Improved synthesis of mestranol and ethinyl estradiol (EE) related degradation products as authentic references

Article abstract of DOI:10.1016/j.steroids.2007.12.024

Preparative chemical methods for the synthesis of 10 degradation or photodecomposition products of mestranol and ethinyl estradiol (EE) are described. The synthesized compounds are useful as reference materials and standards for pharmaceutical analysis of

Full text of DOI:10.1016/j.steroids.2007.12.024

steroids 7 3 ( 2 0 0 8 ) 488–494
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/steroids
Improved synthesis of mestranol and ethinyl estradiol (EE)
related degradation products as authentic references
Hongqi Lia,∗, Yanxi Songb, Xianfu Penga
a
Key Laboratory of Science & Technology of Eco-Textile, Ministry of Education, College of Chemistry and Chemical Engineering,
Donghua University, 2999 North Renmin Road, Shanghai 201620, PR China
b
College of Environmental Science and Technology, Donghua University, 2999 North Renmin Road,
Shanghai 201620, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Preparative chemical methods for the synthesis of 10 degradation or photodecomposition
products of mestranol and ethinyl estradiol (EE) are described. The synthesized compounds
are useful as reference materials and standards for pharmaceutical analysis of mestranol
and EE as bulk chemical or in formulated product. New synthetic methods were presented
and the known synthetic procedures were improved. Detailed structural characterization
of the degradation or photodecomposition products of mestranol and EE and related com-
pounds was reported.
Received 26 October 2007
Received in revised form
13 December 2007
Accepted 13 December 2007
Published on line 28 December 2007
© 2007 Elsevier Inc. All rights reserved.
Keywords:
Steroid
Mestranol
Ethinyl estradiol
Synthesis
Degradation product
1.
Introduction
the beginning of the study. It was also found that decom-
position of mestranol and EE in the solid state could be
Mestranol and ethinyl estradiol (EE) are common components
of widely used hormone regulation and therapy medications,
e.g. the estrogen components of the combined oral contracep-
tive agents. Numerous steroid–protein conjugates have been
synthesized and used as antigens for the production of spe-
cific antisera required for radioimmunoassay [1–5]. Estradiol
derivatives were also found recently to act as multitargeted
antitumor agents [6–17]. Mestranol and EE have both been
proved to be stable in air. Nevertheless, stability samples of
formulated drug products containing mestranol and EE stored
for years under ambient laboratory conditions were observed
by HPLC to contain several oxidative transformation prod-
ucts of the parent compound which were not present at
accelerated at elevated temperature in the presence of air,
as a result of auto-oxidation. On the other hand, although
it is mentioned in the monographs in pharmacopoeias that
estrogenic steroids have to be protected from light, little is
known about the photochemical decomposition of these com-
pounds.
The main degradation or photodecomposition products of
mestranol and EE are shown in Fig. 1. Though the chemical
synthesis and structural characterization of these compounds
are important in view of providing authentic samples for fur-
ther studies, only several papers described the preparation
and characterization of these steroid compounds [1,18–21].
Cotter et al. reported the synthesis of compounds 1–8 (Fig. 1)
∗
Corresponding author. Tel.: +86 21 67792612; fax: +86 21 67792608.
E-mail address: hongqili@dhu.edu.cn (H. Li).
0039-128X/$ – see front matter © 2007 Elsevier Inc. All rights reserved.
doi:10.1016/j.steroids.2007.12.024

steroids 7 3 ( 2 0 0 8 ) 488–494
489
Fig. 1 – Degradation or photodecomposition products of EE and MEE.
but no details was presented in the letter [18]. Rao men-
tioned preparation of steroids 1,2,7, and 8 by a tedious
synthetic sequence [1]. Synthesis of compound 9 and 10
appeared only in paper [19] and [20], respectively. In this
paper, systematic studies on the main degradation or pho-
todecomposition products of mestranol and EE (compounds
1–10) and related compounds including their efficient syn-
thesis, isolation, and detailed structural characterization are
presented.
2.2.
Synthesis of compounds
2.2.1. Synthesis of 3,17ˇ-dihydroxy-19-norpregna-
1,3,5(10)-triene-20-yne-6-one
(7)
Norethindrone (11) was used as purchased from Zhejiang
Xianju Junye Pharmaceutical Co. Ltd., mp 207.8–208.6 ◦C. 1H
NMR (CDCl3) ı 5.81 (s, 1H), 2.57 (s, 1H), 2.40–2.50 (m, 2H),
2.23–2.33 (m), 1.68–2.10 (m), 1.51–1.65 (m), 1.23–1.40 (m),
1.04–1.14 (m), 0.92 (s, 3H).
Norethindrone (17.9 g, 60 mmol) and anhydrous potas-
sium acetate (9.5 g, 96 mmol) in dry dimethylformamide (DMF,
120 mL) was heated to 120 ◦C and stirred for 20 h while oxygen
or air was bubbled through the solution. The reaction mix-
ture was poured onto ice water (100 mL) containing methylene
chloride (300 mL). Hydrochloric acid (1N, 150 mL) was added
then the organic layer was separated. The aqueous phase was
extracted with methylene chloride (150 mL 3×). The organic
phases were combined and washed with 150 mL each of 1N
hydrochloric acid, water, and brine then dried over MgSO4.
After evaporation to remove solvent, the crude product was
purified by column chromatography on silica gel with 20%
ethyl acetate in petroleum ether (bp 60–90 ◦C) to afford 7
(11.4 g, 61%) as pale yellow solid, mp 228.6–229.5 ◦C (Ref. [19]
value: 229–230 ◦C), Rf 0.25 (petroleum ether/ethyl acetate, 2:1,
v/v). 1H NMR (CDCl3) ı 7.53 (d, J = 2.9 Hz, 1H), 7.33 (d, J = 8.5 Hz,
1H), 7.07 (dd, J = 8.5 and 2.9 Hz, 1H), 5.24 (s, 1H), 2.74 (dd,
J = 16.9 and 3.3 Hz, 1H), 2.64 (s, 1H), 2.22–2.55 (m), 1.74–2.08 (m),
2.
Experimental
2.1.
General procedures
All chemical reagents were purchased from commercial
sources and used as received unless other statements. Melt-
ing points were determined on a WRS-2A capillary melting
apparatus and the quoted temperatures were uncorrected. 1
H
NMR and 13C NMR spectra were recorded on a Bruker AM
400 spectrometer. CDCl3 was used as solvent and chemical
shifts recorded were internally referenced to Me4Si (0 ppm). IR
spectra were obtained on a Thermo Electron Corporation Nico-
let 380 FT-IR spectrophotometer. Mass spectra were recorded
on a Finnigan-MAT-8430 instrument using electron ioniza-
tion (EI) at 70 eV. X-ray crystal structure was measured on a
Bruker Smart CCD diffractometer by using Mo K␣ radiation at
293 K.

490
steroids 7 3 ( 2 0 0 8 ) 488–494
1.57–1.66 (m), 1.24–1.43 (m), 0.90 (s, 3H). IR (KBr pellet) ꢀ 3563,
2.2.4. Synthesis of 17˛-ethinyl-17-hydroxy-3-
3388, 3277, 2965, 2945, 2891, 2865, 1664, 1607, 1498, 1385, 1311,
methoxyestra-1,3,5(10)-triene-6-one
(8)
1259, 1215, 1178, 1133, 1045 cm−1
.
A mixture consisting of 7 (4.34 g, 14 mmol), anhydrous potas-
sium carbonate (6.36 g, 46 mmol), methyl iodide (6 mL, 13.7 g,
97 mmol), and acetone (40 mL) was stirred at room temper-
ature for 36 h then refluxed for 6 h. The reaction mixture
was allowed to cool to room temperature and poured into
water (150 mL). The mixture was extracted with ethyl acetate
(80 mL 4×) and the combined organic phase was dried over
Na2SO4. After evaporation to remove solvent, the crude prod-
uct was purified by column chromatography on silica gel with
petroleum ether/ethyl acetate (2:1, v/v) as eluent or by recrys-
tallization from methylene dichloride/hexane to give 8 (4.3 g,
95%) as pale yellow needles, mp 161.8–162.5 ◦C (Ref. [1] value:
162–163 ◦C from ether), Rf 0.57 (petroleum ether/ethyl acetate,
2:1, v/v). 1H NMR (CDCl3) ı 7.57 (d, J = 2.9 Hz, 1H), 7.36 (d,
J = 8.6 Hz, 1H), 7.12 (dd, J = 8.6 and 2.9 Hz, 1H), 3.85 (s, 3H), 2.75
(dd, J = 16.9 and 3.3 Hz, 1H), 2.63 (s, 1H), 2.23–2.57 (m), 1.72–2.05
(m), 1.56–1.66 (m), 1.26–1.49 (m), 0.90 (s, 3H). 13C NMR (CDCl3)
ı 197.8 (C O), 158.2 (3-C), 139.5 (10-C), 133.4 (5-C), 126.6 (1-C),
121.6 (2-C), 109.7 (4-C), 87.2 (21-C), 79.6 (17-C), 74.4 (22-C), 55.5
(OCH3), 49.3 (13-C), 46.9 (14-C), 44.0 (9-C), 42.6 (7-C), 40.7 (8-
C), 38.9 (16-C), 32.4 (12-C), 25.7 (11-C), 22.5 (15-C), 12.5 (CH3).
IR (KBr pellet) ꢀ 3523, 3275, 2946, 1674, 1605, 1493, 1327, 1286,
1246, 1224, 1038 cm−1. MS (EI, 70 eV): m/z (%) 324 (M+, 77), 256
(50), 241 (68), 227 (12), 214 (15), 200 (60), 188 (100), 174 (19), 161
(23), 145 (10), 128 (12), 115 (18), 103 (11), 91 (11), 77 (13).
2.2.2. Synthesis of
19-norpregna-1,3,5(10)-triene-20-yne-3,6˛,17ˇ-triol (1) and
19-norpregna-1,3,5(10)-triene-20-yne-3,6ˇ,17ˇ-triol (3)
Compound 7 (4.97 g, 16 mmol) was dissolved in methanol
(70 mL). The solution was cooled in ice-water bath and sodium
borohydride (0.73 g, 19.3 mmol) was added in portions. After
the mixture was stirred for 12 h at room temperature the
excess sodium borohydride was destroyed by the addition of
acetone. The reaction mixture was concentrated at reduced
pressure then ethyl acetate (120 mL) and dilute hydrochlo-
ric acid (1N, 60 mL) were added to the residue. The organic
layer was separated and the aqueous phase was extracted
with ethyl acetate (40 mL 3×). The organic phases were com-
bined and washed with water and brine then dried over
MgSO4. After evaporation to remove solvent, the crude prod-
uct was purified by column chromatography on silica gel with
ethyl acetate/petroleum ether (1:1, v/v) to afford 1 (3.20 g,
64%) as pale yellow powder, mp 160–161 ◦C (Ref. [18] value:
158–161 ◦C), Rf 0.29 (petroleum ether/ethyl acetate, 1:1, v/v).
1H NMR (CDCl3) ı 7.17 (d, J = 8.6 Hz, 1H), 7.06 (d, J = 2.5 Hz, 1H),
6.72 (dd, J = 8.5 and 2.7 Hz, 1H), 4.80 (s, 1H), 4.10 (t, J = 7.1 Hz, 1H),
2.60 (s, 1H), 2.23–2.40 (m), 1.68–2.05 (m), 1.21–1.53 (m), 0.90 (s,
3H). IR (KBr pellet) ꢀ 3289, 2935, 2870, 1612, 1499, 1448, 1377,
1290, 1255, 1066, 1047, 1018 cm−1. MS (EI, 70 eV): m/z (%) 312
(M+, 25), 295 (17), 294 (70), 237 (10), 229 (35), 227 (13), 226 (36),
224 (25), 213 (13), 212 (19), 211 (100), 209 (17), 208 (11), 207 (16),
198 (10), 197 (23), 195 (12), 185 (10), 184 (12), 183 (19), 182 (10),
181 (12), 174 (13), 173 (11), 171 (18), 170 (20), 167 (15), 165 (13),
161 (11), 160 (10), 159 (31), 158 (51), 157 (68), 153 (10), 149 (11),
147 (15), 145 (18), 144 (20), 137 (14), 135 (10), 133 (15), 132 (10),
131 (19), 129 (11), 128 (15), 127 (12), 125 (10), 124 (19), 123 (12),
121 (11), 119 (10), 115 (15), 111 (15), 107 (20), 105 (17), 98 (23), 97
(24), 96 (10), 95 (22), 91 (22), 85 (15), 83 (24), 82 (11), 81 (21), 79
(14), 77 (20), 71 (20), 70 (11), 69 (26), 67 (16), 57 (27), 55 (32), 53
(13), 44 (27), 43 (41), 41 (21).
2.2.5. Synthesis of
17˛-ethinyl-3-methoxyestra-1,3,5(10)-triene-6˛,17ˇ-diol (2)
Treatment of 8 with sodium borohydride in a manner simi-
lar to reduction of 7 gave compound 5 as white solid, yield
95%, mp 144.2–145.6 ◦C (Ref. [18] value: 144–146 ◦C), Rf 0.38
(petroleum ether/ethyl acetate, 2:1, v/v). 1H NMR (CDCl3) ı
7.21 (d, J = 8.6 Hz, 1H), 7.15 (d, J = 2.7 Hz, 1H), 6.80 (dd, J = 8.6
and 2.8 Hz, 1H), 4.84 (t, 1H), 3.83 (s, 3H), 2.60 (s, 1H), 2.25–2.38
(m), 1.99–2.08 (m), 1.89–1.93 (m), 1.71–1.85(m), 1.51–1.58 (m),
1.32–1.48 (m), 1.24–1.28 (m), 0.90 (s, 3H). IR (KBr pellet) ꢀ 3412,
2931, 2870, 1610, 1497, 1465, 1383, 1280, 1237, 1090, 1067,
Compound 3 (1.01 g, 20%) was obtained as pale yellow solid
as the minor product, mp 119–120 ◦C (Ref. [18] value: 120 ◦C),
Rf 0.44 (petroleum ether/ethyl acetate, 1:1, v/v).
1038 cm−1
.
2.2.6. Synthesis of
6ˇ,17ˇ-dihydroxy-19-norpregna-1,3,5(10)-triene-20-yne
6-(4-nitrobenzoate) (12)
2.2.3. Synthesis of
3,17ˇ-dihydroxy-19-norpregna-1,3,5(10),6-tetraene-20-yne
(5)
A
solution of diethyl azodicarboxylate (DEAD, 2.40 g,
13.8 mmol) in dry tetrahydrofuran (THF, 10 mL) was added
dropwise to a stirred solution containing 2 (1.80 g, 5.5 mmol),
triphenylphosphine (1.45 g, 5.5 mmol), and 4-nitrobenzoic
acid (2.30 g, 13.8 mmol) in dry THF (30 mL) maintained in
ice-water bath under nitrogen atmosphere. The mixture was
stirred at room temperature overnight. After evaporation
under reduced pressure the residue was chromatographed
on a silica gel column. Upon elution with 50% petroleum
ether in dichloromethane, a fore running yellow coloration
was removed. Further elution with 10% petroleum ether in
dichloromethane gave the desired 4-nitrobenzoate derivative
12 (2.5 g, 95%) as pale yellow solid, mp 86.5–88.0 ◦C, Rf 0.67
(petroleum ether/ethyl acetate, 2:1, v/v). 1H NMR (CDCl3) ı
8.19 (d, J = 8.6 Hz, 2H), 8.11 (d, J = 8.6 Hz, 2H), 7.26 (d, J = 8.3 Hz,
A mixture consisting of 1 and 3 (1.72 g, 5.5 mmol) was heated
to 230 ◦C then was allowed to cool to room temperature. The
residue was dissolved in ethyl acetate and the solution was
dried over MgSO4. After evaporation to remove solvent, the
crude product was purified by column chromatography on sil-
ica gel with petroleum ether/ethyl acetate (3:1, v/v) as eluent
to give 5 (0.99 g, 61%) as pale yellow solid, mp 181.8–183.7 ◦C, Rf
0.64 (petroleum ether/ethyl acetate, 2:1, v/v). 1H NMR (CDCl3)
ı 7.05 (d, J = 7.8 Hz, 1H), 6.66 (dd, J = 8.2 and 2.6 Hz, 1H), 6.51 (d,
J = 2.7 Hz, 1H), 6.35 (dd, J = 9.5 and 2.8 Hz, 1H), 5.91 (dd, J = 9.6
and 1.6 Hz, 1H), 2.54 (s, 1H), 0.82 (s, 3H). IR (KBr pellet) ꢀ 3268,
2923, 2855, 1631, 1606, 1574, 1449, 1381, 1328, 1263, 1191, 1136,
1051, 1015, 798 cm−1
.

steroids 7 3 ( 2 0 0 8 ) 488–494
491
1H), 6.84 (s, 1H), 6.82 (s, 1H), 6.20 (s, 1H), 3.69 (s, 3H), 2.55 (s,
2.2.10. Synthesis of
1H), 2.07–2.26 (m), 1.89–1.97 (m), 1.55–1.77 (m), 1.18–1.27 (m),
0.86 (s, 3H). 13C NMR (CDCl3) ı 166.6 (C O), 160.3 (3-C), 152.9
(4ꢀ-C), 138.4 (5- or 1ꢀ-C), 136.6 (1ꢀ- or 5-C), 135.8 (10-C), 133.2
(2ꢀ-C), 129.0 (1-C), 125.9 (3ꢀ-C), 117.4 (2- and 4-C), 89.7 (21-C),
82.0 (17-C), 76.6 (22-C), 74.0 (6-C), 57.7 (OCH3), 51.1 (12-C),
49.5 (13-C), 45.8 (9-C), 41.2 (15-C), 37.1 (7-C), 36.3 (8-C), 35.0
(11-C), 28.3 (10-C), 25.1 (14-C), 15.1 (CH3). IR (KBr pellet) ꢀ 3450,
2940, 1717, 1611, 1528, 1502, 1344, 1272, 1105, 1038, 1009, 853,
720 cm−1. MS (EI, 70 eV): m/z (%) 475 (M+, 12), 308 (57), 240 (29),
226 (20), 225 (100), 184 (28), 173 (21), 172 (67), 171 (89), 159 (23),
158 (32), 124 (43), 121 (20), 115 (21), 108 (20), 104 (17), 65 (22), 55
(14).
17˛-ethinyl-3-methoxyestra-1,3,5(10),9(11)-tetraene-17-ol
(10)
A mixture containing 9 (0.50 g, 1.7 mmol), anhydrous potas-
sium carbonate (0.76 g, 5.5 mmol), methyl iodide (0.7 mL, 1.6 g,
11.3 mmol), and acetone (10 mL) was stirred at room tempera-
ture for 45 h then was allowed to cool to room temperature.
After water (20 mL) was added the reaction mixture was
extracted with ethyl acetate (20 mL 3×) and the combined
organic phase was dried over Na2SO4. After evaporation to
remove solvent, the crude product was purified by column
chromatography on silica gel with petroleum ether/ethyl
acetate (3:1, v/v) to give 10 (0.45 g, 86%) as pale yellow needles,
mp 144.7–145.9 ◦C, Rf 0.60 (petroleum ether/ethyl acetate, 3:1,
v/v). 1H NMR (CDCl3) ı 7.57 (d, J = 8.0 Hz, 1H), 6.60 (brs, 1H), 6.72
(dd, J = 8.0 and 2.5 Hz, 1H), 6.17 (t, 1H), 3.83 (s, 3H), 2.87 (m, 2H),
2.78 (m, 1H), 2.60 (s, 1H), 2.36 (m, 1H), 2.01–2.09 (m, 4H), 1.93
(m, 1H), 1.85 (m, 1H), 1.48 (m, 1H), 1.40 (m, 1H), 0.91 (s, 3H).
IR (KBr pellet) ꢀ 3463, 3254, 2972, 2927, 2890, 2874, 2833, 1606,
2.2.7. Synthesis of
17˛-ethinyl-3-methoxyestra-1,3,5(10)-triene-6ˇ,17ˇ-diol (4)
To
a flask containing 12 (2.38 g, 5.0 mmol) were added
methanol (20 mL) and THF (20 mL) followed by LiOH·H2O
(0.67 g, 16.0 mmol). The mixture was stirred at room temper-
ature overnight. The solvent was evaporated under reduced
pressure, and to the residue was added ethyl acetate (65 mL),
saturated ammonium chloride solution (22 mL), and 1.0N
hydrochloric acid (18 mL). The organic layer was separated and
the aqueous phase was further extracted with ethyl acetate
(15 mL 3×). The combined organic extract was dried with
anhydrous MgSO4 and evaporated to a solid residue. Chro-
matography on a silica gel column eluted with 20% ethyl
acetate in petroleum ether gave the desired 6␤-alcohol 4 (1.1 g,
67%) as pale yellow solid, mp 198.5–199.5 ◦C (Ref. [18] value:
199–200 ◦C), Rf 0.36 (petroleum ether/ethyl acetate, 2:1, v/v).
1499, 1295, 1230, 1111, 1057, 1032 cm−1
.
3.
Results and discussion
The thermal (178 ◦C) degradation products 1, 3, 5, and 7 were
synthesized starting from norethindrone (11). It was first
reported by Wiechert and co-workers that norethidrone could
be oxidized to 6-keto EE (7) by oxygen in DMF containing potas-
sium acetate at 120 ◦C [21]. This procedure was followed and
the yield of compound 7 was about 40% [18,19]. We found
that the yield of 7 could be improved up to 61% by prolong-
ing the reaction time from 12 h to 18 h. And the oxidation
procedure could be simplified by replacing oxygen with air
without substantial decrease in yields (Scheme 1). Reduction
of 7 with sodium borohydride in methanol afforded a mix-
ture of the 6␣-hydroxy isomer (1) and the 6␤-hydroxy isomer
(3) by a similar procedure as reported [18]. The conversion
was about 84% and the produced mixture was separated by
column chromatography to give 1 and 3 in a yield of 64%
and 20%, respectively. Heating a mixture of 1 and 3 at 230 ◦C
resulted elimination of the secondary alcohols to afford 5 in
61% yield.
Methylation of compound 7 with methyl iodide in the
presence of potassium carbonate afforded 8, the minor degra-
dation product of mestranol, in high yield (95%). Reduction
of 8 with sodium borohydride showed high stereoselectivity,
contrary to the reduction of 7. The 6␣-hydroxy isomer (2) was
obtained in over 95% yield after chromatography and no 6␤-
hydroxy isomer (4) was isolated. The later could be prepared
by transconfiguration of 2 through an esterification/hydrolysis
process as shown in Scheme 1. Mitsunobu reaction between
compound 2 and 4-nitrobenzoic acid in the presence of DEAD
and triphenyl phosphine produced the 4-nitrobenzoate 12 in
95% yield. Hydrolysis of 12 in the presence of lithium hydrox-
ide in THF/H2O afforded the 6␤-hydroxy isomer 4 in about
67% yield, thus providing a practical and scalable preparation
method for the 6␤-hydroxy isomer 4.
2.2.8. Synthesis of
17˛-ethinyl-3-methoxyestra-1,3,5(10),6-tetraene-17-ol (6)
A flask containing 2 (0.76 g, 2.33 mmol) was heated to 230 ◦C
then was allowed to cool to room temperature. The formed
brown solid was dissolved in ethyl acetate and the solution
was dried over MgSO4. After evaporation to remove solvent,
the crude product was purified by column chromatography
on silica gel with petroleum ether/ethyl acetate (4:1, v/v) to
give 6 (0.66 g, 92%) as pale yellow solid, mp 124.4–125.3 ◦C, Rf
0.58 (petroleum ether/ethyl acetate, 4:1, v/v). 1H NMR (CDCl3)
ı 7.17 (d, J = 8.3 Hz, 1H), 6.74 (dd, J = 8.3 and 2.5 Hz, 1H), 6.65 (d,
J = 2.4 Hz, 1H), 6.45 (dd, J = 9.6 and 2.5 Hz, 1H), 5.97 (d, J = 9.6 Hz,
1H), 3.80 (s, 3H), 2.60 (s, 1H), 2.25–2.40 (m), 2.03–2.14 (m),
1.87–1.95 (m), 1.69–1.77 (m), 1.43–1.57 (m), 1.26 (t), 0.89 (s, 3H).
IR (KBr pellet) ꢀ 3386, 3273, 3026, 2934, 2867, 2830, 1604, 1568,
1485, 1279, 1257, 1148, 1060, 1035, 1011 cm−1
.
2.2.9. Synthesis of 3,17ˇ-dihydroxy-19-norpregna-
1,3,5(10),9(11)-tetraene-20-yne
(9)
Compound 9 was synthesized as reported in Ref. [19] and
was obtained as pale yellow solid, mp 181.1–181.9 ◦C (Ref. [19]
value: 180–182 ◦C), Rf 0.53 (petroleum ether/ethyl acetate, 2:1,
v/v). 1H NMR (CDCl3) ı 7.51 (d, J = 7.5 Hz, 1H), 6.57 (brs, 1H),
6.65 (dd, J = 7.5 Hz, 1H), 6.15 (brs, 1H), 3.77–2.85 (m), 2.59 (s, 1H),
2.32–2.36 (m), 1.83–2.07 (m), 1.25–1.63 (m), 0.89 (s, 3H). IR (KBr
pellet) ꢀ 3387, 3286, 2927, 2927, 1629, 1607, 1459, 1384, 1294,
Compound 6 was synthesized as shown in Scheme 2. Cotter
et al. reported an indirect synthesis of 6 without its physical
data [18]. Compound 2 was first transformed by acetylation
1232 cm−1
.

492
steroids 7 3 ( 2 0 0 8 ) 488–494
Scheme 1
with acetic anhydride to its monoacetate 13 and diacetate
14, which could be separated by chromatography. When 13
was heated at 230 ◦C, the C-6 secondary acetate was elimi-
nated to yield 6 as an oil after chromatographic separation.
We improved the preparative procedure of 6 by direct heating
of compound 2 at 230 ◦C, to afford 6 as a pale yellow solid in
92% yield after purification with column chromatography. The
chemical structure of 6 was fully characterized by 1H NMR, IR
spectrum, and melting point measurements.
Compound 9, a major oxidative transformation product
of EE, was synthesized starting from commercially available
estrone by a three-step sequence as reported by Hurley and
co-workers [19]. Methylation of 9 with methyl iodide and
potassium carbonate at room temperature produced 10 in 86%
yield as shown in Scheme 3, providing a practical synthetic
method of compound 10, a photodecomposition product of
mestranol [22] for the first time. Single crystals suitable for X-
ray crystal diffraction of 10 were obtained by recrystallization
Scheme 2

steroids 7 3 ( 2 0 0 8 ) 488–494
493
Scheme 3
Fig. 2 – Crystal structure of compound 10.
boronate esters: efficient access to antigenic C-3 linked
from ethyl acetate. The crystal structure which was shown in
Fig. 2 undoubtedly identified the stereochemistry of 10.
In summary, synthetic procedures of ten degradation or
photodecomposition products of mestranol and ethinyl estra-
diol were detailed. A practical method for scalable preparation
of 17␣-ethinyl-3-methoxyestra-1,3,5(10)-triene-6␤,17␤-diol (4)
by Mitsunobu reaction was described. The preparative proce-
dure of 17␣-ethinyl-3-methoxyestra-1,3,5(10),6-tetraene-17-ol
(6) was simplified. A four-step synthetic protocol for 17␣-
ethinyl-3-methoxyestra-1,3,5(10),9(11)-tetraene-17-ol (10) was
also presented. Synthesis of other degradation or photode-
composition products of mestranol and ethinyl estradiol was
optimized and their structures were fully characterized.
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Acknowledgments
Financial support of the project by Program for Changjiang
Scholars and Innovative Research Team in University (No.
IRT0526) and Shanghai Natural Science Foundation (No.
06ZR14001) was acknowledged.
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