Syntheses and ligand-binding studies of 1α- and 17α-aminoalkyl dihydrotestosterone derivatives to human sex hormone-binding globulin

We report on the syntheses of 1α- and 17α-aminoalkyl dihydrotestosterone (DHT) derivatives and the particularly high binding affinity of the 1α-aminohexyl ligand for human sex hormone-binding globulin (SHBG). The two 17α-aminopropyl-17β-hydroxy-5α -androstan-3-one (1) and 17α-aminocaproylamidoethyl-17β -hydroxy-5α-androstan-3-one (2) derivatives were synthesized via a 17β-spirooxirane intermediate in high yields. The 1α -aminohexyl-17β-hydroxy-5α-androstan-3-one compound (3) was obtained in a seven step synthesis using a copper-catalyzed conjugate addition of a ω-silyloxyhexyl Grignard reagent to 17β-benzoyloxy-5α -androst-1-en-3-one. All structures were elucidated based on ¹H NMR spectroscopy and mass spectral analyses. The three aminosteroid derivatives were tested as ligands for SHBG by competition experiments with tritiated testosterone as tracer under equilibrium conditions. The association constants of the two 17α-DHT derivatives were approximately 1×10 ⁷M^-1, whereas the 1α-DHT derivative showed a remarkably high binding affinity to SHBG with an association constant of 1.40×10⁹M^-1. These aminoalkyl derivatives, substituted either at the D-ring or the A-ring of the steroid skeleton, can be easily coupled onto a carboxymethylated solid state surface of a biosensor. Such a device lends itself to kinetic and thermodynamic studies aimed to provide a better understanding of the biospecific interaction of steroids with SHBG.