Estradiol-mimetic probes. Preparation of 17α-(6-amino-hexynyl)estradiol biotin, fluorescein and acridinium conjugates

3-O-tert-Butyldimethylsilyl-17α-(6-mesyloxyhexynyl)estradiol was converted to the azide in 60–70% yield with NaN3/DMPU, then reduced to the corresponding amine (>95% yield). Acylation with the N-hydroxysuccinimide esters of biotin, 5-carboxyfluorescein and 10-(3-sulfopropyl)-N-tosyl-N-(3-carboxypropyl)acridinium-9-carboxamide gave the title conjugates. The KDs of the tracers with an estradiol antibody ranged from 97–197 nM.