WO2002040494A1

WO2002040494A1 - Ruthenium-aryl-compounds in cancer therapy

Info

Publication number: WO2002040494A1
Application number: PCT/GB2001/005047
Authority: WO
Inventors: Paul Dyson
Original assignee: University of York
Current assignee: University of York
Priority date: 2000-11-17
Filing date: 2001-11-16
Publication date: 2002-05-23
Anticipated expiration: 2003-05-17
Also published as: AU2002215111A1; GB0028025D0

Abstract

There is described a compound of general formula (I), or a salt thereof, in which R1 is an arene group; R2, R3 and R4, which may be the same or different, are each alkyl C1 to 6, aryl or substituted aryl, or R2, R3 and R4 may together with the phosphorous atom form a cycloalkyl group, such group being optionally heterocyclic; Y is a halogen, SCN or is a group R5R6R7P-, in which R5, R6 and R7, which may be the same or different, are each alkyl C1 to 6, aryl or substituted aryl, or R5, R6 and R7 may together with the phosphorous atom form a cycloalkyl group, such group being optionally heterocyclic; and X1 is a halogen or SCN, and a dimer thereof.

Description

COMPOUNDS

This invention relates to novel compounds, compositions containing such compounds and methods of treatment using such compounds.

European Patent Application No 0471 709 describes a ruthenium-based drug NAMI- A (see Figure 2). NAMI-A has proved particularly useful against tumour metastases and has low general toxicity, which is thought to be a property of the ruthenium centre. This is thought to be because ruthenium can mimic iron in binding to biological molecules, including serum transferrin. Accordingly, the body is well equipped to transport ruthenium based compounds in a non-toxic form and delivers the drug to cells based on their iron requirement. Furthermore, rapidly dividing cancer cells have a higher iron requirement compared to healthy cells.

However, there have been formulation problems with cancer drugs in general including NAMI-A, mainly due to poor solubility and/or stability properties. For example- NAMI-A was originally made as a sodium salt (NAMI) but poor solubility prevented entry into the clinic. Solubility problems were overcome by preparing the drug as the more complex imidazolium salt (NAMI-A).

In contrast, we have now found a novel group of compounds which have good solubility and stability properties and appears to meet formulation criteria or which otherwise possess advantageous properties over prior art compounds such as NAMI- A.

The RAPTA compounds [Ru(arene)ligand_xpta_y], are of particular interest due to the properties of the pta (l,3,5-triaza-7-phosphatricyclo[3.3.1.1]decane) phosphine. Pta is very stable phosphine the protonation state of which influences its solubility properties; the uncharged species is able to diffuse across the cell membrane, allowing free passage throughout the body, where as the charged species is only soluble in aqueous solution and therefore can be trapped in cells. The pK_a for protonation is within the physiological range, specifically in healthy cells the pta ligand will carry no charge, but where the_. pH _. is reduced„due. to the accelerated metabolism of cancer cells the pta group will become charged, essentially trapping it in these cell types.

Thus according to the invention we provide a compound of the^* general formula I, or a salt thereof :

I

in which Ri is an arene group;

R₂, R₃ and R , which may be the same or different, are each alkyl CI to 6, aryl or substituted aryl, or R , R₃ and R₄ may together with the phosphorous atom form a cycloalkyl group, such group being optionally heterocyclic;

Y is a halogen, SCN or is a group R₅R₆R₇P-, in which R₅, R₆ and R₇, which may be the same or different, are each alkyl CI to^' 6, aryl or substituted aryl, or R₅, R₆ and R₇ may together with the phosphorous atom form a cycloalkyl group, such group being optionally heterocyclic; and

Xi is a halogen or is SCN, and di ers thereof.

The arene group j, may be optionally substituted or unsubstituted. Therefore i is Dreferentially a compound of formula II:

in which R₈, R , Rι₀, Rn, Rι₂ and R₁₃, which may be the same or different, are each hydrogen or alkyl CI to 6.

An arene group which may be mentioned is one in which at least one of R₈, R₉, Rio, Rn, Rι₂ and Rι₃, is methyl. A further arene group which may be mentioned is one in which at least one of R₈, R₉, R₁₀, Rn, Rι₂ and Rι₃ is isopropyl. Specific examples of arene groups include benzene, hexamethylbenzene, toluene and cymene e.g. p- cymene. One specific arene which may be mentioned is -cymene.

R₂, R and j preferentially together with the phosphorous atom form a heterocyclic group. In such a heterocyclic group heteroatoms other than phosphorous may be present. Such other heteratoms are preferably nitrogen and one, two or three nitrogen atoms may be present depending upon the desired nature of the grouping. When one of the R₂, R₃ and i is a substituted aryl group, the substituent may be a sulphonate group. In one embodiment, each of R₂, R₃ and R₄ is a sulphonated aryl group, e.g. a 3-sulphophenyl group, or a salt thereof. The most preferred grouping is such that the moiety R₂R₃R_tP- represents a 1,3,5- triaza-7-phosphaadamantane group.

When Y is a halogen it may be the same or different to Xi. Thus Y may be chlorine, fluorine, bromine or iodine. In a preferred embodiment Y is chlorine. When Y is a group R₅R₆R₇P-, the moiety R₅, R₆ and R₇ preferentially together with the phosphorous atom form a heterocyclic group. In such a heterocyclic group heteroatoms other than phosphorous may be present. Such other heteroatoms are preferably nitrogen and one, two or three nitrogen atoms may be present depending upon the desired nature of the grouping. When one of the R₅, Re and R is a substituted aryl group, the substituent may be a sulphonate group. In one embodiment, each of R₅, Re and R₇ is a sulphonated aryl group, e.g. a 3-sulphophenyl group, or a salt thereof. The most preferred grouping is such that the moiety

RsRβ zP- represents a 1,-3,5- triaza-7-phosphaadamantane group. Xi may be chlorine, fluorine, bromine or iodine. In a preferred embodiment Xi is chlorine.

A particular group of compounds which may be mentioned are compounds of the general formula I as hereinbefore described, or a salt thereof, in which R is an arene group;

R , R and R , which may be the same or different, are each alkyl CI to 6, aryl or substituted aryl, or R , R₃ and R₄ may together with the phosphorous atom form a cycloalkyl group, such group being optionally heterocyclic; Y is a halogen or is a group R₅R₆R₇P-, in which R₅, R₆ and R₇, which may be the same or different, are each alkyl CI to 6, aryl or substituted aryl, or R₅, R₆ and R₇ may together with the phosphorous atom form a cycloalkyl group, such group being optionally heterocyclic; and Xi is a halogen.

Salts of the compounds of the invention may comprise any conventionally known anionic salts. Such salts include, but are not limited to chloride, bromide, sulphate, phosphate, maleate, tartrate, citrate, benzoate, 4-methoxybenzoate, 2- or 4- hydroxybenzoate, 4-chlorobenzoate, p-toluensulphonate, methanesulphonate, ascorbate, salicylate, acetate, fumarate, succinate, lactate, glutarate, gluconate, oleate and fluoroborate. When one of R₂, R₃, _t, R₅, R₆ and R is a sulphonated aryl group, the sulphonated aryl group may be present as an alkali metal salt, e.g. a sodium or potassium salt.

Thus a preferred group of compounds of the invention is a compound as hereinbefore described characterised in that the compound is selected from the group; benzene-ruthenium (U) - 1, 3, 5 - triaza - 7 - phosphaadamantane dichloride

(RAPTA-B); hexamethylbenzene-ruthenium (S) - 1, 3, 5 - triaza - 7 - phosphaadamantane dichloride (RAPTA-H); toluene-ruthenium (II) - 1, 3, 5 - triaza - 7 - phosphaadamantane dichloride (RAPTA-

T); -cymene-rathenium (IT) - 1, 3, 5 - triaza - 7 - phosphaadamantane dichloride (RAPTA-C); ^-cymene-ruthenium (IT) - 1, 3, 5 - triaza - 7 - phosphaadamantane dibromide (RAPTA-CBr₂);

^-cymene-ruthenium (H) - 1, 3, 5 - triaza - 7 - phosphaadamantane chloride fluoroborate;

^-cymene-ruthenium (IT) - triphenylphosphine -3,3 ',3^" - trisulphonic acid dichloride trisodium salt; p-cymene-ruthenium (H) - 1,3,5-triaza - 7 - phosphaadamantane diodide;

p-cymene - ruthenium (E-) - 1,3,5 - triaza - 7- phosphaadamantane dithiocyanate;

p-cymene- ruthenium (H) - 1,3,5 - triaza - 7 - phosphaadamantane dichloride dimer;

P-cymene-ruthenium (II) - 1,3,5 - triaza - 7 - phosphaadamantane dibromide dimer;

hexamethylbenzene - ruthenium (H) - 1 ,3 ,5 - triaza - 7 - phosphaadamantane dichloride dimer; and benzene - ruthenium (II) - 1,3,5 - triaza - 7 - phosphaadamantane dichloride.

Thus a further group of compounds of the invention which may be mentioned is one in which the compound is selected from the group; benzene-ruthenium (II) - 1, 3, 5 - triaza - 7 - phosphaadamantane dichloride

(RAPTA-B); hexamethylbenzene-ruthenium (II) - 1, 3, 5 - triaza - 7 - phosphaadamantane dichloride (RAPTA-H); toluene-ruthenium (II) - 1, 3, 5 - triaza - 7 - phosphaadamantane dichloride (RAPTA-

T); >-cymene-ruthenium (E) - 1, 3, 5 - triaza - 7 - phosphaadamantane dichloride (RAPTA-C); _/ -cγmene-ruthenium (TJ) - 1, 3, 5 - triaza - 7 - phosphaadamantane dibromide (RAPTA-CBr₂); j?-cymene-ruthenium (H) - 1, 3, 5 - triaza - 7 - phosphaadamantane chloride fluoroborate, and »-cymene-rutheriium (H) - triphenylphosphine -3,3 ',3 - trisulphonic acid dichloride trisodium salt.

One preferred compound which may be mentioned is _/ -cymene-ruthemum QJ) - 1, 3, 5 - triaza - 7 - phosphaadamantane dichloride.

-According to a further feature of the invention we provide a process for the preparation of a compound of formula I which comprises reacting a compound of formula HI with l,3,5-triaza-7-adamantane (PTA);

in which Ri, Y and Xi are as defined above;

with a compound of formula R R₃R P-, in which R , R andR are as defined above.

The compound of formula IE in which Xi and Y are both chlorine and Ri is p- cymene is commercially available in the UK from Aldrich Chemical Company. PTA is also commercially available in the UK from Aldrich Chemical Company.

Alternatively, the compound of formula IH in which Xi and Y are both chlorine and may be synthesised by reaction of ruthenium (UT) halide with an appropriate dihydroarene, such as cc-terpinene to give p-c msne, in an alcohol medium, e.g. an alkanol such as methanol. PTA may be synthesised by reacting tetrakis(hydroxmethyl)phosphonium chloride with hexamethyltetraamine, optionally in the presence of an alkali, such as sodium hydroxide.

The salts of the compounds of formula I may be prepared, for example, by reacting a compound of formula I in which Y and Xi are both halide with an appropriate anion. The anion may be in the form of a salt, for example, silver tetrafluoroborate. The reaction may optionally be carried out in the presence of PTA.

When Y and Xi are different, the compounds of formula I may exhibit chirality. In such a case the racemic mixture of such chiral molecules is most likely to be formed.

The compounds of the invention have been shown to bind to DNA, and proteins. The main activity of NAMI-A is believed to involve protein interactions, resulting in the thickening of the capsule surrounding the tumour, reducing blood flow and containing cells. Ruthenium based compounds have also been shown to bind to the Ca²⁺ channels of the mitochondria and are used as histochemical dyes (Ru Red). Full biological characterisation of the RAPTA series is ongoing, but we have shown these compounds can bind serum transferrin, cause DNA damage and induce apoptosis in SK-N-SH neuroblastoma cell lines (Figure 8).

Thus the compounds of the invention are especially suited for the treatment and/or alleviation of various disorders, characterised by accelerated cell growth including and especially cancer. Thus the compounds of the invention are active against metastatic cell lines.

The compounds of the invention are advantageous in that, inter alia, they have good solubility and stability properties and appear to meet formulation criteria better than prior art compounds. For example, RAPTA-C is highly soluble in water, PBS and polar organic solvents. In the solid forms, RAPTA-C is stable in both light and dark conditions for a number of weeks, giving the ideal properties for a tablet form drug. In neutral water at room temperature, in the absence of light, RAPTA-C is stable for about nine days. In light this is reduced to just under two days (see Figure 5).

According to a further feature of the invention we provide a pharmaceutical formulation comprising a compound of formula I in admixture with a pharmaceutically acceptable adjuvant, diluent or carrier.

Such a composition may be administered by any conventional means, for example, by inj ection or infusion or enterally.

Thus according to a yet further feature of the invention we provide a method of treating cancer which comprises administering a compound of formula I to a patient suffering from such a disorder.

We further provide the use of a compound of formula I in the manufacture of a medicament e.g. for use in the treatment of cancer.

The invention will now be described by way of example only in which Figure 2 is the structure of a compound of the prior art, NAMI-A;

Figure 5 is the UN spectra showing the stability of RAPTA-C in water at room temperature;

Figure 6 shows DΝA damage induced by a series of metal compounds: Lane 1, Phage λ Hind HI digest;

Lane 2, RuACETO-B;

Lane 3, RuACETO-C;

Lane 4, RAPTA-B;

Lane 5, RAPTA-C Lane 6, PTA alone

Lane 7, DΝA alone. Figure 7 is the structure of the acetonitrile analogue of RAPTA-C (RuACETO-C) (which reacts immediately with water);

Figure 8 plates showing cell studies on the induction of apoptosis in SK-N-SH cells. Figure 9 shows the results of gel shift assay to detect the pH dependent DNA damage induced by incubation with RAPTA-C; and

Figure 10 shows the results of a gel shift assay showing the effect of pH on DNA binding of various compounds, in which Lane 1 is control pH 7.5; Lane 2, Ex. 1 at pH 7.5; Lane 3, Ex 1 at pH 6.5; Lane 4, Ex 2 at pH 7.5; Lane 5, Ex 1 at pH 6.5; Lane 6, control at pH 6.5; Lane 7, pta at pH 6.5; Lane 8, Ex 6c at pH 6.5; Lane 9, Ex 6e at pH 6.5.

Example 1

Synthesis of />-cymene-ruthenium (II) - 1, 3, 5 - triaza - 7 - phosphaadamantane dichloride (RAPTA-C)

(i) [Rw(/?-cymene)Cl₂]₂ was prepared in a single step in quantitative yield by reacting RuCl with α-terpinene in refluxing methanol.

(ii) 1, 3, 5 - triaza - 7 - phosphaadamantane (PTA) was obtained in 86% yield from a reaction between tetrakis(hydroxymethyl)phosphonium chloride, sodium hydroxide, formaldehyde and hexamethylenetetraamine in water.

(iii) [R«(p-cymene)Cl₂]₂ and 2 equivalents of PTA were heated to reflux in methanol for 3 hours. The reaction mixture was allowed to cool to room temperature, filtered, and then the solvent was removed under vacuum. The orange product was then dried for a further 2 hours under high vacuum. No further purification was required.

Spectroscopic data: ESMS - m/z 428 [Ru(η⁶-C₆H₄MeCHMe₂)(PTA)Cl₂]⁺; ³¹P-{1H} NMR (CDC1₃) δ -36.24 (s); 1H NMR (CDCI3) δ 5.46 (q, J = 19.73 Hz, 4H, CH aromatic), 4.53 (s, 6H, NCH₂N), 4.32 (s, 6Η, NCH₂P), 2.78 (septet, J = 41.37 Ηz, 1Η, CH(CΗ₃)₂), 2.08 (s, 3H, CH₃), 1.22 (d, J = 6.93 Ηz, 6Η, CH(CH₃)₂).

Example 2 Synthesis of hexamethylbenzene-ruthenium (II) - 1, 3, 5 - triaza - 7 - phosphaadamantane dichloride (RAPTA-Η)

A solution of Ru(η⁶-C₆Me₆)Cl]₂ (420 mg, 0.61 mmol) and PTA (192 mg, 1.22 mmol) in methanol (100 ml) was heated to reflux for 1 h during which the initial orange-red solution changed in colour to brown. Removal of the solvent under reduced pressure and further drying on a vacuum line gave a brown microcrystalline solid (520 mg, 1.059 mmol, 86% yield/Ru.

Spectroscopic data: ESMS - m/z 456 [Ru(η⁶-C₆Me₆)(PTA)Cl₂]⁺, 332 [Ru(η⁶- C₆Me₆)Cl₂ ; ³¹P-{1H} NMR (CDC1₃) δ -34.78 (s); 1H NMR (CDCI₃) δ 4.48 (s, 6Η, NCH₂N), 4.26(s, 6Η, NCH₂P), 2.08 (s, 18Η, C₆(CH₃)₆)

Example 3

Synthesis of ?-cymene-ruthenium (II) - 1, 3, 5 - triaza - 7 - phosphaadamantane dibromide (RAPTA-CBr₂)

A solution of [Ru(p-cymene)Br₂]₂ (393 mg, 0.5 mmol) and PTA (157 MG, 1.0 mmol) in methanol (100 ml) was heated to reflux for 3 h during which the initial orange solution became deep red in colour. Upon cooling, the solution was filtered and removal of the solvent under reduced pressure and further drying for 2 h on a vacuum line gave a deep red microcrystalline solid (524 mg, 0.953 mmol, 95% yield/Ru). The product was used without further purification for the investigation of its catalytic properties.

Spectroscopic data: ESMS - m/z 553 Ru(p-cymene (PTA)Br]⁺; ³¹P-{1H} NMR (CDCI₃) δ -34.78 (s); ^!Η NMR (CDCI₃) δ 5.46 (q, J = 17.22 Hz, 4H, CH aromatic), 4.53 (s, 6H, NCH₂N), 4.36 (s, 6Η, NCH₂P), 2.90 (septet, J = 40.07 Ηz, 1Η, CH(CΗ₃)₂), 2.90 (s, 3H, CH₃), 1.21 (d, J = 6.79 Ηz, CΗ(CH₃)₂).

Example 4 Synthesis of p-cymene-ruthenium (II) - 1, 3, 5 - triaza - 7 - phosphaadamantane chloride fluoroborate

PTA (58 mg, 0.432 mmol, e eq.) was added to a dichloromethane (25 ml) solution of RAPTA-C, (200 mg, 0.432 mmol). Addition of silver tetrafluoroborate 84 mg, 0.432 mmol, 1 eq.) in methanol solution (2 ml) gave an immediate colour change from red orange to a yellow solution accompanied with the formation of a fine grey precipitate. The precipitate was removed via filtration on a glass microfibre filter apparatus. Removal of the solvent under reduced pressure followed by further drying on a vacuum line resulted in a yellow/orange solid (257 mg, 0.382 mmol, 88% yield).

Example 5

Synthesis of p-cymene-ruthenium (II) -triphenylphosphine - 3,3 ,3" - trisulphonic acid trisodium salt

A solution of [Ru (p-cymene) Cl₂]₂ (153 mg, 0.25 mmol) and triphenylphosphine - 3, 3 , 3" - trisulphonic acid trisodium salt (TPPTS*) (284 mg, 0.5 mmol) in methanol was heated to reflux for 5 h during which the solution changed from orange to deep red in colour. Removal of the solvent under reduced pressure followed by washing in dichloromethane (2 10 ml) and further drying on a vacuum line resulted in a dark red microcrystalline solid (400 mg, 0.458 mmol, 92% yield/Ru).

Spectroscopic data for 4 : ESMS m/z 851 ³¹P - {1H} nmr (D₂o) δ 34.81 (s, p(M- C₆H SO₃Na)₃), 29.92 (s, OE(m-C₆H₄SO₃Na)₃; 1H NMR (CD₃OD) δ 8.30 - 7.60 (multi, 12Η P (m - C₆H₄SO₃), 5.90 - 5.30 (rnulti, 4Η, aromatic (CH), 2.55 (septet, J = 43.91 Ηz, 1Η, 1Η, CH(CΗ₃)₂), 1.77 (s, 3H, CH₃), 0.99 (d, 6Η, CH(CH₃)2) * available from Aldrich Chemicals in the UK

Example 6

The following compounds were prepared using the methods as hereinbefore

described;

a) p-cymene-ruthenium (II) - 1 ,3,5-triaza - 7 - phosphaadamantane diodide;

b) p-cymene - ruthenium (II) - 1 ,3,5 - triaza - 7- phosphaadamantane

dithiocyanate;

c) p-cymene- ruthenium (II) - 1,3,5 - triaza - 7 - phosphaadamantane dichloride

dimer;

d) P-cymene-ruthenium (II) - 1 ,3,5 - triaza - 7 - phosphaadamantane dibromide

dimer;

e) hexamethylbenzene - ruthenium (II) - 1 ,3,5 - triaza - 7 -

phosphaadamantane dichloride dimer; and

f) benzene - ruthenium (II) - 1 ,3 ,5 - triaza - 7 - phosphaadamantane

dichloride.

Example 7

(i) DNA binding and damage studies

Figure 6 shows three DNA agarose gels (1% agarose in IxTAE buffer containing lμg/ml ethidium bromide) illustrating the effect of RAPTA-C on ρBR322 (95% supercoiled) DNA, with time. Samples prepared using 0.25 μg DNA per well, incubated in 10 μl of 3.2 mM of the test compounds in double distilled water. Loading dye was added to a final concentration of 10% and the gels run for 4 hours at 30 mN in 4X TAE buffer. Gels were destained in distilled water for 1 hour prior to photodocumentation.

The gels show how RAPTA-C induces rapid damage, whereas PTA alone has little effect on the DΝA. RAPTA-B is less active than RAPTA-C, but induces damage at a similar rate to its acetonitrile analogue (RuACETO-B). The acetonitrile analogue of RAPTA-C (RuACETO-C; Figure 7) does not significantly affect DΝA over this time scale, demonstrating the synergistic behaviour of the p-cymene and PTA ligands.

(ii) In vitro cell studies

RAPTA-C was tested against SK-Ν-SH neuroblastoma cells (American Type Culture Collection). This cell line was from human metastases and showed three structural forms: undifferentiated (1); partially differentiated (S); and neuron shaped (Ν).

The cells were grown in the S state and underwent two responses to stress: differentiation to the Ν state or cell death. Differentiation was observed by the more 'dentritic' appearance of the cells, which occurred after 1-3 hours, subsequently cells either dedifferentiated to the S phase, if the stress could be overcome, or they died.

RAPTA-C and its acetonitrile analogue were dissolved in water to a final concentration of 32 mM. This was then diluted 250 times in serum free medium and filter sterilised. Subsequently 10% serum was added and a stock solution, diluted a further ten times in complete medium, prepared. In a six well plate SK-Ν-SH neuroblastoma cells were grown to a semidifferentiated state in foetal calf serum (Gibco). The growth medium was removed and replaced with fresh medium, where appropriate including 13 - 0.0013 μM of the ruthenium compounds (RAPTA-C OR RuACETO-C). Over a 2 day period cell death by aopotosis was induced by RuACETO-C at the highest concentration (13 μM) and by RAPTA-C at the three highest concentrations (13, 1.3 and 0.13 μM), however, the control cells were unaffected (see Figure 8). The cells were harvested and are currently awaiting further analysis to identify the mechanism of aopotosis and the target for RAPTA-C.

Example 8

The compounds of the invention were incubated with supercoiled DNA at the pH of healthy cells (pH 7.5) the mobility of the resultant species during agarose gel electrophoresis is measured with RAPTA-C at pH 7.5 the mobility is unaltered (see Figure 9), but when the pH is reduced the migration of the DNA is retarded, indicating that DNA damage has occurred.

Example 9

We have previously shown that compound RAPTA-C selectively retards the migration of supercoiled DNA through an agarose gel during electrophoresis according to pH. At pH 7.5 the migration of the DNA species was not effected by incubation with RAPTA-C, however, a pH 7.0, the supercoiled form of DNA incubated with RAPTA-C is slightly retarded compared to the substrate DNA and the retardation is progressively increased as the pH is reduced further. In this study we have examined the interaction of the series of compounds described in Table 1 with

DNA at pH 7.5 and t.5, along with the interaction of pta and other control compounds. At pH 7.5 none of the compounds were shown to inhibit the migration of DNA through the agarose gel, suggesting that these compounds do not bind to

DNA under these conditions. In contracts, compounds RAPTA-C and RAPTA-H demonstrated DNA binding activity at pH 6.5, as shown in Figure 10. Table 1

P36262 O

Claims

rr A ΛITTMr.Sc

1. Thus according to the invention we provide a compound of the general formula I, or a salt thereof :

I

in which Ri is an arene group;

R₂, R₃ and R , which may be the same or different, are each alkyl CI to 6, aryl or substituted aryl, or R₂, R₃ and R may together with the phosphorous atom form a cycloalkyl group, such group being optionally heterocyclic;

Y is a halogen, SCN or is a group R₅R₆R₇P-, in which R₅, R₆ and R₇, which may be the same or different, are each alkyl CI to 6, aryl or substituted aryl, or R₅, R₆ and R₇ may together with the phosphorous atom form a cycloalkyl group, such group being optionally heterocyclic; and i is a halogen pr SCN, and dimers thereof.

2. A compound according to Claim 1 characterised in that the group Ri is substituted.

3. A compound according to Claim 1 characterised in that the i is a compound of formula IE:

in which R₈, R , Rι₀, Rn, Rj₂ and R₁₃, which may be the same or different, are each hydrogen or alkyl CI to 6.

4. A compound according to Claim 3 characterised in that at least one of R₈, R₉, R₁₀, Rn, Rι₂ and Rn, is methyl.

5. A compound according to Claim 3 characterised in that the at least one of R₈, R₉, R₁₀, Rn, R₁₂ and R₁₃ is isopropyl.

6. A compound according to Claim 3 characterised in that the arene group is selected from a group consisting of benzene, hexamethylbenzene, toluene and cymene.

7. A compound according to Claim 3 characterised in that the arene group is p- cymene.

8. A compound according to Claim 1 characterised in that the groups R₂, R₃ and R together with the phosphorous atom form a heterocyclic group.

9. A compound according to Claim 8 characterised in that the groups R₂, R₃ and R together with the phosphorous atom form a heterocyclic group comprising three nitrogen atoms.

10. A compound according to Claim 9 characterised in that the moiety R₂R₃R₄P- represents a 1,-3,5- triaza-7-phosphaadamantane group.

11. A compound according to Claim 1 characterised in that at least one of the groups R , R₃ and R₄ is an aryl group.

12. A compound according to Claim 11 characterised in that at least one of the aryl group is a sulphonated aryl group.

13. A compound according to Claim 1 characterised in that the Xi is chlorine,

14. A compound according to Claim 1 characterised in that Y is chlorine.

15. A compound according to Claim 1 characterised in that the both Xi and Y are each chlorine.

16. A compound according to Claim 1 characterised in that Y is a group

17. A compound according to Claim 15 characterised in that the moiety R₅R₆R₇P- together with the phosphorous atom form a heterocyclic group.

18. A compound according to Claim 17 characterised in that the moiety R₅R₆R₇P- represents a 1,-3,5- triaza-7-phosphaadamantane group.

19. A compound according to Claim 1 characterised in that at least one of the groups R₅, R₆ and R is an aryl group.

20. A compound according to Claim 19 characterised in that at least one of the aryl group is a sulphonated aryl group.

21. A compound according to Claim 1 characterised in that the salt of a compound of formula I is a fluoroborate salt.

22. A compound according to claim 1 characterised in that the compound, or a salt thereof is one in which,

Ri is an arene group;

R₂, R₃ and Rj, which may be the same or different, are each alkyl CI to 6, aryl or substituted aryl, or R₂, R₃ and i may together with the phosphorous atom form a cycloalkyl group, such group being optionally heterocyclic; Y is a halogen or is a group R₅R₆R₇P-, in which R₅, R₆ and R₇, which may be the same or different, are each alkyl CI to 6, aryl or substituted aryl, or R₅, R₆ and R₇ may together with the phosphorous atom form a cycloalkyl group, such group being optionally heterocyclic; and Xi is a halogen.

23. A compound according to Claim 1 characterised in that the compound is selected from the group benzene-ruthenium (II) - 1, 3, 5 - triaza - 7 - phosphaadamantane dichloride (RAPTA-B); hexamethylbenzene-ruthenium (II) - 1, 3, 5 - triaza - 7 - phosphaadamantane dichloride (RAPTA-H); toluene-ruthenium (II) - 1, 3, 5 - triaza - 7 - phosphaadamantane dichloride (RAPTA-

T); p-cymene-ruthenium (II) - 1, 3, 5 - triaza - 7 - phosphaadamantane dichloride (RAPTA-C); p-cymene-ruthenium (IT) - 1, 3, 5 - triaza - 7 - phosphaadamantane dibromide

(RAPTA-CBr₂); p-cymene-ruthenium (II) - 1, 3, 5 - triaza - 7 - phosphaadamantane chloride fluoroborate; p-cymene-ruthenium (II) - triphenylphosphine -3,3 ',3 - trisulphonic acid dichloride trisodium salt; p-cymene-ruthenium (II) - 1,3,5-triaza - 7 - phosphaadamantane diodide;

p-cymene - ruthenium (IT) - 1,3,5 - triaza- 7- phosphaadamantane dithiocyanate;

p-cymene- ruthenium (II) - 1 ,3,5 - triaza - 7 - phosphaadamantane dichloride dimer;

hexamethylbenzene - ruthenium (H) - 1,3,5 - triaza - 7 - phosphaadamantane

dichloride dimer; and

benzene - ruthenium (E) - 1,3,5 - triaza - 7 - phosphaadamantane dichloride.

24. A compound according to Claim 23 characterised in that the compound is selected from the group benzene-ruthenium (IT) - 1, 3, 5 - triaza - 7 - phosphaadamantane dichloride (RAPTA-B); hexamethylbenzene-ruthenium (E) - 1, 3, 5 - triaza - 7 - phosphaadamantane dichloride (RAPTA-H); toluene-ruthenium (TJ) - 1, 3, 5 - triaza - 7 - phosphaadamantane dichloride (RAPTA-

T); p-cymene-ruthenium S) - 1, 3, 5 - triaza - 7 - phosphaadamantane dichloride

(RAPTA-C); p-cymene-ruthenium (II) - 1, 3, 5 - triaza - 7 - phosphaadamantane dibromide

(RAPTA-CBr₂); p-cymene-ruthenium (II) - 1, 3, 5 - triaza - 7 - phosphaadamantane chloride fluoroborate; and p-cymene-ruthenium (H) - triphenylphosphine -3,3 ',3 - trisulphonic acid dichloride trisodium salt.

25. A compound according to Claim 23 characterised in that the compound is p- cymene-ruthenium (II) - 1, 3, 5 - triaza - 7 - phosphaadamantane dichloride.

26. A compound according to Claim 23 characterised in that the compound is hexamethylbenzene - ruthenium (II) - 1,3,5 - triaza - 7 - phosphaadamantane dichloride.

27. A compound according to Claim 23 characterised in that the compound is benzene - ruthenium (IT) - 1,3,5 - triaza - 7 - phosphaadamantane dichloride.

28. A process for the preparation of a compound of formula I which comprises reacting a compound of formula IE with R₂R₃RιP-

in which R;, Y and Xj are as defined in^' claim 1; with a compound of formula R2R₃R₄P-, in which R₂, R₃ and R₄ are as defined in claim 1.

29. A process according to Claim 28 characterised in that the compound of formula HI is (p-cymene)mthenium(IT) chloride dimer.

30. A process according to Claim 28 characterised in that the compound of formula R₂R₃R₄P- is PTA.

31. A pharmaceutical formulation comprising a compound according to claim 1 in admixture with a pharmaceutically acceptable adjuvant, diluent or carrier.

32. A method of treating cancer which comprises administering a therapeutically effective amount of a compound according to claim 1 to a patient suffering from such a disorder.

32. The use of a compound according to claim 1 in the manufacture of a medicament.

33. The use according to claim 31 characterised in that the medicament is for use in the treatment of cancer.

34. A compound substantially as described with reference to the accompanying examples.