Structure elucidation by synthesis of four metabolites of the antitumor drug ENMD-1198 detected in human plasma samples

ENMD-1198 is a biologically active analogue of the antitumor drug 2-methoxyestradiol. Four human metabolites of ENMD-1198 were identified through synthesis and liquid chromatography/mass spectrometry comparisons of the metabolites with the synthetic standards. Two metabolites (3 and 4) are epimers resulting from benzylic hydroxylation at C-6. Two additional metabolites (5 and 6) are formed by epimeric hydroxylation at C-6 and α-epoxidation of the 16,17-alkene. The syntheses provided sufficient quantities of the metabolites for cytotoxicity studies to proceed. The 6-β-ol 4 was moderately less cytotoxic than the parent drug, while the remaining three metabolites (3, 5, and 6) were significantly less cytotoxic.