Synthesis of N-acetylcysteine conjugates of catechol estrogens

The synthesis of N-acetylcysteine conjugates of 2-hydroxyestrone (2-OHE1) and 4-hydroxyestrone (4-OHE1) is described. The reaction of estrone 2,3-quinone with N-acetylcysteine provided 2-OHE1 and its C-4 and C-1 thioether conjugates in a ratio of 1:1, while estrone 3,4-quinone with N-acetylcysteine gave 4-OHE1 and its C-2 thioether conjugate as a sole product. Their structures were characterized by inspection of NMR spectra, chemical derivatization (methylation and acetylation), and comparison with the reactivity of 4-bromoestrone 2,3-quinone or 2-bromoestrone 3,4-quinone toward N-acetylcysteine.