Binding Analysis of 1α- and 17α-Dihydrotestosterone Derivatives to Homodimeric Sex Hormone-Binding Globulin

Binding studies of the interaction of immobilized 1α- and 17α-aminoalkyl derivatives of 5α-dihydrotestosterone (DHT) with purified N-deglycosylated homodimeric human sex hormone-binding globulin (SHBG) were performed using a surface plasmon resonance biosensor. These 1α- and 17α-derivatives with spacers of appropriate lengths between the amine function and the steroid ring skeleton enabled privileged, sterically undisturbed, interactions of either the 17- or 3-characteristic functional groups of DHT with SHBG. The association constants (Ka1) for the binding of these immobilized DHT derivatives to the first binding site of SHBG, determined by SPR measurements, were 0.16 × 107 M-1 for 17α-aminopropyl-17β-hydroxy-5α-androstan-3-one (1), 1.64 × 107 M-1 for 17α-aminocaproyl-17β-hydroxy-5α-androstan-3-one (2), and 1.2 × 108 M-1 for 1α-aminohexyl-17β-hydroxy-5α-androstan-3-one (3). These values were compared with global Ka data for the corresponding nonimmobilized DHT derivatives from equilibrium measurements us...