Bromine- and iodine-substituted 16α,17α-dioxolane progestins for breast tumor imaging and radiotherapy: Synthesis and receptor binding affinity

Article abstract of DOI:10.1021/jm060348q

Progesterone receptors (PRs) are present in many breast tumors, and their levels are increased by certain endocrine therapies. We describe the synthesis and PR binding affinities of a series of bromine- and iodine-substituted 16α,17α-dioxolane progestins, some of which, when appropriately radiolabeled, are potential agents for diagnostic imaging of PR-positive breast tumors using positron emission tomography (PET) and for radiotherapy. These compounds were synthesized from halogenated furanyl, phenyl, and thiophenyl aldehydes and a progestin 16α,17α,21-triol (5) in the presence of HClO₄ or Sc(OTf)₃ in high yields under optimized conditions. A new reagent, perfluoro-1-butanesulfonyl fluoride (PBSF), was used to convert the C-21 OH to F in high yields. The relative binding affinities (RBAs) of the most promising compounds for the PR (RBA of R5020 = 100) were 16α,17α-[(R)-1′-α-(5-bromofurylmethylidene)dioxyl] -21-hydroxy-19-norpregn-4-ene-3,20-dione (endo-6; RBA = 65 and moderate lipophilicity), 21-fluoro-16α,17α-[(R)-1′-α-(5- iodofurylmethylidene)dioxyl]-19-norpregn-4-ene-3,20-dione (endo-14; RBA = 40) and 21-fluoro-16α,17α-[(S)-1′-β-(-iodophenylmethylidene) dioxyl]-19-norpregn-4-cne-3,20-dione (exo-16; RBA = 34).

Full text of DOI:10.1021/jm060348q

J. Med. Chem. 2006, 49, 4737-4744
4737
Bromine- and Iodine-Substituted 16r,17r-Dioxolane Progestins for Breast Tumor Imaging and
Radiotherapy: Synthesis and Receptor Binding Affinity
Dong Zhou,† Kathryn E. Carlson,‡ John A. Katzenellenbogen,‡ and Michael J. Welch*,†
Mallinckrodt Institute of Radiology, Washington UniVersity School of Medicine, St. Louis, Missouri 63110, and Department of Chemistry,
UniVersity of Illinois, Urbana, Illinois 61801
ReceiVed March 24, 2006
Progesterone receptors (PRs) are present in many breast tumors, and their levels are increased by certain
endocrine therapies. We describe the synthesis and PR binding affinities of a series of bromine- and iodine-
substituted 16R,17R-dioxolane progestins, some of which, when appropriately radiolabeled, are potential
agents for diagnostic imaging of PR-positive breast tumors using positron emission tomography (PET) and
for radiotherapy. These compounds were synthesized from halogenated furanyl, phenyl, and thiophenyl
aldehydes and a progestin 16R,17R,21-triol (5) in the presence of HClO4 or Sc(OTf)3 in high yields under
optimized conditions. A new reagent, perfluoro-1-butanesulfonyl fluoride (PBSF), was used to convert the
C-21 OH to F in high yields. The relative binding affinities (RBAs) of the most promising compounds for
the PR (RBA of R5020 ) 100) were 16R,17R-[(R)-1′-R-(5-bromofurylmethylidene)dioxyl]-21-hydroxy-
19-norpregn-4-ene-3,20-dione (endo-6; RBA ) 65 and moderate lipophilicity), 21-fluoro-16R,17R-[(R)-1′-
R-(5-iodofurylmethylidene)dioxyl]-19-norpregn-4-ene-3,20-dione (endo-14; RBA ) 40) and 21-fluoro-
16R,17R-[(S)-1′-â-(4-iodophenylmethylidene)dioxyl]-19-norpregn-4-ene-3,20-dione (exo-16; RBA ) 34).
Introduction
are studies in breast cancer using 16R-[18F]fluoroestradiol
(FES),2 and in prostate cancer using 16â-[18F]fluoro-5R-
dihydrotestosterone (FDHT).3 Although a number of steroids
labeled with bromine and iodine radioisotopes have been
prepared,4 their use in imaging studies, particularly in humans,
has been more limited.4f These agents have been studied quite
extensively, however, in terms of their potential for selective
radiotherapy.
Steroid receptors are found in a number of endocrine-
responsive cancers, estrogen receptors (ERs), and progesterone
receptors (PRs)a in many breast tumors, and androgen receptors
(ARs) in most prostate cancers. These receptors serve as targets
for endocrine therapies of these cancers, but they also can be
used as targets for diagnostic imaging and radiotherapy.
Diagnostic imaging can be achieved by the administration of a
suitably radiolabeled ligand (an estrogen, progestin, or androgen
for their cognate receptor, ER, PR, or AR, respectively) that
accumulates in the receptor-positive tumor, where it can be
detected and quantified by imaging. Such images can sometimes
be used to predict whether hormone therapy will be effective.1,2
In a related manner, a hormone receptor ligand labeled with a
different radionuclide (e.g., an Auger electron emitting isotope)
that accumulates in a tumor through a receptor-mediated uptake
process can deliver a cytotoxic dose of high linear energy
transfer (LET) radiation selectively to the tumor cells, ablating
the tumor while limiting widespread radiation toxicity. There-
fore, the development of such hormone receptor ligands for both
diagnostic imaging and radiotherapy is a promising area of great
current interest.
It was shown by Bronzert, Lippman, and Hochberg that 16R-
[
125I]iodoestradiol was selectively cytotoxic to human mammary
cancer cells (MCF-7) when bound to ER.5 Similar experiments
were reported by Bloomer et al. using [125I]iodotamoxifen and
various I-125 and I-123 labeled estrogens.6 A number of
bromine- and iodine-substituted estrogens have been developed
by DeSombre and co-workers for selective radiotherapy, and
they have quantified both chromosome damage and cell survival
following the exposure of ER+ cells to 17R-[123I]iodovinyl-
11â-methoxyestradiol.7 DeSombre and others also determined
the mean lethal dose for I-123 or Br-77 to be 300-600 decays
per cell, and they established that the radiation damage from
the electron shakeoff following the decay of these isotopes was
spatially limited to a sphere of ca. 10 Å radius.8,9 These
experiments establish the feasibility of using various Auger
electron-emitting isotopes for selective cellular therapy.
Other Auger electron-emitting halogens, namely iodine-124
and bromine-76, decay with a significant amount of positron
emission, a characteristic that allows for diagnostic PET imaging
to be used to complement their use in radiotherapy. All of these
radionuclides have a half-life that is sufficiently long to permit
target tissue-selective distribution while being sufficiently short
so that the bulk of the dose can be delivered to the tissue prior
to metabolism and elimination of the radiopharmaceutical. It is
of note that in order for radiolabeled steroids to be used
successfully for diagnostic imaging or therapy, the labeled ligand
must maintain very high affinity for its receptor, with low
binding for other nonspecific sites.
Diagnostic imaging of breast and prostate tumors by positron
emission tomography (PET) is well established and has been
achieved using steroids labeled with fluorine-18. Most extensive
* To whom correspondence should be addressed. Phone: 314-362-8436.
Fax: 314-362-8399. E-mail: welchm@mir.wustl.edu.
† Washington University School of Medicine.
‡ University of Illinois.
a Abbreviations used: PR, progesterone receptor; ER, estrogen receptor;
AR, androgen receptor; RBA, relative binding affinity; PET, positron
emission tomography; LET, linear energy transfer; R5020, promegestone;
FES, 16R-fluoroestradiol; FDHT, 16â-fluoro-5R-dihydrotestosterone; FFNP,
fluoro furanyl norprogesterone, compound 1; PBSF, perfluoro-1-butane-
sulfonyl fluoride; EtOAc, ethyl acetate; endo/exo refer to the stereochemistry
at the acetal carbon; Sc(OTf)3, scandium trifluoromethanesulfonate; PM3,
B3LYP, computational methods; TBAF, tetrabutylammonium fluoride;
DAST, diethylaminosulfur trifluoride; TMS, tetramethylsilane; ESI, Elec-
trospray ionization.
In applications in breast tumor imaging and therapy, a PR-
based radioligand has some potential advantages over an ER-
10.1021/jm060348q CCC: $33.50 © 2006 American Chemical Society
Published on Web 06/21/2006

4738 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 15
Zhou et al.
Scheme 1
based one: (1) there is a better correlation between PR status
and hormonal responsiveness than there is with ER status;10
(2) a PR-based ligand could be used after the initiation of anti-
estrogen hormonal therapy, whereas an ER-based one would
not be useful when tumor ER is saturated by the hormonal
agent.11 Moreover, (3) PR-based ligands may benefit from the
increased PR levels induced by the transient agonistic effect of
tamoxifen during the initial course of tamoxifen treatment of
breast tumor.12
reported method,14 with some modification, as shown in Scheme
1. In the previously reported method,14 acetylation to prepare 4
was carried out in refluxing benzene with acetic acid and
trifluoroacetic anhydride (TFA) as catalyst, which formed the
mixed anhydride as the active acylating agent. We had difficulty
in reproducibly obtaining the high yield reported for this
transformation.14,15 We believe this is due to the low boiling
point of TFA, which makes formation of the mixed anhydride
inefficient.
Because scandium trifluoromethanesulfonate Sc(OTf)3 is
reported to be an extremely active acylation catalyst16 as well
as acetalization catalyst,17 this acylation reaction was carried
out with acetic anhydride using Sc(OTf)3 as catalyst. The
reaction went smoothly in CH3CN at ambient temperature and
gave a 90% yield within 1 h. This yield is comparable to the
reported one,14 but this reaction is much easier to carry out.
Therefore, with this modification, the key intermediate triol 5
was synthesized according to the reported route.14
Based on what is known about the structure-affinity relation-
ships of PR ligands, a good candidate molecule for labeling
with bromine or iodine should have a skeleton related to fluoro
furanyl norprogesterone (FFNP) 1.13 This compound appears
to have promise as an agent for PET imaging,13 and it is being
developed for this purpose. FFNP has a high relative binding
affinity to PR (190% relative to R5020 ) 100%), low
nonspecific binding (log Po/w ) 3.87), and high binding
selectivity index (the ratio of PR binding affinity to nonspecific
binding). In tissue biodistribution studies in estrogen-primed
immature female Sprague-Dawley rats, FFNP demonstrated
high PR-selective uptake in the principal target tissues, uterus
and ovaries, and relatively low uptake in fat and bone. Also,
the metabolism at the 20-position in FFNP is likely to be less
than that in other 20-fluoroprogestins,13b because the bulk of
the 16R,17R-furanyl group protects the C-20 ketone from attack
by steroid dehydrogenases. In addition to these favorable
pharmacokinetic and pharmacodynamic attributes, the 16R,17R-
dioxolane group of FFNP (and its C-21 OH precursor, 2)
provides a convenient aromatic site where bromine or iodine
can be introduced easily by electrophilic substitution reactions.
These haloarenes are much more stable than would be the
corresponding 21-iodo or bromo analogues, which are reactive
R-haloketones.
Formation of the Norprogesterone 16R,17R-Acetal. The
acetalization of the norprogesterone triol 5 was carried out with
the corresponding aldehyde in the presence of 70% HClO4,
according to the procedure of Fried,18 or Sc(OTf)3 as reported
by us.14 Formation of the dioxolane ring generates a new
stereogenic center, so that a mixture of endo and exo diaster-
eomers is produced, as shown in Scheme 2. In early studies on
the formation of progestin 16R,17R-dioxolanes, Fried18 showed
that with aromatic aldehydes the endo isomer was more stable;
the less stable exo isomer was kinetically preferred (low acid,
short time), whereas the more stable one was thermodynamically
preferred (high acid, longer time).
In the presence of HClO4, we found previously that triol 5
gave nearly 1:1 mixtures of diastereomers when reacted with
furfural under a variety of conditions,13,14 but that when Sc-
(OTf)3 was used as catalyst, exo isomers were obtained as the
major products at low catalyst level (1 mol %), whereas 1:1
endo/exo mixtures were produced at high catalyst level (10 mol
%) level and longer reaction time.14 In the presence of both
catalysts, isomerization between endo and exo was observed
by 1H NMR and 19F NMR in the case of HClO419 or by direct
conversion from exo isomer to endo isomer in the case of Sc-
(OTf)3.14 Our results for the acetalization with the halogen
substituted aldehydes are shown in Table 1.
In this report, we describe the synthesis of a series of
16R,17R-dioxolane bromine- and iodine-substituted and C-21
hydroxyl- or fluoride-substituted norprogesterones that have a
skeleton similar to that of FFNP and a determination of their
relative binding affinities to PR. The norprogesterone with a
5-bromofuranyl system (endo-6) has good binding affinity and
moderate lipophilicity and thus appears to be a promising PR
ligand for radiobromine labeling for diagnostic imaging and
radiotherapy purposes.
In the reactions in which HClO4 was used as catalyst, a nearly
1:1 of endo and exo diastereomers were obtained, which is the
same as that reported for furfural.13,14,18 When we tried the
acetalization with bromofurfural under the same conditions as
for furfural, however, using 10 mol % Sc(OTf)3 as catalyst in
an attempt to get a 1:1 mixture of endo/exo isomers,14 almost
all of the expected product decomposed after 20 h, even though
it appeared that product 6 was being formed when the reaction
was followed by TLC.
Results and Discussion
Synthesis of a Key Precursor, Norprogesterone Triol 5.
The key intermediate in the synthesis of FFNP and its analogues
is the 19-norprogesterone 16R,17R,21-triol 5, which was
synthesized from commercially available 17R-ethynyl-nortes-
tosterone (3, 19-norethindrone) according to our recently
Therefore, we limited the reaction time to a couple hours, at
which point triol 5 was consumed. Under these conditions with
10 mol % Sc(OTf)3, the endo and exo isomers were obtained
in a 1:2 ratio for the furfural analogues; by contrast, the

16R,17R-Dioxolane Progestins
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 15 4739
Scheme 2
Table 1. Acetalization of Norprogesterone Triol 5
catalyst
Sc(OTf)3
(% M)
reaction time
(min)
ratioa
endo/exo
yieldb
(%)
∆Hc (endo - exo)
entry
compd
ratio triol:aldehyde
in furfural
HClO4 (M)
(kcal/mol)
1
2
3
4
5
6
7
8
2
0.04
0.04
70
80
50
120
20 h
45
60
60
120
45
90
240
80
210
50/50
37/63
42/58
36/64
-
64
92
95
69
0
90
90
83
81
98
78
80
81
70
2.6 (0.11)
1.8
12
6
1:10
1:20
1:22
1:8
12
12
7
8
9
0.04
0.08
0.04
2/3
1.7
1.1
1.1
1:8
45/54
52/48
54/45
55/44
55/44
70/30
65/35
1/2
1:10
1:20
1:7
1:15
1:18
1:13
1:22
9
12
10
11
12
13
14
0.04
12
10
12
12
10
11
12
1.6
1.6
1.1
a The ratio is reported as HPLC integration ratio. b The yield is reported as isolated yield of the endo/exo isomers. c Geometry was optimized at the PM3
(or B3LYP) level using Spartan for Windows software package,and ∆H was calculated from the heat of formation of the geometry-optimized compound.
benzaldehyde analogues gave a 1:1 ratio, and the thiophene
carboxaldehyde analogues gave a 2:1 ratio.
column to quench the reaction. The isomer mixture could then
be isolated quickly, in very good yields, by flash chromatog-
raphy.
Because of the unusual behavior of the acetalization reaction,
we studied this transformation further in a model system. Using
cis-1,2-cyclopentanediol instead of the norprogesterone triol 5,
we attempted to establish reaction conditions for the acetalization
with bromofurfural. Surprisingly, we found that Sc(OTf)3 did
not catalyze this acetalization at all, yet the reaction proceeded
smoothly in the presence of HClO4. This observation indicates
that HClO4 is a strong catalyst, in that both the acetalization
and isomerization are very fast with this reagent, whereas Sc-
(OTf)3 is a mild catalyst, resulting in slow formation of mixtures
of the endo and exo isomers and being slow in effecting their
isomerization.
The pure diastereomers are obtained by preparative reversed
phase HPLC, and the stereochemistry of the newly formed
stereogenic center was assigned by an analysis of the 1H NMR
of the C-21 protons: those of the exo isomers are shifted upfield
by about 0.5 ppm because of shielding by the aromatic ring.20
This assignment is consistent with the HPLC retention times
of the endo/exo isomers, where the endo isomers elute faster,
as expected based on greater shielding of the polar functionality.
1
All the acetals synthesized show the same H NMR pattern of
C-21 protons, and all of the endo isomers eluted faster than
exo isomers.
Conversion of the Norprogestin Acetal C-21 OH to C-21
F. Previously, we obtained FFNP 1 from the precursor C-21
alcohol 2 via a triflate13 or mesylate14 intermediate with an
overall yield of 9% and ca. 30%, respectively. The conversion
took place via a nucleophilic substitution on the triflate or
mesylate with tetrabutylammonium fluoride (TBAF) in THF.
Because of these low yields, however, we found this route to
be impractical for the synthesis of the ring-halogenated acetals
and looked for an alternative method. We first tried the widely
used fluorinating reagent, diethylaminosulfur trifluoride (DAST),
but it did not give a clean reaction. This is not surprising because
the byproduct, HF, makes the reaction mixture highly acidic.
Computational calculations at the semiempirical PM3 level
and density function B3LYP level indicate that the endo isomer
of acetal 2 is the more stable one, but only by <2 kcal/mol.
Therefore, in the presence of the strong catalyst, HClO4, the
endo/exo diastereomers form in nearly a 1:1 ratio due to the
fast acetalization and isomerization, whereas Sc(OTf)3 affords
kinetically controlled products under the reaction conditions.
After understanding the difference resulting from the two
catalysts, we made further efforts to optimize the acetalization
to obtain a high yield. We found that this acetal is not very
stable under acidic conditions; in fact, it even appears to
decompose slowly on a silica gel column or in aqueous solution.
Therefore, we bypassed the aqueous workup and loaded the
reaction mixture (2 mL in CH2Cl2) directly onto a silica gel
Huffman21 reported a direct and convenient conversion of
alcohols to fluorides using a combination of perfluoro-1-
butanesulfonyl fluoride (PBSF)/NEt3(HF)3/NEt3 in THF or CH3-

4740 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 15
Zhou et al.
Scheme 3
isomer (RBA ) 6.4). In fact, the exo isomer of 16 could be a
good candidate for labeling with iodine.
On the basis of the compounds synthesized previously,13 we
expected that the conversion of C-21 substituent from OH to F
would enhance the binding affinity considerably. For example,
this conversion results in a ca. 4-fold increase in the case of
compounds 2 (C-21 OH) and 1 (C-21 F). For the bromine- and
iodine-substituted ligands, the increase in binding affinity for
this conversion was observed for all exo isomers: the increase
was only 2-fold for the bromofuranyl derivatives (exo isomer
6 to 13) and 4-fold for the iodofuranyl derivatives (exo isomer
7 to 14), but the increase was 10-fold for the bromophenyl
derivatives (exo isomer 8 to 15) and 20-fold for the iodophenyl
ones (exo isomer 9 to 16).
Table 2. Conversion of C-21 OH to C-21 F Using PBSF
starting material
product
reaction time (h)
yield (%)
2 (endo)
2 (exo)
6 (endo)
6 (exo)
7 (endo)
7 (exo)
8 (endo)
8 (exo)
9 (endo)
9 (exo)
1 (FFNP)
1 (exo)
3
3
3
3
2.8
2.8
3
3
3
85
81
80
90
75
92
83
83
81
80
Not all of the endo isomers benefit from the C-21 OH to F
conversion. The binding affinity increased for those with iodine
substituents (endo isomer 7 and 9), but it decreased for those
with bromine substituents (endo isomer 6 and 8). The endo
isomer of 14 shows good binding affinity, and it could also be
a good candidate for iodine labeling. The conversion of C-21
OH to C-21 acetyl decreases the binding affinity, so the acetyl
analogues do not merit further consideration.
13 (endo)
13 (exo)
14(endo)
14 (exo)
15 (endo)
15 (exo)
16 (endo)
16 (exo)
4
Comparing bromine and iodine analogues with the same
aromatic ring systems, the bromo-substituted ones have better
binding affinity than the iodo-substituted ones in the endo series,
but this is reversed in the exo series. When the aromatic ring
structures are compared, the furanyl group furnishes the best
binding affinity, while thiophenyl group gives the worst results.
Because the lipophilicity of a steroidal ligand is directly
related to its binding affinity for low-affinity, non specific sites,24
the octanol/water partition coefficients values (log Po/w) were
calculated, and the results are shown in Table 3, along with
those measured previously by an experimental method for
comparison.13 It is clear that compound 6 has the lowest
lipophilicity among the bromine- and iodine-substituted ligands.
The phenyl ligands have the highest lipophilicity.
In terms of binding affinity to PR and lipophilicity, the endo
isomer of compound 6 has the best binding affinity for PR with
the least lipophilicity. Thus, the endo epimer of 6, along with
the endo epimer of 14 and the exo epimer of 16 are most likely
to meet our requirement for radiolabeling for both diagnostic
imaging and radiotherapy purpose. Further study of radiolabeling
is underway and will be reported separately.
CN. The conversion takes place under nearly neutral conditions,
which are favorable to our highly acid-labile acetals. We used
the reported optimized reaction conditions, that is 1:2:6:2 of
alcohol/NEt3(HF)3/NEt3/PBSF, to convert the C-21 OH to C-21
F, and we found that the reaction proceeded smoothly in CH3-
CN at ambient temperature in high yields, as shown in Scheme
3 and Table 2. Activation of this SN2 reaction by the C-20 ketone
undoubtedly contributed to these good yields.
Progestin Receptor Binding Affinities. The relative binding
affinities of the new compounds we have prepared as ligands
for the PR were determined by a competitive radiometric binding
assay using [3H]R5020 as tracer and R5020 as a standard, as
previously described.22 The binding affinities are expressed as
relative binding affinity (RBA) values, with the RBA of the
R5020 standard set to 100 (R5020 binds to PR with a Kd of 0.4
nM). The values given are the average ( range or SD of two
or more independent determinations. The results are shown in
Table 3 together with the octanol/water partition coefficient
calculated using ACD software.
First, the RBA values of the two known compounds 1 and
FFNP (2), previously determined using rat uterine PR (entries
3 and 4),22 were determined again here with human recombinant
PR (entries 1 and 2), which is commercially available. The
binding affinities are very similar in both systems. Therefore,
the other ligands were assayed using human recombinant PR
rather than the rat uterine PR.
Generally, 16R or 17R substitutents are expected to enhance
the binding of ligands to the PR.23 All the bromine- and iodine-
substituted progestin ligands synthesized show binding affinities
to PR that range from poor to good, but none are as high as
those of the fluorine-substituted dioxolane ligands reported
previously.13,19 This could be due both to the greater bulk of
the bromine and iodine atoms, as well as to their electronic
effects.
Conclusion
We have synthesized a series of bromine- and iodine-
substituted 16R,17R-dioxolane progestins, potential agentsswith
proper radiolabelingsfor diagnostic imaging using positron
emission tomography (PET) or for radiotherapy. These com-
pounds were synthesized from the halogenated aromatic alde-
hydes and the key 19-norprogestin 6R,17R,21-triol 5 in the
presence of HClO4 or Sc(OTf)3, using a procedure that was
carefully optimized to achieve high yields. Conversion of the
C-21 substituent from OH to F was effected in high yield by a
combination of perfluoro-1-butanesulfonyl fluoride (PBSF),
(NEt3)(HF)3, and NEt3. The binding affinities of these com-
pounds for human progesterone receptor (PR) were determined
using a competitive radiometric binding assay. On the basis of
PR binding affinity and lipophilicity (estimated from the
calculated octanol-water partition coefficient), 16R,17R-[(R)-
1′-R-(5-bromofurylmethylidene)dioxyl]-21-hydroxy-19-norpregn-
4-ene-3,20-dione (endo-6) (having a relative binding affinity
of 65 compared to 100 for the standard R5020) was determined
to be the most promising agent, along with 21-fluoro-16R,17R-
We13,19,20 and others18 have shown that when the 16R,17R-
dioxolane aromatic substituent is endo, the PR binding affinity
is better than when it is exo. The higher affinity of the endo
isomer, however, does not hold for all of the phenyl ligands.
The exo isomer binds better than the endo for compounds 9,
15, and 16, especially for compound 16, for which exo isomer
(RBA ) 34) has a 5-fold higher affinity compared to the endo

16R,17R-Dioxolane Progestins
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 15 4741
Table 3. Progesterone Receptor Binding Affinities and Octanol-Water Partition Coefficients
relative binding affinity
relative binding affinity
b
entry
compd
endo
exo
log Po/w
entry
compd
endo
exo
log Po/w
1
3
5
7
2
53 ( 15
55 ( 19
65 ( 6
2.4 ( 0.5
2.5 ( 0.9
2.3 ( 0.3
2.6 ( 0.2
0.41 ( 0.09
1.8 ( 0.6
1.7 ( 0.8
1.4 ( 0.2
4.15 ( 0.69 (3.78/4.01)c
2
4
6
8
10
12
14
1
180 ( 40
190 ( 22
24 ( 4
5.0 ( 0.9
11 ( 4
4.40 ( 0.82 (3.87/4.11)c
2a
6
1a
13
14
15
16
11
5.09 ( 0.84
5.48 ( 0.75
5.76 ( 0.73
6.02 ( 0.73
5.52 ( 0.78
6.21 ( 0.86
4.4 ( 1.1
9.0 ( 0.8
4.7 ( 0.8
34 ( 4
5.34 ( 0.89
5.73 ( 0.85
6.01 ( 0.85
6.27 ( 0.85
6.00 ( 0.76
7
8
9
10
12
23 ( 3
40 ( 6
9
23 ( 4
3.9 ( 1.7
6.4 ( 1.4
3.2 ( 0.7
11
13
15
0.81 ( 0.14
5.2 ( 0.7
7.1 ( 0.1
0.95 ( 0.25
a Determined using rat uterine PR. b Calculated using ACD LogP software. c Measured by HPLC, see ref 13.
100 mg triol 5, 10-fold excess of the corresponding aromatic
aldehyde, and 2 mL dry CH2Cl2, followed by addition of 7 µL
70% HClO4 via a syringe. The reaction mixture became brown in
color, and the triol solid dissolved in CH2Cl2 gradually during the
reaction. The reaction was checked by TLC, and usually it was
complete within 1 h. Upon completion of the reaction, the reaction
mixture was loaded onto a silica gel column directly to quench the
reaction and for purification. The excess of aldehyde was eluted
using 1:1 EtOAc/hexane, and the two isomers were eluted using
7:3 EtOAc/hexane. After removal of solvents under reduced
pressure, the isomer mixture was purified further using reversed
phase C18 preparative HPLC with CH3CN and water as mobile
phase. Pure isomer was obtained by removing HPLC solvents under
vacuum (<10 Torr) at ambient temperature. The yield for the
mixture before HPLC purification was around 90%.
[(R)-1′-R-(5-iodofurylmethylidene)dioxyl]-19-norpregn-4-ene-
3,20-dione (endo-14) (RBA ) 40) and 21-fluoro-16R,17R-[(S)-
1′-â-(4-iodophenylmethylidene)dioxyl]-19-norpregn-4-ene-3,20-
dione (exo-16) (RBA ) 34). These compounds are planned for
further study.
Experimental Section
All chemicals were obtained from standard commercial sources
and used without further purification. All reactions were carried
out by standard air-free and moisture-free techniques under an inert
argon atmosphere with dry solvents unless otherwise stated. Flash
column chromatography was conducted using Scientific Adsorbents,
Inc. silica gel, 60A, “40 Micron Flash” (32-63 µm). Melting points
were determined using MEL-TEMP 3.0 apparatus and are uncor-
rected. 1H NMR spectra were recorded on a Varian Unity-300 (300
MHz) NMR spectrometer. All chemical shifts were reported a part
per million (ppm) downfield from tetramethylsilane (TMS). Chlo-
roform-d was used as solvent, and the residual CHCl3 solvent peak
at δ 7.25 ppm was used as an internal standard. All coupling
constants (J) are given in Hertz (Hz). Splitting patterns are typically
described as follows: s, singlet; d, doublet; t, triplet; m, multiplet.
19F NMR spectra were recorded at 282.22 MHz, and chemical shifts
are reported as ppm upfield from an external CFCl3 standard. High-
pressure liquid chromatography (HPLC) was performed with UV
detection at 254 nm with acetonitrile and water as mobile phase
using Alltech Altima C18 250 × 22 mm preparative column for
separation and Altech Altima C18 250 × 4.6 mm analytical column
for analysis. Elemental analyses (C, H) were determined by Atlantic
Microlab, Inc. ESI/MS was performed on a Waters ZQ 4000 single
quadrupole mass spectrometer equipped with an electrospray
ionization (ESI) LC-MS interface. 5-Iodothiophene-2-carboxalde-
hyde25 and 5-iodofurane-2-carboxaldehyde26 were synthesized ac-
cording to literature procedures.
General Procedure: Synthesis of 16R,17R-Dioxolane Deriva-
tives Using Sc(OTf)3 as Catalyst. Into a 5 mL dry round-bottom
flask equipped with a magnetic stirring bar and septum were loaded
100 mg triol 5, 10-20-fold excess of the corresponding aromatic
aldehyde, 10% mmol Sc(OTf)3, 100 mg anhydrous magnesium
sulfate, and 2 mL dry CH2Cl2. The reaction mixture was stirred at
ambient temperature and checked by TLC. Upon completion of
the reaction, the reaction mixture was loaded onto a silica gel
column directly for purification. The excess of aldehyde was eluted
using 1:1 EtOAc/hexane, and the two isomers were eluted using
7:3 EtOAc/hexane. After removal of solvents under reduced
pressure, the isomer mixture was purified further using reversed
phase C18 preparative HPLC with CH3CN and water as mobile
phase. Pure isomer was obtained by removing HPLC solvents under
vacuum (<10 Torr) at ambient temperature.
General Procedure: Fluorination Using Perfluoro-1-butane-
sulfonyl Fluoride (PBSF). Into a 10 mL dry round-bottom flask
equipped with a magnetic stirring bar and septum were loaded 0.064
mmol 21-hydroxy acetal derivative and 6 mL CH3CN, followed
by 22.5 µL (0.127 mmol) PBSF, 53.4 µL (0.38 mmol) NEt3, and
20.7 µL (0.127 mmol) (NEt3)(HF)3. The reaction mixture was stirred
at room temperature for 3 h to complete the reaction. Solvent was
evaporated under reduced pressure, and the residue was purified
by silica gel chromatography using 1:1 EtOAc/hexane to afford
the product as white solids in 80% to 90% yield.
Synthesis of Progargylic Ester (4). To a stirred mixture of 2.0
g (6.7 mmol) 3 and 160 mg (0.33 mmol) Sc(OTf)3 in 40 mL dry
CH3CN was added 850 µL (8.3 mmol) acetic anhydride. The
reaction mixture became homogeneous in 10 min, and almost all
of 3 was consumed in 1 h according to TLC. Upon completion of
the reaction, the mixture was diluted with 100 mL ethyl acetate
and washed with saturated NaHCO3 and NaCl solution. Solvent
was evaporated and flash chromatography (1:4 EtOAc/hexane, Rf)
1
1
Data for endo-6. H NMR (CDCl3, 300 MHz) δ: 6.48 (d, 1H,
0.1) gave 1.97 g 4 as white solid in 86% yield. H NMR (CDCl3,
J ) 3.3 Hz), 6.31 (d, 1H, J ) 3.3 Hz), 5.85 (s, 1H), 5.55 (s, 1H),
5.08 (d, 1H, J ) 5.7 Hz), 4.48 (AB, q, 2H, ∆υ ) 0.32 ppm, J )
20.4 Hz), 3.0 (s, br, 1H), 2.6-0.8 (m, 18H), 0.72 (s, 3H); mp.
155.3-156.0 °C; Elemental analysis: Calcd for C25H29BrO6 + H2O
300 MHz): δ 5.84 (s, 1H), 2.05 (s, 3H, COCH3), 0.93 (s, 3H, CH3).
General Procedure: Synthesis of 16R,17R-dioxolane Deriva-
tives Using HClO4 as Catalyst. Into a 5 mL dry round-bottom
flask equipped with a magnetic stirring bar and septum were loaded

4742 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 15
Zhou et al.
(522.13): C 57.37, H 5.97; Found: C 57.11, H 5.85. MS (ESI):
m/z 526.84 (M+ + 23).
20.1 Hz), 2.9 (br, 1H), 2.6-0.8 (m, 18H), 0.75 (s, 3H); mp. 199.0-
201.0 °C; Elemental analysis: Calcd for C25H29IO5S (568.5): C
52.82, H 5.14; Found: C 52.80, H 5.30; MS (ESI): m/z 591.1 (M+
+ 23).
Data for exo-6. 1H NMR (CDCl3, 300 MHz) δ: 6.29 (d, 1H, J
) 3.3 Hz), 6.23 (d, 1H, J ) 3.3 Hz), 6.11 (s, 1H), 5.84 (s, 1H),
5.31 (d, 1H, J ) 6.0 Hz), 4.21 (AB, q, 2H, ∆υ ) 0.18 ppm, J )
20.1 Hz), 2.6-0.8 (m, 18H), 0.72 (s, 3H); mp. 150.0-151.0 °C;
Elemental analysis: Calcd for C25H29BrO6 (504.11): C 59.41, H
5.78; Found: C 59.14, H 5.90; MS (ESI): m/z 526.74 (M+ + 23).
Data for endo-12. 1H NMR (CDCl3, 300 MHz) δ: 6.50 (d, 1H,
J ) 3.3 Hz), 6.32 (d, 1H, J ) 3.3 Hz), 5.85 (s, 1H), 5.63 (s, 1H),
5.05 (d, 1H, J ) 5.7 Hz), 4.92 (AB, q, 2H, ∆υ ) 0.12 ppm, J )
18.0 Hz), 2.6-0.8 (m, 18H), 2.19 (s, 3H), 0.77 (s, 3H); Elemental
analysis: Calcd for C27H31BrO7 (546.13): C 59.24, H 5.71;
Found: C 59.11, H 5.72; MS (ESI): m/z 569.08 (M+ + 23).
1
Data for endo-7. H NMR (CDCl3, 300 MHz) δ: 6.54 (d, 1H,
J ) 3.3 Hz), 6.43 (d, 1H, J ) 3.3 Hz), 5.85 (s, 1H), 5.59 (s, 1H),
5.08 (d, 1H, J ) 5.4 Hz), 4.48 (AB, qd, 2H, ∆υ ) 0.32 ppm, J )
4.5, 20.1 Hz), 2.98 (t, 1H, J ) 4.8 Hz), 2.6-0.8 (m, 18H), 0.73 (s,
3H); mp. 135 °C decomposition; Elemental analysis: Calcd for
C25H29IO6 + H2O (570.11): C 52.64, H 5.48; Found: C 52.96, H
5.20; MS (ESI): m/z 574.76 (M+ + 23).
1
Data for exo-12. H NMR (CDCl3, 300 MHz) δ: 6.34 (d, 1H,
J ) 3.3 Hz), 6.27 (d, 1H, J ) 3.3 Hz), 6.11 (s, 1H), 5.84 (s, 1H),
5.27 (d, 1H, J ) 5.7 Hz), 4.68 (AB, q, 2H, ∆υ ) 0.0.38 ppm, J )
17.4 Hz), 2.6-0.8 (m, 18H), 2.15 (s, 3H), 0.72 (s, 3H); mp. 157.9-
160.2°C; Elemental analysis: Calcd for C27H31BrO7 (546.13): C
59.24, H 5.71; Found: C 59.10, H 5.61; MS (ESI): m/z 569.10
(M+ + 23).
Data for exo-7. 1H NMR (CDCl3, 300 MHz) δ: 6.46 (d, 1H, J
) 3.3 Hz), 6.23 (d, 1H, J ) 3.3 Hz), 6.15 (s, 1H), 5.85 (s, 1H),
5.32 (d, 1H, J ) 5.7 Hz), 4.19 (AB, qd, 2H, ∆υ ) 0.16 ppm, J )
4.2, 20.1 Hz), 2.83 (t, 1H, J ) 4.8 Hz) 2.6-0.8 (m, 18H), 0.73 (s,
3H); mp. 145 °C decomposition; Elemental analysis: Calcd for
C25H29IO6 + H2O (570.11): C 52.64, H 5.48; Found: C 52.81, H
5.17; MS (ESI): m/z 574.76 (M+ + 23).
Data for endo-13. 1H NMR (CDCl3, 300 MHz) δ: 6.49 (d, 1H,
J ) 3.3 Hz), 6.31 (d, 1H, J ) 3.3 Hz), 5.85 (s, 1H), 5.58 (s, 1H),
5.27 (d, 1H, J ) 55.2, JH-F ) 17.1 Hz), 5.11 (d, 1H, J ) 54.9,
J
) 17.4 Hz), 5.09 (d, 1H, J ) 5.4 Hz), 2.6-0.8 (m, 18H), 0.77
H-F
(s, 3H); 19F (CDCl3, 282.4 MHz) δ: - 56.88 (t, J ) 47.3 Hz); mp.
156.1-158.1 °C; Elemental analysis: Calcd for C25H28BrFO5 + 2
H2O (542.13): C 55.26, H 5.94; Found: C 54.90, H 5.33; MS
(ESI): m/z 529.08 (M+ + 23). HRMS: Calcd for C25H28BrFO5 +
Na+, 529.1002; found, 529.0996.
1
Data for endo-8. H NMR (CDCl3, 300 MHz) δ: 7.53 (d, 2H,
J ) 8.7 Hz), 7.33 (d, 2H, J ) 8.1 Hz), 5.84 (s, 1H), 5.43 (s, 1H),
5.08 (d, 1H, J ) 5.4 Hz), 4.49 (AB, q, 2H, ∆υ ) 0.32 ppm, J )
20.4 Hz), 2.6-0.8 (m, 18H), 0.73 (s, 3H); mp. 133.5-135.0 °C;
Elemental analysis: Calcd for C27H31BrO5 + 0.5 H2O (523.14):
C 61.83, H 6.15; Found: C 62.14, H 6.20; MS (ESI): m/z 514.87
(M+ + 1).
1
Data for exo-13. H NMR (CDCl3, 300 MHz) δ: 6.32 (d, 1H,
J ) 3.3 Hz), 6.25 (d, 1H, J ) 3.3 Hz), 6.09 (s, 1H), 5.83 (s, 1H),
5.28 (d, 1H, J ) 6.0 Hz), 5.00 (d, 1H, J ) 12.6, JH-F ) 17.1 Hz),
4.85 (d, 1H, J ) 12.6, JH-F ) 17.1 Hz), 2.6-0.8 (m, 18H), 0.77
(s, 3H); 19F (CDCl3, 282.4 MHz) δ: - 56.49 (t, J ) 47.3 Hz); mp.
183.8-184.6 °C; Elemental analysis: Calcd for C25H28BrFO5
(506.11): C 59.18, H 5.56. Found: C 58.63, H 5.65; MS (ESI):
m/z 529.08 (M+ + 23). HRMS: Calcd for C25H28BrFO5 + Na+,
529.1002; found, 529.0976.
Data for exo-8. 1H NMR (CDCl3, 300 MHz) δ: 7.49 (d, 2H, J
) 6.6 Hz), 7.20 (d, 2H, J ) 6.9 Hz), 6.11 (s, 1H), 5.85 (s, 1H),
5.40 (d, 1H, J ) 6.3 Hz), 4.20 (AB, q, 2H, ∆υ ) 0.19 ppm, J )
20.1 Hz), 2.6-0.9 (m, 18H), 0.75 (s, 3H); mp. 215.0-219.0 °C;
Elemental analysis: Calcd for C27H31BrO5 (514.14): C 62.92, H
6.06; Found: C 62.87, H 6.20; MS (ESI): m/z 514.81 (M+ + 1).
1
Data for endo-9. H NMR (CDCl3, 300 MHz) δ: 7.75 (d, 2H,
Data for endo-14. 1H NMR (CDCl3, 300 MHz) δ: 6.54 (d, 1H,
J ) 3.3 Hz), 6.42 (d, 1H, J ) 3.3 Hz), 5.85 (s, 1H), 5.62 (s, 1H),
5.27 (d, 1H, J ) 55.2, JH-F ) 17.1 Hz), 5.11 (d, 1H, J ) 55.5,
J ) 8.7 Hz), 7.19 (d, 2H, J ) 8.1 Hz), 5.84 (s, 1H), 5.42 (s, 1H),
5.08 (d, 1H, J ) 5.4 Hz), 4.49 (AB, q, 2H, ∆υ ) 0.32 ppm, J )
20.4 Hz), 3.0 (s, br, 1H), 2.6-0.8 (m, 18H), 0.73 (s, 3H); mp.
239.5-241.9 °C; Elemental analysis: Calcd for C27H31IO5 + 0.5
H2O (571.45): C 56.75, H 5.64; Found: C 56.96, H 5.63; MS
(ESI): m/z 584.83 (M+ + 23).
J
) 17.4 Hz), 5.09 (d, 1H, J ) 5.7 Hz), 2.6-0.8 (m, 18H), 0.77
H-F
(s, 3H); 19F (CDCl3, 282.4 MHz) δ: - 56.88 (t, J ) 48.9 Hz); mp.
170.6-171.6 °C; Elemental analysis: Calcd for C25H28FIO5
(554.10): C 54.16, H 5.09; Found: C54.22, H 5.33; MS (ESI):
m/z 576.89 (M+ + 23).
Data for exo-9. 1H NMR (CDCl3, 300 MHz) δ: 7.69 (d, 2H, J
) 8.1 Hz), 7.06 (d, 2H, J ) 8.4 Hz), 6.09 (s, 1H), 5.85 (s, 1H),
5.40 (d, 1H, J ) 6.0 Hz), 4.19 (AB, q, 2H, ∆υ ) 0.19 ppm, J )
19.8 Hz), 2.6-0.9 (m, 18H), 0.75 (s, 3H); mp. 239.0-241.0 °C;
Elemental analysis: Calcd for C27H31IO5 (562.12): C 57.66, H 5.56;
Found: C57.38, H 5.57; MS (ESI): m/z 584.70 (M+ + 23).
Data for endo-10. 1H NMR (CDCl3, 300 MHz) δ: 6.96 (d, 1H,
J ) 3.9 Hz), 6.92 (d, 1H, J ) 3.6 Hz), 5.87 (s, 1H), 5.71 (s, 1H),
5.06 (d, 1H, J ) 5.4 Hz), 4.48 (AB, q, 2H, ∆υ ) 0.33 ppm, J )
20.4 Hz), 3.0 (s, br, 1H), 2.6-0.8 (m, 18H), 0.72 (s, 3H); mp.
131.5-134.4 °C; Elemental analysis: Calcd for C25H29BrO5S
(520.09): C 57.58, H 5.61; Found: C 57.41, H 5.68; MS (ESI):
m/z 542.75 (M+ + 23).
1
Data for exo-14. H NMR (CDCl3, 300 MHz) δ: 6.47 (d, 1H,
J ) 3.63 Hz), 6.26 (d, 1H, J ) 3.63 Hz), 6.13 (s, 1H), 5.83 (s,
1H), 5.28 (d, 1H, J ) 3.0 Hz),4.98 (d, 1H, J ) 6.6, JH-F ) 17.1
Hz), 4.82 (d, 1H, J ) 6.6, JH-F ) 17.1 Hz), 2.6-0.8 (m, 18H),
0.77 (s, 3H); 19F (CDCl3, 282.4 MHz) δ: - 56.48 (t, J ) 48.8
Hz); mp. 150 °C decomposition; MS (ESI): m/z 576.89 (M+
+
23). HRMS: Calcd for C25H28FIO5 + H+, 555.1044; found,
555.1066.
Data for endo-15. 1H NMR (CDCl3, 300 MHz) δ: 7.54 (d, 2H,
J ) 8.4 Hz), 7.33 (d, 2H, J ) 8.4 Hz), 5.84 (s, 1H), 5.46 (s, 1H),
5.27 (d, 1H, J ) 52.5, JH-F ) 17 Hz), 5.11 (d, 1H, J ) 52.5, JH-F
) 17 Hz), 5.09 (d, 1H, J ) 5.4 Hz), 2.6-0.8 (m, 18H), 0.77 (s,
3H); 19F (CDCl3, 282.4 MHz) δ: - 56.88 (t, J ) 48.9 Hz); mp.
148.0-152.0 °C; Elemental analysis: Calcd for C27H30BrFO4
(516.13): C 62.67, H 5.84; Found: C 62.74, H 6.09; MS (ESI):
m/z 539.09 (M+ + 23).
1
Data for exo-10. H NMR (CDCl3, 300 MHz) δ: 6.92 (d, 1H,
J ) 3.6 Hz), 6.86 (d, 1H, J ) 3.9 Hz), 6.29 (s, 1H), 5.85 (s, 1H),
5.37 (d, 1H, J ) 6.3 Hz), 4.33 (AB, qd, 2H, ∆υ ) 0.35 ppm, J )
3.9, 20.4 Hz), 2.6-0.8 (m, 18H), 0.75 (s, 3H); mp. 206.4-208.4
°C; Elemental analysis: Calcd for C25H29BrO5S + 0.5 H2O
(529.09): C 56.60, H 5.70; Found: C 56.36, H 5.66; MS (ESI):
m/z 542.85 (M+ + 23).
Data for exo-15.
1H NMR (CDCl3, 300 MHz) δ: 7.50 (d, 2H,
J ) 8.7 Hz), 7.21 (d, 2H, J ) 8.1 Hz), 6.10 (s, 1H), 5.84 (s, 1H),
5.40 (d, 1H, J ) 6.3 Hz), 4.93 (d, 1H, J ) 2.7, JH-F
) 17.4 Hz),
Data for endo-11. 1H NMR (CDCl3, 300 MHz) δ: 7.15 (d, 1H,
J ) 3.9 Hz), 6.83 (d, 1H, J ) 3.6 Hz), 5.87 (s, 1H), 5.75 (s, 1H),
5.06 (d, 1H, J ) 5.4 Hz), 4.48 (AB, q, 2H, ∆υ ) 0.33 ppm, J )
20.4 Hz), 2.6-0.8 (m, 18H), 0.72 (s, 3H); mp. 174.0-175.3 °C;
Elemental analysis: Calcd for C25H29IO5S (568.5): C 52.82, H 5.14;
Found: C 52.87, H 5.11; MS (ESI): m/z 591.1 (M+ + 23).
4.77 (d, 1H, J ) 2.7, JH-F ) 17.4 Hz), 2.6-0.8 (m, 18H), 0.79 (s,
3H); 19F (CDCl3, 282.4 MHz) δ: - 55.58 (t, J ) 48.9 Hz); mp.
156.7-162.3 °C; Elemental analysis: Calcd for C27H30BrFO4
(516.13): C 62.67, H 5.84; Found: C 62.68, H 6.06; MS (ESI):
m/z 539.09 (M+ + 23).
Data for endo-16. 1H NMR (CDCl3, 300 MHz) δ: 7.75 (d, 2H,
J ) 8.4 Hz), 7.18 (d, 2H, J ) 8.4 Hz), 5.83 (s, 1H), 5.45 (s, 1H),
5.27 (d, 1H, J ) 52.2, JH-F ) 17.1 Hz), 5.11 (d, 1H, J ) 52.2,
1
Data for exo-11. H NMR (CDCl3, 300 MHz) δ: 7.11 (d, 1H,
J ) 3.6 Hz), 6.78 (d, 1H, J ) 3.6 Hz), 6.33 (s, 1H), 5.85 (s, 1H),
5.37 (d, 1H, J ) 5.7 Hz), 4.33 (AB, q, 2H, ∆υ ) 0.35 ppm, J )
J
) 17.1 Hz), 5.08 (d, 1H, J ) 5.7 Hz), 2.6-0.8 (m, 18H), 0.77
H-F

16R,17R-Dioxolane Progestins
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 15 4743
(s, 3H); 19F (CDCl3, 282.4 MHz) δ: - 56.89 (t, J ) 48.9 Hz); mp.
181.6-185.0 °C; Elemental analysis: Calcd for C27H30FIO4
(564.12): C 57.45, H 5.36; Found: C56.80, H 5.44; MS (ESI):
m/z 587.10 (M+ + 23).
bogen, J. A.; McElvany, K. D.; Senderoff, S. G.; Carlson, K. E.;
Landvatter, S. W.; Welch, M. J. 16R-[77Br]bromo-11â-methoxyestra-
diol-17â: a gamma-emitting estrogen imaging agent with high uptake
and retention by target organs. J. Nucl. Med. 1982, 23, 411-419.
(d) Katzenellenbogen, J. A.; Senderoff, S. G.; McElvany, K. D.;
O’Brien, H. A., Jr.; Welch, M. J. 16R-[bromine-77]bromoestradiol-
17â: a high specific-activity, gamma-emitting tracer with uptake in
rat uterus and induced mammary tumors. J. Nucl. Med. 1981, 22,
42-47. (e) Landvatter, S. W.; Katzenellenbogen, J. A.; McElvany,
K. D.; Welch, M. J. (2R*,3S*)-1-[125I]Iodo-2,3-bis(4-hydroxyphenyl)-
pentane ([125I]iodonorhexestrol) and (2R*,3S*)-1-[77Br]Bromo-2,3-
bis(4-hydroxyphenyl)pentane ([77Br]bromonorhexestrol), two gamma-
emitting estrogens that show receptor-mediated uptake by target
tissues in vivo. J. Med. Chem. 1982, 25, 1307-1312. (f) McElvany,
K. D.; Katzenellenbogen, J. A.; Shafer, K. E.; Siegel, B. A.;
Senderoff, S. G.; Welch, M. J. 16 alpha-[77Br]bromoestradiol:
dosimetry and preliminary clinical studies. J. Nucl. Med. 1982, 23,
425-430. (g) Ali, H.; Rousseau, J.; Ahmed, N.; Guertin, V.;
Hochberg, R. B.; van Lier, J. E., Synthesis of the 7R-cyano-(17R,-
20E/Z)-[125I]iodovinyl-19-nortestosterones: potential radioligands for
androgen and progesterone receptors. Steroids 2003, 68, 1163-71.
(h) Downer, J. B.; Jones, L. A.; Engelbach, J. A.; Lich, L. L.; Mao,
W.; Carlson, K. E.; Katzenellenbogen, J. A.; Welch, M. J., Com-
parison of animal models for the evaluation of radiolabeled androgens.
Nucl Med Biol 2001, 28, 613-26. (i) Hoyte, R. M.; Brown, T. J.;
MacLusky, N. J.; Hochberg, R. B. 7R-Methyl-17R-(E-2′-[125I]-
iodovinyl)-19-nortestosterone: a new radioligand for the detection
of androgen receptor. Steroids 1993, 58, 13-23. (j) Labaree, D. C.;
Hoyte, R. M.; Nazareth, L. V.; Weigel, N. L.; Hochberg, R. B. 7R-
Iodo and 7R-fluoro steroids as androgen receptor-mediated imaging
agents. J Med Chem 1999, 42, 2021-34. (k) Lamb, D. J.; Bullock,
D. W.; Hoyte, R. M.; Hochberg, R. B., ∆9-[16R-125I]iodo-19-
nortestosterone: a gamma-emitting photoaffinity label for the proges-
terone receptor. Endocrinology 1988, 122, 1923-32.
1
Data for exo-16. H NMR (CDCl3, 300 MHz) δ: 7.71 (d, 2H,
J ) 8.7 Hz), 7.07 (d, 2H, J ) 8.1 Hz), 6.08 (s, 1H), 5.84 (s, 1H),
5.39 (d, 1H, J ) 6.0 Hz), 4.93 (d, 1H, J ) 2.7, JH-F ) 17.1 Hz),
4.77 (d, 1H, J ) 2.7, JH-F ) 17.1 Hz), 2.6-0.8 (m, 18H), 0.79 (s,
3H); 19F (CDCl3, 282.4 MHz) δ: - 55.58 (t, J ) 48.9 Hz); mp.
190.4-194.2 °C; Elemental analysis: Calcd for C27H30FIO4
(564.12): C 57.45, H 5.36; Found: C57.68, H 5.59; MS (ESI):
m/z 587.04 (M+ + 23).
Progesterone Receptor Binding Affinity Assays. Relative
binding affinities were determined by a competitive radiometric
binding assay as previously described,19 using 10 nM [3H]R5020
as tracer ([17R-methyl-3H]-promegestone) (Perkin-Elmer, Boston,
MA), unlabeled R5020 as standard, and purified full length
progesterone receptor B from PanVera/Invitrogen (Carlsbad, CA).
Incubations were for 18-24 h at 0 °C. Hydroxyapatite (BioRad,
Hercules, CA) was used to absorb the receptor-ligand complexes,
and free ligand was removed by washing with cold buffer. The
binding affinities are expressed as relative binding affinity values
with the RBA of R5020 set to 100%. The values given are the
average ( range or SD of two or more independent determinations.
R5020 binds to PR with a Kd of 0.4 nM.
Acknowledgment. This work was supported by the United
States Department of Energy grants (DE FG02 86ER60401 to
J.A.K and DE FG02 84ER60218 to M.J.W.). High resolution
mass spectrometry was provided by the Washington University
Mass Spectrometry Resource with support from the NIH
National Center for Research Resources (Grant No. P41RR0954).
(5) Bronzert, D. A.; Hochberg, R. B.; Lippman, M. E. Specific
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Supporting Information Available: Elemental analyses and
mass spectrometry data of compound 6-16, HPLC conditions for
1
separation of isomers of compound 6-12. H NMR spectra of
compound 6-16. This material is available free of charge via the
Internet at http://pubs.acs.org
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