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http://www.google.com/patents/WO2014023775A1?cl=en

The non-natural amino acid [ F]-l-amino-3-fluorocyclobutane-l-carboxylic acid

([¹⁸F]-FACBC, also known as [¹⁸F]-Fluciclovine) is taken up specifically by amino acid transporters and has shown promise for tumour imaging with positron emission tomography (PET).

A known synthesis of [¹⁸F]-FACBC begins with the provision of the protected precursor compound 1 -(N-(t-butoxycarbonyl)amino)-3 –

[((trifluoromethyl)sulfonyl)oxy]-cyclobutane-l-carboxylic acid ethyl ester. This precursor compound is first labelled with [¹⁸F]-fluoride:

II before removal of the two protecting groups:

IT III

EP2017258 (Al) teaches removal of the ethyl protecting group by trapping the [¹⁸F]- labelled precursor compound (II) onto a solid phase extraction (SPE) cartridge and incubating with 0.8 mL of a 4 mol/L solution of sodium hydroxide (NaOH). After 3 minutes incubation the NaOH solution was collected in a vial and a further 0.8 mL 4 mol/L NaOH added to the SPE cartridge to repeat the procedure. Thereafter the SPE cartridge was washed with 3 mL water and the wash solution combined with the collected NaOH solution. Then 2.2 mL of 6 mol/L HCl was then added with heating to 60°C for 5 minutes to remove the Boc protecting group. The resulting solution was purified by passing through (i) an ion retardation column to remove Na⁺ from excess NaOH and Cl^~ from extra HCl needed to neutralise excess of NaOH to get a highly acidic solution before the acidic hydrolysis step, (ii) an alumina column, and (iii) a reverse-phase column. There is scope for the deprotection step(s) and/or the

purification step in the production of [¹⁸F]-FACBC to be simplified.

Example 1: Synthesis of f FIFACBC

No-carrier- added [¹⁸F]fluoride was produced via the ¹⁸0(p,n)¹⁸F nuclear reaction on a GE PETtrace 6 cyclotron (Norwegian Cyclotron Centre, Oslo). Irradiations were performed using a dual-beam, 30μΑ current on two equal Ag targets with HAVAR foils using 16.5 MeV protons. Each target contained 1.6 ml of > 96% [¹⁸0]water (Marshall Isotopes). Subsequent to irradiation and delivery to a hotcell, each target was washed with 1.6 ml of [¹⁶0]water (Merck, water for GR analysis), giving approximately 2-5 Gbq in 3.2 ml of [¹⁶0]water. 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 [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. Synthesis of

[¹⁸F]FACBC followed the three general steps: (a) [¹⁸F]fluorination, (b) hydrolysis of protection groups and (c) SPE purification.

Vial A contained K₂₂₂ (58.8 mg, 156 μπιοΐ), K₂C0₃ (8.1 mg, 60.8 μπιοΐ) in 79.5% (v/v)

MeCN(a_q) (1105 μΐ). Vial B contained 4M HC1 (2.0 ml). Vial C contained MeCN

(4.1ml). Vial D contained the precursor (48.4 mg, 123.5 μιηοΐ) 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). Aqueous

[¹⁸F]fluoride (1-1.5 ml, 100-200 Mbq) was passed through the QMA and into the ¹⁸0-

H₂0 recovery vial. The QMA was then flushed with MeCN and sent to waste. The trapped [¹⁸F]fluoride was eluted into the reactor using eluent from vial A (730 μΐ) and then concentrated to dryness by azeotropic distillation with acetonitrile (80 μΐ, vial C). Approximately 1.7 ml of MeCN was mixed with precursor in vial D from which 1.0 ml of the dissolved precursor (corresponds to 28.5 mg, 72.7 mmol precursor) was added to the reactor and heated for 3 min at 85°C. 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 (2.0 ml) for 5 min after which the 2M NaOH was sent to waste. 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 HC1 (1.4 ml) and heating the reactor for 5 min at 60 °C. The reactor content with the crude [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 (9.1 ml total) and collected in the product vial. Finally, 2M NaOH (0.9 ml) and water (2.1 ml) was added to the product vial, giving a purified formulation of [¹⁸F]FACBC with a total volume of 26 ml. Radiochemical purity was measured by radio-TLC using a mixture of MeCN:MeOH:H₂0:CH₃COOH (20:5:5: 1) as the mobile phase. The radiochemical yield (RCY) was expressed as the amount of radioactivity in the [¹⁸F]FACBC fraction divided by the total used [¹⁸F]fluoride activity (decay corrected). Total synthesis time was 43 min.

The RCY of [¹⁸F]FACBC was 62.5% ± 1.93 (SD), n=4.

/////FDA,  diagnostic imaging agent,  recurrent prostate cancer, fda 2016, Axumin, marketed, Blue Earth Diagnostics, Ltd., Oxford, United Kingdom, fluciclovine F 18

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