RADIOLABELLED BISPHOSPHONATES AND METHOD

Abstract: A method of making a bisphosphonate RC(OH)(PO.]OH]2)2 comprises reacting a <i>tris</i>(silyl)phosphite with an activated carbonyl compound and hydrolysing the resulting intermediate. Preferably the <i>tris</i>(silyl)phosphite is labelled with <32>P or <33>P. Radiolabelled bisphosphonates are used to treat patients suffering from osteosarcoma or bone metastases.

Description: RADIOLABELLED BISPHOSPHONATES AND METHOD Field of the Invention. The present invention relates to 32 P or 33 P-labelled bisphosphonates as radiotherapeutic radiopharmaceuticals. The 32 P- or 33 P-labelled bisphosphonates, which are chemically identical to the unlabelled agent, are expected to target the lesion site in an identical manner, but also deliver a significant radiocytotoxic effect to the surrounding cells. This should result, given the favourable energetics of the β particle emission from the 33 P nuclide, in a loss of proliferative capacity of cells associated with the tumour lesion. The relative stability and in vivo localisation of bisphosphonates makes them good candidates as 32 p/ 33 p delivery vehicles. Background of the Invention Bisphosphonates are known as palliatives to treat osteosarcoma or bone metastases associated with carcinoma such as breast or prostate. These agents, such as Pamidronate and Clodronate, exert a negative effect upon osteoclasts at the site of the lesion resulting in decreased bone resorption at this site. Bisphosphonates, however, appear to lose activity with time necessitating repeat administration. There have been extensive examples of bisphosphonate syntheses in the literature over the last 25 years. Synthesis of the α-hydroxyl-methylene bisphosphonates, those most commonly studied with respect to bone disorders, have largely been performed under harsh conditions of elevated temperatures, often resulting in low-yielding reactions. The common route of synthesis to such compounds involves heating a source of phosphorus, usually phosphorous acid, with the CONΠRMAΠON COPY appropriate carboxylic acid and PCI 3 . This synthesis is not ideal for the incorporation of 32 33 p into a bisphosphonate, due to the safety and radiological hazards associated with volatile 32 33 PCI 3 , and the fact that the primary role of the PCI 3 is to generate an activated carbonyl compound rather than as a source of the phosphonate groups. The poor yields often obtained from the traditional syntheses are not appropriate for radiolabelling with an expensive radionuclide. Tr/s(trimethylsilyl) phosphite, P(OTms) 3 , has been synthesised from PCI 3 and, alternatively, from phosphorous acid and, subsequently, used to introduce phosphorus into compounds. US Patent 3,965,254 describes the use of 32/33 P in bisphosphonates for the treatment of bone cancer. It was shown that the 32 P or 33 P radionuclide could be targeted to the tumour site. The patent describes the incorporation of 32 P into EHDP (disodium ethane-1-hydroxy- 1 ,1-diphosphonate) and its subsequent use in in vivo studies. The synthesis used to generate the radiolabelled bisphosphonates followed the conventional synthesis using 32/33 PCI 3 . Within the synthetic route the reaction is, at times heated to 145°C for up to 6 hours and a reflux of 40 hours duration. The final yield was approximately 65%. This route of preparation for these compounds is seen as inappropriate for the reasons outlined above. Accordingly, it is one object of this invention to supply a convenient and improved route of synthesis for radiolabelled bisphosphonates, for the use in therapeutic treatment of bone metastatic disease. Summary of the Invention In one aspect the invention provides a method of making a bisphosphonate, which method comprises reacting a -r/s(silyl)phosphite with an activated carbonyl compound and hydrolysing the resulting intermediate according to the reaction scheme: P(OX) 3 + RCO.Y → Intermediate → RC(OH)(PO.[OH] 2 ) 2 where each X is the same or different and is tri-(C-ι - C-ι 2 hydrocarbyl)silyl, R is C-i - C 12 alkyl, C 2 - Cι 2 alkenyl, C - Cι 2 alkynyl, C 2 - Cι 2 aryl (including heteroaryl) or substituted variants of these where functionalised groups, if present, are appropriately masked (ie. protected) during the synthesis, and Y is an activating moiety. The functional group(s) of the 'substituted variants' can be amino (primary, secondary or tertiary), hydroxy, alkoxy or fluorine. R is preferably Ci - C-| 2 alkyl, Ci - C 12 fluoroalkyl or Ci - Cι 2 primary, secondary or tertiary aminoalkyl or a derivative of these, or a substituted alkyl group containing nitrogen as part of a heterocyclic ring system. R is most preferably Ci - CQ alkyl or C 2 - Cg primary, secondary or tertiary aminoalkyl. Preferred C 2 - Cg aminoalkyl groups are -(CH 2 ) P NQ 2 where p is 2 or 3 and Q is H or d - C 5 alkyl, with -(CH 2 ) 2 NH 2 , -(CH 2 ) 3 NH 2 and (CH 2 ) 3 NMe(pentyl) being especially preferred. In the starting fr7s(silyl)phosphite P(OX) 3) X is tri-(C-ι - C-ι 2 hydrocarbyl)silyl, e.g. trialkylsilyl or triarylsilyl, conveniently trimethylsilyl since derivatised thmethylsilanes are readily commercially available. Mixed phosphites are possible and may be preferred. The starting activated carbonyl compound of formula RCO.Y is preferably an acid halide, particularly an acid chloride or acid bromide; an acid anhydride; an α-ketophosphonate; or an active ester such as that derived from N-hydroxysuccinimide. Hence the activating moiety Y can be: a leaving group such as halogen (especially Cl or Br), or an acid anhydride linkage (RCO) 2 0, or an active ester, examples of which are well known to those skilled in the art. Alternatively, Y can be a phosphonate -PO(OR"') 2 , ie. RCOY may be an α-ketophosphonate. Preparation of bisphosphonates has also been achieved using an active ester derived from 2- hydroxypyridine and also acid anhydrides. Active esters derived from pentafluorophenol and hydroxybenztriazole are also possible. These reactions show how the increased nucleophilicity of the silylated phosphites (compared with trialkyl phosphites) permits the use of much less activated carbonyl compounds in the formation of the desired products. When Y is a leaving group, the Intermediate generally has the formula RC(OZ)(PO.[OX] 2 ) 2 where Z is H or X. When RCOY is an α-ketophosphonate, an addition reaction rather than a substitution reaction may take place, e.g.: P(OX) 3 + RCO.PO(OR"') 2 → RC(OZ)(PO)[OX] 2 )(PO[OR'"] 2 ) → RC(OH)(PO[OH] 2 ) 2 where R"' is C- 1 - 12 alkyl or X (by treatment of the -O-alkyl system with TmsBr or Tmsl). The R group is chosen to provide a desired substituent on the hydroxymethane-bisphosphonate unit. Various bisphosphonate drugs R 1 CR 2 (PO[OH] 2 ) 2 have been commercialised as follows:- Preferably the fr/s(silyl)phosphite contains 32 P or 33 P, either at 100% abundance or at least at an artificially high isotopic abundance of e.g. at least 1 %. Preferably 2 molar equivalents of the fr/s(silyl)phosphite are reacted with 1 molar equivalent of the activated carbonyl compound. Although use of elevated temperatures is possible, the reaction is found to go in high yield at ambient temperature, thus providing a convenient route for introducing 32 P or 33 P into a bisphosphonate molecule of choice. Dry aprotic solvents such as diethyl ether or tetrahydrofuran can be used to help facilitate handling of the reactants. Reaction times depend on the leaving group and on the quantity of solvent used. With modest quantities of solvent, reaction times are typically 10 to 15 min with an acid chloride or anhydride but it can require heating for several hours with less activated carbonyl compounds. There results an intermediate having the formula RC(OZ)(PO.[OX] 2 ) 2 or RC(OZ)(PO)[OX] 2 )(PO[OR"']). In general these intermediates are believed novel and form further aspects of this invention. They may readily be hydrolysed to the desired bisphosphonates by the addition of excess methanol or water at elevated or preferably ambient temperature. Some of the resulting bisphosphonates are new compounds. Thus the invention also provides radiolabelled bisphosphonates of the formula: R"C(OH)( n PO[OH] 2 ) 2 where n is at least partly 32 or 33 whereby the compound contains an artificially high proportion of 32 P or 33 P, and R" is Ci - C-ι 2 primary, secondary or tertiary aminoalkyl or a derivative of these, or a substituted alkyl group containing nitrogen as part of a heterocyclic ring system. R" is preferably C 2 - Cg primary, secondary or tertiary aminoalkyl, most preferably -(CH 2 ) P NQ 2 where p is 2 or 3 and Q is H or Ci - C 5 alkyl, with -(CH 2 ) 2 NH 2 , -(CH 2 ) 3 NH 2 and (CH 2 ) 3 NMe(pentyl) being especially preferred. It may be advantageous to provide one of the starting reagents, e.g. the fr/s(silyl)phosphite POX 3 or the activated carbonyl compound RCOY, in immobilised form. This facilitates purification of the starting compound, which may be particularly useful when an isotopically labelled phosphite is used, and also facilitates purification of the desired bisphosphonate product. The radiolabelled bisphosphonates of the present invention have useful properties as palliatives to treat osteosarcoma or bone metastasis associated with carcinoma such as breast or prostate, with the additional advantage of comprising an artificially high isotopic abundance of 32 P or 33 P for targeting either bone metastasis or tumours or other diseases that may be treated with radiotherapy. Also included within the scope of the invention are radiolabelled phosphorus compounds of the formula R' q n P(OX) 3-q where R' is Ci - C-ι 2 alkyl or C 2 - d 2 aryl, q is O, 1 or 2, n is at least partly 32 or 33 whereby the compound contains an artificially high proportion of 32 P or 33 P, each X is the same or different and is tri-(Cι - C 12 hydrocarbyl)silyl. When q is 0, these are radiolabelled trialkylsilylphosphites, useful as starting materials in the method of the invention described above. Detailed Description of Invention Example 1 - Preparation of Tr/sftrimethylsilyl) Phosphite (compound 1) Triethylamine (40.4 g, 40.4 mmol) was added dropwise to a mechanically stirred solution of phosphorous acid (16.5 g, 201 mmol) and chlorotrimethylsilane (44 g, 405 mmol) in diethyl ether (1200 cm 3 ). Immediately, a white precipitate of triethlyamine hydrochloride formed. After the addition was complete (2 h) the mixture was stirred for a further 2 hours. The insoluble salt was removed by filtration and the filtrate concentrated to about 200 cm 3 . The small quantity of additional precipitate formed during this process was subsequently filtered off and the filtrate evaporated to give a cloudy liquid. The product was purified by distillation under reduced pressure, the fraction boiling in the range 45-50°C at 0.1 mbar being collected. The £>/s(trimethylsilyl) phosphite was isolated as a colourless oil (35 g, 77%). 31 P NMR: δ -12.8. Chlorotrimethylsilane (20 g, 185 mmol) was added dropwise to a stirred solution of £)/s(trimethylsilyl)phosphite (30 g, 132 mmol) and N,N- diethyltrimethylsilylamine (20 g, 137 mmol) and the mixture stirred at room temperature for 1 h. The solid formed was removed by filtration and the filtrate distilled in vacuo. A colourless fraction boiling at 77-80°C at 0.1 mbar was collected (30g, 75%). 31 P NMR: δ +116.3. Example 2 - Synthesis of Hvdroxyethylidene Bisphosphonic Acid (compound 2) 7/7s(trimethylsilyl) phosphite (2 molar equiv.) in an appropriate dry solvent was added dropwise to a stirred solution of acetyl chloride (1 molar equiv.) in an appropriate dry solvent at room temperature and the mixture stirred for 10 minutes. Excess methanol was then added and the mixture stirred for 5 minutes to decompose the silyl esters. The volatile components in the reaction mixture were then removed under reduced pressure to leave the title compound in good purity. It is anticipated that this reaction can be performed using 32 P(OTms) 3 or 33 P(OTms) 3 in order to introduce a 32 P label or a 33 P label. 2 3 Compounds 2 and 3 Example 3 - Synthesis of 4-Amino-1 -hydroxybutane-1,1- bisphosphonic Acid (compound 3) A solution of benzylchloroformate (9.4 g, 5.5 mmol) in acetone (15 ml) was added dropwise to a mixture of 4-aminobutanoic acid (5.2 g, 5 mmol), sodium bicarbonate (8.6 g, 10 mmol), water (25 ml) and acetone (25 ml) causing vigorous effervescence. The solution was allowed to stir overnight. The acetone was removed using a rotary evaporator to leave an aqueous phase which was washed with ether (2 x 25ml). The resulting aqueous layer was acidified to pH2 with dilute hydrochloric acid and then extracted with dichloromethane (3 x 50 ml). The dichloromethane extracts were combined, dried over magnesium sulphate and volatile components removed under reduced pressure to leave 4-[(benzyloxycarbonyl)amino]butanoic acid as a white solid in a good state of purity. This material was used without further purification. A solution of dicyclohexylcarbodiimide (2.5 g, 12 mmol) in dry tetrahydrofuran (10 ml) was added in one portion to a stirred solution of 4-[(benzyloxycarbonyl)amino] butanoic acid (2.4 g, 10 mmol) and N-hydroxysuccinimide (1.5 g, 13 mmol) in dry tetrahydrofuran (10ml). After about 20 minutes dicyclohexylurea began to precipitate from the solution. Stirring was continued for 16 hours and the resulting solution was then filtered. The insoluble white solid was removed and washed with tetrahydrofuran (20ml) and the washings combined with the filtrate. Volatile components were removed from the tetrahydrofuran solution in vacuo to leave a white waxy solid. This residue was purified by chromatography on silica using ethyl acetate as the eluant. Removal of the solvent under reduced pressure gave a viscous colourless oil that was triturated with dry ether to produce a white powder. 1 H NMR: δH (CDCI 3 ); 7.35-7.27 (5H, m), 5.09 (3H, br), 3.30 (2H, br q), 2.79 (4H, s), 2.66 (2H, , 1 -97 (2H, pentet). Tr/s(trimethylsilyl)phosphite (900 mg, 3 mmol) was added to a solution of succinyl 4-[(benzyloxycarbonyl) amino]butanoate (340 mg, 1 mmol) in dioxane (0.5 ml) and the mixture warmed at 65 - 70°C with the exclusion of moisture until shown by 31 P NMR spectroscopy to be completed. Bromotrimethylsilane (0.5 g, 3.25 mmol) was added and the solution stirred for ca 1 h at room temperature. Volatile components were removed in vacuo to leave a viscous oil. Methanol (20 ml) was added and the resulting mixture stirred for 1 h. The solid product was then filtered off. More product precipitated on addition of acetone to the filtrate and this was added to the filtered solid. After drying the required bisphosphonate (compound 3) was obtained as a white solid (130 mg, 52%). δ P 19.5, δ c (D 2 0) 73.0 (t, JPC = 138 Hz), 39.9 (s), 27.0 (t, JPC = 7 Hz), δ H (D 2 0) 2.76 (2H, m, CH 2 N), 1.75 (4H, m, CH 2 CH 2 ). Example 4 - Solid Phase Synthesis of 4-Amino-1-hydroxybutane-1,1 bisphosphonic Acid (compound 3) To 0.5g of 2-chlorotrityl chloride resin suspended in anhydrous dimethylformamide was added 5 molar equivalents of β-alanine ethyl ester hydrochloride and 10 molar equivalents of triethylamine. The resin was agitated for 48 hours and then washed exhaustively with dichloromethane and dimethylformamide. The ester was cleaved by the addition of KOH in dioxan and agitation for 8 hours. The resin was washed thoroughly with methanol and dichloromethane after filtration. Addition of N-hydroxy succinimide (5 molar equiv.) and dicyclohexylcabodiimide (5 molar equiv.) in dichloromethane with stirring for 24 hours afforded the activated ester. After filtration the resin was washed with methanol and dichloromethane. To this resin in dichloromethane was added tris(trimethylsilyl) phosphite (5 molar equiv.) and agitated for 48 hours at room temperature. The resin was then washed with dichloromethane and methanol followed by treatment with 10% trifiuoroacetic acid in dichloromethane to cleave the product. 1, H 2 0 2, TFA Synthetic route to an amino-bisphosphonate on a solid support

Claims: CLAIMS 1. A method of preparation of a bisphosphonate, which method comprises reacting a fr7s(silyl)phosphite with an activated carbonyl compound and hydrolysing the resulting intermediate according to the reaction scheme: P(OX) 3 + RCO.Y → Intermediate → RC(OH)(PO.[OH] 2 ) 2 where each X is the same or different and is tri-(Cι - C 12 hydrocarbyl)silyl, R is Ci - C12 alkyl, C 2 - C12 alkenyl, C 2 - C12 alkynyl, C 2 - C 2 aryl (including heteroaryl) or substituted variants of these where functionalised groups, if present, are appropriately masked during the synthesis, and Y is an activating moiety. 2. The method of claim 1 , wherein X is trimethylsilyl. 3. The method of claim 1 or claim 2, wherein R is Ci - C 12 primary, secondary or tertiary aminoalkyl. 4. The method of any one of claims 1 to 3, wherein Y is an active ester or N-hydroxysuccinimide. 5. The method of any one of claims 1 to 4, wherein the -r/s(silyl)phosphite contains an artificially high proportion of 32 P or 33 P. 6. The method of any one of claims 1 to 5, wherein the reactions are performed at ambient temperature. 7. The method of any one of claims 1 to 6, wherein the Intermediate has the formula RC(OZ)(PO.[OX] 2 ) 2 where Z is H or X. 8. The method of any one of claims 1 to 6, wherein the reaction scheme is P(OX) 3 + RCO.PO(OR'") 2 → RC(OZ)(PO)[OX] 2 )(PO[OR ,,, ] 2 ) → RC(OH)(PO[OH] 2 ) 2 , where R'" is Cι_ι 2 alkyl or X. 9. The method of any one of claims 1 to 8, wherein the fr7 ' s(silyl)phosphite P(OX) 3 or the activated carbonyl compound RCO.Y is immobilised on a solid support. 10. Radiolabelled phosphorus compounds of the formula R' q n P(OX) 3-q where R' is Ci - C 12 alkyl or aryl, q is 0, 1 or 2, n is at least partly 32 or 33 whereby the compound contains an artificially high proportion of 32 P or 33 P, each X is the same or different as other X's and each X is tri-(Cι - C 12 hydrocarbyl)silyl. 1 1. The radiolabelled phosphorus compounds of claim 10, where q is 0 and X is trimethylsilyl. 12. Radiolabelled bisphosphonates of the formula R"C(OH)( n PO[OH] 2 ) 2 where n is at least partly 32 or 33 whereby the compound contains an artificially high proportion of 32 P or 33 P, and R" is Ci - C 1 primary, secondary or tertiary aminoalkyl or a derivative of these, or a substituted alkyl group containing nitrogen as part of a heterocyclic ring system. 13. The radiolabelled bisphosphonate of claim 12, where R" is -(CH 2 ) P NQ 2 , where p is 2 or 3, and Q is H or d -5 alkyl. 14. A method of treating a patient suffering from osteosarcoma or bone metastases, which method comprises administering to the patient an effective amount of the radiolabelled bisphosphonate of claims 12 or 13. 15. Compounds of the formula RC(OZ)((PO[OX] 2 ) 2 or RC(OZ)(PO[OX] 2 )(PO[OR'"]) where each X is the same or different as other X's and each X is tri-(Cι - Cι 2 hydrocarbyl)silyl, Z is H or X, R^ is d-^ alkyl or X, and R is Ci - d 2 alkyl, alkenyl, alkynyl, aryl (including heteroaryl) or substituted variants of these where functionalised groups, if present, are appropriately masked during the synthesis. 16. The compounds of claim 15, wherein there is present an artificially high proportion of 32 P or 33 P.

Inventors: DUNCANSON PHILIP, GIBSON ALEXANDER MARK, GRIFFITHS VAUGHAN, MENDIZABAL MARIVI, PITHER RICHARD, PULLAN SHIRLEY ELIZABETH, DUNCANSON, PHILIP, GIBSON, ALEXANDER, MARK, GRIFFITHS, VAUGHAN, MENDIZABAL, MARIVI, PITHER, RICHARD, PULLAN, SHIRLEY, ELIZABETH
Applicants: DUNCANSON PHILIP, GIBSON ALEXANDER MARK, GRIFFITHS VAUGHAN, MENDIZABAL MARIVI, NYCOMED AMERSHAM PLC, PITHER RICHARD, PULLAN SHIRLEY ELIZABETH, DUNCANSON, PHILIP, GIBSON, ALEXANDER, MARK, GRIFFITHS, VAUGHAN, MENDIZABAL, MARIVI, PITHER, RICHARD, PULLAN, SHIRLEY, ELIZABETH
Application year: 2000
Main classification: C07F9
IPC codes: A61K31, A61K51, A61P35, A61P43, C07B59, C07F9