Application of robotics to radiopharmaceutical preparation: controlled synthesis of fluorine-18 16 alpha-fluoroestradiol-17 beta

A commercially available robot system, the Zymark Zymate Laboratory Automation System, has been utilized for the preparation of a positron-emitting radiopharmaceutical, 16 alpha-[18F] fluoroestradiol-17 beta. This radiopharmaceutical is prepared in a three-step synthesis (preparation of [18F]-tetrabutylammonium fluoride, SN2 displacement of a triflate, and ketone reduction) and is purified by high performance liquid chromatography (HPLC). All steps in the synthesis and HPLC purification are controlled by the robot system with no manual intervention. This represents a new approach to the complete automation of radiopharmaceutical production.

17 alpha-allyl estradiol analogues as candidates for development of high-affinity fluorescein-estradiol conjugates

In order to develop stable, high-affinity fluorescein-estradiol conjugates, the fluorescein moiety must be leashed to the estradiol molecule at a point which interferes least with estradiol's binding to the receptor. Because of the high affinity of 17 alpha-substituted estradiol (e.g. ethynyl estradiol), we investigated a series of 17 alpha-substituted estradiol compounds to determine the optimal properties of a leash at this position. Twelve estradiol derivatives bearing a three-carbon 17 alpha side chain with or without a terminal functional group and with varying degrees of unsaturation were synthesized. Initial comparison of the receptor binding affinities of some of these derivatives suggested that three factors might reduce affinity: internal hydrogen bonding of the 17 beta-hydroxyl proton with an oxygen atom of the 17 alpha side chain; hydrophilicity of the ligand; or steric interference of the side chain with receptor binding. Further comparisons were designed to evaluate the relative contribution of these factors. The results suggest that the relative affinities of these 17 alpha-substituted estradiol derivatives are influenced primarily by the steric interference of the side chains and also by their hydrophilicity. Internal hydrogen bonding involving the 17 beta-hydroxyl proton does not seem to have a profound effect.

A new synthetic route to 2- and 4-methoxyestradiols by nucleophilic substitution

A new snythetic route to 2- and 4-methoxyestradiols is described. Benzo-15-crown-5 with CuI catalyzes the specific nucleophilic substitution at the carbon atom carrying a non-activated halogen on ring A of the estradiol.

Synthesis and biological assessment of long-acting estradiol fatty acid esters in ovariectomized rats

Diesters of 17 beta-estradiol using palmitic acid (16:0) and oleic acid (18:1, cis-9-Octadecenoic acid) have been synthesized for potential evaluation as long-acting compounds. Female castrated rats were injected 1 mumol of estradiol dipalmitate and estradiol dioleate, using estradiol benzoate and estradiol enanthate as controls. Biological activity was determined by uterine wet weight and uterine diameter as well as on the suppression of serum anterior pituitary gonadotropins. A delayed absorption of estradiol was observed after administration of both diesters which was well correlated with the duration of biological effects. The data demonstrate that esterification with palmitic or oleic acids at 3 and 17 positions provides long-acting properties to 17 beta-estradiol, which could be applied in substitutive therapy and or in hormonal contraception.

Synthesis of some analogs of estradiol

As part of a search for estradiol derivatives designed for conjugation to carboxyl or amine functions of anti-cancer agents or suitable derivatives thereof, estradiol analogs with side chains at the C-16 or -17 position were prepared for biological assay. These analogs include several which have a substituted nitrogenous function at C-17. The avidity of some of these analogs for binding to estrogen receptor was found to be of a low order.

Reactivation of human placental 17 beta,20 alpha-hydroxysteroid dehydrogenase affinity alkylated by estrone 3-(bromoacetate): topographic studies with 16 alpha-(bromoacetoxy)estradiol 3-(methyl ether)

Estradiol 17 beta-dehydrogenase and 20 alpha-hydroxysteroid dehydrogenase, oxidoreductase activities copurified from the cytosol of human-term placenta as a homogeneous protein (native enzyme), were reactivated at equal rates to 100% activity following complete inactivation in the presence of cofactor (NADPH) with the affinity alkylator estrone 3-(bromoacetate). Reactivation was accomplished by base-catalyzed hydrolysis of steroidal ester-amino acid linkages in the enzyme active site. The rate of enzyme reactivation was pH dependent. In identical studies without NADPH, only 12% of the original enzyme activity was restored. Completely reactivated enzyme was repurified by dialysis. Enzyme in control mixtures (control enzyme) that contained estrone in place of alkylator was treated the same as the reactivated enzyme. Reactivated enzyme exhibited a 6.0-fold lower affinity for common substrates, a 1.8-fold lesser affinity for NAD+ and NADH, and the same affinity for NADP+ and NADPH compared to control enzyme. In incubations that included NADPH, the reactivated enzyme maintained full activity during a 20-h second exposure to estrone 3-(bromoacetate), but in identical incubations without NADPH, the reactivated enzyme was rapidly inactivated at the same rate as the control and native enzymes. The control and reactivated enzymes were inactivated at equal rates by 16 alpha-(bromoacetoxy)estradiol 3-(methyl ether) in the presence or absence of cofactor (NADP+) and exhibited similar Kitz and Wilson inhibition constants for this affinity alkylator. Estrone 3-(bromo[2'-14C]acetate) incubated with native enzyme and NADPH produced radiolabeled 3-(carboxymethyl)histidine and S-(carboxymethyl)cysteine.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis and pharmacokinetics of 131I labeled benzoyl derivatives of estrone and estradiol

3-(2-[131I]iodobenzoyl)estradiol-17 beta (1), 3-(2-[131I]iodobenzoyl)estrone (2) and 17 beta-(2-[131I]iodobenzoyl)-estradiol (3) have been prepared by bromine-iodine exchange followed by preparative HPLC in radiochemical yields greater than 70% (isolated). The specific activities were greater than 200 Ci/mmol. Tissue distribution studies in DMBA-induced tumor bearing rats showed a rapid clearance via the kidneys and poor accumulation in the target tissues. The relative binding affinities to the estrogen receptor were estimated as 3.5% 1, 1.7% 2 and 0.05% 3 of the affinity of estradiol (100%).

The preparation of estradiol-17 beta sulfates with triethylamine-sulfur trioxide

Reaction of estradiol-17 beta with triethylamine-sulfur trioxide in pyridine gives exclusively monosulfation at the C17-hydroxyl group with the preparation of 17 beta-sulfooxyestra-1,3,5(10)-trien-3-ol triethylammonium salt (V). The structural assignment suggested by spectroscopic measurements was confirmed by synthetic studies. (Formula: see text) A synthesis of 3-sulfooxyestra-1,3,5(10)-trien-17 beta-ol triethylammonium salt (II) has been accomplished based on the preparation of 17 beta-formyloxyestra-1,3,5(10)-trien-3-ol (XIII). Fusion of the 3-sulfate triethylammonium salt II gives rise to the 17-sulfate triethylamine salt V. The preparation of estradiol-17 beta disulfate has also been achieved.

The synthesis of 16 alpha-[131I]iodo-oestradiol and evaluation of its use as a radiotracer for oestrogen receptor positive breast tumours

16 alpha-Iodo-oestradiol binds with high affinity to the oestrogen receptor and has been shown to accumulate in oestrogen sensitive tissues in many test systems. We have prepared the compound labelled with 131I at four specific activities. Using these preparations we have attempted to image human primary and metastatic breast cancer deposits at various times from 15 min to 24 h post injection by external gamma scintigraphy. Clinical studies were conducted on 10 post-menopausal patients. The receptor status was determined in seven cases, four were positive and three negative. The imaging results were very poor, in only two cases were images obtained, these were very faint and only of the primary, never of the metastatic deposits. The oestrogen receptor status was only available in one of these cases, it was positive. Dynamic studies in vivo revealed that the compound is cleared rapidly from the circulation during the first 5 min and thereafter undergoes extensive enterohepatic recycling. Studies of the radiochemical identity of the circulating species revealed that the injected compound was extensively metabolised. Neither an increase in specific activity of injected radiotracer nor imaging at shorter times after injection improved the results.

Preparation of four fluorine- 18-labeled estrogens and their selective uptakes in target tissues of immature rats

Four fluorine- 18-labeled estrogens--16 alpha-[18F]fluoro-estradiol-17 beta (1), 16 beta-[18F]fluoro-estradiol-17 beta (2), (2R, 3S)-1-[18F]fluoro-2,3-bis(4-hydroxyphenyl)-pentane (1-[18F]fluoropentestrol) (3), and (3R, 4S)-1-[18F]fluoro-3,4-bis(4-hydroxyphenyl)hexane (1-[18F]fluorohexestrol) (4)--have been prepared by simple displacement reactions utilizing reactive trifluoromethane sulfonate (triflate) precursors and F-18 fluoride ion. All four fluoroestrogens have high affinity for the estrogen receptor. In immature female rats, they are taken up by target tissues, such as the uterus, with very high selectivity: uterus-to-blood ratios at 1 hr are: Compound 1, 39; Compound 2, 12; Compound 3, 13; and Compound 4, 19. Average uterus-to-blood ratios exceed 80 for Compound 1 at 2 hr. That the uptake process involves an estrogen-specific binder of limited capacity is demonstrated by the suppressive effect of coadministered unlabeled estradiol on target tissue uptake.

[1,2,3,4-13C] testosterone and [1,2,3,4-13C] estradiol

The preparation of [1,2,3,4-13C] testosterone and of [1,2,3,4-13C] estradiol by total synthesis is described. The 13C labels are introduced by alkylating intermediate 1 with [1,2,3,4-13C]l-iodo-3,3-ethylenedioxybutane (2) to obtain intermediate 10. Hydrolysis of the ketal function, cyclization, aromatization and removal of protective groups gave [1,2,3,4-13C] estradiol. Labeled testosterone was prepared by methylating intermediate 10 and by subsequent treatment with acid. The labeled steroids can be used as tracers for in vivo metabolic studies and as internal standards for the development of definitive gc-ms quantitative methods.

Synthesis and evaluation of (17 alpha,20E)-21-[125I]iodo-19-norpregna-1,3,5(10),20-tetraene-3,17 -diol and (17 alpha,20E)-21-[125I]iodo-11 beta-methoxy-19-norpregna-1,3,5(10),20-tetraene-3,17-diol (17 alpha-(iodovinyl)estradiol derivatives) as high specific activity potential radiopharmaceuticals

Two 17 alpha-[125I]iodovinyl estradiol derivatives 4b,d possessing high specific activity have been prepared and tested as potential radiopharmaceuticals. The use of the 3-acetyl derivatives 2c,e and the replacement of iodine monochloride with sodium iodide and Chloramine-T in THF/phosphate buffer (pH 7.0) permitted us to synthesize no-carrier-added (17 alpha,20E)-21-[125I]iodo-19-norpregna-1,3,5(10),20-tetraene-3,17-d iol (4b) and (17 alpha,20E)-21-[125I]iodo-11 beta-methoxy-19-norpregna-1,3,5(10),20-tetraene-3,17-diol (4d) with 50% radiochemical yield and high purity. Although the specific activity represents only half of the theoretical value in some cases, this modified approach is a substantial improvement over the previously published method. Our preliminary distribution studies indicate that although both 4b and 4d localize in the tissues known to have a large concentration of estrogen receptors, 4d accumulates in higher amounts in target tissues and provides a high target to nontarget ratio.

Radioiodinated ligands for the estrogen receptor: effect of 3-o-methylation on tissue distribution

The 3-o-methyl ethers of 17 alpha-[125I]iodovinylestradiol and 17 alpha-[125I]iodovinyl-11 beta-methoxyestradiol were prepared in 95% and 89% isolated yields, respectively, at the no-carrier-added level from the corresponding (tri-n-butystannyl)-vinyl intermediates. The new radioligands were evaluated in immature female rats to determine their uptake in, and selectivity for, estrogen-receptor-containing tissues. At 0.5-6 hr after administration, both agents showed preferential uptake and retention by the target tissue. The values for the 11 beta-methoxy derivative, however, were significantly better than those of the 11-unsubstituted compound. Compared with the parent 3-hydroxy radioligands, the [125I]VE2-3-o-Me had lower uptake and target-to-blood ratios at all time periods, but by 6 hr the [125I]VME2-3-o-Me compound showed as high an uptake in the uterus and higher uterus-to-blood ratios. This may be related to metabolic cleavage of the 3-o-methyl group generating the parent compound, which is then sequestered by the target tissue. The results suggest that iodine-123-labeled VME2-3-o-Me would be a good candidate for in vivo gamma imaging of estrogen-containing tissues.

Radiohalodestannylation: synthesis of 125I-labeled 17 alpha-E-iodovinylestradiol

17 alpha-E-Iodovinylestradiol and its iodine-125-labeled analog were prepared by halodestannylation. The synthesis of the unlabeled compound was achieved from estrone in two steps with an overall yield of 30%. The tributylstannylvinylestradiol intermediate reacted with sodium [125I]iodide (specific activity = 2200 Ci/mmol) in the presence of hydrogen peroxide and acetic acid to give the 17 alpha-E-[125I]iodovinylestradiol in 40-60% yield after isolation by reversed phase column chromatography. The radiochemical purity was greater than 98% and no other u.v. active components could be detected by HPLC. The ease of preparation and isolation of this radioligand suggests that radiohalodestannylation may be the method of choice for this and structurally similar compounds.

Synthesis of 1-chloroestradiol

The synthesis of the previously unknown 1-chloroestradiol (1), is reported. Addition of N-chlorosuccinimide/NaI in dioxane to 4-amino-estradiol 3-methyl ether (2), resulted in exclusive chlorination of the 1-position. Subsequent deamination and demethylation afforded 1 in good yields.

Org 4333, a potent, irreversibly binding estrogen agonist

Two synthetic routes to 11 beta-chloromethylestra-1,3,5(10)-trien-3,17 beta-diol (Org 4333) are described. In biological tests this compound was found to be a potent irreversibly binding estrogen agonist.

Synthesis of C-2 and C-4 deuterium-labeled estradiol-17 beta

Estradiol-17 beta labeled with deuterium in the positions 2 or 4 can be prepared from 2-chloromercurio-1,3,5(10)-estratriene-3,17 beta-diol 3-methyl ether 17-acetate or 4-chloromercurio-1,3,5(10)-estratriene-3,17 beta-diol, respectively, in refluxing CH3COO(2)H/(2)H2O. The same reaction performed on 4-acetoxymercurio-1,3,5(10)-estratriene-3,17 beta-diol afforded 2,4-dideuterio-estradiol-17 beta in good yields.

Methodology for the synthesis and specific activity determination of 16 alpha-[77Br]-bromoestradiol-17 beta and 16 alpha-[77Br]-11 beta-methoxyestradiol-17 beta, two estrogen receptor-binding radiopharmaceuticals

16 alpha-[77 Br]-Bromoestradiol-17 beta (3a) has been synthesized from estrone enol diacetate (1) by bromination with Na77Br and hydrogen peroxide-acetic acid, followed by reduction with lithium aluminum hydride to give a mixture of 16 alpha-[77 Br]-bromoestradiol-17 beta (3a) and 16 alpha-[77Br]-bromoestradiol-17 alpha (3b) from which the desired epimer (3a) can be obtained in 50% overall radiochemical yield (from Na77Br) by HPLC. Analogous procedures can be used in the preparation of 16 alpha-[77Br]-bromo-11 beta-methoxyestradiol-17 beta. (4a) The effective specific activities of these radiopharmaceuticals, determined by binding to the uterine estrogen receptor, are 900-1500 Ci/mmol. Both have affinity and good binding selectivity for the estrogen receptor and are useful as imaging agents for mammary tumors.

E-17 alpha[125I]iodovinylestradiol: an estrogen-receptor-seeking radiopharmaceutical

Through the use of radioiododestannylation, the specifically labeled E-17 alpha-[125I]iodovinylestradiol [(I-125)VE2] was synthesized rapidly and in high yield from the stable precursor E-17 alpha-tributylstannylvinylestradiol (SnVE2), and its biodistribution was determined in immature female rats. The agent accumulated in the uterus, achieving a peak uptake of 0.465% ID-kg/g at 2 hr. Uterus-to-blood ratios of 19 and 16 occurred at 1 and 2 hr, respectively, declining to 7 by 4 hr after injection. The uptake of (I-125)VE2 by the uterus at 2 hr was reduced 58--65% by pretreatment of the immature rats with estradiol (5 micrograms) or tamoxifen (100 micrograms), and compared with 16 alpha-[125I]iodoestradiol, (I-125)VE2 showed greater uterine uptake and similar uterus-to-blood ratios. The ease of preparation of the radioligand represents an advantage over the synthetic procedures for other estrogen-receptor-seeking agents.

A short efficient synthesis of 16-oxygenated estratriene 3-sulfates

A novel synthesis of sodium 17-oxo-16 alpha-hydroxy-1,3,5(10)-estratrien-3-yl sulfate (4), sodium 16 alpha, 16 beta-dihydroxy-1,3,5(10)-estratrien-3-yl sulfate (5) and sodium 16-oxo-17 beta-hydroxy-1,3,5(10)-estratrien-3-yl sulfate (6) is described. 16 alpha-Bromo-3-hydroxy-1,3,5(10)-estratrien-17-one (1) was efficiently synthesized in one step with 70-97% yield by bromination of 3-hydroxy-1,3,5(10)-estratrien-17-one with cupric bromide. 3,16 alpha-Dihydroxy-1,3,5(10)-estratrien-17-one (3) was quantitatively obtained by controlled stereospecific hydrolysis of the bromoketone 1 with sodium hydroxide in aqueous pyridine. The bromoketone 1 was converted to the 16 alpha-hydroxy-17-ketone 3-sulfate 4 by sulfation with chlorosulfonic acid in pyridine and a subsequent controlled hydrolysis in a high yield without formation of the other ketols. Treatment of the sulfate 4 with sodium borohydride have the triol sulfate 5. The sulfate 4 was also rearranged to the 17 beta-hydroxy-16-ketone 6 with sodium hydroxide in water in a quantitative yield.