WO2004014841A1

WO2004014841A1 - Compounds, pro-drugs and conjugates derived from mexiletine

Info

Publication number: WO2004014841A1
Application number: PCT/GB2003/003527
Authority: WO
Inventors: Jonathan Clark
Original assignee: Sirus Pharmaceuticals Ltd
Priority date: 2002-08-13
Filing date: 2003-08-13
Publication date: 2004-02-19
Also published as: GB0218827D0; AU2003267543A1

Abstract

The present invention relates to anaesthetics and in particular to metabolites and derivatives of mexiletine such as compounds of formula (I); wherein R1 to R8 are as defined in the specification. It also relates to a prodrugs including polymer conjugates containing them and their use in therapy.

Description

COMPOUNDS , PRO-DRUGS AND CONJUGATES DERIVED FROM MEXILETINE

Field of the invention

The present invention relates to anaesthetics and in particular to metabolites and derivatives of mexiletine. It also relates to pro-drugs and polymer conjugates containing them and their use in therapy. Background to the invention

It is recognised that in some cases when drugs are administered to a patient, metabolites play an important role in the therapeutic profile of the drug. In extreme cases, the parent drug itself has no activity and the therapeutic effect seen is purely from the metabolites.

Within a patient population, the P450 enzymes that typically produce metabolites (e.g. CYP2D6, CYP1A2 and CYP3A4) are known to vary between patients and also, within a single patient, the levels can vary depending on the patient's diet, other administered drugs, and other factors. Mexiletine is currently used in the treatment of chronic pain conditions with varying degrees of success. Mexiletine and derivatives thereof have been described in US 3,954,872, US 3,659,019 and US 4,031,244.

Turgeon et al (1991) J Pharm Exp Therapeut 259(2) 789-798 discloses certain metabolites of mexiletine such as the p-hydroxy and m-hydroxy derivatives however no therapeutic utility is mentioned for these metabolites.

Lu et al (2000) in Chem Abs XP-002240341 and XP-002240342 disclose metabolites of phenoprolamine hydrochoride (and a related derivative) however no therapeutic utility is mentioned for these metabolites.

WO98/32432 (Zeitlin) discloses the use of mexiletine and derivatives thereof (but not hydroxy derivatives thereof) in the treatment of painful neuropathies.

EP 0869119 A1 (Flippin et al) discloses phenoxymethyl piperidine derivatives which are sodium channel blockers for the treatment of neuropathic pain conditions.

We have now invented novel therapies which are especially useful in the treatment of pain. Summary of the invention

The present invention is based on the finding that the useful activity of mexiletine is due to its metabolites and that treatment may be improved by their administration.

In accordance with one aspect of the invention, certain therapeutic agents of the formulae below are novel. According to another aspect of the invention we provide compounds for use in therapy, especially in anaesthesia and treatment of pain e.g. neuropathic pain. According to another aspect of the invention we provide novel conjugates in which the therapeutic agents are derivatised e.g. as an acyl ester pro-drug or are connected to a polymer through an available hydroxyl functional group at R³, R⁴ or R⁵. A targeting agent attached to the polymer may deliver the drug-polymer construct to the intracellular surface of a neurone. In some cases the targeting agent may also enable the axonal transport of the drug complex and release at sites removed from the site of uptake or administration. Summary of the invention

Thus according to a first aspect of the invention we provide compounds of formula (I) for use in therapy:

(I) wherein R¹ and R² are independently selected from hydrogen, halogen, alkyl and alkyl ether; R⁶ and R⁷ are independently selected from hydrogen, hydroxyl, alkyl, aryl and alkylaryl; and R^δis selected from hydrogen, halogen, hydroxyl, alkyl, aryl and alkylaryl, or R⁷ and R⁸ may be joined, typically through a carbon chain, to form a ring 5, 6, 7 or 8 atoms in size, which may contain heteroatoms, and

R³, R⁴ and R^s are each independently selected from hydrogen, hydroxyl, halogen, alkyl, aryl, hydroxyalkyl, hydroxyaryl, aminoalkyl or aminoaryl, with the proviso that at least one of R³, R⁴ and R⁵ is OH; and acyl ester derivatives thereof; and salts thereof. Description of preferred embodiments

As used herein, the term "alkyl" means a straight or branched chain alkyl group of up to 8 carbon atoms. Examples are methyl and ethyl. "Alkyl ether" i.e. alkoxy may be interpreted accordingly. Examples are methoxy and ethoxy. "Alkyl thioether" i.e. alkylthio may also be interpreted accordingly. Examples are methylthio and ethylthio.

"Aryl" means any aromatic group including heteroaromatic groups, e.g. containing up to three heteroatoms selected from N, O and S, monocyclic or bicyclic, having up to 12, e.g. 5 to 10, ring atoms. Examples are thienyl, phenyl and naphthyl. Aryl groups may optionally be substituted e.g. with one or more groups selected from hydroxy, Cι_-4alkyl, halogen and d. alkoxy, but are preferably unsubstituted. A preferred aryl group is phenyl. "Alkylaryl" may also be interpreted accordingly. Examples include methylphenyl. "Aryl ether" i.e. aryloxy may be interpreted accordingly.

Example of hydroxyalkyl that R³, R⁴ and R⁵ may represent include -CH₂OH. Example of hydroxyaryl that R³, R⁴ and R⁵ may represent include hydroxyphenyl.

Example of aminoalkyl that R³, R⁴ and R⁵ may represent include -CH₂NH₂. Example of aminoaryl that R³, R⁴ and R⁵ may represent include aminophenyl. When R⁷ and R⁸ are joined they may be typically represent an alkylene chain of 3-6 methylene groups, or a variant in which one or more (eg one or two especially one) methylene groups are replaced with a heteroatom eg O, NH or S especially O. When R⁷ and R⁸ are joined preferably they represent (CH₂) . "Halogen" means F, Cl, Br or I.

Salts of compounds of formula (I) include acid salts such as HCI, HBr salts. Preferred salts are pharmaceutically acceptable.

Compounds of formula (I) may contain a stereocentre and therefore may exist as enantiomers. The invention embraces compounds of formula (I) in the form of one purified enantiomer or as mixtures thereof e.g. racemic mixtures.

Compound of formula (I) are claimed whether in purified form or not. However when used in therapy it will be preferred to employ the compound of formula (I) in purified form e.g. greater than 99% especially greater than 99.9% purity.

We prefer R¹ to represent alkyl especially Me. We prefer R² to represent alkyl especially Me.

Those R³, R⁴ and R⁵ groups that do not represent OH we prefer to represent H.

We prefer that R^ε represents OH and R³ and R⁴ represent H or, more preferably, R³ and R⁵ represent H and R⁴ represents OH.

We prefer that R⁸ represents alkyl especially Me. We prefer R⁶ to represent H or alkyl, particularly H, Me or Et, most preferably H or Et. In one embodiment we prefer R⁶ to represent H. In another embodiment we prefer R⁶ to represent Et.

We prefer R⁷ to represent H or alkyl, particularly H, Me or Et, most preferably H or Et. In one embodiment we prefer R⁷ to represent H. In another embodiment we prefer R⁷ to represent Et.

Most preferably one of R⁶ and R⁷ represents Et and the other represent H or Et, especially Et. Preferred compounds are defined by the following structures:

These compounds are metabolites of mexiletine whicti hitherto have not been recognised to be pharmacologically active or important in the treatment of pain conditions, particularly chronic pain such as neuropathic pain.

Other preferred compounds are defined by the following structures:

The above listed compounds are new and we claim them per se as an aspect of the invention. More generally we claim novel compounds of general formula (I) with the proviso that the compound is not m-hydroxymexiletine or p-hydroxymexiletine (which were described by Turgeon et al). For the novel compounds of formula (I), when one of R³, R⁴ and R⁵ represents OH, preferably R⁶ and R⁷ do not both represent hydrogen.

The above mentioned compounds may be prepared by processes generally known per se. For example secondary and tertiary amines can be prepared by alkylating primary amines. Hydroxyphenyl derivatives can be derived from the corresponding nitrophenyl derivatives by successive reduction and treatment with nitrite. Nitrophenyl derivatives may be obtained by nitrating the corresponding unnitrated aromatic compound. The corresponding unnitrated aromatic compounds may be prepared for example by reference to methods described in US 3,954,872 (Koppe et al) and US 3,659,019 (Koppe et al). For example the compound may be assembled by reacting a phenol derivative with a compound of formula Hal-CH₂-CHR⁸-NR⁶R⁷ or a protected derivative thereof wherein Hal represents halogen (or other leaving group). Alternatively the order of steps may be reversed e.g. the nitration of the aromatic ring may be performed before the phenol derivative is reacted with the compound of formula Hal-CH₂- CHR⁸-NR⁶R⁷ A feature of the compounds described herein is that they possess an available OH group on the benzene ring which allows the compound to be connected to an acyl group through a covalent bond thereby forming an ester linkage. Such compounds are capable of acting as pro-drugs. Examples of acyl groups include groups COR where R represents alkyl e.g. methyl or ethyl. Other examples include groups CO(CH₂)_nCOOH wherein n represents an integer 1-10 e.g. 2-5 and corresponding groups CO(CH₂)_πCOOR wherein R represents alkyl e.g. methyl or ethyl.

In a particularly preferred embodiment the acyl group is provided by a polymer (P). Thus as a further aspect of the invention we provide a conjugate of a polymer and a compound of formula (I):

(I) wherein R¹ and R² are independently selected from hydrogen, halogen, alkyl and alkyl ether;

R⁶ and R⁷ are independently selected from hydrogen, hydroxyl, alkyl, aryl and alkylaryl; R⁸is selected from hydrogen, halogen, hydroxyl, alkyl, aryl and alkylaryl, or

R⁷ and R⁸ may be joined, typically through a carbon chain, to form a ring 5, 6, 7 or 8 atoms in size, which may contain heteroatoms, and

R³, R⁴ and R⁵ are each independently selected from hydrogen, hydroxyl, halogen, alkyl, aryl, hydroxyalkyl, hydroxyaryl, aminoalkyl or aminoaryl, with the proviso that at least one of R³, R⁴ and R⁵ is a hydroxyl moiety connected to the polymer through a covalent bond.

The polymer can be a natural polymer such as dextran, dextrin, or a synthetic polymer, preferably biodegradable and non-toxic in nature. Preferably the polymer is water soluble.

The drug is connected either directly to the polymer or, more preferably, through a linker. Example linkers include peptides, amino acids, or short carbon chains such as those derived from succinic acid, 6-aminohexanoic acid, 5-aminopentanoic acid, 4-aminobutanoic acid and 3-aminopropanoic acid or other similar linker.

In one embodiment, the polymer is dextran. A number of dextrans are commercially available e.g. where the number of units per polymer is approximately in the range of 50 to 1000. Examples of commercially available dextrans include those in which this number is 61,

185, 430 or 620. The exact value depends on the supplied batch of dextran. These are all preferred values; by choosing different values, different levels of drug can be attached to the polymer.

In another embodiment, the polymer is dextrin. A number of dextrins are commercially available e.g. where the number of units per polymer is approximately in the range of 50 to 1000.

In another embodiment the polymer is derived from a polyethyleneglycol (PEG) e.g. a PEG acid. For example, the PEG may be condensed with a diacid (e.g. succinic acid) to yield a PEG derivative bearing an acyl group (or two acyl groups) to which the drug may be attached. Examples of PEG conjugates according to this invention are:

where "Drug-O" indicates the compound of formula (I), R is hydrogen, alkyl, aryl or alkylaryl and m is an integer of 0 to 1000, preferably 5 to 1000 particularly 10 to 500. Preferably R represents COalkyl e.g. COMe. R may also represent COCH₂CH₂COO-Drug. These and other acyl derivatives formed at the functional atom (the hydroxyl group on the benzene ring of the drug) are examples of conjugates of the present invention acting as pro-drugs. An acyl group may be used that endows the conjugate with desired solubility or other properties, and that can be removed, typically by hydrolysis, either by a biological process or by natural chemical decomposition, to release the free functional group and thus the active principle.

Preferably the compounds will be connected to the polymer by means of a linker. The linker may be formulated to assist in release of the anaesthetic molecule from the conjugate. For example, the anaesthetic molecule may be coupled via an ester bond which is cleaved by esterases such as lipases within the cell so that the anaesthetic molecule is rapidly released from the polymer.

Different rates of release are required depending on the anaesthetic compound being used and the therapeutic purpose.

The linker may be an amino acid. This may endow some enzyme specificity on release of the drug from the complex in addition to release based on chemistry dependent on other bonds being present. The linker can contain several amino acids in sequence (i.e. be a peptide) to confer greater enzymatic selectivity. Examples include amino acid sequences recognised by specific peptidases eg cathepsin.

Particularly preferred conjugates according to the invention are polymers comprising units of formulae (I) and (II):

(0

and

(ID wherein B is selected from oxygen, sulphur, alkyl, alkyl ether, alkyl thioether, hydroxyl alkyl and alkyl aryl; s independently represents 0 or an integer of 1 to 100; m is an integer of 1 to 1000; n is 0 or an integer of 1 to 100; and

A is a functional group and Z is a compound of formula (I) as defined herein, in which Z is connected to A by means of the -OH group that R³, R⁴ or R⁵ may represent.

Polymers of this aspect of the present invention may comprise one or more different monomer units (I) and one or more different monomer units (II). For example the units (I) and (II) may contain different A and B groups.

Conjugates according to this aspect of the invention may be prepared by a process comprises co-polymerising one or more first monomers (I¹):

(!') or an analogue derived from a branched PEG, or an activated derivative thereof; with one or more second monomers (II'):

(II')

The invention also provides co-polymers obtainable by and obtained by said process. Preferably the two carboxylic acid moieties of the diacid monomer (I') are activated. Suitable activating groups will be well known to a skilled person. For example, they may suitably be activated by treatment with N-hydroxysuccinimide.

A polymer of the invention may be prepared by methods that are generally known. A typical example includes the polymerisation of a diacid and a diamine. The diacid shown below, which is illustrative of the type of diacid that may be employed according to this aspect of the invention, may be polymerised with a diamine containing substituents. A typical example of a diamine is lysine. The diacid will typically have a range of values for m, the exact range mixture affecting the physical properties of the polymer produced. In one embodiment of this invention the average molecular weight of the PEG unit is 1500, which corresponds to an average value for m of 34. In other embodiments of this invention the PEG unit can have, but is not limited to, an average molecular weight of 200, 400, 600, 800, 900, 2000, 3000 and 4000 which corresponds to average values of m of 4.5, 9, 13.6, 18, 20.5, 45.5, 68 and 91.

The diacid component used in the polymerisation can be selected from a range of diacids made from different batches of PEG with different average values of m. Additionally, branched PEG can also be used, in this case the amount of diamine used in the polymerisation step is adjusted to take account of the additional acid groups introduced by the additional PEG chains. Branched PEG'S, which are commercially available, are generally prepared by incorporating a cross-linking monomer into the polymerisation mixture. An example of a suitable cross-linking monomer is glycerol.

For example, a simple branched PEG would be of formula ^>

CH₂[(OCH₂CH₂)_mOH]CH[(OCH₂CH₂)_mOH] CH₂[(OCH₂CH₂)_mOH] In one preferred embodiment of this invention the diamine is a derivative of lysine, where the two amines of the lysine become part of the polymer backbone and the acid group of the lysine has been added to a therapeutic entity (or other component), preferably through a linker such as 5-amino valeric acid. There may also be additional elements in the linker between the therapeutic and the polymer chain such as a hemiacetal group, amino acid or peptide.

A typical procedure for the preparation of the polymer of the invention involves prior activation of the diacid component as an acid chloride, acid bromide, acid fluoride, or as an active ester such as a N-hydroxysuccinimide. Alternatively the diacid can be activated in-situ using reagents commonly used for the preparation of amide bonds in peptide synthesis. Further, the polymerisation may be carried out by heating the diacid and diamine components together to dehydrate the material to effect polymerisation. The preferred method for this invention is to activate the diacid prior to use, so that the activated material can be purified and stored for use at a later stage. The preferred activation method is to form the N- hydroxysuccinimide ester from N-hydroxysuccinimide, di-isopropylcarbodiimide and the diacid in dichloromethane. The activated diacid can then be reacted with diamine in the ratio of one diacid to one diamine to provide the polymer of the invention. By controlling the exact ratio of diacid to diamine, different molecular weights can be achieved. It is possible that by limiting the diamine ratio to less than one to one of diacid, that the material will contain cyclic material. The molecular weight can also be controlled by varying the polymerisation conditions, such as temperature, time, concentration and by the addition of components which can stop the polymerisation, such as water, mono-amine, alcohols and alkoxide. As is discussed in more detail later in the specification, by the addition of branching (cross-linking) units, such as a tri- amine, the molecular weight can be increased dramatically. In these cases, the ratio of diacid to diamine must be adjusted to take into account the addition of the branching agent, which in the case of a tri-amine branching unit would reduce the amount of diamine required. The aim in this case is to keep the total amine content (triamine plus diamine) the same as with the diamine alone.

If an excess of activated diacid is used, then the termini of the polymer chains will have activated acid groups at the ends. Alternatively additional activated diacid can be added at the end of the bulk polymerisation to achieve a similar result, generally a polymer with higher molecular weight. The termini can then be reacted with further components, such as cell targeting agents, proteins, peptides, saccharides, polysaccharides or cross linking reagents such as tri-amines.

Preferably the co-polymer contains amine equivalents to acid equivalents in a ratio of 1:1 or (1:1)+1 or (1:1)- 1 to take account of the fact that the termini of the polymer may be formed from the diacid monomer or the diamine monomer or one may be diacid monomer and the other may be diamine monomer. When the monomers are straight chain then this ratio will be the ratio of monomers will be (I') to (II'). However when cross linking components are used (whether acid or amine) then a correction will need to be applied accordingly.

In some cases the polymers are preferably straight-chain. In other cases they are preferably cross linked. The polymer may also be cyclic (in which case the ratio is 1:1). In order to make it more likely that one of the monomers forms the termini then an excess of that monomer can be used. The termini of the polymer may be derivatised (capped) e.g. an acid terminus with an alcohol (to form an ester) or an amine (to form an amide) and/or an amine terminus with an acid (to form an amide).

Advantageously the polymer may be capped with a substance K capable of usefully modifying the properties of the polymer. Example polymer property modifying agents include targeting agents. Such a targeting agent K will be an agent capable of directing or aiding direction of the polymer to the target for the therapeutic agent. Examples of targeting agents include cell adhesion moieties. Such substances can assist with intracellular delivery. Of particular interest in the context of the present invention are targeting agents which can direct the polymer to neuronal cells, for example a neuronal cell adhesion moiety e.g. a sensory nerve adhesion moiety. Particular examples of nerve adhesion moieties include: antibodies and in particular those which have affinity for nerve cell membranes, lectins such as lectins derived from vertebrates, mammals or humans or other lectins such as plant lectins, and in particular wheat germ agglutinin, hormone receptor ligands, cytokines, growth factors, such as nerve growth factor, epidermal growth factor and insulin-related growth factors, neuropeptides such as endorphins, vasoactive intestinal polypeptide, calcitonin, cholceystokinin, substance P, somatostatin, neuropeptide Y, fragments of neurotrophic viruses such as viral coat proteins of herpes simplex virus, polio virus, rabies virus or fragments thereof, bacterial toxins and in particular non-toxic fragments thereof such as cholera toxin B chain and tetanus toxin fragment C, or fragments thereof.

For example if the polymer has at least one acid termini then the termini may be reacted with a substance bearing amine groups e.g. a protein with surface lysine residues. Examples include lectins such a wheat germ agglutinin. It may be necessary to activate the acid termini to facilitate reaction e.g. by reaction with N-hydroxysuccinimide. Peptides as well as proteins may also conveniently be used as capping groups, and may readily be attached when the terminus is an amine or an acid.

Other capping groups of particular interest include saccharides especially mono and disaccharides.

In another embodiment of this aspect of the invention K is an agent capable of enhancing the solubility of the polymer e.g. a polyethylene glycol or a derivative thereof.

Preferably the polymer contains up to 10,000 especially up to 1000 repeats of each unit. Preferably the polymer contains at least 5, more preferably at least 10 repeats of each unit. Most preferably the number of each unit is 10-30 especially 15-20.

The molecule weight of polymer conjugates according to this aspect of the invention will typically be in the range 6kDa to 2000kDa, preferably 15kDa to 250kDa excluding the contribution of the further components conjugated to A or any terminal capping groups. The total molecular weight of the polymer (including further components and capping groups) will typically be in the range 10kDa to 2500kDa, preferably 25kDa to 300kDa. In polymers of this aspect of the invention, examples of [B]s include O and (CH₂)_1-3 e.g. CH₂. However preferably s represents 0. Preferably n represents 1 to 10, more preferably 3- 6 eg 4.

Thus monomer (I') is preferably a compound of formula:

or an analogue derived from a branched PEG, or an activated derivative thereof. Preferably m represents an integer 20-100, especially 30-40.

The preferred activated derivative is a compound of formula:

An alternative activated derivative is a compound of formula: o o ^cl T L °^". o o

Preferably m represents an average integer of 20-100, especially 30-40.

This monomer is particularly favoured since it is capable of degradation to PEG and succinic acid products, which are physiologically benign.

The carboxylic acid groups of monomer (I') are preferably activated. Such monomers can be prepared by treating a polyethylene glycol (PEG) with succinic anhydride under standard conditions. For example the reagents may be mixed in the presence of dimethylaminopyridine (DMAP) in an inert solvent such as dichloromethane (DCM). A suitable PEG is PEG 1500 (average molecular weight 1500) which results in a value m of around 34. PEG'S for use in preparing the copolymers of the invention are commercially available.

The functional group A preferably comprises a carbonyl moiety, i.e. it is derived from a carboxy group, and optional linker J such that a preferred monomer (II') is a compound of the formula:

wherein J is an optional linker and Z is a compound of formula (I) as defined herein wherein J- CO is connected to Z by means of the -OH group that R³, R⁴ or R⁵ may represent.

J therefore represents a linker or a bond but preferably J represents a linker. Preferably n represents an integer of 1 to 10, especially 3 to 6 particularly 4. When J represents a linker it preferably represents the group J¹-J²-J³.

Suitable linkers include amino acids, peptides or a chain such as 6-aminohexanoic acid, 5-aminopentanoic acid, 4-aminobutanoic acid and 3-aminopropanoic acid. 5- Aminopentanoic acid is a particularly preferred linker.

Examples of other linkers that may usefully be used include those described in US 6,214,345.

Additionally, tri-functional groups such as tri-amines can be added to the polymerisation mix to increase cross-linking, e.g. compounds of the formula:

Wherein preferably n represents 1 to 10, more preferably 3-6, especially 4 and p represents 1 to 10, more preferably 3-6 especially 4. Cross linking may have a significant effect on polymer properties which would be understood by those skilled in the art of polymer chemistry. Solubility and molecular weight in particular may be altered. The degree of cross-linking also has an impact on biodegradability which would also be understood by someone skilled in the art of polymer therapeutics and delivery systems. Thus according to a preferred aspect of the invention there is provided a process for preparing a polymer which comprises co-polymerising one or more first monomers (F):

or an analogue derived from branched PEG, or an activated derivative thereof; with one or more second monomers (II")

The invention also provides polymers obtainable and obtained by such a process.

Drug moiety Z contains a free hydroxyl group which allows it to be connected to the diamine via linker J¹-J²-J³ if present. Z may then be released from the polymer by hydrolysis of the ester connection. J¹ preferably represents a sulphur, oxygen or an amino group (e.g. NH or NMe, preferably NH), preferably oxygen or an amino group, especially an amino group. J² preferably represents a spacer group. J³ preferably represents a carbonyl group. This permits Z to be released from the polymer by hydrolysis of the ester connection between J³ and Z. Spacer group J² may represent an alkylene group e.g. a Cι-ι₀alkylene group e.g. - (CH₂)_3-6. The preferred linker J¹-J²-J³ is -NH(CH₂) CO-.

It will be understood that polymers according to the invention may be prepared in which more than one monomer (I') (which monomers may, for example, differ in chain length m) with more than one monomer (IT) (which monomers may, for example, differ in values for n and nature of (I)). Typically monomer (I') comprises a dispersion of chain length m based on the dispersion of the polyethylene glycol from which it is derived.

A preferred diamine monomer has the formula:

For most purposes it will be most suitable to use a single monomer (IT). However a futher aspect of the invention provides the formation of multi-functional polymers in which different functional groups A are incorporated through use of two or more monomers (II').

For example, therapeutic agent Z could be^lifferent for different second monomers (i.e. the polymer would comprise more than one therapeutic agent) if combination therapy were desired.

An advantageous feature of the polymers of the present invention is that synthesis is ready and efficient. As described above, components such as therapeutically active agents, targeting agents and the like may be incorporated into the polymer by incorporating such components into monomer (II'). Alternatively it may be preferred to incorporate a precursor of the component into the monomer, and hence into the polymer, and then convert the precursor to the component after polymerisation. In this connection, precursors include derivatives such as protected derivatives and other chemical intermediates. For example it may be desired or necessary to incorporate the compound of formula (I) into monomer (II') in protected form and to deprotect it after polymerisation has taken place.

During the synthesis of the compounds and polymers of the invention labile functional groups in the intermediate compounds, e.g. hydroxy, carboxy and amino groups, may if desired or necessary, be protected. A comprehensive discussion of the ways in which various labile functional groups may be protected and methods for cleaving the resulting protected derivatives is given in for example Protective Groups in Organic Chemistry, T.W. Greene and P.G.M. Wuts, (Wiley-lnterscience, New York, 2nd edition, 1991). As a further aspect of the invention we provide polymers which incorporate anaesthetic and pain-relieving substances as herein described for use in therapy. We also provide pharmaceutical compositions comprising a polymer incorporating an anaesethetic or pain- relieving substance as hereindescribed together with a pharmaceutically acceptable diluent or carrier. Polymers incorporating anaesthetic substances according to the present invention may be administered in therapy by whatever route of administration and in whatever presentation may be deemed most suitable.

An anaesthetic composition of the invention may comprise a suitable pharmaceutically acceptable carrier or diluent. The preparation of compositions which contain an anaesthetic as active ingredient(s), is known to one skilled in the art. Typically, such anaesthetics are prepared as injectables, either as liquid solutions or suspensions; solid forms suitable for solution or suspension in liquid prior to injection may also be prepared. The preparation may also be emulsified. The active anaesthetic ingredients are often mixed with excipients which are pharmaceutically acceptable and compatible with the active ingredient. Suitable excipients are for example, water, saline, dextrose, glycerol, ethanol, or the like and combinations thereof. In addition, if desired, the anaesthetic composition may contain minor amounts of auxiliary substances such as wetting or emulsifying agents, pH-buffering agents and antibacterial agents (e.g. thimerosal).

Anaesthetic compositions are administered parenterally, by injection, for example subcutaneously, intercostally, intramuscularly, intravenously or by epidural or spinal injection. Alternatively, the compositions may be formulated for topical administration and in particular for administration to a mucosal surface such as oral, rectal, vaginal or nasal administration. Aditionally the anesthetic compositions can be administered orally in tablet form. The compositions may also be delivered intradermally, for example using a needleless injection device.

The compositions are administered in a manner compatible with the dosage required and in such amount as will be therapeutically or prophylactically effective. The quantity to be administered, which is generally in the range 5pg/kg to 10g/kg, preferably 250μg/kg to 30mg/kg per dose depends on a number of factors. These include the subject to be treated, and the degree of therapeutic or prophylactic activity desired and, if applicable, the size of the area to be treated Precise amounts of active ingredient required to be administered may depend on the judgment of the practitioner and may be peculiar to each subject. Depending on the therapeutic substance and the condition being treated, compositions of the present invention may also potentially be administered by the ocular, intraocular, intrathecal and intraarticular routes.

Further aspects of the invention include the use of polymers incorporating compounds according to the invention in the manufacture of a medicament for anaesthesia or the treatment of a pain, e.g. neuropathic pain and a method of anaesthesia or treatment of pain, e.g. neuropathic pain which comprises administering to a patient a polymer incorporating an anaesthetic agent according to the invention.

Certain monomers described above are new and these form an aspect of the invention.

The compounds, compositions and conjugates of the invention have the advantage they may be more bioavailable, more water or plasma soluble, more orally active, may have longer duration of action, may effect more complete drug release, may more rapidly release drug, may be more biodegradable, may be more benign or otherwise less toxic, are susceptible to more ready or economic synthesis or have other advantages over prior art compounds and compositions. All documents referred to herein, including patents and patent applications, are incorporated herein in their entirety by reference.

Further details and embodiments concerning polymers conjugates containing compounds according to the present invention may be obtained from a co-pending patent application in the name of the same inventors and filed on the same day entitled "Biodegradable Polymers" which is herein incorporated in its entirely by reference.

Abbeviations:

WGA Wheat Germ Agglutinin DCM dichloromethane

DIG Diisopropylcarbodiimide CBZ benzyloxycarbonyl

NHS N-hydroxy-succinimide NMM N-methyl morpholine Boc t-butyloxycarbonyl DMF dimethyl ormamTde DMAP dimethylaminopyridine Ac acetyl-

PEG polyethyleneglycol Me methyl Et ethyl

Su NHS active ester TFA trifluoroacetic acid Sue succinyl

GPC Gel permeation chromatography

The invention will now be illustrated by reference to the following examples: Examples

Processes

Processes for preparing certain preferred conjugates according to this invention are illustrated bv reference to the following flow chart:

Polymer

Example 1

Synthesis of hvdroxy-N.N-diethyl mexiletine

Example 2

Conjugate of polymer with 4-hvdroxy-N,N-diethylmexiletine

(a) Preparation of N.N-diethyl mexiletine Mexiletine monohydrochloride (0.3g, 1.4 mmol) was dissolved in AcOH (18 mL) and the solution was^~heated at 55°C. Sodium borohydride (1-.3g, 34-mmol) was added-in small portions. The reaction was heated at 55°C for three days then cooled and poured into ice.

The pH was adjusted to 12 and the aqueous layer was extracted with DCM. Combined organic extracts were washed with brine, dried over MgSO and concentrated. Purification by normal phase chromatography yielded the product (0.2g, 62%).

(b. Nitration of N.N-diethyl mexiletine

N,N-Diethyl mexiletine (0.2g, 0.85 mmol) was dissolved in a cooled solution of water (1 mL) and concentrated sulphuric acid (3.6 mL). The resulting solution was cooled to 0°C and a solution of 1M nitric acid (0.85 mL, 0.85 mmol) was added drop wise. The cooled reaction mixture was stirred for 1h then poured into ice. The pH was adjusted to 12 and the aqueous layer was extracted with DCM. Combined organic extracts were washed with brine, dried over MgSO₄ and concentrated. Purification by normal phase chromatography yielded the product (0.19g, 80%).

(c) Hvdrogenation of nitrated N.N-diethyl mexiletine 5% Pd/C (20 mg) was suspended in EtOH (0.5 mL) under nitrogen. The nitro compound (0.17g, 0.63 mmol) prepared above was added as a solution in EtOH (1.5 mL). The resulting reaction mixture was flushed with hydrogen, stirred overnight then filtered through celite. The filtrate was concentrated then purified by normal phase chromatography to afford the product (0.11g, 70%). (d) Preparation of 4-hydroxy-N,N-diethyl mexiletine

The aniline prepared above (95 mg, 0.38 mmol) was dissolved in a cooled solution of water (1.7 mL) and 2M sulphuric acid (0.5 mL). The resulting solution was cooled to 0°C and sodium nitrite (30mg, 0.42 mmol) was added slowly as a cooled solution in water (0.7 mL). The resulting solution was allowed to warm up to room temperature and stirred for three days. After cooling, the pH was adjusted to 7-8 and the aqueous layer was extracted with EtOAc. Combined organic extracts were washed with brine, dried over MgSO₄ and concentrated. Purification by normal phase chromatography yielded the product. (e. Preparation of polv(ethylene glvcol)-bis succinic acid

Polyethylene glycol (Mw = 1500, 119 g), succinic anhydride (24.0 g, 237.6 mmol, 3.0 eq) and DMAP (1.0 g, 8.20 mmol, 0.1 eq) were dissolved in DCM (300 mL). The solution was then heated to reflux and left at reflux for 48h. The precipitate that formed was then filtered off and the filtrate concentrated to give a white solid, the crude diacid product. Purification via precipitation and reverse phase chromatography yielded the PEG diacid compound. (f) Preparation of N-hydroxysuccinimide activated bis (succinic acid) polyethylene glycol) ester The bis (succinic acid) polyethylene glycol) ester (1.3 g), DIC (362 μL,3 eq), DMAP (1 mg, 0.01 eq) and N-hydroxysuccinimide (266 mg, 3.0 eq) were dissolved in dry DCM (10 mL) and stirred overnight. The reaction was then concentrated down and acetonitrile added. The solution was filtered, concentrated and precipitated to yield bis (succinic acid N- hydroxysuccinimide ester) poly(ethylene glycol) ester. (a) Preparation of Boc-lvsine(Boc)-5-aminovaleric acid

5-Aminovaleric acid monohydrochloride (693 mg, 4.5 mmol, 1.0 eq) was dissolved in water (15 mL) and MeCN (10 mL). Sodium carbonate (478 mg, 4.5 mmol, 1.0 eq) was added as a solution in water (5 mL), followed by Boc-Lys(Boc)OSu (2.0 g, 4.5 mmol, 1.0 eq) as a solution in MeCN (20 mL). The reaction was then left to stir overnight. The reaction mixture was concentrated and water added before being extracted with ethyl acetate (3 x 50 mL). The combined organic layers were then washed with 0.01 N HCI (2 x 50 mL), brine, dried over MgSO and concentrated. Purification by normal phase chromatography yielded the product (1.6g, 80%). (h Boc-lysine (Boc)-5-aminovaleric acid coupling to 4-hydroxy-N,N-diethyl mexiletine ester Boc-Lys(Boc)-5-aminovaleric acid (3.66 mmol) was dissolved in dry DCM (16 mL). To this was added DIC (573 μL, 3.66 mmol, 1.0 eq) and DMAP (58 mg, 0.48 mmol, 0.13 eq). The now cloudy solution was left to stir for 15 min. Hydroxy-N,N-diethyl mexiletine ester (4.03 5 mmol, 1.1 eq) was added as a solution in DCM. This was then left to stir overnight. The solvent was evaporated, the residue dissolved in ethyl acetate and washed with water. The organic layer was then washed with a weak base solution, dried and evaporated to dryness.

Purfication via reverse phase chromoatography yielded the product (pale yellow solid, 75%).

(0 Deprotection of BocLys(BocH5-aminovalerate)-4-hydroxy-N,N-diethyl mexiletine ester 10 The BocLys(Boc)-(5-amiovalerate)-hydroxy-N,N-diethyl mexiletine ester (0.29 mmol) was dissolved in TFA:water (95:5, 10 mL) and stirred at room temperature for 30 min. The solvents were evaporated, the residue taken up in water (15 mL) and freeze dried to give the deprotected material.

(i) Polymerisation of Lvs-(5-aminovalerate)-4-hydroxy-N,N-diethyl mexiletine ester with bis 15 (succinic acid N-hydroxysuccinimide ester) poly(ethylene glycol) ester

The Lys-(5-aminovalerate)-4-hydroxy-N,N-diethyl mexiletine ester (0.15 mmol) and bis

(succinic acid N-hydroxysuccinimide ester) poly(ethylene glycol) ester (0.28g, 0.15 mmol) were dissolved in DMF (400 μL) and treated with NMM (64 μL, 0.58 mmol). The oil was left to stand overnight, then precipitated from ether. The resulting polymer was dried on high vac line for 20 30 min.

Example 3

For syntheses described herein it may be advantageous to employ a cross-linking agent.

Example of the synthesis of a crosslinking agent. 25 Preparation of Boc-Lvs(Boc,-CONH-butyl-NHBoc

N-Boc-1,4-diaminobutane monohydrochloride (430 mg, 2.25 mmol, 1.0 eq) was dissolved in water (15 mL) and MeCN (10mL). Sodium carbonate (120 mg, 1.12 mmol, 0.5 eq) was added as a solution in water (5 mL), followed by Boc-Lys(Boc)OSu (1.0 g, 2.25 mmol, 1.0 eq) as a solution in MeCN (20 mL). The reaction was then left to stir overnight. The reaction 30 mixture was concentrated and water added before being extracted with DCM (3 x 50 mL). The combined organic layers were then washed with 0.01 N HCI (2 x 50 mL), brine, dried over

MgSO and concentrated. Purification by normal phase chromatography yielded the product

(white foam, 1.0 g, 86%).

Deprotection of Boc-Lvs(BocVbutyl-NHBoc 35 The conjugate (0.29mmol) was dissolved in TFA:water (95:5, 10 mL) and stirred at room temperature for 30 min. The solvents were evaporated, the residue taken up in water

(15 mL) and freeze dried to give the deprotected material.

Claims

1. A compound of formula (I)

(I) wherein R¹ and R² are independently selected from hydrogen, halogen, alkyl and alkyl ether; R⁶ and R⁷ are independently selected from hydrogen, hydroxyl, alkyl, aryl and alkylaryl; and

R⁸is selected from hydrogen, halogen, hydroxyl, alkyl, aryl and alkylaryl, or

R³, R⁴ and R⁵ are each independently selected from hydrogen, hydroxyl, halogen, alkyl, aryl, hydroxyalkyl, hydroxyaryl, aminoalkyl or aminoaryl, with the proviso that at least one of R³, R⁴ and R⁵ is OH; or an acyl ester derivative thereof; or a salt thereof; for use in therapy. 2. A compound of formula (I)

(I) wherein R¹ and R² are independently selected from hydrogen, halogen, alkyl and alkyl ether; R⁶ and R⁷-are independently selected from hydrogen, hydroxyl, alkyl, aryl and. alkylaryl; and R⁸is selected from hydrogen, halogen, hydroxyl, alkyl, aryl and alkylaryl, or R⁷ and R⁸ may be joined, typically through a carbon chain, to form a ring 5, 6, 7 or 8 atoms in size, which may contain heteroatoms, and

R³, R⁴ and R⁵ are each independently selected from hydrogen, hydroxyl, halogen, alkyl, aryl, hydroxyalkyl, hydroxyaryl, aminoalkyl or aminoaryl, with the proviso that at least one of R³, R⁴ and R⁵ is OH; or an acyl ester derivative thereof; or a salt thereof and with the proviso that the compound is not p-hydroxymexiletine or m-hydroxymexiletine.

3. A compound according to claim 1 or claim 2 which is not an acyl ester derivative.

4. A compound according to claim 1 or claim 2 which is an acyl ester derivative formed with a polymer.

5. A compound according to any one of claims 1 to 4 wherein R¹ represents Me. 5 6. A compound according to any one of claims 1 to 5 wherein R² represents Me

7. A compound according to any one of claims 1 to 6 wherein R³ represents hydrogen.

8. A compound according to any one of claims 1 to 7 wherein R⁵ represents OH and R⁴ represents H or R⁴ represents OH and R⁵ represents H.

9. A compound according to any one of the preceding claims wherein R⁸ represents Me. 10 10. A compound according to any one of the preceding claims wherein R⁶ represents H,

Me or Et.

11. A compound according to claim 10 wherein R^s represents Et.

12. A compound according to any one of the preceding claims wherein R⁷ represents H, Me or Et.

15 13. A compound according to claim 12 wherein R⁷ represents Et.

14. A compound according to claim 2 selected from the following group:

15. A compound according to any one of claims 12 to 14 for use in therapy.

16. A pharmaceutical composition comprising a compound as defined in any one of claims 1 to 14 together with a pharmaceutically acceptable diluent or carrier.

17. A method of treatment or prophylaxis of pain which comprises administering to a 35 patient a compound as defined in any one of claims 1 to 14.

18. Use of a compound as defined in any one of claims 1 to 14 in the manufacture of ε medicament for the treatment or prophylaxis of pain.

19. Use of a compound as defined in any one of claims 1 to 14 in the treatment or prophylaxis of pain.

20. A conjugate of a compound as defined in any one of claims 1 to 14 with a polymer wherein the compound is covalently joined to the polymer by means of the hydroxyl moiety that

5 R³, R⁴ or R⁵ may represent.

21. A conjugate according to claim 20 wherein the polymer is a dextran or a dextrin.

22. A conjugate according to claim 20 wherein the polymer is a polyethyleneglycol.

23. A conjugate according to any one of claims 20 to 22 wherein the compound is connected to the polymer by means of a linking group.

10 24. A conjugate according to claim 23 wherein the linking group is an amino acid, a peptide or the residue from succinic acid, 6-aminohexanoic acid, 5-aminopentanoic acid, 4- aminobutanoic acid or 3-aminopropanoic acid.

25. A conjugate according to any of claims 20, 23 and 24 wherein the polymer is composed of units of the following formulae (I) and (II):

15 (I)

and

(II) wherein B is is selected from oxygen, sulphur, alkyl, alkyl ether, alkyl thioether, hydroxyl alkyl

20 and alkyl aryl; s independently represents 0 or an integer of 1 to 100; m is O dr an Integer of T to 1000; n is 0 or an integer of 1 to 100; and

A is a functional group and Z is a compound of formula (I) as defined herein, in which Z is 25 connected to A by means of the hydroxyl moiety that R³, R⁴ or R⁵ may represent.

26. A conjugate according to claim 25 wherein the polymer contains at least 5 repeats of each unit.

27. A conjugate according to claim 25 or 26 wherein the polymer contains up to 10,000 repeats of each unit.

30 28. A conjugate according to any one of claims 25 to 27 wherein s represents 0.

29. A conjugate according to any one of claims 25 to 28 wherein m represents an integer 20 to 100.

30. A conjugate according to any one of claims 25 to 29 wherein n represents an integer 1 to 10. 31. A conjugate according to claim 30 wherein n represents 4.

32. A conjugate according to any one of claims 20 to 31 wherein the anaesthetic agent is connected to the polymer by means of a linker.

33. A process for preparing a conjugate according to any one of claims 20 to 32 which comprises reacting a polymer optionally incorporating a linker or an activated and/or protected derivative thereof with an amine of formula:

(0 wherein R¹ and R² are independently selected from hydrogen, halogen, alkyl and alkyl ether groups;

R⁶ and R⁷ are independently selected from hydrogen, hydroxyl, alkyl, aryl and alkylaryl groups; and

R⁸ is selected from hydrogen, halogen, hydroxyl, alkyl, aryl and alkylaryl, or

R³, R⁴ and R^s are each independently selected from hydrogen, hydroxyl, halogen, alkyl, aryl, hydroxyalkyl, hydroxyaryl, aminoalkyl or aminoaryl, with the proviso that at least one of R³, R⁴ and R⁵ is OH; optionally connected to a linker or an activated and/or protected derivative thereof such that The amine is connected to the polymer by means of the -OH group that R³, R⁴ or R⁵ may represent.

34. A process for preparing a conjugate according to any one of claims 25 to 32 which comprises co-polymerising one or more first monomers (I')

0'. or an analogue derived from branched PEG, or an activated derivative thereof; with one or more second monomers (II')

(II') 35. A process according to claim 34 wherein one or more monomers (I') is a monomer of formula:

or an analogue derived from branched PEG, or an activated derivative thereof

36. A process according to claim 34 or 35 wherein one or more monomers (II') is a monomer of formula:

wherein J is an optionally linker and Z is a compound of formula (I) or an activated derivative thereof.

37. A process according to claim 36 wherein one or more monomers (II') is a monomer of

formula: wherein J¹-J²-J³ represents a linker group.

38. A process according to claim 37 wherein J¹ represents sulphur, oxygen or an amino group.

39. A process according to claim 37 or 38 wherein J¹ represents an amino group.

40. A process according to any of claims 37 to 39 wherein J² represents a spacer group.

41. A process according to claim 40 wherein J² represents an alkylene group.

42. A process according to any one of claims 37 to 41 wherein J³ represents a carbonyl group.

5 43. A process according to any one of claims 34 to A2 wherein the polymerisation mix includes a cross-linking amine monomer.

44. A process according to claim 43 wherein the cross-linking amine monomer has the formula:

wherein n represents an integer 1 to 10 and p represents an integer 1 to 10. 10 45. A conjugate obtainable by the process of any one of claims 33 to 44. A6. A conjugate obtained by the process of any one of claims 33 to 44.

47. A conjugate according to any one of claims 20 to 32, 45 or 46 wherein one or both ends of the polymer are capped with a polymer property modifying agent.

48. A conjugate according to claim 47 wherein the polymer property modifying agent is a 15 targeting agent.

49. A pharmaceutical composition comprising a conjugate according to any one of claims 20 to 32 or 45 to 48 together with a pharmaceutically acceptable diluent or carrier.

50. A conjugate according to any one of claims 20 to 32 or 45 to 48 for use in therapy.

51. Use of a conjugate according to any one of claims 20 to 32 or 45 to 48 in the 20 manufacture of a medicament for the treatment or prevention of pain.

52. Use of a conjugate according to any one of claims 20 to 32 or 45 to 48 in the treatment or prevention of pain.

53. A method of treating or preventing pain which comprises administering to a patient an effective a^"mouhf of a^" conjugate according to any one of claims 20 to 32 or 45 to 48.

25 54. A compound of formula

wherein Z represents a compound of formula (I) as defined in any one of claims 1 to 14 and A represents a functional group in which A is connected to Z by means of the -OH group that R³, R⁴ or R⁵ may represent.

55. A compound of formula

wherein Z represents a compound of formula (I) as defined in any one of claims 1 to 14, J is an optional linker, and Z is connected to J-CO by means of the -OH group that R³, R⁴ or R⁵ may 5 represent.

56. A compound of formula

wherein n represents an integer 1 to 10; J¹ represents sulphur, oxygen or amino; 10 J² represents a spacer group; J³ represents carbonyl; and Z represents a compound of according to any one of claims 1 to 14.

57. A compound according to any one of claims 54 to 56 wherein n represents 4.

58. A compound according to claim 56 or claim 57 wherein J¹ represents amino. 15 59. A compound according to any one of claims 56 to 58 wherein J² represents (CH₂)_: 3-6

60. A compound of formula:

20 61. A polymer conjugate incorporating a compound of formula (I) as defined in claim 1 substantially as described by reference to the examples.