Temperature effects on the stereospecificity of nucleophilic fluorination: formation of trans‐[18F]4‐fluoro‐l‐proline during the synthesis of cis‐[18F]4‐fluoro‐l‐proline

Fluorine‐18 labeled (2 S ,4 S )‐4‐fluoro‐ l ‐proline ( cis ‐[ 18 F]4‐FPro) has been reported to be a potential positron emission tomography tracer to study abnormal collagen synthesis occurring in pulmonary fibrosis, osteosarcomas, mammary and colon carcinomas. In this paper, we report the stereospecific radiofluorination of (2 S ,4 R )‐ N‐tert ‐butoxycarbonyl‐4‐( p ‐toluenesulfonyloxy) proline methyl ester (at 110°C) to produce …