Structure of lysine adducts with 16α-hydroxyestrone and cortisol

Recent studies indicate that steroids containing a vicinal hydroxyketone moiety can react with proteins both in vitro and in vivo to form covalent addition products. This reaction is non-enzymatic and occurs via the Heyns rearrangement of an initial Schiff base adduct between the steroid carbonyl and the ϵ-amino group of lysine residues. The present study describes the synthesis, isolation, and structural analysis of model adducts prepared by the incubation of 16α-hydroxyestrone or cortisol with NaCNBH 3 and lysine derivatives blocked in the N α-position. The product formed from the reaction of 16α-hydroxyestrone and lysine was found to have the structure predicted for a reduced Schiff base between these molecules. A stable, cortisol-lysine adduct was similarly synthesized and isolated. This conjugate was found not to be the expected reduced Schiff base but rather a C-20 cyano amine. This compound most likely was formed by the nucleophilic addition of cyanide during the course of the incubation. The observation that the cortisol-lysine Schiff base is not reducible with NaCNBH 3 accounts for the observation that the incorporation rate of glucocorticoids into proteins is not increased by the presence of NaCNBH 3.