Synthesis and stability of S-(2-[18F]fluoroethyl)-L-homocysteine for potential tumour imaging

The F‐18 labelled methionine derivative S‐(2‐[18F]fluoroethyl)‐L‐homocysteine ([18F]FEHCys) was prepared by a one‐pot two‐step synthesis via the protected S‐(2‐bromoethyl)‐L‐homocysteine 1 and S‐(2‐chloroethyl)‐L‐homocysteine 2 precursors. The bromoethyl derivative 1 gave higher radiochemical yields (40% at 5 min) at 100°C compared with the chloro‐analogue (22% at 100°C in 30 min). However, [18F]FEHCys was found to be unstable in aqueous systems being transformed to the corresponding hydroxyl derivative within 20 min. Copyright © 2008 John Wiley & Sons, Ltd. The F‐18 labelled methionine derivative S‐(2‐[18F]fluoroethyl)‐L‐homocysteine ([18F]FEHCys) was prepared by a one‐pot two‐step synthesis via the protected S‐(2‐bromoethyl)‐L‐homocysteine and S‐(2‐chloroethyl)‐L‐homocysteine precursors. The bromoethyl derivative gave higher radiochemical yields compared to the chloro analogue. However, [18F]FEHCys was found to be unstable in aqueous systems. Copyright © 2008 John Wiley & Sons, Ltd.