F Radiochemistry. Robert H. Mach, Ph.D.

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1 Slides are not to be reproduced 18 F Radiochemistry Robert. Mach, Ph.D. Division of Radiological Sciences University School of Medicine St. Louis, M WASIGT UIVERSITY UIVERSITY I ST LUIS

2 Slides are not to be reproduced Principles of Radiochemstry ucleophilic vs electrophilic Methods of incorporating into pharmacologically-active molecules -Radiotracer design WASIGT UIVERSITY UIVERSITY I ST LUIS

3 References Slides are not to be reproduced 1. P.. Elsinga. Radiopharmaceutical Chemistry for Positron Emission Tomography. Methods 27: (2002); 2. F. Wuest. Aspects of Positron Emission Tomography Radiochemistry as Relevant for Food Chemistry. Amino Acids 29: (2005); 3. D.J. Schlyer. PET Tracers and Radiochemistry. Ann. Acad. Med. Singapore 33: (2004); 4. S.E. Snyder and M.R. Kilbourn. Chemistry of Fluorine-18 Radiopharmaceuticals. In: andbook of Radiopharmaceuticals : Radiochemistry and Applications. M.J. Welch and C.S. Redvanly, Editors. John Wiley & Sons, Inc., M.R. Kilbourn. Fluorine-18 Labeling of Radiopharmaceuticals. uclear Science Series. ational Academy Press, L. Cai, S. Lu and V.W. Pike, Chemistry with [ ]Fluoride Ion. Eur. J. rg. Chem. 2008, WASIGT UIVERSITY UIVERSITY I ST LUIS

4 Radionuclides Used in PET Slides are not to be reproduced Radionuclide alf- Life (min) uclear Reaction Rb Sr/Rb Generator Average Β + Energy (kev) Β+ range mm ( 2 ) Maximum Specific Activity (Ci/µmol)* 1, (p,n) , C-13(p,n) ,900 C (p,α)C ,220 F (p,n)F ,710 Routine: Carbon-11: ~10 Ci/µmol; [ ]fluoride: 2 10 Ci/µmol WASIGT UIVERSITY UIVERSITY I ST LUIS

5 Electrophilic Fluorination Slides are not to be reproduced 20 e d,α 2% F 2 [ ]F 2 [ ]F 2 2% F 2 /Ar 2% F 2 /Ar irradiate passivation [ 18 ] 2 p, n [ ]/target Recovery irradiate [ 18 ] 2 WASIGT UIVERSITY UIVERSITY I ST LUIS

6 Slides are not to be reproduced Initial Synthesis of [ ]FDPA C [ ]F 2 or C [ ]C 3 CF FDPA C C DPA 6-FDPA Target Compound Ratioof2:5:6=35:5:59 WASIGT UIVERSITY UIVERSITY I ST LUIS

7 Slides are not to be reproduced ew Synthesis of FDPA: rganotin Chemistry Boc CC 2 C 3 Boc CC 2 C 3 [ ]F 2 Boc Sn(C 3 ) 3 C Freon-11 Boc C Cl C 140 o Cfor5min 2 Specific Activity: 1,700 mci/mmol (USP 100 mci/mmol) Replaced with Freon with CCl 3 $25,000/incidence for volatilization! WASIGT UIVERSITY UIVERSITY I ST LUIS

8 ucleophilic Fluorination Slides are not to be reproduced uclear reaction: [ 18 ] 2 (p,n) [ ]F Convert to salt -add [ ]F to solution of base (i.e., K 2 C 3 ) referred to as untreated fluoride -Pass [ ]F through an anion exchange resin and elute with base- treated fluoride -Anion exchange resin traps fluoride and removes trace metals which can interfere with incorporation Common counter ions: K (K 2 C 3 /2.2.2 Kryptofix) Tetrabutyl (TB) Cs (Cs 2 C 3 ) WASIGT UIVERSITY UIVERSITY I ST LUIS

9 Disadvantages of Fluorine-18 Radiochemistry S C 3 2 [ ]KF Kryptofix 180 o C 30 min 2 [ ]KF Kryptofix S C 3 [ ]MSP [ ]Setoperone Yield: 1-3% Yield: 55%

10 BL Synthesis of [ ]MSP [ ]CsF Cl/C 3 2 aq. DMS 160 o C Cl amine/ki C 3 [ ]MSP verall Yield: 7-15%

11 Slides are not to be reproduced ucleophilic Fluorination: Activating and Leaving Groups X X [ ]MF or microwave SAr2 Mechanism LG = Cl. Br, 2,Me 3 + LG X = electron withdrawing group C, C, ketone, 2,S 2 R, CR R S [ ]MF or microwave S2 Mechamism R=C 3,p-C 3 Ph, CF 3 WASIGT UIVERSITY UIVERSITY I ST LUIS

12 Effect of Leaving Group 2 itro analog of GBR Me 3 + [ ]GBR Easy to remove via Sep-Pak puriication Simplifies PLC purification of final compoud aka et al., 1989

13 F-18 Chemistry: Prosthetic Groups CF 3 S 2 Bis-triflate S 2 CF 3 [ ]KF CF 3 S 2 spiperone [ ]FESP C C C 2 I C 3 [ ]CsF 1. LiB 4 2. I amine 2 Me 3 + Cl [ ]FCP [ ]FBI

14 Slides are not to be reproduced Metabolism of 2-FE and 4-Fluorobenzyl Groups [ ]FESP [ ]fluroroacetaldehyde Crosses Blood-Brain Barrier C 3 C 2 Cl [ ]FCP [ ]4-fluorohippuric acid Does not cross BBB WASIGT UIVERSITY UIVERSITY I ST LUIS

15 Boc Me 3 + Boc Slides are not to be reproduced K /K 222 DMS 70% yield Ding et al., Synapse 1996 Br K /K 222 DMS 50 min 10% yield >2000 mci/mmol orti et al., JLCR 1996 Boc + Me 3 K /K 222 DMS/150 o C/2 min or microwave1min TFA C 2 C 2 RT/1 min 70-90% Dolle et al, J. Med. Chem WASIGT UIVERSITY UIVERSITY I ST LUIS

16 Slides are not to be reproduced Substituent Constants for Radionuclides Used in PET Substituent π σ p MR C F I Br C 2 C 2 F C 2 C 2 C 2 F F and are bond acceptors WASIGT UIVERSITY UIVERSITY I ST LUIS

17 Structures of the PET Radiotracers 11 C 3 C 3 C 3 C 3 C 3 C 3 C 3 [ 11 C]RTC-11 [ ]RTF-18 σ 1 =3078nM σ 2 =10.3nM Log D = 2.84 σ 1 =330±24 σ 2 =6.95±1.63 Log D = 3.06 WASIGT UIVERSITY UIVERSITY I ST LUIS

18 Fluoroalkyl Strategy: FC 2 C 2 C 2 for I Substitution Ts [ ]KF C 3 C 3 Kryptofix C 3 C 3 ucl. Med. Biol. 26: ; 1999 [ ]Fallylpride Ts 1. [ ]KF/K 222 Boc 2. TFA/C 2 Cl 2 [ ]ifrolidine J. ucl. Med. 46: ; 2005

19 F for Substitution FforSubstitution C 3 C 3 [ ]6-FA [ ]FMAU [ ]FLT FC 2 C 2 C 2 for I Substitution C 3 C 3 [ ]Fallylpride [ ]ifrolidine WASIGT UIVERSITY UIVERSITY I ST LUIS

20 Labeling Peptides with F-18 Slides are not to be reproduced Amine Reactive Prosthetic Groups 2 C 3 [ ]-succinimidyl-4-fluorobenzoate ([ ]SFB) Sulfur Reactive Prosthetic Groups Br [ ]4-fluorobenzoate ([ ]FBA) [ ]Methyl-3-fluoro-5-nitrobenzamidate ([ ]FB) Br [ ]-(4-fluorobenzyl)-2-bromoacetamide [ ]2-bromo--[3-(2-fluoropyridin)-3-yloxy)propyl]acetamide [ ]-4[(4-(4- fluorobenzylidene)aminooxy]butylmaleimide Ref: Bioconjugate Chem. 16: ; 2005 [ ]-[3-(2-fluoropyridin)-3-yloxy)propyl]maleimide WASIGT UIVERSITY UIVERSITY I ST LUIS

21 Click Chemistry Slides are not to be reproduced Bioconjugate Chem. 18: ; 2007 WASIGT UIVERSITY UIVERSITY I ST LUIS

22 Slides are not to be reproduced Click Chemistry : Peptide Synthesis 2 2 Ts 3 [ ]KF C 3 C, 15 min 3 "Click Chemistry" Cu 2+ /ascorbate 15 min/room temperature 2 2 Yield: 92% Bioconjugate Chem. 18: ; 2007 WASIGT UIVERSITY UIVERSITY I ST LUIS

23 Summary Slides are not to be reproduced F-18 will continue to be the preferred radionuclide for PET tracer development because of its ideal half-life for imaging studies; ucleophilic incorporation will continue to be the method of choice for labeling compounds with F-18; ew methods such as click chemistry and thiol-reactive prosthetic groups will lead to increase the utilization of F-18 in the preparation of radiolabeled peptides. WASIGT UIVERSITY UIVERSITY I ST LUIS

24 Metabolism of [ ]FCP Slides are not to be reproduced WASIGT UIVERSITY UIVERSITY I ST LUIS

25 Slides are not to be reproduced Remote Chemistry System WASIGT UIVERSITY UIVERSITY I ST LUIS

26 Labeling Peptides with F-18 Slides are not to be reproduced Ref: Bioconjugate Chem. 16: ; 2005 WASIGT UIVERSITY UIVERSITY I ST LUIS

27 Slides are not to be reproduced Labeling Peptides with F-18 continued ucl. Med. Biol. 34: 5 15; 2007 WASIGT UIVERSITY UIVERSITY I ST LUIS

28 Slides are not to be reproduced Remote Chemistry System WASIGT UIVERSITY UIVERSITY I ST LUIS

29 Slides are not to be reproduced Automated Chemistry System WASIGT UIVERSITY UIVERSITY I ST LUIS

30 Robotic Chemistry System Slides are not to be reproduced WASIGT UIVERSITY UIVERSITY I ST LUIS