TY - JOUR T1 - Improved synthesis and purification of C-11 PBR-28 JF - Journal of Nuclear Medicine JO - J Nucl Med SP - 2720a LP - 2720a VL - 57 IS - supplement 2 AU - Daniel Yokell AU - Nancy Nguyen AU - Steven Gallo AU - Tiffany L'Heureux AU - Peter Rice AU - Danielle Vesper AU - Georges El Fakhri Y1 - 2016/05/01 UR - http://jnm.snmjournals.org/content/57/supplement_2/2720a.abstract N2 - 2720aObjectives C-11 PBR-28 has been reported in the literature to be difficult to be purified and formulated into a readily injectable formulation for human use. Previous reports included formulation via rotary evaporation or solid phase extraction (SPE) requiring HPLC fraction dilution in a large volume of water to facilitate trapping of C-11 PBR-28. These methods would be problematic for automation on commonly used automated synthesis units for C-11 radiopharmaceuticals, since most lack rotary evaporation capability and the proposed SPE methods would add unacceptable amounts of time to the C-11 PBR-28 synthesis. We set out to develop a new direct cut semi-preparative HPLC purification method using a readily injectable mobile phase to address these issues. In addition, we desired to develop a reaction mixture which contained only ICH/USP Class III solvents to eliminate the residual solvent testing requirement on each batch prior to release.Methods Methylation of C-11 PBR-28 was performed using C-11 methyl iodide or methyl triflate on the GE TRACERlab FX-C Pro synthesis unit using acetone-d6 (ICH/USP Class III) as the reaction solvent with the N-(2-hydroxybenzyl)-N-(4-phenoxypyridin-3-yl)acetamide precursor in the presence of TBAOH, pH 8-9. A new semi-preparative HPLC method was developed using 40% Ethanol/60% Phosphate Buffered Saline, pH 7 on an Agilent Eclipse XDB C18 5µ 9.6x250mm column, flow rate 5mL/min. Based on a C-11 PBR28 peak width of 45 seconds, the collected peak fraction was immediately diluted with 12mL of 0.9% Sodium Chloride for Injection, USP to obtain a ethanol content of <10% w/v to be suitable for injection.Results C-11 PBR-28 was successfully synthesized using C-11 methyl iodide and methyl triflate using the loop method and acetone-d6 as the reaction solvent. C-11 PBR-28 precursor eluted at 9.5 minutes and C-11 PBR-28 eluted at 13.5 minutes (Figure 1). Average specific activity was 3000mCi/µmol at EOS and chemical purity met specification of ≤1µg/mL of impurities. Ethanol content was determined to be <10% w/v by gas chromatography and no other solvents were detected. All other quality control tests were within FDA/USP limits for human use. Yields were higher with methyl triflate, but a radioactive impurity eluting immediately prior to the C-11 PBR-28 peak lead us to select labeling with methyl iodide, as the radioactive impurity peak was minimized; improving radiochemical purity of the final product to >99.9%. Conclusions C-11 PBR-28 can be successfully synthesized in a acetone reaction mixture using either C-11 methyl iodide or C-11 methyl triflate. Yields are higher with methyl triflate but an unknown radioactivity peak elutes close to C-11 PBR-28, which is minimized with methyl iodide. The proposed synthesis and purification method can obtain a pure C-11 PBR-28 product in a readily injectable formulation containing ≤10% ethanol w/v and meets all FDA and USP specifications for human use. ER -