NOVEL FORMULATION AND METHOD OF SYNTHESIS

Abstract

The present invention provides a composition comprising anti-1-amino-3-.sup.18F-fluorocyclobutyl-1-carboxylic acid (.sup.18F-FACBC) having an improved impurity profile compared with previous such compositions. Also provided is a method to obtain said composition.

Claims

1-24. (canceled)

25. A positron emission tomography (PET) tracer composition comprising anti-1-amino-3-.sup.18F-fluorocyclobutyl-1-carboxylic acid (.sup.18F-FACBC) having an end of synthesis (EOS) radiochemical purity (RCP) of at least 95% and said composition comprises no more than 5.0 μg/mL dissolved aluminium (Al) and no more than 25 μg/mL acetonitrile (MeCN), wherein the PET tracer is made by a method comprising: (a) reacting in a reaction vessel a source of .sup.18F-fluoride with a precursor compound of Formula I: ##STR00008## wherein: LG is a leaving group; PG.sup.1 is a carboxy protecting group; and, PG.sup.2 is an amine protecting group; wherein said reacting step is carried out in acetonitrile; to obtain a reaction mixture comprising a compound of Formula II: ##STR00009## wherein PG.sup.1 and PG.sup.2 are as defined for Formula I; (b) transferring said reaction mixture comprising said compound of Formula II out of said reaction vessel and carrying out removal of PG.sup.1 to obtain a reaction mixture comprising a compound of Formula III: ##STR00010## wherein PG.sup.2 is as defined for Formula I; (c) applying heat to said reaction vessel at the same time as carrying out removal of PG.sup.1; (d) transferring said reaction mixture comprising said compound of Formula III back into said reaction vessel and carrying out removal of PG.sup.2 to obtain a reaction mixture comprising .sup.18F-FACBC; (e) purifying said reaction mixture comprising .sup.18F-FACBC by passing it through a hydrophilic lipophilic balanced (HLB) solid phase, characterized in that said purifying does not comprise passing the reaction mixture comprising .sup.18F-FACBC through an alumina solid phase.

26. The PET tracer as defined in claim 25, wherein said composition comprises no more than 3.0 μg/mL dissolved Al.

27. The PET tracer as defined in claim 26, wherein said composition comprises no more than 1.5 μg/mL dissolved Al.

28. The PET tracer as defined in claim 27, having an EOS RCP of at least 98%.

29. The PET tracer as defined in claim 28, having an EOS RCP of at least 99%.

30. The PET tracer as defined in claim 25, comprising 50-100 mM citrate buffer.

31. The PET tracer as defined in claim 25, wherein LG is a linear or branched C.sub.1-10 haloalkyl sulfonic acid substituent, a linear or branched C.sub.1-10 alkyl sulfonic acid substituent, a fluorosulfonic acid substituent, or an aromatic sulfonic acid substituent.

32. The PET tracer as defined in claim 31, wherein LG is methanesulfonic acid, toluenesulfonic acid, nitrobenzenesulfonic acid, benzenesulfonic acid, trifluoromethanesulfonic acid, fluorosulfonic acid, and perfluoroalkylsulfonic acid.

33. The PET tracer as defined in claim 32, wherein LG is trifluoromethanesulfonic acid.

34. The PET tracer as defined in claim 25, wherein PG.sup.1 is ethyl.

35. The PET tracer as defined in claim 25, wherein PG.sup.2 is t-butoxycarbonyl.

36. The PET tracer as defined in claim 25, wherein the method is automated.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0066] FIG. 1 illustrates an exemplary cassette to carry out the method of the invention.

BRIEF DESCRIPTION OF THE EXAMPLES

[0067] The following non-limiting examples serve to illustrate particular embodiments of the subject matter of the present invention.

LIST OF ABBREVIATIONS USED IN THE EXAMPLES

[0068] BOC tert-Butyloxycarbonyl [0069] DP drug product [0070] HLB hydrophobic-lipophilic balance [0071] K.sub.222 Kryptofix 222 [0072] MeCN acetonitrile [0073] QMA quaternary methyl ammonium [0074] RAC radioactive concentration [0075] RCP: radiochemical purity

EXAMPLES

Comparative Example 1: Prior Art Synthesis of .SUP.18.F-FACBC

[0076] 1(i) FASTlab Cassette All radiochemistry was performed on a commercially-available GE FASTlab™ with single-use cassettes. Each cassette is built around a one-piece-moulded manifold with 25 three-way stopcocks, all made of polypropylene. Briefly, the cassette includes a 5 ml reactor (cyclic olefin copolymer), one 1 ml syringe and two 5 ml syringes, spikes for connection with five prefilled vials, one water bag (100 ml) as well as various SPE cartridges and filters. Fluid paths are controlled with nitrogen purging, vacuum and the three syringes. The fully automated system is designed for single-step fluorinations with cyclotron-produced .sup.18F-fluoride. The FASTlab was programmed by the software package in a step-by-step time-dependent sequence of events such as moving the syringes, nitrogen purging, vacuum, and temperature regulation. Vial A contained K.sub.222 (58.8 mg, 156 μmol), K.sub.2CO.sub.3 (8.1 mg, 60.8 μmol) in 79.5% (v/v) MeCN.sub.(aq) (1105 μl). Vial B contained 4M HCl (2.0 ml). Vial C contained MeCN (4.1 ml). Vial D contained the precursor (48.4 mg, 123.5 μmol) in its dry form (stored at −20° C. until cassette assembly). Vial E contained 2 M NaOH (4.1 ml). The 30 ml product collection glass vial was filled with 200 mM trisodium citrate (10 ml).

1(ii) Production of .sup.18F-Fluoride

[0077] No-carrier-added .sup.18F-fluoride was produced via the .sup.18O(p,n).sup.18F nuclear reaction on a GE PETtrace 6 cyclotron (Norwegian Cyclotron Centre, Oslo). Irradiations were performed using a dual-beam, 30 μA current on two equal Ag targets with HAVAR foils using 16.5 MeV protons. Each target contained 1.6 ml of >96% [.sup.18O]water (Marshall Isotopes). Subsequent to irradiation and delivery to a hotcell, each target was washed with [.sup.16O]water (Merck, water for GR analysis). Aqueous .sup.18F-fluoride was passed through the QMA and into the .sup.18O—H.sub.2O recovery vial. The QMA was then flushed with MeCN and sent to waste.

1(iii) .sup.18F-Fluoride Labelling

[0078] The trapped .sup.18F-fluoride was eluted into the reactor using eluent from vial A and then concentrated to dryness by azeotropic distillation with acetonitrile (vial C). MeCN was mixed with precursor in vial D from which the dissolved precursor was added to the reactor and heated to 85° C.

1(iv) Removal of Ester Protecting Group

[0079] The reaction mixture was diluted with water and sent through the tC18 cartridge. Reactor was washed with water and sent through the tC18 cartridge. The labelled intermediate, fixed on the tC18 cartridge was washed with water, and then incubated with 2M NaOH after which the 2M NaOH was sent to waste.

1(v) Removal of BOC Protecting Group

[0080] The labelled intermediate (without the ester group) was then eluted off the tC18 cartridge into the reactor using water. The BOC group was hydrolysed by adding 4M HCl and heating the reactor.

1(vi) Purification

[0081] The reactor content with the crude .sup.18F-FACBC was sent through the HLB and Alumina cartridges and into the 30 ml product vial. The HLB and Alumina cartridges were washed with water and collected in the product vial.

1(vii) Formulation

[0082] 2M NaOH and water was added to the product vial, giving a purified drug product (DP) with a total volume of 26 ml.

(1viii) Acetonitrile Concentration

[0083] Acetonitrile (MeCN) concentration was determined using a gas chromatographic system with FID, an automated liquid injector, a fused silica capillary column with USP stationary phase G43 (6% cyanopropylphenyl-94% dimethyl polysiloxane) and a reporting integrator or data system with reintegration capacity. 1000 μg/ml of MeCN was used as a standard. Blank was prepared by transferring 1 ml of purified water to a 2 ml GC crimp cap vial, which was capped immediately. 1 ml of the standard was transferred to a 2 ml GC crimp cap vials and capped immediately. 0.20 ml of the sample was transferred to a 2 ml GC crimp cap vial with low volume insert (0.25 ml) and capped immediately. The experimental conditions of the GC instrument were as follows: [0084] Carrier gas flow, Helium: 2.0 ml/min [0085] Oven temperature program: 40° C. for 6 minutes then 20° C./min to 240° C. for 4 minutes [0086] Injector temperature: 225° C. [0087] Split ratio: 10:1 [0088] Detector: FID [0089] Detector temperature: 250° C. [0090] Hydrogen flow rate: 30 ml/min [0091] Air flow rate: 400 ml/min [0092] Make up gas flow rate (He): 25 ml/min

[0093] The experimental conditions of the automatic liquid injector were as follows: [0094] Solvent pre washes: 3 [0095] Sample pumps: 3 [0096] Solvent post washes: 3 [0097] Injection volume: 1 ml

[0098] The column was conditioned at 250° C. for at least one hour prior to use.

[0099] One injection of each standard and two replicate injections of the sample solution were performed in addition to blank injections in the following order: [0100] 1. Blank [0101] 2. Calibration standard [0102] 3. Calibration standard [0103] 4. Blank [0104] 5. Sample, replicate 1 [0105] 6. Sample, replicate 2 [0106] 7. Blank

[0107] The concentration of each analyte, C.sub.sample, was calculated in pg/ml using the following formula:

[00001]$C_{\mathrm{sample}}=\frac{A_{\mathrm{sample}}\times C_{\mathrm{std}}}{A_{\mathrm{std}}}$

where:
A.sub.sample: Peak area of the analyte in sample
C.sub.std: Concentration of the analyte in calibration standard (μg/ml)
A.sub.std: Peak area of the analyte in calibration standard, average of 2 injections (1ix) Aluminium Concentration

[0108] Aluminium concentration was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

(1x) Radiochemical Parameters

[0109] Radiochemical purity (RCP) and radioactive concentration (RAC) of .sup.18F-FACBC were measured.

[0110] RCP was determined by thin layer chromatography (TLC). The TLC strip was eluted using a mobile phase consisting of acetonitrile:methanol:water:acetic acid, 20:5:5:1 v/v. The RCP and any radiochemical impurities including .sup.18F-fluoride were reported as percentages of the net sum of all peaks.

(1xi) Results

[0111] The following results were obtained:

TABLE-US-00001 Production # RAC (MBq/ml) RCP(%)T0 MeCN (μg/ml) Al (μg/ml) 1 1915 >99 506 14 2 1804 >99 324 14 3 1950 >99 302 13 4 1698 >99 89 15 5 1570 >99 596 17 6 1815 >99 218 15

Example 2: Synthesis of .SUP.18.F-FACBC Using Inventive Method

2(i) Modified Sequence

[0112] A modified FASTlab™ cassette was used, as illustrated in FIG. 1. The sequence described in Example 1 was used except that the sequence included the extra heating/purging of the reaction vessel. The hydrolysis step was replaced with two steps, the first step of which included hydrolysis and in parallel heating of the reactor at 85° C., nitrogen purging (600 mbar HF) of the reaction vessel and vacuum (−600 mbar). The second step also included hydrolysis but heating of the reaction vessel was stopped. Nitrogen purging (600 mbar HF) and vacuum (−600 mbar) were used for cooling of the reaction vessel. Furthermore, the alumina SPE was removed and the sequence was changed to transfer the product directly to the formulation buffer vial after the HLB cartridge step.

2(i) Analysis

[0113] The analysis methods as described in Example 1 were used.

TABLE-US-00002 Production # RAC (MBq/ml) RCP(%)T0 MeCN (μg/ml) Al (μg/ml) 7 3112 99.1 20 0.7 8 3900 99.1 20 0.8 9 1631 99.1 21 1.3 10 731 99.9 22 0.8 11 1831 99.8 25 0.8 12 1654 99.9 24 1.3 13 1573 99.1 21 1.1 14 1750 99.4 23 1.1 15 788 99.0 19 1.1 16 1023 99.2 17 1.1