Synthesis of (5-azido-2-nitrobenzoyl)amido, (4-azido-2-nitrophenyl)amino, and (5-azido-2-nitro-3,4,6-trifluorophenyl)amino derivatives of 17α-methylamino-, 17α-ethylamino-, and 17α-propylamino-5α-dihydrotestosterone as reagents of different linker lengths for the photoaffinity labeling of sex hormone binding globulins and androgen receptors

The photoactivable aryl azide reagents, N-(5-azido-2-nitrobenzoyl)oxysuccinimide, 4-azido-1-fluoro-2-nitrobenzene, and 4-azido-1-nitro-2,4,5,6-tetrafluorobenzene have been condensed at the extremity of three 17α-aminomethyl, 17α-aminoethyl, and 17α-aminopropyl side-chains introduced on (17S)-spiro-(3,3-dimethoxy)-5α-androstan-17β,2′-oxirane either directly, by ammonolysis, in the first case, or by conversion to nitrile intermediates with cyano or cyanomethyl anions and subsequent reduction to amines with lithium aluminum hydride, in the two other cases. The 3,3-dimethoxy group of these photoreagents was cleaved by acidolysis to a 3-ketone, which was reduced with sodium borohydride to a 3β-alcohol. All of these compounds were characterized by 1H- and 13C-NMR as well as by 1H, 13C heteronuclear 2D NMR, which helped to resolve ambiguous assignments. Significant differences of substituent-induced effects on 13C NMR signals were observed according to the 17α-side-chain length, the structure of the terminal aryl azide groups, and the solvent, showing a different behavior of N-5-azido-2-nitrobenzoyl derivatives as compared with 4-azido-2-nitrophenylamino and 5-azido-2-nitro-3,4,6-trifluorophenylamino derivatives. The N-5-azido-2-nitrobenzoyl conjugates of the three 17α-aminomethyl, aminoethyl, and aminopropyl derivatives of 5α-dihydrotestosterone were tested as ligands for purified human sex hormone-binding globulin and for the cytosolic androgen receptor of rat ventral prostate by competition experiments with tritiated 5α-dihydrotestosterone. The increasing lengths of the aminomethyl, aminoethyl, and aminopropyl spacer arms of N-5-azido-2-nitrobenzoyl conjugates were found to correspond to decreasing relative binding affinities for sex hormone-binding globulin (0.76, 0.47, and 0.10, respectively, versus 1.00 for 5α-dihydrotestosterone) while only the longer aminoethyl and aminopropyl conjugates interacted significantly with the androgen receptors (0.05 and 0.10, respectively).