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. 2014 May 27;2014:361329. doi: 10.1155/2014/361329

Table 2.

Summary of the prosthetic groups, reaction conditions, and reaction partners applied for copper-free click fluorination.

18F-prosthetic group Steps/reaction time1 RCY2 Reacting agent Reaction type/catalytic system Overall reaction time1 
(CCA)		 RCY2 
CCA		 Literature
[18F]COT 1 step, 15 min 71% 3,6-diaryl-s-tetrazine inverse electron-demand DA cyclo-addition 30 min (without HPLC) >98% [14]
[18F]FB-DBCO 1 step, 60 min 85% Various azides Strain-promoted click 1,3-dipolar cycloaddition 2 h 69–98% [7]
TCO-derivative:
Aza-DBCO-BN
(bombesin)		 9 steps, — 17% Three different [18F]azides 30 min (without HPLC) 19–37%
(depending on azide)		 [8]
[18F]DBCO 1 step, 1 h 21% Tyr3-octreotide-N3(TATE) 1.5 h 95% [9]
[18F]TCO [14] [14] Tetrazine-RGD Inverse electron-demand DA cyclo-addition 30 min 90% [15]
[18F]bifunctional azadibenzocyclo-octyne 1 step, 30 min 24.5% Alkyl azide Strain-promoted click 1,3-dipolar cycloaddition 202 ± 34 min 74 ± 4.8% [10]
[18F]PEG4 azide 1 step, 45 min 63% cRGD-DBCO 80 min 92% [11]
[18F]cyclooctyne 6–11 steps,
30–80 h (depending on the derivative)		 20–57% (depending on the derivative) [18F]2-fluoro-
ethylazide		 30 min. 9.6–97% (depending on COT and solvent) [12]
[79]
[18F]trans-cyclooctene ([18F]TCO) 1 step, 102 min 46.1 ± 12.2% Tetrazine modified exendin-4 Inverse electron-demand DA cycloaddition 3 h 46.7 ± 17.3% [16]
Polymer modified tetrazine 89.2% in vivo [80]
[18F]amine-functionalised norbornene 1 step, 52 min 60 ± 17% Tetrazine
(peptide-/bombesin-derivatives)		 82 min (without preparation of [18F]SFB) 46–97% (depending on the tetrazine) [18]
[18F]FBA-C6-DBCO [10] [10] α V β 6-specific peptide Strain-promoted click 1,3-dipolar cycloaddition click: 40 ± 4 min 11.9 ± 3.2% [13]

1Calculated as sum from all steps, for the 18F-prosthetic group, respectively, for the overall reaction leading to the click product, starting from fluorine-18.

2Radiochemical yields for the 18F-prosthetic group starting from fluorine-18 for the click reaction, respectively; decay corrected, as long as not noted elsewise.

CCA: click cycloaddition; DA: Diels Alder; DBCO: aza-dibenzocyclooctyne; TCO: trans-cyclooctyne.