetramethylsilane (TMS) as internal standard determined at 300 MHz or 400 MHz using the indicated solvent. f) Chemical symbols have their usual meanings: the following abbreviations have also been used : v (volume), w (weight), Bp. (boiling point), Mp. (melting point), L ( litres) , ml (milliliters), gms (grams), mg (milligrams), mol(moles) mmole (milimoles), eq (equivalents), °C (degree centigrade), cone, (concentrated), Si0₂ (silicon dioxide) , Na₂S0₄ (sodium sulphate).

g) The starting materials used in the following examples have been sourced from .

Sigma. .

EXAMPLE 1: Process for the preparation of estradiol from estrone

Sodium hyroxide solution (7.32 gm in 36 ml water) was added to a stirred solution of estrone (45 gm) in Methanol (225ml) at room temperature until a clear solution was achieved. This solution is cooled to -10°C after which an alkaline sodium borohydride solution (4.4 gm sodium borohydride in 3.328 gm of NaOH dissolved in 18 ml water) was added to the Estrone solution at -10 to -5°C over 2 hours. The progress of the reaction was , monitored by HPLC. After the reaction had gone to completion, the reaction mixture was raised to 10°C and stirred for 1 hour. The reaction mixture was thenacidified to pH 2 using 10% diltute HC1 solution (90ml) and stirred at room temperature till until precipitation occurred. The crude estradiol precipitate was then filtered off, washed free of acid and dried.

The crude estradiol (45 gm) obtained was found to have 99.14% purity with an amount of 17a-Estradiol of 0.64% as confirmed by HPLC, with moisture content of 3.5%. The crude estradiol (45 gm) was then recrystallised by dissolving in 540 ml of 5 % aqueous isopropyl alcohol with heating under reflux conditions. The product was obtained by cooling to 0°C and filtering off the precipitate. After drying, the purified product weighed 42 gm (yield 82.2%o) with a purity of 99.8 % with an amount of 17a-Estradiol of 0.07% and moisture content of 3.38%.

Yield = 82-85%

Purity passes Pharmacopoeial standard

Individual impurity not more than 0.3%

Total impurities not more than 0.5%

EXAMPLE 2: Effect of reaction conditions on the amount of 17a-Estradiol produced a) Reducing agent

A reduction of estrone to Estradiol was carried out using reduced alumina in THF as described in the prior art. It was observed that at a reaction temperature of from 0-5°C 17P-Estradiol was obtained in 96.85% purity with an amount of 17a- Estradiol of 1.71%.

Further it was observed that alkaline sodium borohydride solution was more effective in reducing estrone as compared to sodium borohydride reagents. b) Solvent

Sodium borohydride reductions of estrone to Estradiol were carried out using methanol, tetrahydrofuran (THF), alkaline methanol and alkaline THF as solvents. It was observed that alkaline methanol was effective in complete dissolution of estrone and conversion to Estradiol within 4 hours whereas it took about 12- 16 hours with methanol and THF. With alkaline THF the purity of 17 -Estradiol obtained, was 97% as compared to 99% with alkaline methanol. c) Reaction temperature

Sodium borohydride reductions of Estrone to Estradiol were carried at a variety^' of temperatures. It was found that the reduction of estrone to 17p-Estradiol was most favoured at -5 to -10°C. The optimum reaction conditions for reduction reaction involved addition of sodium borohydride at a temperature of from -5 to -7°C followed by maintenance at 10°C after the reaction had proceeded substantially to completion. These specific conditions gave 17p-Estradiol of 99% purity. d) Recrystallisation solvents

Recrystallisations of crude Estradiol were carried out using methanol, aqueous methanol, isopropyl alcohol (IP A) and aqueous IPA. For methanol and aqueous methanol, it was observed that although the moisture content and the amount of 17oc-Estradiol were reduced following recrystallisation, a drop in yield was also observed as compared to recrystallisation from aqueous IPA. 5% aqueous IPA was found to be the most suitable solvent for recrstallising crude Estradiol. This gave 17P-Estradiol with a purity of 99.84% and moisture content of 3.32% without resulting in a significant lowering of the yield.

Thus, while we have described fundamental novel features of the invention, it will be understood that various omissions and substitutions and changes in the form and details may be possible without departing from the spirit of the invention. For example, it is expressly intended that, all combinations of those elements and/or method steps, which perform substantially the same function in substantially the same way to achieve the same results, be within the scope of the invention.

Claims

1. A process for the preparation of a compound of formula I

Formula I

wherein Ri represents a hydrogen atom, halogen atom, cyano group, hydroxyl group, straight or branched C^Qo alkyl group, straight or branched C₂-Cio alkenyl group or C₆-Cio_.aryl group; or a -OR₂, -0(CO)R₂, or -R₂-OH group, wherein R₂ is a straight or branched Ci-C alkyl group or a straight or branched C₂-C₆ alkenyl group, which process comprises treating a compound of formula II

Formula II

wherein R_\ is as defined above, with a compound of formula III

M(BH₄) III

2. A process according to claim 1, wherein Ri is a hydrogen atom.

3. A process according to claim 1 or claim 2, wherein the temperature is from -7 to -5°C.

4. A process according to any one of the preceding claims, wherein the solvent is

methanol.

5. , A process according to any one of the. preceding claims, where process is conducted under alkaline conditions.

6. . A process according to any one of the preceding claims, wherein the ratio of compound of formula (III) to compound of formula (II) is from 0.5:1 to 0.8: 1.

7. A process according to any one of the preceding claims, wherein the reaction

mixture is maintained at -10°C to 0°C for 1-4 hours.

8. A process according to any one the preceding claims wherein, after the reaction has proceeded to > 97% of Estradiol with ~ 3% of Estrone remaining, the reaction mixture is maintained at a temperature of from 0 to 10°C for a period of from 0.5 to 1.5 hours.

9. , A process according to any one of the preceding claims, which process comprises:

(i) preparing an alkaline solution of a compound of formula (II), as defined in claim 1; and

(ii) adding to the alkaline solution prepared in step (i) an alkaline solution of έ· compound of formula (III), as defined in claim 1, and maintaining the ^' ·. resulting reaction mixture at a temperature as defined in claim 1.

10. A compound of formula (I) as defined in claim 1, obtained by a process as defined in any one of the preceding claims.