Reductive dehalogenation of 2,4-dihalogeno estrogens having a 3-hydroxy substituent by formic acid, potassium iodide, or ascorbic acid

Estrogen conjugation and antibody binding interactions in surface plasmon resonance biosensing

Thioether-linked 3-mercaptopropionic acid derivatives of 17beta-estradiol and estrone were formed at the A-ring 4-position of the steroids by substitution of their 4-bromo analogues. The carboxylic acid terminal was used to link to an oligoethylene glycol (OEG) chain of 15-atoms in length. The OEG derivative of 17beta-estradiol was then in situ immobilized on a carboxymethylated dextran-coated gold sensor surface used to detect refractive index changes upon protein binding to the surface by surface plasmon propagation in a BIAcore surface plasmon resonance (SPR) instrument. Two other estradiol-OEG derivatives with Mannich reaction linkage at the 2-position and hemisuccinate linkage at the 3-position were also immobilized on the sensor surfaces for comparison. Binding performance between these immobilized different positional conjugates and monoclonal anti-estradiol antibody, raised from a 6-position conjugate, clearly demonstrated that both 2- and 4-conjugates, not conjugated through existing functional groups, gave strong antibody bindings, whereas the 3-conjugate through an existing functional group (3-OH) gave very little binding (2% compared to the 2-conjugate). Both 2- and 4-position conjugates were then applied in a highly sensitive estradiol SPR immunoassay with secondary antibody mediated signal enhancement that gave up to a 9.5-fold signal enhancement of primary antibody binding, and a detection limit of 25 pg/mL was achieved for a rapid and convenient flow-through immunoassay of estradiol.

2-Bromo- and 16-bromo-estrogens and related compounds: potential inhibitors for both estradiol 2- and 16 alpha-hydroxylases in rat liver microsomes

Kinetic studies of inhibition of estradiol 2- and 16 alpha-hydroxylase activities in male rat liver microsomes with 2-bromoestrogens, 4-bromo-estrone (4-BrE1), 16 alpha- and 16 beta-bromoestrones and 16 beta-acetylthioestrone (16-AcSE1) were carried out. 2-Bromoestrogens and 4-BrE1 nonspecifically blocked the two enzyme activities in a competitive manner, and 2-bromo-estradiol (2-BrE2) was the most potent inhibitor for the two hydroxylases among the 2- and 4-bromo steroids. Kinetic data, the apparent Ki's for the inhibitors and the apparent Km's for the substrate E2 in the assay, demonstrate that the A-ring bromo steroids are potent inhibitors for the two enzymes (Ki/Km ranging from 0.28 to 0.48 for the 2-hydroxylation and ranging from 0.26 to 0.49 for the 16 alpha-hydroxylation). In contrast, 16-bromoestrones and 16-AcSE1 non-competitively inhibited the 2-hydroxylation (Ki = ca. 70 microM) while the other was competitively blocked by them (Ki/Km ranging from 0.24 to 0.30). These 16-substituted steroids were very potent inhibitors for the 16 alpha-hydroxylase rather than the 2-hydroxylase and preferentially blocked the former.

Regioselective A-ring iodination of estradiol diacetates

Treatment of estrone or estradiol acetate with thallium trifluoroacetate in TFA and subsequent reaction with KI gave the 2-iodoestrogens as the major product. In the case of estradiol diacetate, treatment of the thallation product with [125I]NaI, using the same reaction conditions, gave exclusively the 2-iodo isomer. Thus, regioselectivity combined with rapidity, renders this procedure particularly suitable for A-ring radioiodination of estradiol with short-lived isotopes.

Synthesis of 2-methoxy and 4-methoxy equine estrogens

4-Methoxyequilin and 2-methoxyequilin were synthesized from the corresponding 4-bromoequilin and 2-iodoequilin derivatives, respectively, by nucleophilic displacement of halogen with methoxide ion in the presence of copper (II) chloride and 15-crown-5-ether. 4-Bromoequilin was prepared by reacting equilin with one equivalent of N-bromoacetamide. 2-Iodoequilin was prepared by reductive dehalogenation of 2,4-diiodoequilin, which in turn was obtained by treatment of equilin with two equivalents of iodine in methanolic ammonium hydroxide solution. 4-Methoxy-equilenin and 2-methoxyequilenin were prepared from the corresponding 4-iodo- and 2-iodo-7 epsilon, 8 epsilon-epoxyestrone derivatives, respectively. Nucleophilic displacement of iodine with methoxide ion was carried out as described earlier with simultaneous aromatization of the B ring leading to 4- and 2-methoxyequilenin derivatives. Alternatively, 4-methoxyequilenin was obtained from 4-methoxyequilin by selenium dioxide oxidation.