Steroidal 21-diazo ketones: photogenerated corticosteroid receptor labels

New steroidal diazo ketones as potential photoaffinity labeling reagents for the mineralocorticoid receptor: synthesis and biological activities

Three diazo ketones in the progesterone series were synthesized as potential photoaffinity reagents. The diazo ketone group was introduced at the C17 (21-diazopregn-4-ene-3,20-dione, 1) or C13 (18-(diazomethyl)-20-hydroxypregn-4-ene-3,18-dione, 2, 18-(diazomethyl)pregn-4-ene-3, 18,20-trione, 3) position of the pregnene skeleton. Whereas compound 1 could be easily obtained from the corresponding acid chloride, preparation of 2 and 3 required a less straightforward route involving reaction of tosyl azide on the formyl derivative of methyl ketone 5. The affinity of the diazo ketones for the human mineralocorticoid receptor (hMR), expressed in Sf9 insect cells using the Baculovirus system, was estimated by competition experiments using [3H]aldosterone as specific ligand. The affinity of 1 for hMR was almost identical with that of aldosterone. The affinities of 2 and 3 were 1, order of magnitude lower than that of aldosterone. The mineralocorticoid activity of the diazo ketones was measured in cis-trans cotransfection assays in CV-1 cells with the mouse mammary tumor virus as DNA target sequence. Compound 1 exhibits an agonist activity (ED50 = 6 x 10(-9) M) with no antagonist activity. In contrast 2 and 3 behave as antagonists, displaying an IC50 of approximately 10(-6) M whether the substituent at the C20 position is a hydroxy (2) or an oxo (3) group.

Biotin-labelled and photoactivatable aldosterone and progesterone derivatives as ligands for affinity chromatography, fluorescence immunoassays and photoaffinity labelling

New derivatives of progesterone and aldosterone were synthesized and functionally tested with commercially available antibodies. The covalent labelling of antibodies specific for aldosterone and progesterone was detected by SDS/PAGE analysis and subsequent autoradiography after using 3-(O-carboxymethyl)-oximino-(3-[125I]iodo-4-azidosalicylamidobu tylamine) derivatives of aldosterone and progesterone, respectively, as photoactivatable radioligands. Labelling was not observed in the presence of an excess of the unlabelled steroid. Aldosterone was labelled with biotin and used as a tracer in a time-resolved fluorescence immunoassay. The nonradioactive tracer is highly selective for its antibody-binding site, with almost no detectable cross-reactivity for other steroids. Biotin-labelled progesterone was immobilized by avidin-agarose and used for affinity chromatography. This yielded a more than 20-fold enrichment of an anti-progesterone polyclonal antibody. These results demonstrate that derivatives of steroids are particularly useful for the development of nonradioactive assays for the determination of natural steroids and may be also useful for the detection of specific binding sites in biological material such as plasma membranes.

17-Ketosteroids via a base induced cleavage of C-17-dihydroxy acetone side chains

A new, base-catalyzed cleavage of C21-steroids to give 17-ketosteroids is described. This reaction is specific for those steroids containing the C-17-dihydroxy acetone side chain. In the presence of oxygen, these same reaction conditions readily degrade corticosterone to the 17 beta-carboxylic acid.

Photoaffinity site-specific covalent labeling of human corticosteroid-binding globulin

A method was developed for the synthesis of high-specific-activity 21-diazo-21-[6,7-(3)H]deoxycorticosterone, an analog of corticosterone. This analog was used as a photoaffinity label of a high affinity steroid-binding protein, human corticosteroid-binding globulin. Based on direct binding studies and crosscompetition experiments, this diazo derivative exhibited the requisite affinity (within a factor of 1.5 times that of corticosterone) and site specificity to qualify as an affinity labeling legand. Irradiation of corticosteroid-binding globulin with the 21-diazo derivative resulted in irreversible binding to corticosteroid-binding globulin, identified by polyacrylamide gel electrophoresis. Specificity of covalent binding to corticosteroid-binding globulin was established by competition analysis with various steroids. Irreversibility of photodependent binding was shown by persistence of the complex on electrophoresis (in contrast to the noncovalently linked complex), and resistance to exchange with corticosterone or pregnanediol and to solvent extraction. Site specificity of covalent binding was inferred from the effects of a scavenger, Tris-HC1, and fluorescence quenching of a neighboring tryptophan.