Effect of metal ions on the stable adduct formation of 16 alpha-hydroxyestrone with a primary amine via the Heyns rearrangement

16 alpha-Hydroxyestrone (16 alpha-OHE1), one of the major estrogen metaboli tes in humans that may plays a role in cell transformation, has been found to form stable adducts with nuclear proteins. The mechanism for the formati on of a stable covalent adduct of 16 alpha- OHE1 with protein has been post ulated via the Heyns rearrangement after Schiff base formation. The Heyns r earrangement on the steroidal D-ring alpha-hydroxyimine was investigated us ing 17-(2-methoxyethylimino)estra- 1,3,5(10)-triene-3,16 alpha-diol as a mo del intermediate. Rates of the Heyns rearrangement and hydrolysis of the st eroidal alpha-hydroxyimine were determined by a high-performance liquid chr omatography (HPLC) simultaneously. The Heyns rearrangement was demonstrated to be optimum at pH 6.2 and the reaction rate at physiological pH 7.3-7.5, was more than 90% of that at the optimum pH. On the other hand, modulator( s) to the reactions were also examined. According to our previous finding o f the proton-mediated mechanism of the Heyns rearrangement, the effects of cationic metal ions on the reactions were examined with 29 metal chlorides. Five metal ions, Pt4+, Cu2+, Ni2+, Co2+, and Mn2+, suppressed the formatio n of Heyns product significantly while Fe2+, Y3+, Gd3+, and Er3+ slightly i ncreased it. The suppression rate was synergistically enhanced by the combi nation of pt(4+) with Co2+, Cu2+, or Ni2+. These results suggest the five m etal ions, Pt4+, Cu2+, Ni2+, Co2+, and Mn2+, reduce the formation of the He yns product in vivo and, therefore, would be useful tools to clarify the im plication of the stable adduct formation of 16 alpha-OHE1 with protein. (C) 1999 Elsevier Science Inc. All rights reserved.