Synthesis of a fluorescent steroid derivative with high affinities for the glucocorticoid and progesterone receptors

The synthesis of RU 45196, an 11 beta-substituted 19-norsteroid of the estra-4,9-diene series, incorporating the nitrobenzoxadiazole (NBD) fluorophore, is reported. The highly fluorescent target compound displayed remarkable affinity for both the progesterone and glucocorticoid receptors. The present work demonstrates for the first time that it is indeed possible to design fluorescent steroid conjugates which maintain very high affinities for their cognate receptors and which are potentially useful for mechanistic and diagnostic purposes.