Metal-marked steroids of the estrane group from the reaction of steroidal functional groups with arene-iron(Cp) complexes

Reaction of (η 6 -p-chlorotoluene)(η 5 -cyclopentadienyliron)(II) hexafluorophosphate with the phenolic hydroxy group of estrane steroids, under mild conditions, leads to the formation of 3-O-p-tolyle thers of steroids, with an iron(Cp) marker. Employing this reaction, estrone, estradiol and 17-α-ethynylestradiol have been marked in high yield. The utility of such marked steroids in metalloimmunoassay has been examined. Steroids marked in such a way show no measurable affinity for the estradiol receptor. The 3-O-p-tolyestrone complex is stable at room temperature for 24 h, in water solutions of buffers at pH 2.0 and 7.41, as well as in a THF solution in the presence of pyrrolidine. The marker fragment may be removed at room temperature upon the action of pyrrolidine in a 1:1 water-THF solution or potassium hydroxide in water for 24 h with the efficient recovery of steroid. Treatment of marked estrone with an excess of potassium t-butoxide leads to demetallation and the formation of 3-O-p-tolylestrone. Attempts to mark estrone and testosterone via the carbonyl group or estradiol and cholesterol via the secondary hydroxyl group, under mild conditions, have been unsuccesful.