Looking for a 5-HT7 radiotracer for positron emission tomography

In search of a serotonin 5-HT7 radiotracer for positron emission tomography, we developed 1-{2-[(2S)-1-(phenylsulfonyl)pyrrolidin-2-yl]ethyl}piperidin-4-yl 4-fluorobenzoate. After labeling in good yield with fluorine-18 via nitro for fluorine exchange, preliminary biological experiments with autoradiographies failed to evidence any specific 5-HT7 receptor delineation.