WO2002096918A1

WO2002096918A1 - Purification process

Info

Publication number: WO2002096918A1
Application number: PCT/GB2002/002540
Authority: WO
Inventors: Colin John Strawson; Daniel Levin; Anthony Stephen Graham; David Garner
Original assignee: Astrazeneca Ab; Astrazeneca Uk Limited
Priority date: 2001-06-01
Filing date: 2002-05-29
Publication date: 2002-12-05
Also published as: GB0113300D0

Abstract

A process for purification of a compound of formula (II) or a salt thereof, wherein R8 is -OR9, -SR9, -NHR10 or -NR11R12, where R9, R10, R11 and R12 form various specified heterocyclic groups, R2 and R3 are independently hydrogen or fluoro; R14 is a bond or a (1-8C)alkyl group which is optionally substituted by one or more hydroxy groups;which process comprises loading said compound or salt thereof, onto an extraction solid support phase material at a loading of at least 10mg/1g solid support phase material, eluting the product with a suitable solvent in the absence of buffer, and recovering product from the eluate.

Description

Purification Process

The present invention relates to a process for purification of certain oxazolidinone derivatives, and in particular oxazolidinone derivatives which are useful as anti-Gram positive bacterial agents.

Our International Patent Application No. WO 99/64417 describes a new class of antibacterial oxazolidinone compounds which are effective as anti-Gram positive bacterial agents, and certain processes for their preparation. These include compounds of formula (I):

(I) wherein

HET is a C-linked 5-membered heteroaryl ring containing 2 to 4 heteroatoms independently selected from N, O and S, which ring is optionally substituted on an available carbon atom by 1 or 2 substituents independently selected from (l-4C)alkyl, amino, (1 A alkylamino, (1- 4C)alkoxy and halogen, and/or on an available nitrogen atom (provided that the ring is not thereby quaternised) by (l-4C)alkyl; R² and R³ are independently hydrogen or fluoro;

Rep is of the formula R¹³CO- (wherein R¹³ is (l-lOC)alkyl substituted by two or more hydroxy groups; 2 of which are in a 1,2-diol orientation, ie. there is a terminal primary alcohol with an adjacent secondary alcohol), or pharmaceutically-acceptable salts, or in-vivo- hydrolysable esters thereof.

It is to be understood that all terms used in the definition of formula I above are as defined in WO 99/64417.

Of the above compounds, those in which HET is (unsubstituted) isoxazol-3-yl, 1,2,4- oxadiazol-3-yl, isothiazol-3-yl or l,2,5-thiadiazol-3-yl are preferred.

Of the compounds of formula (I), those of formula (1-1) are the pharmaceutically active anti-bacterial enantiomer. The pure enantiomer depicted in (I- 1), or mixtures of the 5R and 5S enantiomers, for example a racemic mixture are included in WO 99/64417. If a mixture of enantiomers is used, a larger amount (depending upon the ratio of the enantiomers) will be required to achieve the same effect as the same weight of the pharmaceutically active enantiomer. For the avoidance of doubt the enantiomer depicted below is the 5R enantiomer.

(1-1)

Furthermore, some compounds of the formula (I) and (1-1) may have other chiral centres, and such optical and diastereo-isomers, and racemic mixtures may possess antibacterial activity. It is well known in the art how to prepare optically-active forms (for example by resolution of the racemic form by recrystallisation techniques, by chiral synthesis, by enzymatic resolution, by biotransformation or by chromatographic separation) and how to determine antibacterial activity.

In- vivo hydrolysable esters include compounds of formula (I) and (1-1) in which any free hydroxy group independently forms a phosphoryl ester of the formula (PD3) :

R∞O

(PD3) where R¹⁹ and R²⁰ are independently selected from hydrogen or a pharmaceutically acceptable cation, as described hereinafter, such as an alkaline metal ion such as sodium or potassium, to give a pharmaceutically acceptable salt. Suitable pharmaceutically-acceptable salts include base salts such as an alkali metal salt for example sodium or potassium, an alkaline earth metal salt for example calcium or magnesium, an organic amine salt for example triethylamine, morpholine, N- methylpiperidine, N-ethylpiperidine, procaine, dibenzylamine, N,N-dibenzylethylamine, tris-(2-hydroxyethyl)amine, N-methyl deglucamine, piperazine, and amino acids such as lysine and arginine. There may be more than one cation or anion depending on the number of charged functions and the valency of the cations or anions. A preferred pharmaceutically- acceptable salt is the sodium salt. Another preferred pharmaceutically acceptable salt is the potassium salt.

However, to facilitate isolation of the salt during preparation, salts which are less soluble in the chosen solvent may be preferred whether pharmaceutically-acceptable or not.

Of the above compounds of formula (I) and (1-1), 5(R)-isoxazol-3-yloxymethyl-3-(4- (l-(2(S)-hydroxy-3-phosphoryl -propanoyl)-l,2,5,6-tetrahydropyrid-4-yl)-3,5- difluorophenyl)oxazolidin-2-one is especially preferred. Various methods for preparing compounds of formula (I) and (1-1) are described in WO 99/64417. Yet further methods are described in copending International Patent Application No. PCT/GB00/04527 (WO

01/40236) which specifically describes and claims a modified route to phosphate prodrags of the compounds of formula (I) and the like.

The routes used in the preparation of these compounds and particularly the phosphate prodrags are relatively long and complex. Although the product obtained is generally acceptable, there is a possibility that impurities will be generated at some stage during the production process. As the compounds are intended for pharmaceutical use, extremely high levels of purity are required.

The applicants have found certain novel techniques for achieving purification effectively. According to the present invention, there is provided a process for purification of a compound of formula (H)

or a salt thereof, wherein R⁸ is -OR⁹, -SR⁹, -NΗR¹⁰ or -NR^πR¹², where

R⁹ is a C-linked 5-membered heteroaryl ring containing 2 to 4 heteroatoms independently selected from N, O and S, which ring is optionally substituted on an available carbon atom by 1 or 2 substituents independently selected from (l-4C)alkyl, amino, (l-4C)alkylamino, (l-4C)alkoxy and halogen, and/or on an available nitrogen atom (provided that the ring is not thereby quaternised) by (l-4C)alkyl; or R⁹ is a C-linked 6-membered heteroaryl ring containing 1 or 2 nitrogen heteroatoms, which ring is optionally substituted on any available C atom (provided that when the N atom is adjacent to the link, there is no substitution on any C atom that is adjacent to this N atom) by 1, 2 or 3 substituents independently selected from (l-4C)alkyl, amino, (l-4C)alkylamino, (l-4C)alkoxy, (l-4C)alkoxycarbonyl and halogen; R¹⁰ is is a C-linked 5-membered heteroaryl ring containing 2 to 4 heteroatoms independently selected from N, O and S, which ring is optionally substituted on an available carbon atom by 1 or 2 substituents independently selected from (l-4C)alkyl, amino, (l-4C)aIkylamino, (1- 4C)alkoxy, (l-4C)alkoxycarbonyl and halogen, and/or on an available nitrogen atom (provided that the ring is not thereby quaternised) by (l-4C)alkyl; or R¹⁰ is a C-linked 6-membered heteroaryl ring containing 2 or 3 nitrogen heteroatoms, which ring is optionally substituted on any available C atom by 1, 2 or 3 substituents independently selected from (l-4C)alkyl, amino, (l-4C)alkylamino, (l-4C)alkoxy, (l-4C)alkoxycarbonyl and halogen; R^π and R¹² together with the nitrogen atom to which they are attached form a 5-membered heteroaryl ring, containing either (i) 1 to 3 further nitrogen heteroatoms or (ii) a further heteroatom selected from O and S together with an optional further nitrogen heteroatom; which ring is optionally substituted on a C atom by an oxo or thioxo group; and/or the ring is optionally substituted on a C atom by 1 or 2 (l-4C)alkyl groups; and/or on an available nitrogen atom (provided that the ring is not thereby quaternised) by (l-4C)alkyl; or R¹¹ and R¹² together with the nitrogen atom to which they are attached form a 6-membered heteroaryl ring containing up to three nitrogen heteroatoms in total (including the linking heteroatom), which ring is substituted on a suitable C atom by oxo or thioxo and optionally substituted on any available C atom by 1 or 2 (l-4C)alkyl substituents; R and R are independently hydrogen or fluoro; R¹⁴ is a bond or a (l-8C)alkyl group which is optionally substituted by one or more hydroxy groups; which process comprises loading said compound or salt thereof, onto a solid support phase material at a loading of at least lOmg/lg solid support phase material, eluting the product with a suitable solvent in the absence of buffer, and recovering product from the eluate.

The term solid support phase material will be understood to mean any solid material suitable for use as a support for the purpose of purification. It may also be referred to as the stationary phase during the purification process.

Preferably the compound of formula (H) as recovered is a salt of formula (DA)

where R², R³, R⁸ and R¹⁴ are as defined above in relation to formula (II) and R¹⁷ and R¹⁸ are each a pharmaceutically acceptable cation, for example an alkaline metal ion such as sodium or potassium.

Crude product or liquor, which may include organic solvents, water, salts, buffers and other organic impurities, is suitably loaded onto the solid support phase material at high loadings, for example from O.lg /lg to 5g/g stationary phase (but typically at about 0.5g/g). The concentration of product within the liquor will vary. However, typically, this will equate to a loading of from lOmg/lg solid support phase material to 500mg/lg solid support phase material of pure product, for example from lOmg/lg solid support phase material to lOOmg/lg solid support phase material of pure product and preferably about 30mg/lg solid support phase material of pure product. Further convenient loadings of crude product or liquor include 0.02g/g to 0. lg g solid support phase. hi general, the crude product will further contain solvents etc. which remain from the production process, such as water and/or dioxane. The pH of the crude product is suitably one which is appropriate for the particular solid support phase material involved. If it is not, then this may be adjusted by addition of suitable buffers as would be understood in the art. Suitable pHs will generally be in the range of from 1 to 14, preferably in the range of 2 to 8 and more preferably at about 7.5. At this pH value, the compound will exist in the form of a dimetal salt. The solid support phase material is suitably packed into a column in a conventional manner. Suitably, the column is part of a high-performance liquid chromatography (hplc) apparatus. The process is then conducted in a conventional hplc manner, using pressures for example of from 4 to 70 bar and preferably at about 40bar. Suitable particle sizes for the solid support phase materials will be in the range of from

3μm -200μm, but typically will be about lOμm. Various solid support phase material may be used but preferably, this will be a silica based bonded phase support medium with a to C₃₀ alkyl chain length (typically C₈ alkyl chain) as available commercially for example from Eka Chemicals under the trade name Kromasil, or a macroporous polymeric support phase equivalent (typically a polystyrene/ divinyl benzene based support/resin) which are also available commercially, for example from Polymer Laboratories Lie where they may be sold as MLRP-S media. An alternative solid support phase material is available from Mitsubishi, Japan where they may be sold as MCI Gel CHP5C.

The selection of elution solvents used in the process will depend upon the precise nature of the compound of formula (U) but will typically comprise water, an alcohol, such as (l-6C)alkyl alcohols including methanol, ethanol, and propanol or isopropanol, or mixtures thereof as well as tetrahydrofuran (THF) and alkylcyanides such as (l-3C)alkylcyanides, for instance acetonitrile.

Purification and desalting is suitably effected in a single step using reverse phase chromatography under gradient elution conditions. Such a process may be effected for example using a mobile phase comprising an elution solvent as described above.

The purified product may then be isolated by various known methods. For example, combination of desired fractions followed by concentration /evaporation by known processes such as vacuum rotary evaporation, wiped film evaporation, thin film evaporation, spray drying and lyophilisation may be used.

In particular, concentration may be effected using a membrane technique which utilises the principle of reverse osmosis as known in the art. In that case, a membrane material is selected which is stable and permeable to the solvent. Examples of suitable materials may include those sold as MP44, 31 or 36 by Koch Membrane Systems, and that sold as AFC30 by PCI Membranes. A preferred material may be MP44 or AFC30. The solution is then contacted with the membrane material under pressure, for example at about 30barg. This results in a reduced volume from which product may be precipitated, for example by adding a organic liquid which is a water miscible non-solvent for the product, such as ethanol.

Alternatively, the collected fractions may be diluted to >3<5% by addition of solvent, and then reapplied to the column previously equilibrated with a mobile phase comprising water and an organic phase (such as 3% ethanol). The required product may then be eluted in a concentrated fraction using a higher proportion of organic phase in water. Typically this may will be an alcohol /water mix, for example in proportions of from 50/50 to 100/0 (e.g 100% ethanol).

Preferred compounds of formula (II) and methods for preparing them are as described in WO 99/64417.

Suitably, in the compound of formula (II), -R⁸ is -OR⁹.

Examples of compounds of formula (JJ) where R⁸ is a group -NRⁿR¹², and methods for preparing them, are described in copending International Patent Application no. PCT/GBOl/01815 (WO 01/81350). Particular examples of group R⁸ in this case are N-linked tetrazole or triazole.

Examples of compounds of formula (II) where R⁸ is a group -NHR¹⁰ and methods of preparation are shown in WO00/21960. Particular examples of R¹⁰ are isoxazol-3-yl, isoxazol-5-yl, l,2,4-oxadiazol-3-yl, isothiazol-3-yl, l,2,4-thiadiazol-3-yl or l,2,5-thiadiazol-3- yl. In addition, it may be preferred that in the compound of formula (H), R⁹ is a C-linked

5-membered heteroaryl ring containing 2 to 4 heteroatoms independently selected from N, O and S, which ring is optionally substituted on an available carbon atom by 1 or 2 substituents independently selected from (l-4C)alkyl, amino, (l-4C)alkylamino, (l-4C)alkoxy and halogen, and/or on an available nitrogen atom (provided that the ring is not thereby quaternised) by (l-4C)alkyl.

Suitably the compound of formula (II) is obtained in the form of a pharmaceutically acceptable salt, such as an alkali metal salt such as sodium or potassium and in particular the disodium phosphate salts, or is converted to such a salt after recovery using conventional methods. Particular examples of compounds of formula (H) are compounds of formula (IV)

(IV) where

R², R³, R⁹ and R¹⁴ are as defined in relation to formula (II) and R¹⁷ and R¹⁸ are as defined in relation to formula (DA).

Most preferably, in the above compounds R¹⁴ is a direct bond. Suitably R² and R³ are fluorine.

Particular examples of R⁹ or R¹⁰ where these are present are isoxazolyl, and particularly isoxazol-3-yl. Thus a particularly preferred compound of formula (H) is

5 (R)-Isoxazol-3-yloxymethyl-3-(4-( 1 -(2(S)-hydroxy-3-phoshoryl-propanoyl)- 1 ,2,5 ,6- -tetrahydropyridy-4-yl)-3,5-difluorophenyl)oxazolidin-2-one (where R¹⁷ and R¹⁸ are hydrogen) and a preferred salt is the disodium salt (where R¹⁷ and R¹⁸ are both sodium).

The invention will now be illustrated but not limited by the following Examples.

Example 1

A liquor (700mg; pH 7.3) comprising 5(R)-isoxazol-3-yloxymethyl-3- (4-(l-(2(S),hydroxy-3-phosphoryl-propanoyl)-l,2,5,6-tetrahydropyridy-4-yl)-3,5- difluorophenyl)oxazolidin-2-one (12.3% w/w); dioxane (22.5% w/w;) sodium chloride (21.3% w/w ) and water (45% w/w) was diluted with water (2ml). This was injected onto a reverse phase HPLC column (Kromasil 100 lOμm C8, 4.6 x 250mm) and eluted with a mobile phase system (A = ethanol/water 3/97; B = ethanol); flowrate (lml/min) using gradient conditions (A/B 100/0 (25min.); A/B 100/0 (10m linear grad) - A/B 30/70 (15m) A/B 30/70). Elution of the product was monitored by UV detection (280nm) and fractions collected which were further analysed by analytical HPLC . Fractions of required purity were concentrated by vacuum rotary evaporation (Yield 70-80% of high purity disodium salt). i.r. (cm^"1) 1,744 (C=O)carbamate, 1637 (C=O) tertiary amide.

¹³C n.m.r. (125MHz) ppm. 172.2, 172.1, 162.3, 160.4(2C), 156.3, 138.4, 127.1, 125.8, 114.3, 102.6 (2C), 96.6, 72.3, 70.4, 69.6, 66.1, 47, 45.5, 40.3, 29.5.

Example 2

The chromatographic procedure was carried out according to the process described in Example 1. The fractions of required purity (at approximately l%w/v concentration) were concentrated by passing the solution repeatedly through a wiped film evaporator (model KD6 supplied by UIC) which had been set to ran at 50mbara with a jacket temperature of 40-50°C. After 2 passes through the evaporator, the solution was added to absolute ethanol or Industrial methylated spirits (IMS) 74 OP at 20-40°C, resulting in a precipitate of the required product.

Example 3 The chromatographic procedure was carried out according to the process described in Example 1. The fractions of required purity (at approximately l%w/v concentration) were concentrated by contact with a membrane (KOCH membranes MP36, M31or MP44; alternatively AFC30 supplied by PCI Membranes) operated at 30 barg and ambient temperature. The resulting concentrated solution was added to IMS 70 OP to give a precipitate of the required product.

Claims

1. A process for purification of a compound of formula (II)

or a salt thereof, wherein

R⁸ is -OR⁹, -SR⁹, -NHR¹⁰ or -NR^πR¹², where

R⁹ is a C-linked 5-membered heteroaryl ring containing 2 to 4 heteroatoms independently selected from N, O and S, which ring is optionally substituted on an available carbon atom by 1 or 2 substituents independently selected from (l-4C)alkyl, amino, (l-4C)alkylamino, (l-4C)alkoxy and halogen, and/or on an available nitrogen atom (provided that the ring is not thereby quaternised) by (l-4C)alkyl; or

R⁹ is a C-linked 6-membered heteroaryl ring containing 1 or 2 nitrogen heteroatoms, which ring is optionally substituted on any available C atom (provided that when the N atom is adjacent to the link, there is no substitution on any C atom that is adjacent to this N atom) by 1, 2 or 3 substituents independently selected from (l-4C)alkyl, amino, (l~4C)alkylamino, (l-4C)alkoxy, (l-4C)alkoxycarbonyl and halogen;

R¹⁰ is is a C-linked 5-membered heteroaryl ring containing 2 to 4 heteroatoms independently selected from N, O and S, which ring is optionally substituted on an available carbon atom by 1 or 2 substituents independently selected from (l-4C)alkyl, amino, (l-4C)alkylamino, (1- 4C)alkoxy, (l-4C)alkoxycarbonyl and halogen, and/or on an available nitrogen atom (provided that the ring is not thereby quaternised) by (l-4C)alkyl; or

R¹⁰ is a C-linked 6-membered heteroaryl ring containing 2 or 3 nitrogen heteroatoms, which ring is optionally substituted on any available C atom by 1, 2 or 3 substituents independently selected from (l-4C)alkyl, amino, (l-4C)alkylamino, (l-4C)alkoxy, (l-4C)alkoxycarbonyl and halogen; R¹¹ and R¹² together with the nitrogen atom to which they are attached form a 5-membered heteroaryl ring, containing either (i) 1 to 3 further nitrogen heteroatoms or (ii) a further heteroatom selected from O and S together with an optional further nitrogen heteroatom; which ring is optionally substituted on a C atom by an oxo or thioxo group; and/or the ring is optionally substituted on a C atom by 1 or 2 (l-4C)alkyl groups; and/or on an available nitrogen atom (provided that the ring is not thereby quaternised) by (l-4C)alkyl; or

R¹¹ and R¹² together with the nitrogen atom to which they are attached form a 6-membered heteroaryl ring containing up to three nitrogen heteroatoms in total (including the linking heteroatom), which ring is substituted on a suitable C atom by oxo or thioxo and optionally substituted on any available C atom by 1 or 2 (l-4C)alkyl substituents; R² and R³ are independently hydrogen or fluoro;

R¹⁴ is a bond or a (l-8C)alkyl group which is optionally substituted by one or more hydroxy groups; which process comprises loading said compound or salt thereof, onto a solid support phase material at a loading of at least lOmg/lg solid support phase material, eluting the product with a suitable solvent in the absence of buffer, and recovering product from the eluate.

2. A process according to claim 1 wherein the compound of formula (II) is recovered as a salt of formula (DA)

where R², R³, R⁸ and R¹⁴ are as defined above in relation to formula (TT) and R¹⁷ and R¹⁸ are a pharmaceutically acceptable cation, such as an alkaline metal ion such as sodium or potassium.

3. A process according to any one of the preceding claims wherein the compound is loaded onto the solid support phase material with a loading of from lOmg /lg to 500mg/g stationary phase.

4. A process according to claim 1 or claim 2 wherein the compound is loaded onto the solid support phase material with a loading of less than lOmg/lg of stationary phase.

5. A process according to claims 1 to 4 wherein the compound is loaded on the solid

5 support phase material in the form of a crade product, which is loaded at from O.lg /lg to 5g/g stationary phase.

6. A process according to any one of claims 1 to 4, wherein the compound is loaded on the solid support phase material in the form of a crade product, which is loaded at from 0.02g

10 /lg to O.lg/g stationary phase.

7. A process according to any one of the preceding claims wherein the solid support phase material is suitably packed into a column and has a particle size in the range of from 3μ m -200μm.

15

8. A process according to any one of the preceding claims which is conducted at a pressure of about 40bar.

9. A process according to any one of the preceding claims wherein purification and 20 desalting is effected in a single step using reverse phase chromatography under gradient elution conditions.

10. A process according to any one of the preceding claims wherein R is a group OR .

25 11. A process according to any one of the preceding claims wherein the compound of formula (H) is a compound of formula (IV)

where R², R³, R⁹ and R¹⁴ are as defined in claim 1 and R¹⁷ and R¹⁸ are as defined in claim 2.

12. A process according to any one of the preceding claims wherein R¹⁴ is a direct bond.

13. A process according to any preceding claim wherein the product is recovered from the eluate by concentration using wiped film evaporation or a membrane technique.

14. A process according to claim 1 wherein the compound of formula (II) is recovered as, or converted to, a pharmaceutically acceptable salt of formula (H).