Estrogen receptor ligands. Part 10: Chromanes: Old scaffolds for new SERAMs

Article abstract of DOI:10.1016/j.bmcl.2005.01.046

The discovery, synthesis, and SAR of chromanes as ERα subtype selective ligands are described. X-ray studies revealed that the origin of the ERα-selectivity resulted from a C-4 trans methyl substitution to the cis-2,3-diphenyl-chromane platform. Selected

Full text of DOI:10.1016/j.bmcl.2005.01.046

Bioorganic & Medicinal Chemistry Letters 15 (2005) 1675–1681
Estrogen receptor ligands. Part 10: Chromanes: old scaffolds
for new SERAMs
Qiang Tan,a,* Timothy A. Blizzard,a Jerry D. Morgan, II,a Elizabeth T. Birzin,b
Wanda Chan,b Yi Tien Yang,b Lee-Yuh Pai,b Edward C. Hayes,b Carolyn A. DaSilva,b
Sudha Warrier,b Joel Yudkovitz,b Hilary A. Wilkinson,b Nandini Sharma,a
Paula M. D. Fitzgerald,a Susan Li,a Lawrence Colwell,a John E. Fisher,b
Sharon Adamski,b Alfred A. Reszka,b Donald Kimmel,b Frank DiNinno,a
Susan P. Rohrer,b Leonard P. Freedman,b James M. Schaefferb and Milton L. Hammonda
aDepartment of Medicinal Chemistry, Merck Research Laboratories, PO Box 2000, RY800-B107, Rahway, NJ 07065, USA
bDepartment of Molecular Endocrinology and Bone Biology, Merck Research Laboratories, PO Box 2000, Rahway,
NJ 07065, USA
Received 22 October 2004; revised 18 January 2005; accepted 19 January 2005
Abstract—The discovery, synthesis, and SAR of chromanes as ERa subtype selective ligands are described. X-ray studies revealed
that the origin of the ERa-selectivity resulted from a C-4 trans methyl substitution to the cis-2,3-diphenyl-chromane platform.
Selected compounds from this class demonstrated very potent in vivo antagonism of estradiol in an immature rat uterine weight
assay, effectively inhibited ovariectomy-induced bone resorption in a 42 days treatment paradigm, and lowered serum cholesterol
levels in ovxÕd adult rat models. The best antagonists 8F and 12F also exhibited potent inhibition of MCF-7 cell growth and were
shown to be estrogen receptor down-regulators (SERDs).
Ó 2005 Elsevier Ltd. All rights reserved.
As part of an evolutionary program designed to exploit
the chromane skeleton for the discovery of selective
ligands for the estrogen receptors, we have recently
reported our findings on the flavanone,1 I, Z = CO,
and dihydrobenzoxathiin,2 I, Z = S, classes. The reports
detailed the generation of ligands with a greater affinity
for the a isoform of the estrogen receptor and were
therefore labeled SERAMs, selective estrogen receptor
alpha modulators. Of the two classes, the more potent
dihydrobenzoxathiins, typically exhibited low to sub-
nanomolar binding to ERa, with 50- to 100-fold selectiv-
ity, and as a result of further study, a derivative, II, was
targeted for development as a potential agent for the
treatment of osteoporosis. This report focuses on the
further extension of this research and discloses the syn-
thesis and biological properties of another new class of
orally bioavailable SERAMs containing the parent
chromane core structure III, wherein, the size and stere-
ogenic placement of the substituent is crucial for both
receptor potency and selectivity. This series of comp-
ounds contrasts our initial finding, wherein the unsubsti-
tuted chromane III, Y = OH, R1 = R2 = H, exhibited
equipotent affinity for both ERa and ERb.1 In addition,
the results of this study contrast the very early studies of
the Central Drug Research Institute (India) in which
similar 3,4-diaryl-chromanes were exploited as potential
antifertility agents and led to the development of the
nonsteroidal contraceptive agent centchroman IV,3
and the more recent studies of the Novo Nordisk,4 as
NSERTs (nonsteroidal estrogen receptor therapeutics)
or early SERMs. Further exploitation of the chromane
scaffold has also provided non-subtype selective, potent
chromenes V5 and VI,6 as SERMs of commercial inter-
est. The series of compounds disclosed herein represent
the first reported chromanes exhibiting ERa-selectivity
(see Figures 1 and 2).
Keywords: Osteoporosis; Estrogen receptor; Chromane; Subtype selec-
tivity; Estrogen receptor alpha; SERM; SERAM; Estrogen receptor
antagonist; Cancer.
*
Corresponding author. Tel.: +1 732 594 1276; fax: +1 732 594 9556;
e-mail: qiang_tan@merck.com
0960-894X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.01.046

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Q. Tan et al. / Bioorg. Med. Chem. Lett. 15 (2005) 1675–1681
Figure 1.
Figure 2. Novel chromanes III. 1, 2, and 3b are racemic and the remainder are chiral.
The synthesis of the series 1–8, 10, 3a, and b is depicted
in Scheme 1 and featured diene 14, which was obtained
from the acid-induced elimination of the carbinol ad-
duct formed by the addition of the Grignard reagent
to coumarin 13. Hydrogenation with Rh on carbon gave
a mixture of alkenyl isomers 15 and 16, in a ratio which
averaged at 1:2.5. It was also found upon scale-up that
the THP group was partially cleaved to give a mixture
of protected and unprotected products. A second hydro-
genation of 16 with Pd on carbon, with or without the
THP group, provided chromanes 17 and 17a (approxi-
mate ratio of 17:17a = 1:1.4, R1 = H; 1:4.5, R1 = Me),
Scheme 1. Synthesis of 1–8, 10, 3a, and b. Reagents and conditions: (a) (i) 4-(2-tetrahydro-2H-pyranoxy)phenylmagnesium bromide, THF, rt;
(ii) 2 N anhydrous HCl in ether, 0 °C; (b) 1 atm H2, EtOAc, 5% Rh–C, rt, ca 50% two steps; (c) 1 atm H2, EtOAc, 10% Pd–C, rt; (d) (i) TFA,
triethylsilane, CH2Cl2, 0 °C; skipped if THP is already completely removed in step c; (ii) chromatographic separation of isomers, ca 60% two steps;
(e) (i) triphenylphosphine, DIAD, ROH, THF, rt; (ii) TBAF, THF, rt, ca 50%.

Q. Tan et al. / Bioorg. Med. Chem. Lett. 15 (2005) 1675–1681
1677
which upon treatment with TFA and subsequent chro-
matographic separation yielded 18. In turn, 18 could
be resolved by chiral HPLC. Finally, the installation
of the aminoethyl side chain, by the use of a Mitsunobu
reaction, in conjunction with protecting group manipul-
ations, provided the target compounds.
Presumably, fluorine-assisted metallation (b) of 28 gen-
erated lithium species 32 and MeI, which rapidly recom-
bined to furnish 30.
Finally, after removal of the benzyl protecting group,
the aminoethyl side chains were installed as previ-
ously described using a Mitsunobu reaction protocol
and the appropriate alcohol to generate final products
after subsequent removal of the TIPS protecting groups.
The synthesis of the series of compounds possessing a C-
5 fluorine substituent, 3F–9F, 11F and 12F, is shown in
Scheme 2. Selective ortho-lithiation with butyllithium
via fluorine participation of the commercially available
19 followed by formylation with DMF gave rise to alde-
hyde 20. After the selective demethylation of 20, directed
by complexation of AlCl3 with the neighboring aldehyde
functionality, the coupling of 21 with 4-methoxy phenyl-
acetic acid yielded coumarin 22. Following a protecting
group switching maneuver, the DIBAL reduction of 24
provided the hemi-ketal 25. This was followed by
replacement of the hydroxyl group with the better phen-
oxyl leaving group, which in turn underwent a Grignard
addition to yield 27, according to the protocol by Grese
and Pennington.7 The trans methyl group was then in-
stalled by either of the two following methods. The first
involved hydroboration followed by an oxidative work-
up to provide for the installation of the hydroxyl group
from the less hindered face of the less hindered carbon
to yield 28. Then under the influence of the nucleophilic,
Lewis-acidic methyl titanium species, generated in situ
from Me2Zn and TiCl4, the stereospecific delivery of
the requisite methyl group was accomplished to provide
30, presumably via the intermediacy of the benzylic cat-
ion (a) or its equivalent.8 Alternatively, introduction of
the trans methyl group was achieved by first converting
28 to iodide 29, in an SN1 manner, followed by treat-
ment of the iodide with MeLi at low temperature.
As previously reported2 by our laboratory, the dihydro-
benzoxathiins I, Z = S exhibit ERa selectivity owing to
the presence of a bulky sulfur atom which is tolerated
by the nearby ERa-Leu384 residue but not by the
ERb-Met336 residue at the same position in the ligand
binding domain of the receptor isoforms. By the same
token, we suspected that a cis-methyl group at C-3 of
the chromane system pointing toward the same residues
should give rise to ERa selectivity. As depicted in Table
1, compounds such as 1 and 2 do exhibit ERa selectivity,
however, with reduced binding affinity in comparison to
I, Z = S. This may be attributed to the elevated steric
congestion and hence the reduced conformational flexi-
bility of the three syn substituents on the chromane ring.
Indeed, when a trans methyl group was introduced, as in
compounds 3 and 3a, the ER binding affinity was dra-
matically improved. Truly surprising however, was the
ERa selectivity found for 3 and 3a, since a trans methyl
group was not predicted to have a direct impact on
selectivity.
A possible explanation for the observed selectivity was
offered by the X-ray crystallography analysis13 of the
ERa complexes of these ligands. The structure of 4 in
ERa (Fig. 3) revealed that although the trans methyl
Scheme 2. Synthesis of 3F–7F. Reagents and conditions: (a) BuLi, then DMF, THF, dry ice–acetone bath, 56%; (b) AlCl3, CH2Cl2, rt, 84%; (c)
4-methoxyphenyl acetic acid, acetic anhydride, triethylamine, 135 ꢀ 145 °C, ca 50%; (d) BBr3, CH2Cl2, 0 °C, 71%; (e) TIPSCl, HunigÕs base, DMF,
rt; (f) DIBAL, CH2Cl2, dry ice–acetone bath; (g) PhOH, CH2Cl2, rt; (h) 4-benzyloxyphenylmagnesium bromide, THF–toluene, 50 °C, 34% four
steps; (i) Borane–THF complex, THF, rt, then 30% H2O2-aq Na2CO3, 82%; (j) KI, Bu4NI, BF3 etherate, CH2Cl2, 0 °C, 74%; (k) MeLi, THF, dry ice–
acetone bath; (l) 1 atm H2, EtOAc, 10% Pd–C, rt; 67% two steps; then chiral HPLC resolution; (m) Me2Zn, TiCl4, CH2Cl2, 51% two steps; (n) (i)
triphenylphosphine, DIAD, ROH, THF, rt; (ii) TBAF, THF, rt, ca 50%.
Table 1. Binding affinity—IC50 (nM)a
Compd
1
2
3
3a
3b
ERa/ERb (a-selectivity)
45/179(4)
38/627(17)
1.4/39(28)
0.66/13(20)
14/171(12)
a The single IC50 values were generated in an estrogen receptor ligand binding assay. This scintillation proximity assay was conducted in NEN Basic
Flashplates using tritiated estradiol and full length recombinant human ER-alpha and ER-beta proteins, with an incubation time of 3 h. In our
experience, this assay provides IC50 values that are reproducible to within a factor of 2–3.

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Q. Tan et al. / Bioorg. Med. Chem. Lett. 15 (2005) 1675–1681
group indeed pointed away from the ERa-Leu384/ERb-
Met336 region, the addition of the methyl group forced
the ligand to bind closer to this region in order to relieve
a steric clash between the ligand methyl group and the
side chain of L428. Therefore, the steric repulsion was
elevated between that region of the receptor and the en-
tire ligand, which then tended to mimic the effect of the
bulky sulfur atom of the dihydrobenzoxathiin system.
This also implied that the binding space in this region
is probably very tight and thus the slightly larger ethyl
analog 3b exhibited dramatically lower binding affinity.
As shown in Table 2, several trans methyl chromane
derivatives were evaluated for their ability (IC50) to inhi-
bit the estrogen dependent growth of both human carci-
noma MCF-7 cells and an immature rat uterus, as well
as, to lower serum cholesterol levels in OVXÕd rats. As
can be seen, all of the derivatives exhibited potent
ERa affinity, with selectivity as high as 50–100-fold, and,
unlike the dihydrobenzoxathiin class, which suffered a
significant reduction in ERa selectivity upon incorpora-
tion of a fluorine atom on the aromatic ring,2d the cor-
responding fluorochromanes were found to be equally
selective. Such an observation may further support the
unique mechanism of selectivity proposed for chrom-
anes which is based on the steric repulsion between the
Figure 3. Comparison of the structures of 4 (cyan) and I, Z = S
(green). The alpha carbons of the two proteins were aligned, and then
the coordinates of 4 were added to the structure of I, where Z = S. The
two residues that differ in sequence between ERa and ERb are labelled.
Oxygen atoms are colored red, and sulfur gold. The positions of the
hydroxyl group are identical, but the added methyl group of 4 forces
the compound to the left in this view, interacting more closely with
L384, an interaction that would not be accommodated by the bulkier
M336 of ERb.
Table 2. Binding affinitya and biological properties of compounds 3–7F
Compd
IC50 (nM) ERa/ERb
(a-selectivity)
MCF-7 inhibitionb IC50
(nM)
Uterine weightc %inhibition/%control
@ 1 mpk
% Serum cholesterol reductiond
(relative to raloxifene)
I(Z = S)
0.8/45 (56)e
1.4/39(28)
0.8/18(23)
1.5/12(8)
3.0
1.6
1.4
1.5
—
99/9
—
3
3F
58/42
65/26
5/24f
35/53
—
38(1.0)
45(1.2)
—
4
4F
0.9/11(12)
1.3/19(15)
0.8/16(20)
2.4/15(6)
38(1.1)
30(0.97)
42(1.2)
20(0.59)
27(0.9)
36(1.1)
29(0.97)
—
5
5F
1.5
0.9
1.2
1.1
0.5
0.5
0.4
0.8
0.6
2.5
0.9
0.07
—
47/54
68/31f
84/2
67/30f
85/1
7/20f
112/3
75/23
—
6
6F
0.8/23(29)
1.4/4.5(32)
0.5/29(58)
1.3/21(16)
0.9/26(29)
2.5/19(8)
7
7F
8
8F
28(0.93)
31(0.97)
—
9F
10
1.5/143(95)
0.3/18(60)
0.7/4.1(6)
1.3/1.1(1)g
11F
12F
Estradiol
41/53
124/ꢁ13
—/100
17(0.57)
—
86h
a The single IC50 values were generated in an estrogen receptor ligand binding assay. This scintillation proximity assay was conducted in NEN Basic
Flashplates using tritiated estradiol and full length recombinant human ER-alpha and ER-beta proteins, with an incubation time of 3 h. In our
experience, this assay provides IC50 values that are reproducible to within a factor of 2–3.
b Estrogen depleted MCF-7 cells were plated into 96-well cell culture plates at a density of 1000 cells/well. The test compounds and 3 pmol estradiol
were applied to the cells on days 1 and 4 in order to evaluate the antagonist activity of compounds. The IC50 value was determined from the cellular
protein content/well on day 9 of the assay.
c Twenty-day old intact female Sprague–Dawley rats were treated (po) with test compounds for 3 days at 1 mpk. The uteri wet weights were
determined on day 4 and dry weights were determined after air-drying the tissue samples for 3 days. The anti-estrogenic (antagonism) activity of
compounds was determined by co-administration of the compound with a subcutaneous injection of 17-beta-estradiol at 0.004 mpk and reported as
% inhibition of uterine growth induced by estradiol. The estrogenic activity (partial agonism) of the compounds was determined by administering
the test compound without estradiol and reported as % control.
d In ovxÕd rats dosed at 1.5 mg/kg/day, po, for 3 days.
e Average of 36 measurements.
f Subcutaneous dosing @ 1 mpk.
g Average of 130 measurements.
h Average of 15 measurements at 0.6 mpk.

Q. Tan et al. / Bioorg. Med. Chem. Lett. 15 (2005) 1675–1681
1679
lize the protein in MCF 7 cells10 to a comparable extent
as the selective estrogen receptor down-regulator
(SERD) Fulvestrant11 (Fig. 5). This is in direct contrast
to Tamoxifen which increased the ER protein level.
Thus, chromanes such as 12F, like their dihydrobenzox-
athiin counterparts, may offer the potential to provide
an alternative means for the treatment of estrogen-sensi-
tive and Tamoxifen-resistant breast cancers.
Table 3 depicts the pharmacokinetic properties exhib-
ited for a representative number of compounds in the
chromane class as determined in female Sprague–Daw-
ley rats. Reminiscent of our findings2d in the dihydro-
benzoxathiin class of SERAMs, the disposition of the
hydroxyl group on the chromane skeleton was crucial
for good oral bioavailability. Thus, the C-7 positioned
phenol, 3a, exhibited very poor oral absorption,
whereas, the analogous C-6 positioned phenol, 3, had
significantly improved absorption. As previously delin-
eated,2d the Rosati model12 and the subtilis present in
dihydrobenzoxathiins appear to be inherent in the chro-
mane system as well. Although, the addition of the
fluorine atom did not appear to further affect oral
Figure 4. Comparison of the structures of 3F (yellow) and I, Z = S
(green). The alpha carbons of the two proteins were aligned, and then
the coordinates of 3F were added to the structure of I, Z = S. The two
residues that differ in sequence between ERa and ERb are labelled.
Oxygen atoms in the ligands are colored red, sulfur gold, and fluorine
cyan. Unlike the comparison of 4 and I, Z = S, the hydroxyl groups of
these two compounds do not occupy identical positions. Rather, the
addition of the fluorine atom forces 3F down in this view, a
repositioning that is combined with the move to the left generated
by the addition of the methyl group.
receptor and the entire ligand (Fig. 4), wherein, the fluo-
rine substituent enhances the bulkiness of the ligand. In
contrast, the decrease in the selectivity of the fluoro-
dihydrobenzoxathiins may arise from a reduction of
the electron density on sulfur, and in turn, a reduction
of the electronic repulsion with the Met366 residue of
ERb.
The introduction of the fluorine substituent on the chro-
mane skeleton also appeared to improve the in vivo
properties of the class, as evidenced by a comparison
of the results from the uterine weight and serum choles-
terol assays performed in rats, with those of the unsub-
stituted versions, in which selected basic side-chains
were varied. It also became apparent that the nature
of the side chain also produced more dramatic effects
on the antagonism of estradiol in the uterine weight
model with the chromane derived compounds than the
corresponding dihydrobenzoxathiins. For example, the
difference in the activities for the piperidine based com-
pounds, 3 and 3F, with those of the corresponding pyr-
rolidine based compounds, 4 and 4F is most profound.
On the other hand, the identical comparison found little
or no difference with dihydrobenzoxathiins.2b Similarly,
the differences observed between 5F and 6F were far less
remarkable in the latter class. (The uterine weight %inhi-
bition/%control @ 1 mpk, for dihydrobenzoxathiins
corresponding to 3, 3F, 4, 4F, 5F and 6F are: 99/9,
102/1, 72/34, 79/19, 91/14, and 106/0, respectively.)
Figure 5. Effect of chromanes on ERa expression: MCF-7 cells were
grown in an estrogen deprived medium for 48 h followed by exposure
to the test compounds at various concentrations for 24 h. The cells
were fixed and immuno-stained for ERa and visualized by fluorescence
conjugated secondary antibody. ERa specific immuno-fluorescence
was quantitated using Arrayscan Technology (Cellomics). Dose
titrations were performed and the EC50s of destabilization as well as
equilibrium levels of ERa attained were calculated. Tam = tamoxifen.
Fas = Faslodex (Fulvestrant).
Table 3. Pharmacokineticsa of selected chromanes
Compd
3
3F
3a
6F
7F
9F
9.0
Clp (mL/min/kg)
t1/2 (h)
F%
7.7
8.1
16.9
11.2
54%
9.5
5.9
2%
17.8
8.0
42.6
4.4
16.1
44%
In addition, all compounds exhibited potent inhibition
of the growth of MCF-7 tumor cells and the best antag-
onists, 8F and 12F, bearing side chains known to effect
the stability of the ERa protein in the dihydrobenzo-
xathiin class of ER ligands,9 were also shown to destabi-
45%
43%
31%
a Mean plasma concentrations and pharmacokinetic parameters in
female, Sprague–Dawley rats following intravenous dosing at 1 mpk
(n = 2) and oral dosing at 2 mpk (n = 3).

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Q. Tan et al. / Bioorg. Med. Chem. Lett. 15 (2005) 1675–1681
Table 4. Six-week bone mineral density study: adult OVX ratsa
Compd
% Cholesterol reduction
% Uterine growth
Bone mineral density
(% repleted to sham)
Distal femur:central
DFM:central
0.15, 0.5, 1.5 mpk
3Fb
6F
15,31,39
37,39,33
39,55,55
46,46,47
49
16,16,18
24,34,24
26,31,34
36,25,34
30
—
55,—,56
—,76,—
55,100,65
57,73,56
64
—,78,—
52,86,60
56,87,48
74
7F
9F
1.5 mpk
Raloxifene
a Six month old rats were ovariectomized (OVX) and treated with vehicle, ethinyl estradiol (EE; 0.6 mg/kg/day, po) or compound for 6 weeks. At the
end of treatment, rats were necropsied and uterine weights measured. Femora were extracted and stored in 70% ethanol. Soft tissue was dissected
from the bone, and bone mineral density (BMD) was measured by dual energy X-ray absorptiometry at both the distal femoral metaphysis (DFM)
and the central femur. To compensate for differences in bone size between animals, results are expressed as the distal to central ratio.
b Raloxifene was not included as control in the assay.
Med. Chem. Lett. 2004, 14, 3747; (f) Tan, Q.; Birzin, E. T.;
Chan, W.; Yang, Y. T.; Pai, L.-Y.; Hayes, E. C.; DaSilva,
C. A.; DiNinno, F.; Rohrer, S. P.; Schaeffer, J. M.;
Hammond, M. L. Bioorg. Med. Chem. Lett. 2004, 14,
3753; (g) Blizzard, T. A.; DiNinno, F.; Morgan, J. D.; Wu,
J. Y.; Chen, H. Y.; Kim, S.; Chan, W.; Birzin, E. T.; Yang,
Y. T.; Pai, L.-Y.; Zhang, Z.; Hayes, E. C.; DaSilva, C. A.;
Tang, W.; Rohrer, S. P.; Schaeffer, J. M.; Hammond, M.
L. Bioorg. Med. Chem. Lett. 2004, 14, 3865; (h) Blizzard,
T. A.; DiNinno, F.; Morgan, J. D.; Wu, J. Y.; Gude, C.;
Kim, S.; Chan, W.; Birzin, E. T.; Yang, Y. T.; Pai, L.-Y.;
Zhang, Z.; Hayes, E. C.; DaSilva, C. A.; Tang, W.;
Rohrer, S. P.; Schaeffer, J. M.; Hammond, M. L. Bioorg.
Med. Chem. Lett. 2004, 14, 3861; (i) Blizzard, T. A.;
DiNinno, F.; Morgan, J. D.; Chen, H. Y.; Wu, J. Y.; Kim,
S.; Chan, W.; Birzin, E. T.; Yang, Y. T.; Pai, L.-Y.;
Fitzgerald, P. M. D.; Sharma, N.; Li, Y.; Zhang, Z.;
Hayes, E. C.; DaSilva, C. A.; Tang, W.; Rohrer, S. P.;
Schaeffer, J. M.; Hammond, M. L. Bioorg. Med. Chem.
Lett. 2005, 15, 107.
bioavailability, it did appear to extend the serum half-
life of 3F.
In order to complete the evaluation of the chromane
class as SERMs, several representative derivatives
underwent evaluation to inhibit ovariectomized induced
bone resorption in a six-week oral treatment paradigm
in rats. As shown in Table 4, all of the chromane deriv-
atives were found to possess raloxifene-like activity on
serum cholesterol and bone mineral density.
In conclusion, given the profile of activity displayed by
the new, highly substituted chromanes, this novel class
qualifies as new SERAMs which may warrant further
investigation.
Acknowledgements
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for X-ray crystallography analysis. Use of the Advanced
Photon Source beamline 17-ID was supported by the
companies of the Industrial Macromolecular Crystallo-
graphy Association through a contract with Illinois
Institute of Technology.
4. (a) Alexandersen, P.; Riis, B. J.; Stakkestad, J. A.;
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(3F). The data were processed with program X-GEN,
which yielded an R-merge of 0.085 for the data from 1 to
˚
1.9 A (4) and an R-merge of 0.120 for the data from 1 to
˚
2.2 A (3F). The structures were refined using program
SHELXL, with final values for R-work and R-free of
13. The complexes of 4 and 3F with the ligand binding domain
of ER-alpha (residues 307–554) were crystallized by vapor
diffusion, using a precipitant containing 100 mM MgCl2,
6% PEG 3350, and 100 mM imidazole buffer, pH 7.1.
Data for both complexes were measured at beamline 17-
ID of the Advanced Photon Source. The crystals have the
symmetry of space group P6522, with cell dimensions
a = b = 58.55, c = 276.60 (4) and a = b = 58.85, c = 277.83
˚
0.190 and 0.258 for the data from 10.0 to 1.90 A resolution
˚
(4) and 0.179 and 0.298 for the data from 10.0 to 2.20 A
(3F). Coordinates and structures factors for both com-
plexes have been deposited with the Protein Data Bank
(entries 1YIM and 1YIN). The structure of I, Z = S has
been described previously (Ref. 2a; PDB ID 1SJ0).