A.J. Lee et al. / Steroids 69 (2004) 61–65
63
with 50 ml ethyl acetate, and vacuum-filtered through Celite.
The filtrate was extracted with 1 N HCl (50 ml) twice to
remove 4-picoline. The organic layer was dried with an-
hydrous Na2SO4 and concentrated under reduced pressure.
The residue was purified by column chromatography eluting
with a gradient from 33% ethyl acetate in hexanes to 100%
ethyl acetate. The fractions were combined, concentrated,
and further purified by column chromatography eluting with
33% ethyl acetate in hexanes. The fractions were combined
and concentrated and the residues were purified by crystal-
lization from ethanol. M16 3-benzyl ether was obtained as
colorless needles: 262 mg (41% yield); m.p. 142–144 ◦C;
Rf of 0.22 on Silica gel TLC (50% ethyl acetate/hexanes);
molecular weight (m/z) 632.3864 (632.3866 calculated for
C43H52O4, 0.3 ppm error); 1H NMR (CD3OD): overlapped
region 7.100–7.197 (5H, for H-1ꢀ, H-meta, and H-ortho),
overlapped region 6.999–7.022 (2H, for H-1 and H-para),
6.903 (d, J = 8.6 Hz, 1H, for H-2), 6.517 (dd, J = 8.6 and
2.6 Hz, 1H, for H-2ꢀ), and 6.444 (d, J = 2.6 Hz, 1H, for
H-4ꢀ) ppm (δ).
2.3.6. M15 3-O-benzyl ether (compound 7) [12]
Into a 50-ml round-bottom flask, 441 mg of crude 2-
bromoestradiol 3-O-benzyl ether (containing 2,4-dibromoe-
stradiol 3-O-benzyl ether), estradiol (272 mg, 1.0 mmol), and
anhydrous K2CO3 (290 mg, 2.1 mmol) in 5 ml 4-picoline
were added. The mixture was first incubated at 130 ◦C for
3 h, and then CuO (40 mg, 0.5 mmol) was added. The reac-
tion mixture was heated at 155–160 ◦C with stirring under ar-
gon for 72 h, cooled to room temperatures, diluted with ethyl
acetate, and vacuum-filtered through Celite. The filtrate was
extracted with 1 N HCl (50 ml) twice to remove 4-picoline.
The organic layer was dried with anhydrous Na2SO4 and
concentrated under a reduced pressure. The residue was pu-
rified by column chromatography eluting with 50% ethyl
acetate in hexanes. The residue was purified again by col-
umn chromatography eluting with 33% ethyl acetate in hex-
anes. The fractions were combined and concentrated and the
yellow-colored residues were not further purified.
2.3.7. M15
Into a Parr flask, crude M15 3-O-benzyl ether in 100 ml
ethanol and Pd-C (500 mg) were added. The reaction mix-
ture was subjected to hydrogen at 40 psi for 4 h and the
catalyst was removed by vacuum filtration through Celite.
The filtrate was concentrated and the residue was dissolved
in hot acetonitrile. During the concentration of acetonitrile
solution with heating, white amorphous powder was ob-
tained as M15: 39 mg; Rf of 0.25 on Silica gel TLC (50%
ethyl acetate/hexanes); molecular weight (m/z) 542.3407
2.3.4. M16
Into a Parr flask, M16 3-benzyl ether (240 mg, 0.38 mmol)
in 100 ml ethanol and Pd-C (500 mg) were added. The re-
action mixture was subjected to hydrogen at 40 psi for 4 h
and the catalyst was removed by vacuum filtration through
Celite. The filtrate was concentrated and the residue was
dissolved in hot acetonitrile. During the concentration of the
acetonitrile solution with heating, white amorphous pow-
der was obtained as M16: 136 mg (66% yield); Rf of 0.22
on Silica gel TLC (50% ethyl acetate/hexanes); molecular
weight (m/z) 542.3387 (542.3396 calculated for C36H46O4,
1.7 ppm of error); 1H NMR (CD3OD): 7.140 (d, J = 8.5 Hz,
1H, for H-1ꢀ), 7.040 (d, J = 8.5 Hz, 1H, for H-1), 6.740 (d,
J = 8.5 Hz, 1H, for H-2), 6.530 (dd, J = 8.5 and 2.5 Hz,
1H, for H-2ꢀ), and 6.470 (d, J = 2.5 Hz, 1H, for H-4ꢀ)
ppm (δ).
1
(542.3396 calculated for C36H46O4, 2.0 ppm of error); H
NMR (CD3OD): 7.178 (d, J = 8.5 Hz, 1H, for H-1ꢀ), 6.773
(s, 1H, for H-1), 6.639 (dd, J = 8.5 and 2.3 Hz, 1H, for
H-2ꢀ), 6.612 (s, 1H, for H-4), and 6.564 (d, J = 2.3 Hz,
1H, for H-4ꢀ) ppm (δ).
3. Results and discussion
2.3.5. 2-Bromoestradiol 3-O-benzyl ether (compound 6)
A 50-ml round-bottom flask was charged with 2-bromoe-
stradiol (527 mg, 1.5 mmol) and anhydrous K2CO3 (1.382 g,
10 mmol) in 25 ml acetonitrile, and then benzyl bromide
(180 l, 1.5 mmol) was added. The reaction mixture was re-
fluxed with stirring for 1 h. The hot reaction mixture was then
filtered under a reduced pressure, and the filtrate was con-
centrated. 2-Bromoestradiol 3-O-benzyl ether was obtained
as white powder (539 mg, 82%). Although TLC analysis
showed a single spot (Silica gel, toluene/chloroform/ethyl
acetate, 1/10/2, Rf = 0.49), further mass spectrometric
analysis showed two molecular weights: one correspond-
ing to 2-bromoestradiol 3-O-benzyl ether (compound 6),
with a molecular weight (m/z) of 440.1339 (440.1351 cal-
culated for C25H29BrO2, 2.7 ppm error), and the other one
corresponding to 2,4-dibromoestradiol 3-O-benzyl ether,
with m/z 520 (its high-resolution mass was not deter-
mined).
The key structural characteristic of M15 and M16 (struc-
tures shown in Fig. 1) is the presence of a diaryl ether bond
between two estradiol moieties. The method commonly used
for preparation of a diaryl ether linkage has been the reaction
between an alkali metal phenolate and a halogenated ben-
zene in the presence of copper (or a copper salt) as catalyst,
which was originally developed by Ullmann and is widely
known as the Ullmann condensation reaction [13–15]. Ac-
cordingly, a four-step synthetic scheme (depicted in Fig. 2)
for the synthesis of M15 and M16 was designed with the
Ullmann condensation reaction as a key step. Step 1: Syn-
thesis of 2- or 4-bromoestradiol from estradiol. Step 2: Pro-
tection of the C-3 phenolic hydroxyl group of the 2- or
4-bromoestradiol. Step 3: The Ullmann condensation reac-
tion of the phenol-protected bromoestradiol and the estradiol
potassium salt under our modified reaction conditions (with
a 41% product yield). Step 4: Removal of the C-3 benzyl
group by catalytic hydrogenation.