Fluorinated benzamide neuroleptics--2. Synthesis and radiosynthesis of (S)-N-[(1-ethyl-2-pyrrolidinyl)methyl]-5-(3-[18F]fluoropropyl)-3- substituted-2-methoxybenzamides.

Synthesis of a fluorinated benzamide neuroleptic, (S)-N-[(1-ethyl-2- pyrrolidinyl)methyl]-5-(3-fluoropropyl)-2,3- dimethoxybenzamide starting from 3-(3,4-dimethoxyphenyl)-1-propanol in 20-25% overall yield is reported. Radiosynthesis of (S)-N-[(1-ethyl-2-pyrrolidinyl)methyl]- 5-(3[18F]fluoropropyl)-2-methoxybenzamide([18F]FPHB) and (S)-N-[(1-ethyl-2-pyrrolidinyl)methyl]-5-(3[18F]fluoropropyl)-2,3- dimethoxybenzamide([18F]FPHB) was carried out by nucleophilic substitution reaction of (S)-N-[(1-ethyl-2-pyrrolidinyl)methyl-5-(3-tosyloxypropyl)-2-me tho xybenzamide and (S)-N-[(1-ethyl-2-pyrrolidinyl)methyl]-5-(3-tosyloxypropyl)-2,3- dimethoxybenzamide respectively, with no carrier added [18F]fluoride. Both, [18F]FPHB and [18F]FPHB were obtained in approx. 20-30% yields (EOS/EOB, decay corrected). Specific activities of 900-1700 Ci/mmol for [18F]FPHB and 800-1400 Ci/mmol for [18F]FPMB were obtained by reverse phase HPLC purification. Total synthesis and purification time required for either [18F]FPHB or [18F]FPMB was 120 min from EOB.