Design and synthesis of carbon-11-labeled dual aromatase–steroid sulfatase inhibitors as new potential PET agents for imaging of aromatase and steroid sulfatase expression in breast cancer

Aromatase and steroid sulfatase (STS) are particularly attractive targets in the treatment of estrogen-receptor-positive breast cancer and the development of enzyme-based cancer imaging agents for the biomedical imaging technique positron emission tomography (PET). New carbon-11-labeled sulfamate derivatives were first designed and synthesized as potential PET dual aromatase–steroid sulfatase inhibitor (DASSI) radiotracers for imaging of aromatase and STS expression in breast cancer. The target tracers 5-(((4-cyanophenyl)(4H-1,2,4-triazol-4-yl)amino)methyl)-2-¹¹C]methoxyphenyl sulfamate (¹¹C]8a) and 4-(((4-cyanophenyl)(4H-1,2,4-triazol-4-yl)amino)methyl)-2-¹¹C]methoxyphenyl sulfamate (¹¹C]8b) were prepared from their corresponding precursors 5-(((4-cyanophenyl)(4H-1,2,4-triazol-4-yl)amino)methyl)-2-hydroxyphenyl sulfamate (16) and 4-(((4-cyanophenyl)(4H-1,2,4-triazol-4-yl)amino)methyl)-2-hydroxyphenyl sulfamate (21) with ¹¹C]CH₃OTf under basic conditions through the O-¹¹C]methylation and isolated by the reversed-phase high pressure liquid chromatography (HPLC) method in 30–45% radiochemical yields based on ¹¹C]CO₂ and decay corrected to end of bombardment (EOB). The specific activity at end of synthesis (EOS) was 111–185 GBq/μmol.