Synthesis and biological evaluation of two new radiolabelled estrogens: [125I](E)-3-methoxy-17α-iodovinylestra-1,3,5(10),6-tetraen-17β-ol and [125I](Z)-3-methoxy-17α-iodovinylestra-1,3,5(10),6-tetraen-17β-ol

The synthesis of two novel radiolabelled estrogen derivatives, [125I](E)-3-methoxy-17α-iodovinylestra-1,3,5(10),6-tetraen-17β-ol (E[125I]IVDE) and [125I](Z)-3-methoxy-17α-iodovinylestra-1,3,5(10),6-tetraen-17β-ol (Z[125I]IVDE), was carried out aiming to study the influence of the introduction of a C6–C7 double bond on the biological properties of the estradiol molecule. 3-Methoxyestra-1,3,5(10),6-tetraen-17-one was synthesised starting from a suitably protected estrone and subsequently converted into the 17α-ethynyl derivative. The radioiodinated derivatives were stereoselectively formed by radioiododestannylation of the corresponding tributylstannyl precursors. The biodistribution of the novel [125I]iodovinylestradiol derivatives was evaluated in immature female mice. Biological data indicated that the Z-isomer, owing to its higher in vivo uptake by the target tissue, has the preferable configuration for further development of similar compounds for estrogen receptor detection.