- Email: [email protected]
Semiautomated synthesis of a novel [18F] amine fluorocyanoborane for PET imaging studies. Radiosynthesis and in vivo characterization in rats
ARTICLE IN PRESS
Applied Radiation and Isotopes 65 (2007) 204–208 www.elsevier.com/locate/apradiso
Semiautomated synthesis of a novel [18F] amine fluorocyanoborane for PET imaging studies. Radiosynthesis and in vivo characterization in rats Eli Shaloma, Khuloud Takrouria, Nir Metsuyanimb, Arik Grufib, Jehoshua Katzhendlera, Morris Srebnika, a
Department of Natural Products and Medicinal Chemistry, School of Pharmacy, Hebrew University in Jerusalem, 91120 Israel b Soreq Nuclear Research Center, Yavne, 88100 Israel Received 5 March 2006; received in revised form 6 July 2006; accepted 15 August 2006
Abstract A novel fluorine-18 labeled amine fluorocyanoborane derivative was synthesized from the bromo-derivative precursor in 22% radiochemical yield. The [18F] labeling was accomplished by a semiautomatic method that is based on the synthesis of Ag18F from Ag2CO3 and H18F in a platinum dish followed by sonication of the bromo-precursor with Ag18F in dry benzene to produce [18F] labeled amine fluorocyanoborane which was used with no further purification. A total of 50 mCi of the [18F] labeled amine fluorocyanoborane was injected into normal, female Sprague–Dawley rats (250–300 g) via the tail vein and monitored by Positron emission tomography (PET)/CT to detect its biodistribution in the rat body. The images showed an uptake of this compound in the bones of rats. r 2006 Elsevier Ltd. All rights reserved. Keywords: Semiautomatic radiosynthesis; Pet imaging; [18F] undecyldimethylamine fluorocyanoborane; Ag18F
1. Introduction Amine carboxyboranes can be regarded as isoelectronic analoges of protonated a-amino acids (Carboni and Monnier, 1999). While the compounds are similar in size and geometry, they have very different electronic and hydrogen bonding properties and, therefore, different biological responses (Spielvogel, 1988; Spielvogel et al., 1994). Amine carboxyboranes and amine cyanoboranes have been shown to be anti-hyperlipidemic in laboratory animals and showed considerable reduction in serum cholesterol levels (Hall et al., 1981, 1994). Additional physiological activities include anti-inflammatory (Hall et al., 1995, 1980), anti-osteoporotic and anti-obesity (Murphy et al., 1996). Since positron emission tomography (PET) is a remarkable technique that provides a noninvasive approach to measure biochemical processes in vivo, then the synthesis of [18F] labeled amine fluorocyanoboranes would open a technique that reveals the biodistribution uptake of such interesting compounds, and as Corresponding author.
E-mail address: [email protected] (M. Srebnik). 0969-8043/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.apradiso.2006.08.014
a result, may offer a better understanding of the mode of action of these compounds. Amine fluorocyanoboranes were synthesized in our laboratory from amine bromocyanoboranes using fluorinating reagents like AgF and Et3N 3HF (Shalom et al., 2005). Several amine fluorocyanoboranes were tested and shown to possess antimicrobial activities (Srebnik et al., 2005a, b) as well as anti-neoplastic activity in colon tumor cells (unpublished results). In the present study, we have developed a new semiautomatic module that uses a platinum dish and sonication to induce Br/18F replacement of the precursor (amine bromocyanoborane) and produce the desired [18F] labeled amine fluorocyanoborane. 2. Experimental 2.1. Materials Undecyldimethylamine monobromocyanoborane was synthesized according to published methods (Srebnik et al., 2005a, b). Benzene was purchased from Sigma-Aldrich,
ARTICLE IN PRESS E. Shalom et al. / Applied Radiation and Isotopes 65 (2007) 204–208
and dried over sodium for 2 weeks. Sonication was performed with an Astrasons (50/60 Hz, 1.2 A). H18 2 O was purchased from Rotem laboratories. H18F was produced using an IBA cyclotron at 10/5 MeV. All other chemicals were obtained from Sigma-Aldrich and used as received without any further purification. Me3NBH2CN was prepared from Me3N HCl and NaBH3CN in refluxing THF (Sood et al., 1991a, b). Merck silica gel F254 aluminum backed Merck TLC plates were used. PET imaging was performed at the Institute of Nuclear Medicine at Tel HaShomer Combined Medical Center in Israel, using a PET/CT Philips instrument. 2.2. Synthesis of the radioactive fluorinating reagent, Ag18F A total of 100 mCi of H18F dissolved in 1.1 mL of H2O was obtained from the cyclotron and was added to the platinum dish that contained 15 mg of Ag2CO3. The
H218O + P
H18F
Ag2CO 3(s) + 2H 18F / H 218O
250oC
2AgF (s)+ H2O(g) + CO 2(g)
Fig. 1. Scheme for the radiochemical synthesis of Ag18F.
205
reaction mixture was then heated to 250 1C to obtain the desired radioactive fluorinating reagent, Ag18F (Fig. 1). 2.3. Semiautomatic synthesis system The semiautomated radiosynthesis of [18F] labeled amine cyanoboranes was carried out using a modified module that was inserted inside a hot cell. The setup and flow diagram of the system is shown in Fig. 2. All the reaction steps were handled using manipulator arms. Platinum was the element of choice for the reaction vessel because it can resist both HF and high temperatures. Sonication was necessary for the nucleophilic substitution to occur in the fluorination reaction. Since benzene (the reaction solvent) dissolved the plastic stopcocks, special clips were added to hold the silicon crochets (Degania Silicon LTD) from the outside in order to prevent contact of benzene with the plastic stopcocks. Prior to the start of synthesis, Ag2CO3 was loaded into the platinum dish that was then closed using a rubber septum (Sigma-Aldrich). Solutions containing the appropriate reagents were loaded into glass vials type 1 (Bunderglass) which were sealed with silicon rubber septa. The precursor vial, vial no. 2 and the platinum dish were all equipped with an inlet line for nitrogen gas to pressurize the vial, and silicon line (Degania
Fig. 2. Diagram of the semiautomated synthesis system for the synthesis of [18F] labeled amine fluorocyanoborane.
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Silicon LTD) outlets for delivery of the precursor vial contents to the platinum dish and the platinum dish contents to vial no. 2. The 7 mL precursor glass vial was fitted with a silicon rubber stopper (ABX). The 12 mL glass vial no. 2 was fitted with a latex rubber stopper (West). A 25 mL glass vial (Mallinckrodt) was used to collect the product. The 25 mL platinum dish was designed to be hermetically sealed with an o-ring and latex septum in order to withstand the high pressure caused by nitrogen (Fig. 3). 2.4. Semiautomatic synthesis of [18F] undecyldimethylamine fluorocyanoborane The synthesis began with the addition of 100 mCi of H18F dissolved in 1.1 mL of H18 2 O to the platinum dish to dissolve the Ag2CO3. This step was immediately followed by heating the reaction mixture to 250 1C for less than 5 min to get the desired Ag18F as a precipitate. The platinum dish was transferred to the ultrasonic bath, and cooled for 3 min. Then, 0.15 mg of undecyldimethylamine monobromocyanoborane dissolved in 4 mL of dry benzene was added to the platinum dish. (Other solvents were tested. i.e., acetonitrile, toluene and pyridine; but resulted in inferior yields). The sonicator was turned on for 50 min. This is the optimized time for complete chemical conversion as determined by sampling the reaction on TLC (silica gel F254). The product was then transferred and filtered through a stainless steel filter containing a 0.22 mm Teflon membrane. The nitrogen pressure was set at 1.1 bar and controlled by a 0.4 L/min flow rate into glass vial no. 2. Vial no. 2 was transferred to the heater and the benzene vaporized at 110 1C for 15 min while being vented with
nitrogen, after which the vial was sampled once and injected in a GC. No benzene was present. Vial no. 2 was then cooled with external air for 3 min. After the product was dissolved in the saline, a syringe that contained 5 mL saline (0.9% NaCl in water) was injected into vial no. 2 using a needle that reached the bottom of the vial. It was then retracted back into the syringe. A four-way stopcock was turned on to transfer the final product into the product vial via a 0.22 mm cartridge filter. A 22% radiochemical yield at the EOS with a specific radio activity of 455 mCi/mg was obtained in the product vial. The final product as a saline solution (4.5 mCi/mL) was then shielded to prevent irradiation. We have performed 12 syntheses, four of which failed because of the interaction between the benzene and the plastic stopcocks filters. 2.5. PET imaging Normal, female Sprague–Dawley rats (250–300 g) were injected via the tail vein with 50 mCi of the [18F] undecyldimethylamine fluorocyanoborane solution in saline (4.5 mCi/mL). Then, 15 min after injection, the four rats were anesthetized with 45 mg Ketamine and 24 mg Acepromazin. After 30 min each rat was imaged for 15 min. 2.6. Quality control Radiochemical purity and identity, and chemical purity were evaluated using radiometric TLC. The radiochemical purity was 100% T1/2 of 18F and was tested according to the 18F specification. TLC was performed utilizing Merck silica gel F254 plates with a mobile phase of 100% methanol and analyzed with radiometric detection. The Rf of the radiolabeled product was compared with the observed Rf of the non-radioactive form. The pH was determined using pH test papers in the range 3.8–5.5 and 6.0–8.1. The 18F was detected with a Wallac Wizard g-counter with sodium iodide detector. The final product was tested on TLC (silica gel 60 F254) after 10 h and found to the stable. AgF is a solid and does not pass through the 0.22 mm filter. 3. Results and discussion 3.1. Chemistry
Fig. 3. Designed sealed platinum dish.
The precursor undecyldimethylamine monobromocyanoborane was synthesized according to published procedure starting from trimethylamine cyanoborane (Takrouri et al., 2004). Undecyldimethylamine cyanoborane was synthesized from trimethylamine cyanoborane (Sood et al., 1991a, b) by the C-lithiation/alkylation method. This was then followed by bromination with one equivalent of bromine dissolved in water, and fluorinated with 19F using silver fluoride as the fluorination reagent as described in the literature (Shalom et al., 2005) to get the desired
ARTICLE IN PRESS E. Shalom et al. / Applied Radiation and Isotopes 65 (2007) 204–208
non-radiolabeled undecyldimethylamine fluorocyanoborane. The undecyldimethylamine bromocyanoborane was also fluorinated with Ag18F that was synthesized as
207
described in Section 2.2 by the semiautomatic synthesis system as described in Section 2.3 to get the [18F] labeled undecyldimethylamine fluorocyanoborane (Fig. 4).
1) 1.5 equiv. s-BuLi Me3NBH2CN
CH3(CH2)9
2) 1-bromodecane
Me C N BH2CN H2 Me
1.1 equiv. Br2 /H2O
CH3(CH2)9
Me C N BH18FCN H2 Me
Ag18F/ sonication CH3(CH2)9 semiautomatic synthesis
Me C N BHBrCN H2 Me AgF, benzene sonication for 50min
CH3(CH2)9
Me C N BHFCN H2 Me
Fig. 4. Scheme for the synthesis of [18F] labeled undecyldimethylamine fluorocyanoborane.
Fig. 5. PET images taken for normal, female Sprague–Dawley rats (250–300 g) that were injected via the tail vein with 50 mCi of the [18F] undecyldimethylamine fluorocyanoborane solution in saline (4.5 mCi/mL).
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3.2. Semiautomatic synthesis of [18F] undecyldimethylamine fluorocyanoborane The radio-synthesis of [18F] undecyldimethylamine fluorocyanoborane was performed using a new semiautomatic synthesis system that was designed to suit the reaction conditions as shown schematically in Fig. 2. The reactions were performed using manipulator arms. These steps are amenable to automation as well and do not expose personnel to significant levels of radioactivity. The synthesis was performed in three steps. In the first reaction, the fluorinating reagent Ag18F was prepared in the platinum dish. Then the precursor (undecyldimethylamine monobromocyanoborane) was added under sonication. The obtained [18F] product was transferred to another vial where the solvent was removed, and the product was redissolved in physiologic solution (saline). 3.3. PET imaging Fig. 5 shows an image obtained for normal, female Sprague–Dawley rats (250–300 g) that were injected via the tail vein with 50 mCi of the [18F] undecyldimethylamine fluorocyanoborane solution in saline (4.5 mCi/mL). PET image clearly shows uptake into the bones. These preliminary results are proof to our concept that [18F] labeling of amine cyanoborane and amine carboxyborane derivatives could be a useful tool that may lead to a better understanding of their mode of action in the body. 3.4. Quality control The final [18F] labeled undecyldimethylamine fluorocyanoborane was subjected to a number of quality control measures including assessment of radiochemical purity, gdetector and pH measurements. Silica TLC tests were performed to assess the radiochemical purity. TLC of the product on silica plates with 100% methanol demonstrated a single radioactive peak with an Rf of 0.23 which was identical to the Rf of the non-radioactive undecyldimethylamine fluorocyanoborane. The 18F was detected with Wallac Wizard g-counter with sodium iodide detector and showed 511 keV. The tested pH of the radioactive [18F] labeled product solution in saline was 6.3. 4. Conclusion The [18F] labeled form of undecyldimethylamine fluorocyanoborane was synthesized from the bromo derivative as the precursor in 22% radiochemical yield using a specially designed semiautomatic system. The radiolabeling is based on the synthesis of Ag18F from Ag2CO3 and H18F. Ag18F is used in the conversion of the bromo precursor to the title compound by sonication of the latter in dry benzene for 50 min. The product was identified by TLC and a g counter detector. The [18F] labeled amine fluorocyanoborane was injected into normal rats, and was monitored
by a PET/CT Philips camera. The images detected the biodistribution and showed an uptake in the rat’s bones.
Acknowledgments This research was supported in part by the Alex Grass Center for Drug Design and Synthesis of Novel Therapeutics, and by David R. Bloom Center of Pharmacy. The authors thank the Israeli Science Foundation for generous support of this work. ES and KT thank the School of Pharmacy for fellowships. The authors thank Soreq Nuclear Research Center for offering their equipments for the purpose of accomplishing this research, and mainly the chief operator Mr. Kobi Ben-Meir, who built this semiautomatic synthesis system. Also the authors wish to thank Prof. T. Tsvas of the Institute of Nuclear Medicine at Tel HaShomer for allowing access to the PET imaging facility at their institute.
References Carboni, B., Monnier, L., 1999. Recent develpments in the chemistry of amine and phosphine boranes. Tetrahedron 55, 1197–1248. Hall, I.H., Starnes, C.O., McPhail, A.T., Wisian-Neilson, P., Das, M.K., Harchelroad Jr., F., Spielvogel, B.F., 1980. Anti-inflammatory activity of amine cyanoboranes, amine carboxyboranes, and related compounds. J. Pharm. Sci. 69, 1025–1029. Hall, I.H., Das, M.K., Harchelroad Jr., F., Wisian-Neilson, P., McPhail, A.T., Spielvogel, B.F., 1981. Antihyperlipidemic activity of amine cyanoboranes, amine carboxyboranes, and related compounds. J. Pharm. Sci. 70 (3), 339–341. Hall, I.H., Chen, S.Y., Rajendran, K.G., Sood, A., Spielvogel, B.F., Shih, J., 1994. Hypolipidemic, anti-obesity, anti-inflammatory, anti-osteoporotic, and anti-neoplastic properties of amine carboxyboranes. Environ. Health Persp. 102, 21–30. Hall, I.H., Burnham, B.S., Chen, S.Y., Sood, A., Spielvogel, B.F., Morse, K.W., 1995. The anti-inflammatory activity of boron derivatives in rodents. Metal Based Drugs 2 (1), 1–12. Murphy, M.E., Elkins, A.L., Shrewsbury, R.P., Sood, A., Spielvogel, B.F., Hall, I.H., 1996. The effects of amine-carboxyborane related derivatives on umr-106 bone metabolism. Metal Based Drugs 3, 31–56. Shalom, E., Takrouri, K., Goldberg, I., Katzhendler, J., Srebnik, M., 2005. Preparation of novel flouoro dreivatives of amine cyanoboranes and amine carboxyborane. Sood, C.K., Sood, A., Spielvogel, B.F., Yousef, J.A., Burnham, B., Hall, I.H., 1991a. Synthesis and antineoplastic activity of some cyano-, carboxy-, carbomethoxy-, and cabamoylborane adducts of heterocyclic amines. J. Pharm. Sci. 81, 1133–1140. Sood, C.K., Sood, A., Spielvogel, B.F., Yousef, J.A., Burnham, B., Hall, I.H., 1991b. Esters. Organometallics 24, 5776–5779. Spielvogel, B.F., 1988. In: Liebman, J.F., Greenberg, A., Williams, R.E. (Eds.), Advances in Boron and the Boranes. VCH, New York p. 329. Spielvogel, B.F., Sood, A., Shaw, B.R., Hall, I.H., 1994. In: Kabalka, G.W. (Ed.), Current Topics in the Chemistry of Boron. Royal Society of Chemistry, Cambridge p. 193. Srebnik, M., Takrouri, K., Katzhendler, J., Polacheck, I., 2005a. Use of amine-borane compounds as anti-microbial agents. United States Patent , Ref no.: 2966.00. Srebnik, M., Takrouri, K., Shalom, E., 2005b. Novel amine-borane compounds and uses thereof. United States Patent, Ref No.: 3057.00. Takrouri, K., Katzhendler, J., Srebnik, M., 2004. C-Lithiation/alkylation of trimethylamine cyanoborane. Organometallics 23 (11), 2817–2820.
Applied Radiation and Isotopes 65 (2007) 204–208 www.elsevier.com/locate/apradiso
Semiautomated synthesis of a novel [18F] amine fluorocyanoborane for PET imaging studies. Radiosynthesis and in vivo characterization in rats Eli Shaloma, Khuloud Takrouria, Nir Metsuyanimb, Arik Grufib, Jehoshua Katzhendlera, Morris Srebnika, a
Department of Natural Products and Medicinal Chemistry, School of Pharmacy, Hebrew University in Jerusalem, 91120 Israel b Soreq Nuclear Research Center, Yavne, 88100 Israel Received 5 March 2006; received in revised form 6 July 2006; accepted 15 August 2006
Abstract A novel fluorine-18 labeled amine fluorocyanoborane derivative was synthesized from the bromo-derivative precursor in 22% radiochemical yield. The [18F] labeling was accomplished by a semiautomatic method that is based on the synthesis of Ag18F from Ag2CO3 and H18F in a platinum dish followed by sonication of the bromo-precursor with Ag18F in dry benzene to produce [18F] labeled amine fluorocyanoborane which was used with no further purification. A total of 50 mCi of the [18F] labeled amine fluorocyanoborane was injected into normal, female Sprague–Dawley rats (250–300 g) via the tail vein and monitored by Positron emission tomography (PET)/CT to detect its biodistribution in the rat body. The images showed an uptake of this compound in the bones of rats. r 2006 Elsevier Ltd. All rights reserved. Keywords: Semiautomatic radiosynthesis; Pet imaging; [18F] undecyldimethylamine fluorocyanoborane; Ag18F
1. Introduction Amine carboxyboranes can be regarded as isoelectronic analoges of protonated a-amino acids (Carboni and Monnier, 1999). While the compounds are similar in size and geometry, they have very different electronic and hydrogen bonding properties and, therefore, different biological responses (Spielvogel, 1988; Spielvogel et al., 1994). Amine carboxyboranes and amine cyanoboranes have been shown to be anti-hyperlipidemic in laboratory animals and showed considerable reduction in serum cholesterol levels (Hall et al., 1981, 1994). Additional physiological activities include anti-inflammatory (Hall et al., 1995, 1980), anti-osteoporotic and anti-obesity (Murphy et al., 1996). Since positron emission tomography (PET) is a remarkable technique that provides a noninvasive approach to measure biochemical processes in vivo, then the synthesis of [18F] labeled amine fluorocyanoboranes would open a technique that reveals the biodistribution uptake of such interesting compounds, and as Corresponding author.
E-mail address: [email protected] (M. Srebnik). 0969-8043/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.apradiso.2006.08.014
a result, may offer a better understanding of the mode of action of these compounds. Amine fluorocyanoboranes were synthesized in our laboratory from amine bromocyanoboranes using fluorinating reagents like AgF and Et3N 3HF (Shalom et al., 2005). Several amine fluorocyanoboranes were tested and shown to possess antimicrobial activities (Srebnik et al., 2005a, b) as well as anti-neoplastic activity in colon tumor cells (unpublished results). In the present study, we have developed a new semiautomatic module that uses a platinum dish and sonication to induce Br/18F replacement of the precursor (amine bromocyanoborane) and produce the desired [18F] labeled amine fluorocyanoborane. 2. Experimental 2.1. Materials Undecyldimethylamine monobromocyanoborane was synthesized according to published methods (Srebnik et al., 2005a, b). Benzene was purchased from Sigma-Aldrich,
ARTICLE IN PRESS E. Shalom et al. / Applied Radiation and Isotopes 65 (2007) 204–208
and dried over sodium for 2 weeks. Sonication was performed with an Astrasons (50/60 Hz, 1.2 A). H18 2 O was purchased from Rotem laboratories. H18F was produced using an IBA cyclotron at 10/5 MeV. All other chemicals were obtained from Sigma-Aldrich and used as received without any further purification. Me3NBH2CN was prepared from Me3N HCl and NaBH3CN in refluxing THF (Sood et al., 1991a, b). Merck silica gel F254 aluminum backed Merck TLC plates were used. PET imaging was performed at the Institute of Nuclear Medicine at Tel HaShomer Combined Medical Center in Israel, using a PET/CT Philips instrument. 2.2. Synthesis of the radioactive fluorinating reagent, Ag18F A total of 100 mCi of H18F dissolved in 1.1 mL of H2O was obtained from the cyclotron and was added to the platinum dish that contained 15 mg of Ag2CO3. The
H218O + P
H18F
Ag2CO 3(s) + 2H 18F / H 218O
250oC
2AgF (s)+ H2O(g) + CO 2(g)
Fig. 1. Scheme for the radiochemical synthesis of Ag18F.
205
reaction mixture was then heated to 250 1C to obtain the desired radioactive fluorinating reagent, Ag18F (Fig. 1). 2.3. Semiautomatic synthesis system The semiautomated radiosynthesis of [18F] labeled amine cyanoboranes was carried out using a modified module that was inserted inside a hot cell. The setup and flow diagram of the system is shown in Fig. 2. All the reaction steps were handled using manipulator arms. Platinum was the element of choice for the reaction vessel because it can resist both HF and high temperatures. Sonication was necessary for the nucleophilic substitution to occur in the fluorination reaction. Since benzene (the reaction solvent) dissolved the plastic stopcocks, special clips were added to hold the silicon crochets (Degania Silicon LTD) from the outside in order to prevent contact of benzene with the plastic stopcocks. Prior to the start of synthesis, Ag2CO3 was loaded into the platinum dish that was then closed using a rubber septum (Sigma-Aldrich). Solutions containing the appropriate reagents were loaded into glass vials type 1 (Bunderglass) which were sealed with silicon rubber septa. The precursor vial, vial no. 2 and the platinum dish were all equipped with an inlet line for nitrogen gas to pressurize the vial, and silicon line (Degania
Fig. 2. Diagram of the semiautomated synthesis system for the synthesis of [18F] labeled amine fluorocyanoborane.
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Silicon LTD) outlets for delivery of the precursor vial contents to the platinum dish and the platinum dish contents to vial no. 2. The 7 mL precursor glass vial was fitted with a silicon rubber stopper (ABX). The 12 mL glass vial no. 2 was fitted with a latex rubber stopper (West). A 25 mL glass vial (Mallinckrodt) was used to collect the product. The 25 mL platinum dish was designed to be hermetically sealed with an o-ring and latex septum in order to withstand the high pressure caused by nitrogen (Fig. 3). 2.4. Semiautomatic synthesis of [18F] undecyldimethylamine fluorocyanoborane The synthesis began with the addition of 100 mCi of H18F dissolved in 1.1 mL of H18 2 O to the platinum dish to dissolve the Ag2CO3. This step was immediately followed by heating the reaction mixture to 250 1C for less than 5 min to get the desired Ag18F as a precipitate. The platinum dish was transferred to the ultrasonic bath, and cooled for 3 min. Then, 0.15 mg of undecyldimethylamine monobromocyanoborane dissolved in 4 mL of dry benzene was added to the platinum dish. (Other solvents were tested. i.e., acetonitrile, toluene and pyridine; but resulted in inferior yields). The sonicator was turned on for 50 min. This is the optimized time for complete chemical conversion as determined by sampling the reaction on TLC (silica gel F254). The product was then transferred and filtered through a stainless steel filter containing a 0.22 mm Teflon membrane. The nitrogen pressure was set at 1.1 bar and controlled by a 0.4 L/min flow rate into glass vial no. 2. Vial no. 2 was transferred to the heater and the benzene vaporized at 110 1C for 15 min while being vented with
nitrogen, after which the vial was sampled once and injected in a GC. No benzene was present. Vial no. 2 was then cooled with external air for 3 min. After the product was dissolved in the saline, a syringe that contained 5 mL saline (0.9% NaCl in water) was injected into vial no. 2 using a needle that reached the bottom of the vial. It was then retracted back into the syringe. A four-way stopcock was turned on to transfer the final product into the product vial via a 0.22 mm cartridge filter. A 22% radiochemical yield at the EOS with a specific radio activity of 455 mCi/mg was obtained in the product vial. The final product as a saline solution (4.5 mCi/mL) was then shielded to prevent irradiation. We have performed 12 syntheses, four of which failed because of the interaction between the benzene and the plastic stopcocks filters. 2.5. PET imaging Normal, female Sprague–Dawley rats (250–300 g) were injected via the tail vein with 50 mCi of the [18F] undecyldimethylamine fluorocyanoborane solution in saline (4.5 mCi/mL). Then, 15 min after injection, the four rats were anesthetized with 45 mg Ketamine and 24 mg Acepromazin. After 30 min each rat was imaged for 15 min. 2.6. Quality control Radiochemical purity and identity, and chemical purity were evaluated using radiometric TLC. The radiochemical purity was 100% T1/2 of 18F and was tested according to the 18F specification. TLC was performed utilizing Merck silica gel F254 plates with a mobile phase of 100% methanol and analyzed with radiometric detection. The Rf of the radiolabeled product was compared with the observed Rf of the non-radioactive form. The pH was determined using pH test papers in the range 3.8–5.5 and 6.0–8.1. The 18F was detected with a Wallac Wizard g-counter with sodium iodide detector. The final product was tested on TLC (silica gel 60 F254) after 10 h and found to the stable. AgF is a solid and does not pass through the 0.22 mm filter. 3. Results and discussion 3.1. Chemistry
Fig. 3. Designed sealed platinum dish.
The precursor undecyldimethylamine monobromocyanoborane was synthesized according to published procedure starting from trimethylamine cyanoborane (Takrouri et al., 2004). Undecyldimethylamine cyanoborane was synthesized from trimethylamine cyanoborane (Sood et al., 1991a, b) by the C-lithiation/alkylation method. This was then followed by bromination with one equivalent of bromine dissolved in water, and fluorinated with 19F using silver fluoride as the fluorination reagent as described in the literature (Shalom et al., 2005) to get the desired
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non-radiolabeled undecyldimethylamine fluorocyanoborane. The undecyldimethylamine bromocyanoborane was also fluorinated with Ag18F that was synthesized as
207
described in Section 2.2 by the semiautomatic synthesis system as described in Section 2.3 to get the [18F] labeled undecyldimethylamine fluorocyanoborane (Fig. 4).
1) 1.5 equiv. s-BuLi Me3NBH2CN
CH3(CH2)9
2) 1-bromodecane
Me C N BH2CN H2 Me
1.1 equiv. Br2 /H2O
CH3(CH2)9
Me C N BH18FCN H2 Me
Ag18F/ sonication CH3(CH2)9 semiautomatic synthesis
Me C N BHBrCN H2 Me AgF, benzene sonication for 50min
CH3(CH2)9
Me C N BHFCN H2 Me
Fig. 4. Scheme for the synthesis of [18F] labeled undecyldimethylamine fluorocyanoborane.
Fig. 5. PET images taken for normal, female Sprague–Dawley rats (250–300 g) that were injected via the tail vein with 50 mCi of the [18F] undecyldimethylamine fluorocyanoborane solution in saline (4.5 mCi/mL).
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3.2. Semiautomatic synthesis of [18F] undecyldimethylamine fluorocyanoborane The radio-synthesis of [18F] undecyldimethylamine fluorocyanoborane was performed using a new semiautomatic synthesis system that was designed to suit the reaction conditions as shown schematically in Fig. 2. The reactions were performed using manipulator arms. These steps are amenable to automation as well and do not expose personnel to significant levels of radioactivity. The synthesis was performed in three steps. In the first reaction, the fluorinating reagent Ag18F was prepared in the platinum dish. Then the precursor (undecyldimethylamine monobromocyanoborane) was added under sonication. The obtained [18F] product was transferred to another vial where the solvent was removed, and the product was redissolved in physiologic solution (saline). 3.3. PET imaging Fig. 5 shows an image obtained for normal, female Sprague–Dawley rats (250–300 g) that were injected via the tail vein with 50 mCi of the [18F] undecyldimethylamine fluorocyanoborane solution in saline (4.5 mCi/mL). PET image clearly shows uptake into the bones. These preliminary results are proof to our concept that [18F] labeling of amine cyanoborane and amine carboxyborane derivatives could be a useful tool that may lead to a better understanding of their mode of action in the body. 3.4. Quality control The final [18F] labeled undecyldimethylamine fluorocyanoborane was subjected to a number of quality control measures including assessment of radiochemical purity, gdetector and pH measurements. Silica TLC tests were performed to assess the radiochemical purity. TLC of the product on silica plates with 100% methanol demonstrated a single radioactive peak with an Rf of 0.23 which was identical to the Rf of the non-radioactive undecyldimethylamine fluorocyanoborane. The 18F was detected with Wallac Wizard g-counter with sodium iodide detector and showed 511 keV. The tested pH of the radioactive [18F] labeled product solution in saline was 6.3. 4. Conclusion The [18F] labeled form of undecyldimethylamine fluorocyanoborane was synthesized from the bromo derivative as the precursor in 22% radiochemical yield using a specially designed semiautomatic system. The radiolabeling is based on the synthesis of Ag18F from Ag2CO3 and H18F. Ag18F is used in the conversion of the bromo precursor to the title compound by sonication of the latter in dry benzene for 50 min. The product was identified by TLC and a g counter detector. The [18F] labeled amine fluorocyanoborane was injected into normal rats, and was monitored
by a PET/CT Philips camera. The images detected the biodistribution and showed an uptake in the rat’s bones.
Acknowledgments This research was supported in part by the Alex Grass Center for Drug Design and Synthesis of Novel Therapeutics, and by David R. Bloom Center of Pharmacy. The authors thank the Israeli Science Foundation for generous support of this work. ES and KT thank the School of Pharmacy for fellowships. The authors thank Soreq Nuclear Research Center for offering their equipments for the purpose of accomplishing this research, and mainly the chief operator Mr. Kobi Ben-Meir, who built this semiautomatic synthesis system. Also the authors wish to thank Prof. T. Tsvas of the Institute of Nuclear Medicine at Tel HaShomer for allowing access to the PET imaging facility at their institute.
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