RU2223118C1 - Method for preparing [1-11c]-acetate sodium - Google Patents

Abstract

FIELD: radiochemistry, medicine. SUBSTANCE: invention relates to method for preparing [1-¹¹C] -acetate sodium. Synthesis is carried out by column method. Methylmagnesium bromide solution in 0.2 M solution in mixture of tetrahydrofuran and diethyl ether by volume ¹¹C and adsorbent are blown with helium for 10 s. Carbon dioxide, carbon-11 is passed through adsorbent for 3 min. Hydrochloric acid as 0.2 M solution is used in the amount 2-2.5 ml. Adsorbent is blown with 5-10 ml of air and the end product is eluted with 2-4 ml of 1-2% of sodium hydrocarbonate solution. Invention provides the synthesis time 9 min., the practical yield of the end product is 65-75%, an average radiochemical yield is 96%, radiochemical purity of preparation is above 99%. High yield of product is provided in carrying out the reaction at room temperature and product is isolated in medicinal form. Preparation can be used in radionuclide diagnosis by positron emission tomography method. EFFECT: improved and simplified preparing method.

Description

 The invention relates to medicine, more specifically to radiopharmaceuticals (RFP) for diagnostic purposes and may find application in radionuclide diagnostics by positron emission tomography (PET).

 The basis of this method is the use of radionuclides - positron emitters. Carbon-11 is the only radioactive isotope of carbon, the decay of which takes place in the positron type. The use of radiopharmaceuticals labeled with ultra-short-lived carbon-11 (half-life of 20.4 min) in the PET method allows not only to record the magnitude and rate of accumulation of radioactivity in anatomically localized zones of interest, but also to carry out a quantitative measurement of regional physiological and biochemical parameters, since carbon 11 is an isotope of carbon - the main organogen element.

In radiodiagnostic cardiology as PET radiotracer widely used [1- ¹¹ C] sodium acetate (hereinafter [1- ¹¹ C] acetate), consisting of an aqueous isotonic solution containing acetate, labeled with carbon-11, without addition of carrier.

The drug is intended to assess the resource of myocardial oxidative metabolism at rest and during physical exertion, and to identify areas of ischemic tissue. Currently, [1- ¹¹ C] acetate is widely used in clinics in the USA and other countries in the diagnosis of cardiac diseases associated with dysfunction of myocardium.

[1-¹¹C]Ацетат Натрия.

[1- ¹¹ C] sodium acetate.

 To obtain this radiopharmaceutical, chemical synthesis based on the Grignard reaction between carbon dioxide — carbon-11, taken in femtogram amounts and methyl bromide taken in milligram quantities, is widely used.

Классическим способом получения [1-¹¹С]ацетата является способ, основанный на пропускании потока инертного газа, содержащего фемтограммовые количества углекислого газа, углерод-11 через раствор, содержащий бромистый метилмагний. Полученную броммагниевую соль переводят в [1-¹¹С]уксусную кислоту добавлением 6 М водного раствора соляной кислоты. При этом [1-¹¹С]уксусная кислота отделяется от эфира экстракцией и превращается в [1-¹¹С]ацетат добавлением бикарбоната натрия. Время синтеза 20 мин. Радиохимический выход с поправкой на радиоактивный распад углерода-11 во время синтеза 73% (Pike V. W., Eakins M.N., Allan R.M., Selwyn A.P., Preparation of [1-¹¹С]acetate - an agent for the study of myocard metabolism by positron emission tomography. Appl. Radiat. Isot. 33, 502-512 (1982); Pike V.W., Horlock P.L., Brown C., Clark J.C. The remotely controlled preparation of a carbon-11 labelled radiopharmaceutical -[l-¹¹C]acetate, Appl. Radiat. Isot., 35, 623-627, (1984).

The classic way to obtain [1- ¹¹ C] acetate is a method based on passing an inert gas stream containing femtogrammovye amount of carbon dioxide, carbon-11 through a solution containing methyl magnesium bromide. Brommagnievuyu resulting salt is converted into [1- ¹¹ C] acetic acid by addition of 6 M aqueous hydrochloric acid solution. Where [1- ¹¹ C] acetic acid is separated from the extraction with ether and converted to [1- ¹¹ C] acetate by addition of sodium bicarbonate. Synthesis time 20 min. Radiochemical yield corrected for radioactive decay of carbon-11 during the synthesis of 73% (Pike VW, Eakins MN, Allan RM, Selwyn AP, Preparation of [1- ¹¹ C] acetate - an agent for the study of myocard metabolism by positron emission tomography . Appl. Radiat. Isot. 33, 502-512 (1982); Pike VW, Horlock PL, Brown C., Clark JC The remotely controlled preparation of a carbon-11 labelled radiopharmaceutical - [l- ¹¹ C] acetate, Appl. Radiat. Isot., 35, 623-627, (1984).

A method is known, wherein for the isolation acetate [1- ¹¹ C] from the reaction mixture using solid phase extraction technique, which greatly facilitates automation of the application of its preparation process. The use of this method made it possible to reduce the synthesis time from 20 to 10 min, with a radiochemical yield of 50% adjusted for the radioactive decay of carbon-11 during synthesis (Korsakov MV, Solvyov D., Horti AG, Kuznetzova OF, Nilsson L. -E., Ulin J., Robotic Synthesis of [1-carbon-11] acetic acid. Proceedings of the IVth international Workshop on Targetry and Target Chemistry, PSI Villigen, Switzerland September 9-12, 1991).

Known is a method of synthesis of [1- ¹¹ C] acetate, based on the applied film methylmagnesium bromide solution on the surface of the PTFE tube through which is passed an inert gas stream containing femtogrammovye amount of carbon dioxide, carbon-11 (Davenport RJ, Dowsett K., Pike VW A simple technique for the automated production of no -carrier-added [1- ¹¹ C] acetate, Appl. Radiat. Isot, 48, 1117-1120 (1997). time synthesis -16 min, radiochemical yield corrected for radioactive decay of carbon- 11 during the synthesis of 72%.

The closest to the proposed method is the preparation of [1- ¹¹ C] acetate, based on the application of the film of 1 M methylmagnesium bromide solution on the surface of diatomite (Extrelut, Merck), powdered inert polar adsorbent with a surface area that is in microcolumns through which passed a stream of helium and then a stream of inert gas containing femtogram amounts of carbon dioxide, carbon-11 (200 mCi, 7.4 GBq). The resulting salt brommagnievuyu [1- ¹¹ C] acetic acid is converted to [1- ¹¹ C] acetic acid through a column of 0.6 ml of aqueous 3 M hydrochloric acid solution. Excess hydrochloric acid is absorbed into a second Extrelut column. Then both columns are heated to 70 ^{° C.} and purged with a stream of helium for 2 minutes to remove unreacted carbon dioxide, carbon-11. Passed through both columns 6 ml of ethyl alcohol, and [1- ¹¹ C] acetic acid is desorbed and flows through the filter-drier on a third Extrelut column pre-loaded with 1 ml of 0.7% sodium bicarbonate solution. Where [1- ¹¹ C] acetic acid in the aqueous layer is adsorbed, it is converted to the sodium salt and subsequently eluted with alcohol. The alcohol is evaporated, and the residue is dissolved in the required amount of isotonic solution. The synthesis time is 15 min, the radiochemical yield adjusted for the radioactive decay of carbon-11 during synthesis is 90%, if the column with the Grignard reagent during transmission of carbon dioxide, carbon-11 was at -5 ^o C and 60-72% at room temperature (Iwata R., Ido T. Tada M., Column Extraction Method for Rapid Preparation of [ ¹¹ C] Acetic Acid and [ ¹¹ C] Palmitic Acid. Appl. Radiat Isot. 46, 117-121 (1995).

The drawbacks of the method-prototype is relatively low radiochemical yield of [1- ¹¹ C] Acetate, if the reaction is carried out at room temperature (to increase the yield must use negative temperature, which causes technological difficulties). A relatively high synthesis time of 15 min leads to a loss of 38% activity only due to the radioactive decay of carbon-11. The disadvantages of prototype relates also need to use a nonaqueous solvent - alcohol - desorption [1- ¹¹ C] acetic acid, and the complexity of preparation technology.

The technical result of the present invention is to reduce the synthesis time, improved radiochemical yield [1- ¹¹ C] acetate and considerable simplification of its manufacturing technology.

This result is achieved by that in the known method the preparation of [1- ¹¹ C] acetate comprises passing through a porous inert adsorbent methylmagnesium bromide solution successively, helium, then an inert gas containing femtogrammovye amount of carbon dioxide, carbon-11, and hydrochloric acid solution, according to the invention, 500-700 mg of resin with a base of polystyrene divinylbenzene copolymer coated with hydrocarbon residues with a chain length of 18 carbon atoms bonded to the base by chemical bonds is used as an adsorbent In fact, methyl magnesium bromide is used in an amount of 2-3 ml of a 0.2 M solution in a mixture of tetrahydrofuran: diethyl ether - 14: 1 by volume, helium is blown through the adsorbent for 10 s, and carbon dioxide, carbon-11, is passed through the adsorbent into for 3 min, hydrochloric acid is used in an amount of 2-2.5 ml of 0.2 M solution, after which the adsorbent is purged with 5-10 ml of air, neutralized acetic acid is neutralized and the target product is eluted with 2-4 ml of a 1-2% solution sodium bicarbonate.

 The use of a resin coated with highly lipophilic hydrocarbon residues (reverse phase adsorbent) provides an increase in the adsorption of the substances to be separated as their lipophilicity increases. Reverse phase adsorbents are widely used in high performance liquid chromatography (HPLC) to change the sequence of elution of the components of the separated mixture. In contrast to HPLC based on the use of polar adsorbents (silica gel, kieselguhr), reverse phase chromatography has more polar, and therefore more hydrophilic components of the separated mixture, eluting faster than lipophilic compounds. Therefore, when using a reversed-phase adsorbent as a carrier of a film of methylmagnesium bromide, in the synthesis of acetate, more lipophilic acetic acid is retained more strongly than sodium acetate. This allowed us, by selecting the mass of the adsorbent and the concentration of hydrochloric acid, to achieve the retention of acetic acid on the adsorbent, which significantly reduces the synthesis time, thereby increasing the practical yield of the target product. Simplification of the synthesis procedure allows to increase the radiochemical yield.

 The use of methyl magnesium bromide in an amount of 2-3 ml of a 0.2 M solution in a mixture of tetrahydrofuran: diethyl ether in a ratio of 14: 1 ensures its almost complete adsorption on the surface of the resin used.

 Purge the adsorbent with helium for 10 s to remove excess solvents.

 Passing through an adsorbent an inert gas containing femtogram amounts of carbon dioxide, carbon-11, for 3 minutes is necessary and sufficient for its complete carboxylation on the resin surface.

Purging the adsorbent 5-10 ml of air removes excess hydrochloric acid, which allows further reducing the amount of sodium bicarbonate, with 2-4 ml of 2.1% solution of sodium bicarbonate is enough to neutralize the [1- ¹¹ C] acetic acid and stripping its anion in the form of sodium acetate. The use of sodium bicarbonate for this purpose it is expedient, as it is part of the dosage form of the preparation of [1- ¹¹ C] acetate.

Purification of [1- ¹¹ C] acetate, the proposed method allows to achieve a radiochemical purity greater than 99%.

 The method is as follows.

 A 0.2 M solution of methyl magnesium bromide in a mixture of tetrahydrofuran and diethyl ether in a volume ratio of 14: 1 is prepared as follows. 8.4 ml of tetrahydrofuran, previously dehydrated for two hours by boiling over metallic sodium in an atmosphere of dry inert gas and distilled in an atmosphere of dry inert gas, are mixed in an atmosphere of dry inert gas with 0.6 ml of a 3 M ether solution of methyl magnesium bromide.

 For each of two commercially available columns (SPE cartridge Chromafix 250-HR-P, Macherey-Nagel, Germany) filled with 300-350 mg of an inert porous resin with a base of polystyrene divinylbenzene copolymer coated with hydrocarbon residues with a chain length of 18 carbon atoms bound with the basis of chemical bonds, apply 1-1.5 ml of a solution of methyl magnesium bromide. Each column after filling for 10 s is purged with a stream of helium and then closed with sealed plugs from both ends before use.

 Then the columns are connected in series to the assembly, as shown in the drawing.

1 microcolumn filled with 0.5-0.7 g of phosphorus pentoxide deposited on silica gel (Sicapent, Merck, Germany),
2 and 3-reaction microcolumns, (SPE cartridge Chromafix 250-HR-P, Macherey-Nagel, Germany) containing a film of a solution of methyl magnesium bromide,
4-microcolumn filled with 0.5-0.7 g of ascarite.

 Column 1 is used to drain the gas containing carbon dioxide, carbon-11.

 Column 4 serves to absorb unreacted carbon dioxide and prevent the reaction columns from becoming wet due to back diffusion.

 Before the end of the irradiation, the column assembly is connected to the outlet line of the irradiated gas by removing the plug from column 1.

 High purity gaseous nitrogen is irradiated with protons having a kinetic energy of 5–20 MeV in a gas target of a cyclotron under a pressure of 6 bar for 2 min at a proton current of 10 μA.

 At the end of the irradiation, the plug is removed from column 4. At the same time, the irradiated gas is released from the target by gravity, opening the remote shut-off valve of the target, into the transport line of the irradiated gas.

 Irradiated gas is passed through the column assembly for 3 minutes at room temperature.

 Columns 1 and 4 are then disconnected. The activity of each of the columns is measured. 2.5 ml of 0.2 M hydrochloric acid was passed through columns 2 and 3. After that, the remaining hydrochloric acid is blown by passing 5-10 ml of air.

 Next, 2-4 ml of a 1-2% solution of sodium bicarbonate is passed through the columns, obtaining the finished product in dosage form.

 The total synthesis time, counting from the moment of activity release, is 9 minutes. Measure the activity of the obtained product and compare it with the initial activity retained by the columns.

 Columns 2 and 3 retained a total of 800-1100 MBq carbon-11, the activity of the finished product 600-900 MBq. Practical yield - 65-75%. The radiochemical yield adjusted for the radioactive decay of carbon-11 during the synthesis (9 min) is 95-99%.

Radiochemical purity of more than 99%: HPLC, Luna reverse phase column (Phenomenex, USA) 15 cm long, eluent 0.1 M sodium dihydrogen phosphate aqueous solution, acidified with 70% phosphoric acid to pH 2.1. Retention time [1- ¹¹ C] acetate 6.4 min.

 The concentration of magnesium in the preparation is less than 1 mg / ml (trilonometric titration).

 The proposed method in comparison with the known has a number of significant advantages.

 1. Reduces the synthesis time to 9 minutes, while in the prototype method it is 15 minutes

 2. The practical yield of the target product is 65-75%, while in the prototype method - 36-55%.

 3. Provides a radiochemical yield of the target product on average up to 96% compared with 60-96% in the prototype.

 4. The method is much simpler, since a high yield of the target product is ensured when carrying out the reaction at room temperature, the target product is isolated in the dosage form, so there is no need for evaporation of the non-aqueous solvent (ethyl alcohol), as in the prototype.

The method developed in the laboratory of radionuclide technology TSNIRRI MoH and used there for the preparation of [1- ¹¹ C] acetate.

Claims (1)

A process for preparing [1- ¹¹ C] sodium acetate, comprising passing through a porous inert adsorbent methylmagnesium bromide solution successively, helium, then an inert gas containing femtogrammovye amount of carbon dioxide, carbon-11, and hydrochloric acid solution, characterized in that as adsorbent use 500-700 mg of resin with a base of polystyrene divinylbenzene copolymer coated with hydrocarbon residues with a chain length of 18 carbon atoms linked to the base by chemical bonds, methyl magnesium bromide is used in in the amount of 2-3 ml of a 0.2 M solution in a mixture of tetrahydrofuran: diethyl ether - 14: 1 by volume, the adsorbent is purged with helium for 10 s, and carbon dioxide, carbon-11, is passed through the adsorbent for 3 minutes, hydrochloric acid is used in an amount of 2-2.5 ml of a 0.2 M solution, after which the adsorbent is purged with 5-10 ml of air, neutralized acetic acid is neutralized and the target product is eluted with 2-4 ml of a 1-2% solution of sodium bicarbonate.