Synthesis of the equine estrogen metabolites 2-hydroxyequilin and 2-hydroxyequilenin

Equilin and equilenin make up approximately 20% of Premarin which is curren tly the most popular estrogen replacement therapy. Although there are numer ous health benefits of estrogen replacement therapy, there are concerns ove r the link between estrogen replacement therapy and breast and endometrial cancer risk. One potential mechanism of estrogen carcinogenesis involves me tabolism of estrogens to 2- and 4-hydroxylated catechols which are further oxidized to electrophilic/redox active o-quinones which have the potential to both initiate and promote the carcinogenic process. In this investigatio n, we have synthesized potential metabolites of equilin and equilenin, 2-hy droxyequilin and 2-hydroxyequilenin, respectively, as well as their methyl ether metabolites. These compounds were synthesized from commercially avail able optically pure equilin via a practical and efficient approach; five st eps gave 2-methoxyequilin from which 2-hydroxyequilin was prepared by BBr3- catalyzed demethylation in one step. Similarly, treating 2-methoxyequilin w ith SeO2 followed by demethylation with BBr3 produced 2-hydroxyequilenin. T he structures of the catechols as well as those of their methoxy ethers wer e unambiguously characterized by one-dimensional and two-dimensional NMR ex periments, including H-1, C-13, APT, COSY, HMBC, and HMQC as well as mass s pectrometry.