(17alpha,20E/Z)-iodovinyl- and 16alpha-iodP618-homoestradiol derivatives: synthesis and evaluation for estrogen receptor imaging.

Article abstract of DOI:10.1016/S0039-128X(99)00084-7

Three new 125I-radioiodinated estrogens featuring a 13beta-ethyl instead of the natural 13beta-methyl group, i.e. 18-homoestradiols, were synthesized and evaluated as potential estrogen receptor imaging agents. The 16alpha-iodo-18-methylestradiol and the 125I-labeled analog were synthesized from the corresponding 16beta-bromo analog by the halogen-exchange method. The cis-bromohydrin precursor was obtained by bromination of an estrone enolacetate, followed by epimerization and reduction. The isomeric (17alpha,20E/Z)-iodovinyl-18-methylestradiols were prepared via the vinyltin intermediates. Treatment of 18-methyl-17alpha-ethynylestradiol with tri-n-butyltin hydride, in the presence of azobisisobutyronitrile as catalyst and heating at 90-100 degrees C afforded the (17alpha,20E)-tri-n-butylstannyl isomer as the major product. Changing the catalyst for triethyl borane, at room temperature, mainly gave the 20Z-isomer. The nca 125I-labeled analogs were obtained from their corresponding tin intermediates upon treatment with [125I]NaI in the presence of H2O2. The 16alpha-[125I]iodo- and isomeric (17alpha,20E/Z)-[125I]iodovinyl-18-methylestradiols were evaluated for estrogen receptor-mediated uterine uptake in immature female rats. Homologation of the C13-methyl group did improve the uterine uptake of the iodovinyl derivatives, but also increased blood retention, resulting in lower target uptake ratios. In the case of the 16alpha-iodo analog uterine retention decreased upon C13-homologation.

Full text of DOI:10.1016/S0039-128X(99)00084-7

Steroids 65 (2000) 74–84
(17␣,20E/Z)-Iodovinyl- and 16␣-iodo-18-homoestradiol derivatives:
synthesis and evaluation for estrogen receptor imaging
Hasrat Ali, Jacques Rousseau, Julie Lafrenie`re, Johan E. van Lier*
MRC Group in the Radiation Sciences, Department of Nuclear Medicine and Radiobiology, Faculty of Medicine, Universite´ de Sherbrooke,
Sherbrooke, Que´bec, Canada J1H 5N4
Received 15 April 1999; received in revised form 21 June 1999; accepted 23 June 1999
Abstract
Three new 125I-radioiodinated estrogens featuring a 13␤-ethyl instead of the natural 13-methyl group, i.e. 18-homoestradiols, were
synthesized and evaluated as potential estrogen receptor imaging agents. The 16␣-iodo-18-methylestradiol and the 125I-labeled analog were
synthesized from the corresponding 16␤-bromo analog by the halogen-exchange method. The cis-bromohydrin precursor was obtained by
bromination of an estrone enolacetate, followed by epimerization and reduction. The isomeric (17␣,20E/Z)-iodovinyl-18-methylestradiols
were prepared via the vinyltin intermediates. Treatment of 18-methyl-17␣-ethynylestradiol with tri-n-butyltin hydride, in the presence of
azobisisobutyronitrile as catalyst and heating at 90–100°C afforded the (17␣,20E)-tri-n-butylstannyl isomer as the major product. Changing
the catalyst for triethyl borane, at room temperature, mainly gave the 20Z-isomer. The nca 125I-labeled analogs were obtained from their
corresponding tin intermediates upon treatment with [125I]NaI in the presence of H2O2. The 16␣-[125I]iodo- and isomeric (17␣,20E/Z)-
[
125I]iodovinyl-18-methylestradiols were evaluated for estrogen receptor-mediated uterine uptake in immature female rats. Homologation
of the C13-methyl group did improve the uterine uptake of the iodovinyl derivatives, but also increased blood retention, resulting in lower
target uptake ratios. In the case of the 16␣-iodo analog uterine retention decreased upon C13-homologation. © 2000 Elsevier Science Inc.
All rights reserved.
Keywords: 18-Homoestradiols; 16␣-iodoestradiol; (17␣,20E/Z)iodovinylestradiol derivatives; Estrogen receptor; Breast cancer imaging
1. Introduction
current diagnostic procedures include palpation, radiologic,
or ultrasonic imaging and surgery [11]. Non-invasive imag-
ing of breast tumors based on their content of hormonal
receptors would be a useful adjunct to these methods [12].
Such an approach would require a receptor-ligand, labeled
with a radionuclide suitable for imaging, with high affinity
for the estrogen receptor, low affinity for non-specific bind-
ing sites and good in vivo metabolic stability.
Halogenation of the D-ring of estradiol (E2), especially at
the 16␣-position, results in compounds with good affinity
for the ER. Thus a number of estradiol derivatives were
labeled at the 16␣-position with radiohalogens [13–21]. The
16␣-[125I]iodoestradiol (IE2) is an excellent ligand for the
ER and routinely used for the in vitro quantification of ER
in biopsy material. Although a few studies with [123I]IE2
have been reported [22,23], rapid metabolism limits the in
vivo use of these agents. The 18F-labeled analog, [18F]FE2 is
stable and good images of primary and metastatic human
breast cancer have been reported [24,25]. However the short
half-life of 18F (110 min) limits the availability of this agent
The growth and proliferation of many estrogen-respon-
sive cells is stimulated by estrogens, and tumors derived
from these cells often retain this dependency [1,2]. Thus, for
the proper management of breast cancer patients, early di-
agnosis of possible metastases and characterization of the
estrogen receptor (ER) status, are of critical importance
[3–6]. Analysis of receptor concentrations in biopsy mate-
rial is routinely used to estimate tumor response to hor-
monal therapy [7]. Biochemical analyses have however
limitations in that the receptor status may have been altered
during tissue manipulation. Furthermore, inhomogeneity of
the tumor may lead to samples with ER levels that do not
represent the overall receptor status of the primary tumor or
its metastases [8–10]. In addition to biochemical markers,
* Corresponding author. Tel.: ϩ1-819-564-5409; fax: ϩ1-819-564-
5442.
E-mail address: jvanlier@courrier.usherb.ca (J.E. van Lier)
0039-128X/00/$ – see front matter © 2000 Elsevier Science Inc. All rights reserved.
PII: S0039-128X(99)00084-7

H. Ali et al. / Steroids 65 (2000) 74–84
75
to dedicated PET facilities. The 17␣-iodovinylestradiols
(IVE2) were developed as a second generation of radiola-
beled steroids with improved in vivo stability [13,26–29].
As expected, iodine attachment via the vinyl carbon renders
the IVE2 far less prone to in vivo deiodination as compared
to the IE2. Substitution at the 11␤-position further increases
the stability of the ER-steroid complex and reduces non-
specific binding. Likewise, addition of a 7␣-methyl group
enhances interaction of estradiol with ER [30–32], and
several derivatives with various substituents at these posi-
tions have been put forth. The preparation of a series of
IVE2 derivatives, their receptor affinities and biodistribution
pattern have been reported [33–37]. Only the 123I-labeled
11␤-methoxy-IVE2 (MIVE2) has been studied in a clinical
setting [38–40].
Substitution of the 13␤-methyl group in selected proges-
tin receptor-ligands, for a 13␤-ethyl group, increases their
relative binding affinity for the receptor [41,42]. Further-
more, 11␤-substitution of 13␤-ethylgonane derivatives in-
duces reversal of antiprogestational activity of the parent
molecule [42]. A number of 13␤-ethylsteroid analogs ex-
hibit high affinities for androgen receptors and a 17␣-io-
dovinyl derivative of ORG 33236 has been suggested as a
potential receptor-binding radioligand [42]. However, al-
though homologation of the C-13 methyl group in proges-
tins leads to enhanced receptor-binding, for estrogen the
opposite is the case [43–45]. Receptor binding is however
only one of several parameters that control target tissue
uptake and in vivo data on the effect of homologation of the
C-13 group in estrogens have not been reported. Therefore,
in this study we evaluated the effect of 13␤-ethyl substitu-
tion of several radioiodinated estradiol derivatives on ER-
mediated target tissue localization.
priate, by their ␥-radiation that was registered via a sodium
iodide detector.
All chemicals used are commercially available and were
of the highest chemical grade. Carrier-free [125I]NaI was
purchased from Amersham Canada Ltd. Steroids were pur-
chased from Sigma (St. Louis, MO, USA). All other chem-
icals were obtained from Aldrich (St. Louis, MO, USA).
2.2. D-(ϩ)-13␤-Ethylgon-4-ene-3,17-dione (2)
D(Ϫ)norgestrel (1) (1 g, 3.2 mmol) and silver carbonate
on celite (5 g, 9.1 mmol) were heated in toluene (60 ml) to
reflux for 1.5 h. The mixture was filtered and washed with
ethyl acetate. The solvent was evaporated under reduced
pressure to furnish compound D-(ϩ)-13␤-ethylgon-4-ene-
3,17-dione (2) in a quantitative yield: m.p. 175–177°C (lit
1
[46]. 174.5–175.5°C); H NMR (CDCl3) ␦ 0.80 (t, J ϭ 7.5
Hz, 3 H, 13␤-CH2CH3), 5.85 (s, 1 H, 4-CH); MS m/z (rel
int) 286 (Mϩ, 62), 258 (45), 91 (100). HRMS calculated for
C19H26O2 286.1933. Found: 286.1927.
2.3. 3-Hydroxy-18-methyl-estra-1,3,5(10)-trien-17-one (3)
D-(ϩ)-13␤-Ethylgon-4-ene-3,17-dione (2) (916 mg,
3.2 mmol) was dissolved in acetonitrile (400 ml) and
CuBr2 (1.46 g) and LiBr (287 mg) were added. The dark
green mixture was stirred under nitrogen at room tem-
perature for 2 h. Water was added until disappearance of
the green color and acetonitrile was evaporated under
reduced pressure. The product was extracted with ethyl
acetate, dried over sodium sulfate (anhydrous) and con-
centrated to dryness. The residue was purified by column
chromatography over silica gel. Elution with 8% EtOAc
in hexane furnished 3-hydroxy 18-methyl-estra-
1,3,5(10)-trien-17-one (3) (687 mg, 2.4 mmol; 75%):
m.p. 242–245°C (lit [44]. 245–251°C).
2. Experimental
2.1. General
2.4. 3,17-Diacetoxy-18-methyl-estra-1,3,5(10),16-tetraene
(5)
Melting points (m.p.) were determined on a Fischer–
1
Johns apparatus and are uncorrected. The H NMR spectra
3-Hydroxy-18-methyl-estra-1,3,5(10)-trien-17-one (3)
(775 mg, 2.7 mmol) was dissolved in isopropenyl acetate
(40 ml) and p-toluenesulfonic acid (195 mg) was added.
The mixture was heated to reflux and stirred overnight.
Isopropenyl acetate was evaporated under reduced pressure.
The residue was poured into water and products were ex-
tracted with ethyl acetate and purified by column chroma-
tography over silica gel with 5% EtOAc in hexane to yield
4 and 5.
were recorded on a Bru¨cker AC 300 (300 MHz) in CDCl3
or DMSO-d6. Chemical shifts are referenced to the residual
solvent signal (CDCl3 ␦ ϭ 7.26). Low and high resolution
mass spectra (MS, HRMS) were carried out with a VG
micromass model ZAB-1F apparatus at 70 eV ionization
voltage. Analytical thin-layer chromatography (TLC) was
performed with polygram silica gel plates coated with flu-
orescent indicator (UV254) and the compounds were visu-
alized by their UV absorbance and/or color response upon
spraying with H2SO4/EtOH and heating at 120°C. Column
chromatography was performed on silica gel (60–80 mesh).
High-performance liquid chromatography (HPLC) was per-
2.5. 3,17-Diacetoxy-18-methyl-estra-1,3,5(10),16-tetraene
(5)
formed on
a
reversed-phase column (C-18, ODS-2
(124 mg, 0.34 mmol; 12%): m.p. 112–115°C (lit [44].
114–116°C); 1H NMR (CDCl3) ␦ 0.79 (t, J ϭ 7.5 Hz, 3 H,
13␤-CH2CH3), 2.16 (s, 3 H, 17-OCOCH3), 2.28 (s, 3 H,
spherosorb, 5 ␮M, 25 ϫ 0.94 cm, CSC, Montreal, Canada).
The compounds were detected at 280 nm and where appro-

76
H. Ali et al. / Steroids 65 (2000) 74–84
3-OCOCH3), 5.59 (brs, 1 H, 16-H), 6.79, 6.84 (2 H, 2 and
4-CH), 7.23 (d, 7.8 Hz, 1 H, 1-CH); MS m/z (rel int) 368 (8,
Mϩ), 339 (30, Mϩ Ϫ CHO), 326 (25, Mϩ Ϫ CH2CO), 297
(100, Mϩ Ϫ C3H2O2), 255 (70). HRMS calculated for
C23H28O4 368.1987. Found: 368.1980.
1 H, 1-CH); MS m/z (rel int) 362, 364 (100, Mϩ). HRMS
calculated for C19H23BrO2 362.0881. Found: 362.0877.
2.9. 16␤-Bromo-18-methyl-estra-1,3,5(10)-trien-17-one (9)
A mixture of the 16␣-bromoestrogen (7) (140 mg, 0.38
mmol) and LiBr (140 mg) in 1 ml of 2-butanone was heated
for 0.5 h at reflux. The reaction mixture was poured into 20
ml of water and extracted with EtOAc, washed with water,
dried over sodium sulfate (anhydrous), and evaporated to
dryness. The purple residue was filtered over a silica gel
column to furnish a yellow residue that was purified by
HPLC to gave 16␤-bromo-18-methyl-estra-1,3,5(10)-trien-
17-one (9) (37%): m.p. 187–190°C; HPLC (70:30 MeOH/
2.6. 3-Acetoxy-18-methyl-estra-1,3,5(10)-trien-17-one (4)
(283 mg, 0.87 mmol; 32%): m.p. 155–157°C (lit [44].
156–158°C); 1H NMR (CDCl3) ␦ 0.79 (t, J ϭ 7.5 Hz, 3 H,
13␤-CH2CH3), 2.28 (s, 3 H, 3-OCOCH3), 6.80 (d, J ϭ 2.2
Hz, 1 H, 4-CH), 6.85 (dd, J ϭ 2.2 and 9.2 Hz, 1 H, 2-CH),
7.29 (d, J ϭ 9.2 Hz, 1-CH); MS m/z (rel int) 326 (18, Mϩ),
284 (100, Mϩ Ϫ CH2CO). HRMS calculated for C21H26O3
326.1882. Found: 326.1872.
1
H2O) tr ϭ 27 min; H NMR (CDCl3) ␦ 0.85 (t, J ϭ 7 Hz,
3 H, 13␤-CH2CH3), 4.12 (t, J ϭ 8.5 Hz, 1 H, 16␣-H), 6.57
(d, J ϭ 3 Hz, 1 H, 4-CH), 6.63 (dd, J ϭ 2 and 8.5 Hz, 1 H,
2-CH), 7.13 (d, J ϭ 8.5 Hz, 1 H, 1-CH); MS m/z (rel int)
362, 364 (100, Mϩ), 228 (100). HRMS calculated for
C19H23BrO2 362.0881. Found: 362.0877.
2.7. 16␣-Bromo-3-acetoxy-18-methyl-estra-1,3,5(10)-trien-
17-one (6)
3,17-Diacetoxy-18-methyl-estra-1,3,5(10),16-tetraene
(5) (550 mg, 1.5 mmol) was dissolved in ether (10 ml) and
acetate buffer (200 mg of potassium acetate in 4 ml of 85%
acetic acid) was added. The mixture was cooled to 0°C and
1.6 ml of bromine solution was added (0.2 ml of Br2 in 6.5
ml of acetic acid glacial) until the orange color persisted,
whereafter the solution was stirred for an additional 20 min.
The reaction was terminated by the addition of water and
the organic phase was washed with water, 5% sodium thio-
sulfate and 5% aqueous sodium bicarbonate, dried over
sodium sulfate (anhydrous), filtered and evaporated to dry-
ness to afford 16␣-bromo-3-acetoxy-18-methyl-estra-
1,3,5(10)-trien-17-one (6) in a quantitative yield: m.p.
2.10. 16␤-Bromo-18-methyl-estra-1,3,5(10)-trien-3,17␤-
diol (10)
A solution of NaBH4 (105 mg, 2.8 mmol) in ethanol (6.6
ml) was added to 16␤-bromo-18-methyl-estra-1,3,5(10)-
trien-17-one (9) (122 mg, 0.33 mmol) in ethanol (6.6 ml).
The mixture was stirred at room temperature for one hour.
Excess NaBH4 was destroyed with acetone and the reaction
mixture was poured into water, extracted with ethyl acetate,
washed with water, dried over sodium sulfate (anhydrous),
and evaporated to dryness to furnished the crude product
(119 mg). The residue was purified by column chromatog-
raphy over silica gel. Elution with 5% CH3CN in CHCl3
1
133°C; H NMR (CDCl3) ␦ 0.79 (t, J ϭ 7 Hz, 3 H, 13␤-
CH2CH3), 2.28 (s, 3 H, 3-OCOCH3), 4.60 (dd, J ϭ 7.5 Hz,
1 H, 16␤-H), 6.81 (d, J ϭ 2 Hz, 1 H, 4-CH), 6.85 (dd, J ϭ
2.5 and 8 Hz, 1 H, 2-CH), 7.29 (1 H, 1-CH); MS m/z (rel int)
404, 406 (15, Mϩ), 364, 366 (100, Mϩ Ϫ CH2CO). HRMS
calculated for C21H25BrO3 404.0987. Found: 404.0980.
furnished
16␤-bromo-18-methyl-estra-1,3,5(10)-trien-
3,17␤-diol (10) (36 mg, 0.1 mmol, 34%): m.p. 195–199°C;
HPLC (70: 30 MeOH/H2O) tr ϭ 29 min; 1H NMR (CDCl3)
␦ 1.01 (t, J ϭ 7.5 Hz, 3 H, 13␤-CH2CH3), 3.50 (t, J ϭ 8.5
Hz, 1 H, 17␣-H), 4.68 (td, J ϭ 8 Hz, 1 H, 16␣-H), 6.56 (d,
J ϭ 3 Hz, 1 H, 4-CH), 6.63 (dd, J ϭ 3 and 8.5 Hz, 1 H,
2-CH), 7.14 (d, J ϭ 8 Hz, 1 H, 1-CH); MS m/z (rel int) 364,
366 (30, Mϩ), 284 (90, Mϩ-Br), 159 (100). HRMS calcu-
lated for C19H25BrO2 364.1038. Found: 364.1033.
2.8. 16␣-Bromo-18-methyl-estra-1,3,5(10)-trien-17-one (7)
16␣-Bromo-3-acetoxy-18-methyl-estra-1,3,5(10)-trien-
17-one (6) (603 mg, 1.5 mmol) was hydrolyzed by treat-
ment with concentrated sulfuric acid (0.3 ml) in ethanol (30
ml) at room temperature. Water was added and the com-
pound was extracted with CHCl3 and the organic phase was
dried over sodium sulfate (anhydrous), filtered, and concen-
trated under reduced pressure. The residue was purified by
column chromatography over silica gel. Elution with 8%
EtOAc in hexane furnished 16␣-bromo-18-methyl-estra-
1,3,5(10)-trien-17-one (7) (460 mg, 1.3 mmol; 85%): m.p.
97–98°C; HPLC (70:30 MeOH/H2O) tr ϭ 25 min; 1H NMR
(CDCl3) ␦ 0.79 (t, J ϭ 7 Hz, 3 H, 13␤-CH2CH3), 4.61 (dd,
J ϭ 7.5 Hz, 1 H, 16␤-H), 6.57 (d, J ϭ 3 Hz, 1 H, 4-CH),
6.63 (dd, J ϭ 3 and 8 Hz, 1 H, 2-CH), 7.13 (d, J ϭ 8 Hz,
2.11. 16␣-Bromo-18-methyl-estra-1,3,5(10)-trien-3,17␤-
diol (8)
A solution of NaBH4 (18 mg, 0.5 mmol) in ethanol (1
ml) was added to 16␤-bromo-18-methyl-estra-1,3,5(10)-
trien-17-one (7) (20 mg, 0.05 mmol) in ethanol (2 ml). The
mixture was stirred at room temperature for 2 h. Excess
NaBH4 was destroyed with acetone and the reaction mixture
was poured into water, extracted with ethyl acetate, washed
with water, dried over sodium sulfate (anhydrous), and
evaporated to dryness to furnish a crude product (19 mg).
The residue was purified by HPLC to furnish 16␣-bromo-

H. Ali et al. / Steroids 65 (2000) 74–84
77
Scheme 1. Reagents: (i) Ag2CO3/Celite, toluene, (ii) CuBr2, LiBr, CH3CN, (iii) isopropenyl acetate, p-TsOH, (iv) ether, Br2, acetate buffer, (v) EtOH, H2SO4,
(vi) EtOH, NaBH4, (vii) 2-butanone, LiBr, (viii) 2-butanone, NaI.
18-methyl-estra-1,3,5(10)-trien-3,17␤-diol (8) (11 mg, 0.03
in 2-butanone (1 ml) was heated for 1 h at 120°C. After
cooling, the mixture was poured into water and extracted
with ethyl acetate. The organic phase was washed with
water, dried over magnesium sulfate (anhydrous), and evap-
orated under reduced pressure. The residue was purified by
HPLC to give 16␣-iodo-18-methyl-estra-1,3,5(10)-trien-
3,17␤-diol (11) (16 mg, 78%): m.p. 160–163°C; HPLC
(70:30 MeOH/H2O) tr ϭ 38 min; 1H NMR (CDCl3) ␦ 0.99
(t, J ϭ 7.5 Hz, 3 H, 13␤-CH2CH3), 2.82 (dd, J ϭ 4 and 8.5
Hz, 1 H, 17␣-H), 4.15 (d, J ϭ 7 Hz, 1 H, 17␤-OH), 4.26 (td,
J ϭ 5 Hz, 1 H, 16␤-H), 6.56 (d, J ϭ 3 Hz, 1 H, 4-CH), 6.63
(dd, J ϭ 3 and 8 Hz, 1 H, 2-CH), 7.13 (d, J ϭ 8 Hz, 1 H,
1-CH); MS m/z (rel int) 412 (70, Mϩ), 229 (85), 159 (90),
133 (100). HRMS calculated for C19H25IO2 412.0899.
Found: 412.0894.
mmol, 60%): m.p. 98–101°C; HPLC (70:30 MeOH/H2O) tr
1
ϭ 29 min; H NMR (CDCl3) ␦ 1.01 (t, J ϭ 7 Hz, 13␤-
CH2CH3), 4.05 (d, J ϭ 6.6 Hz, 1 H, 17␣-H), 4.27 (1 H,
16␤-H), 6.56 (d, J ϭ 2.5 Hz, 1 H, 4-CH), 6.62 (dd, J ϭ 3
and 8 Hz, 1 H, 2-CH), 7.14 (d, J ϭ 8 Hz, 1 H, 1-CH); MS
m/z (rel int) 364, 366 (38, Mϩ), 284 (75, Mϩ-Br), 159 (100).
HRMS calculated for C19H25BrO2 364.1038. Found:
364.1033.
2.12. 16␣-Iodo-18-methyl-estra-1,3,5(10)-trien-3,17␤-diol
(11)
A mixture of 16␤-bromo-18-methyl-estra-1,3,5(10)-
trien-3,17␤-diol (10) (20 mg, 0.05 mmol) and NaI (50 mg)

78
H. Ali et al. / Steroids 65 (2000) 74–84
Scheme 2. Reagents: (i) CuBr2, LiBr, CH3CN, (ii) Bu3SnH, AIBN, toluene, (iii) Bu3SnH, Et3B, THF, (iv) I2, CHCl3.
2.13. Synthesis of 16␣-[125I]iodo-18-methyl-estra-
1,3,5(10)-trien-3,17␤-diol ([125I]11)
CuBr2 (367 mg) and LiBr (72 mg) were added. The dark
green mixture was stirred under nitrogen at room tempera-
ture for 2–2.5 h. Water was added until disappearance of the
green color and acetonitrile was removed under reduced pres-
sure. The product was extracted with ethyl acetate, dried
over sodium sulfate (anhydrous), filtered, and concentrated
under reduced pressure. The residue was purified by column
chromatography over silica gel. Elution with 10% EtOAc in
hexane furnished a white crystalline compound 18-methyl-
17␣-ethynylestra-1,3,5(10)trien-3,17␤-diol (12) (150 mg,
0.48 mmol; 60%): m.p. 117–120°C (lit [44]. 134–136°C);
1H NMR (CDCl3) ␦ 0.98 (t, J ϭ 7.5 Hz, 3 H, 13␤-CH2CH3),
6.55 (d, J ϭ 3 Hz, 1 H, 4-CH), 6.62 (dd, J ϭ 3 and 8 Hz,
1 H, 2-CH), 7.16 (d, J ϭ 8.5 Hz, 1 H, 1-CH); MS m/z (rel
int) 310 (Mϩ, 32), 242 (12), 227 (100), 160 (40). HRMS
calculated for C21H26O2 310.1933. Found: 310.1924.
The radiosynthesis of [125I]11 was performed as described
earlier [14]. A solution 16␤-bromo-18-methyl-estra-1,3,5(10)-
trien-3,17␤-diol (10) (100 ␮g) in 20 ␮l of methanol was added
to the reaction vial containing 1.5 mCi of Na[125I] in 20 ␮l of
water containing 20 ␮g of Na2S2O3 and the solvent was evap-
orated (N2) close to dryness at 60–65°C and 20 ␮l acetonitrile
was added to the reaction mixture. The reaction vial was tightly
closed and the reaction mixture was heated at 95–100°C for
2 h, whereafter acetonitrile was removed. The residue (1.3
mCi) was dissolved in methanol and purified on an analytical
C-18 reversed-phase HPLC column operated at 1 ml/min with
70% methanol in 30% water. The compound [125I]11 eluted at
35 min in 70% yield (based on radioactivity).
2.14. 18-Methyl-17␣-ethynylestra-1,3,5(10)trien-3,17␤-
diol (12)
2.15. (17␣,20E)-21-(tributylstannyl)-18-methyl-
1,3,5(10),20-tetraene-3,17␤-diol (13)
The D(-)norgestrel (1) (250 mg, 0.8 mmol) was dis-
18-Methyl-17␣-ethynylestra-1,3,5(10)trien-3,17␤-diol
solved in 115 ml of acetonitrile (conc. 0.007 M) and solid
(12) (22 mg, 0.07 mmol) was dissolved in 10 ml of toluene

H. Ali et al. / Steroids 65 (2000) 74–84
79
Table 1
Tissue uptake of 16␣-[125I]iodo-18-methylestradiol ([125I]11) in immature female Fischer rats
%ID/g (SEM)a
Tissue
0.5 h
1 h
2 h
2 h (ϩE)
5 h
24 h
Blood
1.20 (0.06)
1.45 (0.08)
1.23 (0.13)
0.92 (0.10)
1.43 (0.18)
2.88 (0.18)
3.75 (0.26)
388 (35)
0.75 (0.08)
2.85 (0.17)
1.60 (0.04)
1.33 (0.04)
1.67 (0.12)
1.29 (0.09)
1.50 (0.12)
1.16 (0.03)
1.32 (0.44)
1.33 (0.13)
2.82 (0.37)
3.09 (0.34)
710 (24)
0.61 (0.04)
3.86 (0.60)
1.60 (0.16)
1.25 (0.10)
1.44 (0.32)
1.13 (0.08)
1.35 (0.10)
0.87 (0.09)
0.92 (0.08)
1.25 (0.18)
3.10 (0.21)
1.81 (0.11)
732 (98)
0.39 (0.01)
1.88 (0.10)
0.85 (0.08)
0.77 (0.11)
1.05 (0.05)
1.06 (0.18)
1.33 (0.20)
0.79 (0.14)
0.97 (0.05)
1.08 (0.21)
2.71 (0.08)
1.96 (0.37)
1116 (48)
0.36 (0.00)
1.98 (0.22)
0.46 (0.14)
0.50 (0.19)
0.71 (0.25)
0.94 (0.10)
1.07 (0.12)
0.62 (0.03)
0.63 (0.04)
0.77 (0.09)
1.83 (0.24)
1.27 (0.19)
2277 (38)
0.42 (0.13)
0.79 (0.12)
0.50 (0.07)
0.54 (0.02)
0.72 (0.13)
0.22 (0.19)
0.19 (0.01)
0.21 (0.04)
0.17 (0.17)
0.14 (0.01)
0.68 (0.06)
0.33 (0.05)
3618 (258)
0.09 (0.05)
0.20 (0.09)
0.20 (0.09)
0.32 (0.01)
0.47 (0.02)
Plasma
Lungs
Spleen
Kidneys
Liver
Adrenals
Thyroid
Muscle
Fat
Uterus
T/Blood
T/NT
a Mean organ uptake in percent injected dose per gram of tissue (%ID/g) and standard error of the mean (SEM) for 3 to 5 Fisher female immature (21 days)
rats. Each animal received i.v. 10 ␮Ci of [125I]11 in the presence (ϩE2) or the absence of 60 ␮g of co-injected estradiol. T ϭ target (Uterus); NT ϭ Non-target
(average value of Lung, Spleen, Muscle).
and tributyltin hydride (0.2 ml) and azobisisobutyronitrile
(10 mg) were added. The mixture was heated at 90–100°C
under nitrogen for 1 h. The solvent was evaporated under
reduced pressure and the residue was purified by column
chromatography over silica gel. Elution with 8% EtOAc in
hexane furnished (17␣,20E)-21-(tributylstannyl)-18-meth-
yl-1,3,5(10),20-tetraene-3,17␤-diol (13).
2.19. (17␣,20E)-21-Iodo-18-methyl-estra-1,3,5(10),20-
tetraene-3,17␤-diol (15) and (17␣,20Z)-21-Iodo-18-
methyl-estra-1,3,5(10),20-tetraene-3,17␤-diol (16)
Compound (13)/(14) was dissolved in chloroform and a
solution of I2 in chloroform was added until a pink color
persisted. The color was removed with 5% sodium thiosul-
fate and the organic phase was dried over sodium sulfate
(anhydrous), filtered and evaporated to dryness to afford
(15)/(16).
2.16. (17␣,20E)-21-(tributylstannyl)-18-methyl-
1,3,5(10),20-tetraene-3,17␤-diol (13) and (17␣,20Z)-21-
(tributylstannyl)-18-methyl-1,3,5(10),20-tetraene-3,17␤-
diol (14)
2.20. (17␣,20E)-21-Iodo-18-methyl-estra-1,3,5(10),20-
tetraene-3,17␤-diol (15)
18-Methyl-17␣-ethynylestra-1,3,5(10)trien-3,17␤-diol
(12) (25 mg, 0.08 mmol) was dissolved in THF (5 ml) and
tributyltin hydride (0.1 ml) and triethylborane (0.1 ml) were
added. The mixture was stirred under nitrogen at room
temperature for 0.5 h. The solvent was evaporated under
reduced pressure and the residue was purified by HPLC on
a reversed-phase semipreparative column with a gradient of
5% H2O in MeOH to 100% MeOH (20 min).
M.p. 104–106°C; HPLC (80: 20 MeOH/H2O) tr ϭ 19
min; H NMR (CDCl3) ␦ 0.98 (t, J ϭ 7.5 Hz, 3 H, 13␤-
1
CH2CH3), 6.27 (d, J ϭ 14 Hz, 1 H, ϭ CHI), 6.55 (d, J ϭ
3 Hz, 1 H, 4-CH), 6.62 (dd, J ϭ 3 and 8 Hz, 1 H, 2-CH),
6.80 (d, J ϭ 14 Hz, 1 H, CH ϭ ), 7.13 (d, J ϭ 8.5 Hz, 1 H,
1-CH); MS m/z (rel int) 438 (40, Mϩ), 311 (42, Mϩ-I), 242
(32), 227 (100). HRMS calculated for C21H27IO2 438.1056.
Found: 438.1059.
2.17. (17␣,20E)-21-(tributylstannyl)-18-methyl-
1,3,5(10),20-tetraene-3,17␤-diol (13)
2.21. (17␣,20Z)-21-Iodo-18-methyl-estra-1,3,5(10),20-
tetraene-3,17␤-diol (16)
White solid, m.p. 121–122°C; HPLC tr ϭ 12 min; MS
m/z (rel int) 545 (100, M-C4H9)ϩ.
M.p. 75–80°C; HPLC (80: 20 MeOH/H2O) tr ϭ 19 min;
1H NMR (CDCl3) ␦ 1.02 (t, J ϭ 7.5 Hz, 3 H, 13␤-CH2CH3),
6.34 (d, J ϭ 8.5 Hz, 1 H, ϭ CHI), 6.55 (d, J ϭ 3 Hz, 1 H,
4-CH), 6.62 (dd, J ϭ 3 and 8 Hz, 1 H, 2-CH), 6.85 (d, J ϭ
8.5 Hz, 1 H, CH ϭ ), 7.14 (d, J ϭ 8.5 Hz, 1 H, 1-CH); MS
m/z (rel int) 438 (28, Mϩ), 311 (20, Mϩ-I), 242 (35), 227
(100). HRMS calculated for C21H27IO2 438.1056. Found:
438.1059.
2.18. (17␣,20Z)-21-(tributylstannyl)-18-methyl-
1,3,5(10),20-tetraene-3,17␤-diol (14)
Oil; HPLC tr ϭ 17 min; MS m/z (rel int) 602 (5, Mϩ),
312 (45), 227 (100).

80
H. Ali et al. / Steroids 65 (2000) 74–84
Table 2
Tissue uptake of (17␣,20E)-[125I]iodo-18-methylestradiol ([125I]15) and (17␣,20Z)-[125I]iodo-18-methylestradiol ([125I]16) in immature female Fischer
rats
%IDg (SEM)a
Tissue
0.5 h
1 h
2 h
2 h (ϩE)
5 h
24 h
Blood
Plasma
0.79 (0.12)
1.06 (0.13)
2.63 (0.52)
1.42 (0.25)
2.63 (0.60)
5.18 (0.63)
9.36 (1.43)
145 (2.81)
1.70 (0.22)
2.83 (0.53)
3.09 (0.48)
3.90 (0.16)
1.61 (0.04)
0.59 (0.04)
0.82 (0.04)
1.36 (0.10)
0.87 (0.08)
1.64 (0.17)
3.60 (0.24)
5.94 (0.56)
177 (19.17)
1.10 (0.13)
4.33 (0.78)
2.27 (0.23)
3.83 (0.22)
2.06 (0.15)
0.56 (0.04)
0.74 (0.06)
1.23 (0.08)
0.93 (0.07)
1.39 (0.12)
3.27 (0.20)
4.28 (0.22)
363 (22.68)
0.88 (0.14)
6.63 (0.73)
1.84 (0.21)
3.29 (0.26)
1.82 (0.14)
0.52 (0.05)
0.67 (0.05)
1.18 (0.21)
0.77 (0.14)
1.36 (0.31)
3.08 (0.40)
4.32 (0.75)
265 (17.84)
0.89 (0.10)
4.90 (0.76)
0.91 (0.28)
1.93 (0.64)
1.85 (0.15)
0.42 (0.06)
0.52 (0.05)
0.76 (0.10)
0.51 (0.07)
0.87 (0.13)
2.41 (0.24)
2.73 (0.35)
893 (18.7)
0.59 (0.09)
6.08 (0.79)
1.12 (0.08)
2.56 (0.15)
2.63 (1.02)
0.12 (0.03)
0.11 (0.01)
0.12 (0.01)
0.13 (0.00)
0.16 (0.00)
1.05 (0.00)
0.49 (0.09)
1295 (121.05)
0.10 (0.01)
2.11 (0.18)
0.30 (0.12)
2.52 (0.38)
1.54 (0.49)
Lungs
Spleen
Kidneys
Liver
Adrenals
Thyroid
Muscle
Fat
Uterus
T/Blood
T/NT
(20Z)-[125I]16
Blood
3.58 (0.22)
2.89 (0.20)
3.35 (0.33)
2.60 (0.27)
4.09 (0.57)
6.71 (0.85)
14.96 (4.64)
145 (15.88)
2.58 (0.82)
4.10 (1.11)
5.48 (0.23)
1.53 (0.03)
1.97 (0.24)
3.37 (0.12)
2.44 (0.10)
2.68 (0.10)
2.29 (0.16)
2.94 (0.19)
4.92 (0.07)
8.60 (0.59)
217 (10.52)
1.58 (0.30)
6.23 (1.07)
7.52 (0.68)
2.23 (0.18)
3.15 (0.43)
2.98 (0.41)
1.96 (0.27)
2.34 (0.25)
1.89 (0.21)
2.13 (0.35)
4.24 (0.26)
6.15 (1.08)
375 (8.18)
1.25 (0.31)
7.04 (1.28)
7.19 (1.12)
2.39 (0.07)
3.29 (0.86)
2.63 (0.03)
1.79 (0.50)
1.87 (0.01)
2.46 (0.19)
1.74 (0.02)
3.76 (0.24)
3.38 (0.05)
333 (4.18)
0.88 (0.08)
4.60 (0.73)
1.82 (0.04)
0.69 (0.01)
2.52 (0.21)
2.05 (0.20)
1.20 (0.07)
1.34 (0.04)
1.24 (0.12)
1.25 (0.10)
2.40 (0.19)
3.36 (0.37)
729 (97.90)
0.56 (0.06)
6.48 (0.70)
2.60 (0.14)
1.29 (0.13)
3.59 (0.00)
1.18 (0.30)
0.28 (0.03)
0.35 (0.09)
0.45 (0.06)
0.27 (0.04)
0.97 (0.03)
0.41 (0.03)
1004 (61.29)
0.10 (0.02)
0.92 (0.12)
1.07 (0.19)
0.93 (0.08)
1.05 (0.05)
Plasma
Lungs
Spleen
Kidneys
Liver
Adrenals
Thyroid
Muscle
Fat
Uterus
T/Blood
T/NT
a Mean organ uptake in percent injected dose per gram of tissue (%ID/g) and standard error of the mean (SEM) for 3 to 5 Fisher female immature (21 days)
rats. Each animal received i.v. 10 ␮Ci (20E)-[125I]15 or (20Z)-[125I]16 in the presence (ϩE2) or the absence of 60 ␮g of co-injected estradiol.
2.22. Synthesis of (17␣,20E)-21-[125I]Iodovinyl-18-methyl-
estra-1,3,5(10),20-tetraene-3,17␤-diol ([125I]15) and
(17␣,20Z)-21-[125I]Iodovinyl-18-methylestra-1,3,5(10),20-
tetraene-3,17␤-diol ([125I]16)
preparation (10 ␮Ci, 370 KBq) via the lateral tail vein. The
radiopharmaceuticals were dissolved in ethanol and diluted
with sterile physiological saline (0.9% NaCl in H2O) con-
taining 1% Tween-80, to give a final ethanol concentration
of 9%. For the receptor saturation studies 60 ␮g of unla-
beled estradiol was co-injected with the radiopharmaceuti-
cal. The animals were sacrificed under deep halothane an-
esthesia by severing the axillary artery to collect blood
followed by chest opening [47]. Tissues of interest were
removed washed in physiological saline, blotted dry and
placed in pre-weighted tubes. Fats were removed from the
flank of the animals. The radioactivity was counted in a
Model 1282 Compugamma ␥-counter (LKB Wallac, Fin-
land) and specific activity was expressed as percent of
injected dose per gram (%ID/g). Statistical variations are
presented as the SEM [48].
Compound (13)/(14) was dissolved in ethanol and 10 ␮l
of Na125I and 40 ␮l of solution H2O2/acetic acid (2:1) were
added. After 5 min, 50 ␮l of 5% sodium thiosulfate was
added and the mixture was dried. Water was added and
product was extracted with chloroform. Organic phases
were dried and the residue was dissolved in 500 ␮l of
methanol and was purified by HPLC on a spherisorb S5
ODS2 column to furnish ([125I]15)/([125I]16): HPLC (75:25
MeOH/H2O), flow 1 ml min, ␭ 280 nm, tr ϭ 19 and 18 min,
respectively.
2.23. In vivo studies
The animal experiments were conducted in accordance
with the recommendations of the Canadian Council of An-
imal Care and of the in-house Ethic Committee for Animal
Experiments as previously described [26]. Briefly immature
female Fischer rats (21 days old, 36 g SEM ϭ 2.35 g,
Charles River) were injected 200 ␮l of the 125I-labeled
3. Results and discussion
3.1. Chemistry
The 3-hydroxy-18-methylestra-1,3,5(10)-trien-17-one (3)
was prepared from commercially available D(-)norgestrel

H. Ali et al. / Steroids 65 (2000) 74–84
81
Fig. 2. Uterine uptake and uterus-to-blood ratios following i.v. adminis-
tration of 20E-(18-methyl)-IVE2 ([125I]15) and 20Z-(18-methyl)-IVE2
([125I]16) to immature female Fischer rats. Values for the 125I-labeled
isomeric 20E/Z-IVE2 are taken from the literature [33]. The error bars
represent the SE.
Fig. 1. Blood clearance in %ID/g of 20E-(18-methyl)-IVE2 ([125I]15),
20Z-(18-methyl)-IVE2 ([125I]16) and 16␣-iodo-18-methylestradiol
([125I]11) in immature female Fischer rats. Values for the 125I-labeled
isomeric 20E/Z-IVE2 and 16␣-iodoestradiol are taken from the literature
[18,33]. The error bars represent the standard error (SE).
with LiBr in 2-butanone. The 16␤-bromo configuration of 9
was confirmed by the characteristic downfield shift of the
C-18 proton in the 1H NMR. Reduction of the 17-one group
of 16␤-bromo-18-methylestra-1,3,5(10)-trien-17-one (9)
was achieved with NaBH4 and gave 16␤-bromo-18-meth-
ylestra-1,3,5(10)-trien-3,17␤-diol (10) together with a small
amount of the debrominated analog 18-methylestra-
1,3,5(10)-trien-3,17␤-diol. Similarly, the reduction of the
16␣-bromo-18-methylestra-1,3,5(10)-trien-17-one (7) with
NaBH4 gave 16␣-bromo-18-methylestra-1,3,5(10)-trien-
3,17␤-diol (8) (Scheme 1). The presence of a pair of mo-
lecular ions, of equal intensity, in the mass spectra of 6–10
confirmed the presence of bromine in the products. The
(1) accordingly to a published procedure. The initial step
involves de-ethynylation of D(-)norgestrel (1) catalyzed by
Fetizons reagent (silver carbonate on celite) according to the
procedure of Lenz [49] that yielded D-(ϩ)-13-ethylgon-
4-ene-3,17-dione (2). Reaction of 2 with CuBr2/CH3CN in
the presence of LiBr afforded 3-hydroxy-18-methylestra-
1,3,5(10)-trien-17-one (3) in high yield [50]. The 16␣-ha-
losteroids were prepared by the adaptation of the Johnson
and Johns procedure [51]. Reaction of 3-hydroxy-18-meth-
ylestra-1,3,5(10)-trien-17-one (3) with isopropenyl acetate
in the presence of the acid catalyst gave 3,17-diacetoxy-
18-methylestra-1,3,5(10)-16-tetraen (5) along with 3-ace-
toxy-18-methylestra-1,3,5(10)-trien-17-one (4). The enol
diacetate (5) was selectively converted to the 16␣-bromo-
3-acetoxy-18-methylestra-1,3,5(10)-trien-17-one (6) by
treatment with Br2 in acetic acid. Acid hydrolysis of the
3-acetate group of 6 with sulfuric acid in alcohol at room
temperature gave the 16␣-bromo-18-methylestra-1,3,5(10)-
trien-17-one (7) that was converted to the 16␤-bromo-18-
methylestra-1,3,5(10)-trien-17-one (9) via epimerization
16␣-iodo-18-methylestra-1,3,5(10)-trien-3,17␤-diol
(11)
was obtained by halogen exchange of 16␤-bromo-18-meth-
ylestra-1,3,5(10)-trien-3,17␤-diol (10) with NaI and the ra-
dioiodinated analog was obtained with [125I]NaI. The radio-
chemical yield of the product was 70%. The compounds
were purified by reversed-phase HPLC.
18-Methyl-17␣-ethynylestra-1,3,5(10)trien-3,17␤-diol (12)
was obtained by aromatization of the commercially avail-
able D(-)norgestrel (1) using CuBr2/CH3CN in the presence
of LiBr, as reported by Rao et al. [50]. Treatment of 18-
methyl-17␣-ethynylestra-1,3,5 [10]trien-3,17␤-diol (12)
with tri-n-butyltin hydride using azoisobutyronitrile as cat-
alyst in toluene at 90–95°C gave the 20E-isomer of the

82
H. Ali et al. / Steroids 65 (2000) 74–84
H2O. The stannyl intermediates 13–14 were converted to
the radioiodinated products [125I]15 and [125I]16 using nca
Na[125I] in the presence of H2O2 with a radiochemical yield
of 60–70%. The labeled compounds were purified by re-
versed-phase HPLC in batches of about 0.2 mCi and their
identity were confirmed by coinjection with the authentic
iodinated products. During the purification, eluting 125I-
labeled products could not be detected by the UV monitor.
Since the detection limit on our HPLC system is about 10Ϫ7
mmol, the minimum specific activity should be 2000 Ci/
mmol. Thus the specific activities likely are in the same
range as that of the starting [125I]NaI, e.g. up to 2200
Ci/mmol.
3.2. Biologic properties
The biodistribution and uterine uptake of the 125I-labeled
estradiol derivatives of 11, 15, and 16, were studied in
immature Fischer female rats. The animals were injected
through the tail vein with 10 ␮Ci (370 KBq) of the HPLC-
purified 125I-labeled steroid in 200 ␮l of a 9% ethanol-saline
solution containing 1% Tween-80. The animals were sacri-
ficed at 0.5, 1, 2, 5, and 24 h post injection. In order to
establish that the uterine uptake was receptor-mediated,
some rats of the 2 h group were co-injected with 60 ␮g of
unlabeled estradiol. The radioactivity in the various organs
is presented in Tables 1 and 2.
Fig. 3. Uterine uptake and uterus-to-blood ratios following i.v. adminis-
tration of 16␣-iodo-18-methylestradiol ([125I]11) to immature female Fi-
scher rats. Values for the 125I-labeled 16␣-iodoestradiol are taken from the
literature [18]. The error bars represent the SE.
Blood and plasma radioactivity remained the highest
with 20Z-(18-methyl)-IVE2 ([125I]16) followed by 16␣-(18-
methyl)-IE2 ([125I]11) and 20E-(18-methyl)-IVE2 ([125I]15)
(Fig. 1). The plasma radioactivity concentration followed
the same pattern as the total blood activity except that
differences in plasma radioactivity levels between the 3
compounds were less pronounced. The non-target tissue
distribution patterns were similar for all three compounds,
with most of the radioactivity being retained in the adrenals,
liver, and fat. The muscle, lungs and spleen contain the least
activity. Tissue specific activities decreased in the following
order, 20Z-(18-methyl)-IVE2 Ͼ 20E-(18-methyl)-IVE2 Ͼ
16␣-(18-methyl)-IE2. Adrenal uptake of 20Z-(18-methyl)-
IVE2 showed a 45% drop in specific activity in the presence
of cold estradiol, no such effect was observed for the 20E-
isomer or the 16␣-(18-methyl)-IE2.
The highest uterine uptake, uterus-to-non target ratio and
specificity were observed with the 20Z-(18-methyl)-IVE2
(Fig. 2). The 20E-iosomer however presented slightly
higher uterus-to-blood ratios due to more rapid blood clear-
ance. In the presence of cold estradiol the uterine specific
activity dropped by 75%, 50%, and 46%, respectively, for
20Z-(18-methyl)-IVE2, 20E-(18-methyl)-IVE2 and 16␣-
(18-methyl)-IE2. The plasma-to-blood ratio for 20Z-(18-
methyl)-IVE2 indicate that more than half of the blood
radioactivity is associated with the blood cellular elements.
Binding of 20Z-(18-methyl)-IVE2 to blood cells seems to be
strong, because plasma-to-blood ratios decrease with time.
Thyroid uptake reveals that the 20E- and 20Z-isomers un-
vinylstanne 13 as the major product. Nozaki reported [52] a
convenient method for the formation of the 20E/Z-vinyl-
stannes from the acetylenic compound using triethylborane
as a catalyst. Likewise we found that compound 12 with
tri-n-butyltin hydride in the presence of the triethylborane as
catalyst yielded a mixture of the isomeric 20E/Z-vinylstanne
derivatives 13 and 14 (Scheme 2). The isomeric tin inter-
mediates failed to separate on TLC plates developed in
ethylacetate/hexane or chloroform/acetonitrile. However
using reversed-phase (C-18) HPLC in methanol/water the
separation can be achieved. The isomeric ratio of the mix-
ture can be altered on varying the reaction time and the
amount of the reagent used. Longer reaction times and high
amounts of the reagent resulted in the 20E-isomer as the
major product [35,53]. The electrophilic destannylation of
18-homo-17␣-(tri-n-butylstannyl)vinylestradiol proceeds in
high yield with retention of configuration. Addition of a 0.1
M solution of iodine in chloroform to the isomeric interme-
diates 13 and 14 resulted in an immediate destannylation to
give the iodovinyl derivatives 15 and 16. The stereochem-
1
istry of the product was determined by H NMR spectro-
scopic analysis. The coupling constant for the vinylic pro-
tons are greater for the 20E-isomer as compared to that of
the 20Z-isomer, consistent with the reported value for anal-
ogous compounds [26]. The 20Z-isomer also is less polar
than the 20E-isomer on normal phase silica gel TLC and the
isomers separate well on reversed-phase HPLC in MeOH/

H. Ali et al. / Steroids 65 (2000) 74–84
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␥-emitting tracer with uptake in rat uterus and induced mammary
tumor. J Nucl Med 1981;22:42–7.
dergo diiodination at similar rates. Thus the higher activity
levels 20Z-isomer in blood cells likely concerns steroid-
bound radioiodine.
Addition of the 18-methyl group to the 16␣-IE2 deriva-
tive results in a drop of uterine radioactivity uptake (Fig. 3).
Combined with a pronounced increase in blood and non-
target tissue specific activity thus results in poor uterus-to-
blood and uterus-to-non target ratios. In the case of 20E-
and 20Z-IVE2 addition of a 18-methyl group results in an
improved uterine uptake (Fig. 2). This effect is more pro-
nounced with the 20Z-(18-methyl)-IVE2 isomer, but higher
blood activity results overall in a low uterus-to-blood ratio
than observed with the parent steroid. Also, the addition of
a 18-methyl group to 20E/Z-IVE2 results in an increased
uptake by most non-target tissues. Our data suggest that
18-homologation of 16␣-IE2 and IE2 does not improve their
potential as ER-based tumor imaging agents.
[18] Zielinski JE, Yabuki H, Pahuja SL, Larner JM, Hochberg RB. 16␣-
[
125I]iodo-11␤-methoxy-17␤-estradiol: a radiochemical probe for es-
Acknowledgments
trogen-sensitive tissue. Endocrinology 1986;119:130–9.
[19] Zielinski JE, Larner JM, Hoffer PB, Hochberg RB. The synthesis of
11␤-methoxy-[16␣-123I]iodoestradiol and its interaction with the es-
trogen receptor in vivo and in vitro. J Nucl Med 1989;30:209–15.
[20] Katzenellenbogen JA, McElvany KD, Senderoff SG, Carlson KE,
Landvatter SW, Welch MJ. 16␣[77Br]bromo-11␤-methoxyestradiol-
17␤: a ␥-emitting estrogen imaging agent with high uptake and
retention by target organs. J Nucl Med 1982;23:411–9.
[21] Pomper MG, van Brocklin H, Thieme AM, Thomas RD, Kiesewetter
DO, Carlson KE, Mathias CJ, Welch MJ, Katzenellenbogen JA.
11␤-Methoxy-, 11␤-ethyl- and 17␣-ethynyl-substituted 16␣-flu-
oroestradiols receptor-based imaging agents with enhanced uptake
efficiency and selectivity. J Med Chem 1990;33:3143–55.
Supported by the Medical Research Council of Canada.
JEvL is the holder of the Jeanne and J.-Louis Le´vesque
Chair in Radiobiology.
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