Stabilisation of radiopharmaceutical precursors

Abstract

The present invention relates to a method for improving stability of non fluoridated sugar derivatives, and in particular glucose derivatives such as 1,3,4,6-tetra-O-acetyl-2-O-trifluoromethanesulfonyl--D-mannopyranose which are used as precursors for production of radiofluoridated sugar derivatives for use in in vivo imaging procedures such as positron emission tomography (PET). The method comprises storing the non fluoridated sugar derivative in an organic solvent. The resultant formulations of the non fluoridated sugar derivative and cassettes for automated synthesis apparatus comprising the same are also claimed.

Claims

1. A method of storing 1,3,4,6-tetra-O-acetyl-2O-trifluoromethanesulfonyl--D-mannopyranose (mannose triflate), the method comprising dissolving mannose triflate in acetonitrile to form a solution and storing the solution in a sealed container for subsequent storage, wherein the solution consists of mannose triflate and acetonitrile, wherein the stability of the mannose triflate stored in the acetonitrile is better than the stability of mannose triflate stored without the acetonitrile, and wherein the acetonitrile has a water content between 100 ppm and 50000 ppm.

2. The method of claim 1, wherein the concentration of the mannose triflate in the solution is between 10 mg/mL to 18 mg/mL.

3. The method of claim 1, wherein the sealed container is a septum-sealed vial.

4. The method of claim 1, wherein the acetonitrile has a water content of approximately 600 ppm.

5. The method of claim 1, wherein the acetonitrile has a water content between 100 ppm and 600 ppm.

Description

EXAMPLE 1: STABILITY OF MANNOSE TRIFLATE IN DRY ACETONITRILE

(1) With reference to the Figures:

(2) FIG. 1: HPLC-UV chromatogram of Mannose Triflate from ABX (solid material) at start.

(3) FIG. 2: HPLC-UV chromatogram of Mannose Triflate from ABX (dissolved in acetonitrile) at start.

(4) FIG. 3: HPLC-UV chromatogram of Mannose Triflate from ABX (solid material) stored for 2 weeks at 50 C.

(5) FIG. 4: HPLC-UV chromatogram of Mannose Triflate from ABX (dissolved in acetonitrile) stored for 2 weeks at 50 C.

(6) Materials:

(7) Acetonitrile (MeCN): VWR/Merck, 4 L, water content approximately 600 ppm.

(8) Mannose triflate ABX: Ultra-pure quality 1 g units,

(9) Vials: Fiolax 5 ml Glass vials (13 mm), Munnerstdter.

(10) Stoppers: West 4432/50 gray 13 mm, Teflon coated.

(11) Caps: Helvoet Pharma

EXPERIMENTAL

(12) Glass vials to be used are dried before use in a Lytzen heat sterilizer at 210 C. for 5 hours. Stoppers are not treated in any way.

(13) 2.0 g Mannose triflate was weighed into an Erlenmeyerflask and dissolved in 133 ml dry acetonitrile to yield an acetonitrile solution in an extraction hood. Dissolution was rapid, solid disappeared as soon as it came in contact with the acetonitrile.

(14) Dispensing:

(15) This solution was dispensed using a 10 ml glass volumetric cylinder into vial samples of approx. 4.2-4.4 ml.

(16) Control samples of mannose triflate (without solvent) under air and under nitrogen were also prepared.

(17) Filled and capped units are kept in storage at 25 C. and 50 C. in thermally controlled cabinets for set periods of time at which pull points a vial was removed from storage and subjected to the testing outlined below.

(18) Test Methods Used:

(19) Non-radioactive methods (cold) performed: Appearance/organoleptic test, all pull points Purity by HPLC-UV, all pull points .sup.19F-NMR, all pull points Water content analysis, at time zero.

(20) HPLC Method: octadecylsilyl silica gel (5 m) column (Hichrom Nucleosil 100-5C18), temperature 25 C.; injection volume 20 l; mobile phase of water acetonitrile gradient, 1 ml/min. Detection by spectrophotometer at 220 nm.

(21) Radioactive methods (hot) performed: Radiolabelling with .sup.18F.sup. in a glassy carbon reactor (all pull points). Each dry sample of mannose triflate (20 mg) is dissolved in dry acetonitrile (1.6 ml). For the mannose triflate stored in acetonitrile, an aliquot (3.3 ml) was removed and diluted to 4.0 ml with acetonitrile and 1.6 ml of this solution was used in the radiolabelling test. For the samples taken after 2 weeks storage at 50 C., a 1.6 ml sample of the mannose triflate solution was used directly without further dilution. In all cases, the radiolabelling was performed after drying an .sup.18F solution of Kryptofix 2.2.2 (19.4 mg), potassium carbonate (41.0 mg), acetonitrile (0.32 ml) and water (0.04 ml) for 4 minutes at 80 C. before adding the test solution of mannose triflate in acetonitrile. The labelling reaction was carried out at 80 C. for 4 minutes in a glassy carbon reactor.

(22) Results:

(23) HPLC-UV traces for the solid mannose triflate control experiment and the acetonitrile solution of mannose triflate are shown in FIGS. 1 and 2 respectively. Mannose triflate elutes at 32.5 minutes.

(24) After 2 weeks storage at 50 C., all samples of mannose triflate stored as dry powder were black and smelled strongly of acetic acid. No radiolabelling was attempted, IR showed that the material was no longer mannose triflate. The HPLC-UV trace is shown in FIG. 3, no mannose triflate was detected.

(25) After 2 and 4 weeks storage at 50 C., the solutions in acetonitrile however, were still colourless and looked unchanged. Results from HPLC-UV showed one peak indicating no degradation of MT (FIG. 4).

(26) Results from radiolabelling in the glassy carbon reactor at time zero and after storage for different periods at 50 C. are shown in table 1.

(27) TABLE-US-00001 TABLE 1 Storage Time MT Acetonitrile pFDG RCP Sample (weeks) (mg) (ml) % Control (air) 0 20 1.6 87 Control (air) 0 20 1.6 86 Control (N.sub.2) 0 20 1.6 82 Control (N.sub.2) 0 20 1.6 93 MT/acetonitrile 0 20 1.6 91 (15 mg/ml) MT/acetonitrile 0 20 1.6 92 (15 mg/ml) MT/acetonitrile 2 24 1.6 86 (15 mg/ml) MT/acetonitrile 2 24 1.6 85 (15 mg/ml) MT/acetonitrile 3 20 1.6 65 (15 mg/ml) MT/acetonitrile 3 20 1.6 90 (15 mg/ml) MT/acetonitrile 4 20 1.6 88 (15 mg/ml) MT/acetonitrile 4 20 1.6 90 (15 mg/ml) MT/acetonitrile 8 20 1.6 76 (15 mg/ml) MT/acetonitrile 8 20 1.6 95 (15 mg/ml)
Conclusion:

(28) The combination of good labelling and good chemical stability by HPLC even after 8 weeks at 50 C. leads to the conclusion that a clear stabilisation has been achieved by dissolving MT in acetonitrile.

EXAMPLE 2: STABILITY OF MANNOSE TRIFLATE IN ACETONITRILE/WATER

(29) Using similar method to Example 1, the stability of mannose triflate in acetonitrile with water at level of approximately 725, 1450, and 2500 ppm was evaluated.

(30) Results from radiolabelling in the glassy carbon reactor at time zero and after storage for different periods at 50 C. are shown in table 2.

(31) TABLE-US-00002 TABLE 2 Water Content of MT Storage solution Time Acetonitrile/ pFDG Sample (ppm) (weeks) MT (mg) water(ml) RCP % MT/acetonitrile 2435 0 20 1.6 90 (15 mg/ml) MT/acetonitrile 2435 0 20 1.6 78 (15 mg/ml) MT/acetonitrile 1402 0 20 1.6 93 (15 mg/ml) MT/acetonitrile 725 0 20 1.6 89 (15 mg/ml) MT/acetonitrile 725 0 20 1.6 92 (15 mg/ml) MT/acetonitrile 2499 2 20 1.6 91 (15 mg/ml) MT/acetonitrile 2499 2 20 1.6 76 (15 mg/ml) MT/acetonitrile 1450 2 20 1.6 94 (15 mg/ml) MT/acetonitrile 1450 2 20 1.6 91 (15 mg/ml) MT/acetonitrile 2524 4 20 1.6 96 (15 mg/ml) MT/acetonitrile 2524 4 20 1.6 87 (15 mg/ml) MT/acetonitrile 1470 4 20 1.6 87 (15 mg/ml) MT/acetonitrile 1470 4 20 1.6 87 (15 mg/ml)

COMPARATIVE EXAMPLE: STABILITY OF DRY POWDER MANNOSE TRIFLATE

(32) Dry powder mannose triflate was stored in vials at different temperatures and for different time periods.

(33) Radiolabelling Method

(34) A solution of potassium carbonate (41 mg of potassium carbonate in 40 l water) was added to a glassy carbon reactor and then a solution of kryptofix 222 (19.4 mg in 320 l) was added separately. Then a solution of 18-fluoride in water (0.05 ml) was added and the solution dried by heating to 80 C. for 4 mins with a flow of dry nitrogen (at 0.3 liters/min). A solution of 1,3,4,6-tetra-O-acetyl-2-O-trifluoromethanesulfonyl--D-mannopyranose (20 mg in 1.6 ml dry acetonitrile) was then added and the reaction heated for a further 4 minutes at 80 C. The reaction was then cooled to 50 C. and a sample removed for analysis by ITLC (Instant thin layer chromatography) on TLC aluminium sheets silica gel 60 F254 eluting with 95% acetonitrile, 5% water. The radiochemical purity was calculated from the ratio of 1,3,4,6-tetra-O-acetyl-2-fluoro--D-mannopyranose to the total of the sugar and free fluoride (the sole two components from the reaction). Results of the radiolabelling are shown in Table 3.

(35) TABLE-US-00003 TABLE 3 Storage Conditions and time % RCP 0 days under air 87 0 days under air 86 1 day @ room temperature under dry N.sub.2 82 1 day @ room temperature under dry N.sub.2 93 127 days @ 25 C. under air 1 5 days @ 50 C. under air. 5

(36) The data support significant instability of the mannose triflate at room temperature which is much worse when heated to 50 C. The mannose triflate soon becomes black at elevated temperatures and becomes increasingly difficult to dissolve in acetonitrile.