Sugar conjugates of fulvestrant (ICI 182,780): Efficient general procedures for glycosylation of the fulvestrant core

Article abstract of DOI:10.1016/j.tetlet.2003.11.140

We have prepared glucose and cellobiose conjugates at the phenolic 3- and hydroxylic 17-positions of the pure anti-estrogenic compound fulvestrant (ICI 182,780), which has recently been approved in the USA for the treatment of advanced postmenopausal breast cancer. Glycosylation at the 17-position was achieved most effectively using pivaloyl protection of the sugar imidates employed, which we found suppressed the competing transacylation reaction and led to improved yields of the product glycosides.

Full text of DOI:10.1016/j.tetlet.2003.11.140

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 1207–1210
Sugar conjugates of fulvestrant (ICI 182,780): efficient general
procedures for glycosylation of the fulvestrant core
Mark J. Thompson,a Edward J. Hutchinson,b Thomas H. Stratford,b Wayne B. Bowlerb
and G. Michael Blackburna,*
aDepartment of Chemistry, Krebs Institute, University of Sheffield, Brook Hill, Sheffield S3 7HF, UK
bStrakan Pharmaceuticals Ltd., Buckholm Mill Brae, Galashiels TD1 2HB, UK
Received 9 October 2003; accepted 28 November 2003
Abstract—We have prepared glucose and cellobiose conjugates at the phenolic 3- and hydroxylic 17-positions of the pure anti-
estrogenic compound fulvestrant (ICI 182,780), which has recently been approved in the USA for the treatment of advanced
postmenopausal breast cancer. Glycosylation at the 17-position was achieved most effectively using pivaloyl protection of the sugar
imidates employed, which we found suppressed the competing transacylation reaction and led to improved yields of the product
glycosides.
Ó 2003 Elsevier Ltd. All rights reserved.
1. Introduction
Similarly, 2,3,6,20,30,40,60-hepta-O-acetylcellobiose-1-a-
trichloroacetimidate 8 was prepared from octaacetyl-
cellobiose via anomeric deacylation using hydrazine
acetate5 (69%) followed by imidate formation (94%).
The known imidates so obtained were condensed with
17-acetylfulvestrant 96 using BF3ÆOEt2 as catalyst by
means of the inverse addition method.6 A solution of
imidate was added dropwise over 5 min to a premixed
solution of the catalyst and alcohol in 1,2-dichloroeth-
ane (1,2-DCE) at )20 °C (Scheme 1). The peracetylated
3-glycosides 10 and 11 so obtained were deprotected
using NaOH in MeOH–water, providing the 3-glucosyl
2 and 3-cellobiosyl 5 conjugates in good overall yield
after purification by reverse-phase chromatography.
The 7a-substituted estradiol derivative fulvestrant
(ICI 182,780) (7a-[9-(4,4,5,5,5-pentafluoropentylsulfinyl)-
nonyl]estra-1,3,5,(10)-triene-3,17b-diol)
1 is a pure
receptor antagonist of estrogen1 and is an effective
treatment for advanced postmenopausal estrogen-
dependent breast cancer.2 As part of an investigation
into the oral bioavailability of 1 we required access
to the 3-glucosyl 2, 17-glucosyl 3, 3,17-bisglucosyl 4, 3-
cellobiosyl 5, and 17-cellobiosyl 6 conjugates (Fig. 1).
Fulvestrant is currently an injectable product with low
oral bioavailability. These compounds were expected to
enhance oral bioavailability and also improve water
solubility.
Previous exploration6 of the 17-glucuronidation of 1
found significant advantage in the use of the inverse
addition technique and also established that use of the
more hindered isobutyryl protecting group for the gly-
cosyl donor reduced the amount of transacylation, the
major reaction when using acetyl protection. We sought
to investigate these findings further by exploring the
reaction of 3-acetylestradiol7 with a range of differently
protected glucose imidates (Table 1) and found pivaloyl
protection to be the favored choice.
Preparation of the phenolic 3-glycosides 2 and 5 proved
relatively straightforward. 2,3,4,6-Tetra-O-acetylglu-
cose-1-a-trichloroacetimidate 7 was prepared from
pentaacetylglucose via selective anomeric deacylation
using benzylamine3 (90%) followed by cesium carbon-
ate-mediated reaction with trichloroacetonitrile4 (80%).
Keywords: Glycosylation; Carbohydrate chemistry; Trichloroacetim-
idate chemistry; Protecting groups; Estradiol derivatives.
* Corresponding author. Fax: +44-0-114-222-9346; e-mail: g.m.
blackburn@shef.ac.uk
Despite its apparent usefulness we found little prece-
dent8 for the use of the promising intermediate, 2,3,4,6-
tetra-O-pivaloylglucose-1-a-trichloroacetimidate9 12 in
0040-4039/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2003.11.140

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M. J. Thompson et al. / Tetrahedron Letters 45 (2004) 1207–1210
OH
OR2
HO
(CH2)9S(O)(CH2)3C2F5
R1O
(CH2)9S(O)(CH2)3C2F5
1 Fulvestrant
2
3
4
5
6
R1 = Glc (β-D-glucosyl), R2 = H
R1 = H, R2 = Glc
R1 = R2 = Glc
R1 = Cel (β-D-cellobiosyl), R2 = H
R1 = H, R2 = Cel
RCO2
RCO2
RCO2
O
RCO2
RCO2
RCO2
O2CR
O
RCO2
O
RCO2
O
O
CCl3
RCO2
RCO2
NH
R = Me
O
CCl3
NH
8
R = Me
7
16 R = CMe3
12 R = CMe3
Figure 1. The structure of fulvestrant, imidates, and the glycoside derivatives prepared.
OR1
OAc
(i)
BF3.OEt2,
DCE, —20 ˚C
OR1
R1O
R2O
(ii)
O
imidate, 7 or 8
DCE
(CH2)9S(O)(CH2)3C2F5
HO
(CH2)9S(O)(CH2)3C2F5
O
OR1
9
R1 = R2 = Ac (98%)
10
2
11
5
NaOH/MeOH/H2O
R1 = R2 = H (75%)
R1 = Ac, R2 = Ac4Glc (88%)
R1 = H, R2 = Glc (84%)
NaOH/MeOH/H2O
Scheme 1. Glycosylation at the phenolic 3-position of 17-acetylfulvestrant.
Table 1. Comparative yields for glucosylation of 3-acetylestradiol
using differently protected glucose imidates (reactions were performed
at )20 °C using 0.5 equiv BF3ÆOEt2 and 1.5 equiv of imidate)
(Scheme 2) giving conjugate 3. In a similar fashion,
direct glycosylation of fulvestrant (80%) using imidate
12 (3.5 equiv) and BF3ÆOEt2 (2.5 equiv) to give inter-
mediate 15 followed by deprotection of the pivaloyl
groups (63%) provided the 3,17-bisglucoside 4.
Imidate protecting Yield of 3-acetylestra-
group
Yield of transacyl-
ation product, %
diol 17-glucoside, %
Benzoyl
Isobutyryl
Pivaloyl
22
23
68
45
37
In order to access the 17-cellobiosyl conjugate 6, the
novel 2,3,6,20,30,40,60-hepta-O-pivaloyl-cellobiose-1-a-
trichloroacetimidate 16 was prepared by peracylation of
Trace
b-D-cellobiose with pivaloyl chloride (26%; a heptapi-
valoyl product was also separated chromatographically)
followed by anomeric deprotection (67%) and imidate
formation (88%). Glycosylation of 3-benzoylfulvestrant
13 using 16 proceeded in high yield (Scheme 3); how-
ever, in the deprotection of glycoside 17, 17-cellobiosyl
conjugate 6 was only obtained as a minor product
(16%). The major product (54%) was established by
NMR and MS to be a dipivaloyl derivative of 6 whose
regiochemistry is unknown.12 Optimization of this final
step is therefore necessary to effect complete deprotec-
tion of 17.
the glycosylation of hindered alcohols. We established
that 12 could best be prepared by anomeric deprotection
of pentapivaloylglucose10 using hydrazine monohydrate
in THF (50 °C, 7 d, 61%) and subsequent imidate for-
mation by the usual method (81%).
Glycosylation of 3-benzoylfulvestrant6 13 using 12 was
also found to be very efficient (81% yield). The peracyl-
ated glycoside 14 could best be deprotected using tetra-
ethylammonium hydroxide in 2-propanol–water11

M. J. Thompson et al. / Tetrahedron Letters 45 (2004) 1207–1210
1209
OR2
OR2
OH
O
O
R2O
(i)
BF3.OEt2,
OR2
DCE, –20 ˚C
(ii)
imidate 12,
DCE,
R1O
BzO
(CH2)9S(O)(CH2)3C2F5
(CH2)9S(O)(CH2)3C2F5
(81%)
14 R1 = Bz, R2 = Piv
R1 = R2 = H (Yield 65%)
13
Et4N+OH-/H2O/PriOH
3
Scheme 2. Glycosylation at the hindered 17-position using a pivaloyl-protected imidate.
OR2
R2O
OR2
OR2
OR2
OH
O
O
O
R2O
O
(i)
BF3.OEt2,
OR2
DCE, –20 ˚C
(ii)
imidate 16,
DCE,
R1O
BzO
(CH2)9S(O)(CH2)3C2F5
(CH2)9S(O)(CH2)3C2F5
(78%)
17 R1 = Bz, R2 = Piv
R1 = R2 = H (Yield 16%)
Et4+OH-/PriOH/H2O
13
6
Scheme 3. Pivaloyl protection of the imidate of the disaccharide cellobiose also leads to effective glycosylation of the hindered 17-hydroxy group.
Table 2. Summary of yields obtained for the glycosylation step in the
synthesis of compounds 2–6
2,3,4,6-tetra-O-pivaloylglucose-1-a-trichloroacetimidate
12 (3.9 g, 1.75 equiv) in the same solvent (16 ml) was
added dropwise over 5 min. The mixture was stirred for
4 h, by which time the temperature had risen to +10 °C.
Solvent was evaporated and the residue taken up in
DCM then washed with satd aq NaHCO3 and then
water. After evaporation of solvent, purification by
silica column chromatography (20–25% EtOAc in tolu-
ene) gave pure glycoside 14 (3.27 g, 81%) as a white
foam after re-evaporation from ether.
Substrate
Sugar
Imidate protect- Yield, %
ing group
(product)
17-Ac Fulvestrant 9 Glucose
Ac
98 (10)
88 (11)
81 (14)
78 (17)
80 (16)
17-Ac Fulvestrant 9 Cellobiose Ac
3-Bz Fulvestrant 13 Glucose Piv
3-Bz Fulvestrant 13 Cellobiose Piv
Fulvestrant 1 Glucose Piv
In conclusion, we have prepared five glycoside deriva-
tives of fulvestrant and have achieved high glycosylation
yields using the appropriate choice of protecting groups
(Table 2). These results particularly establish the use-
fulness of pivaloyl-protected sugar imidates in the gly-
cosylation of the hindered 17-position and show the
advantage offered by this approach over more com-
monly employed protection strategies. Although they
have not been widely used, we hope the present work
will establish their value in the general glycosylation of
hindered alcohols. The inverse addition method
was found to be superior for glycosylation using both
acetyl- and pivaloyl-protected imidates. Finally, only the
2.2. Representative deprotection procedure
Acylated glycoside 14 (1.20 g, 0.99 mmol) was dissolved
in 2-propanol (19 ml) and the solution cooled to 0 °C
then tetraethylammonium hydroxide (35% w/w aq soln,
2.9 ml, 7 equiv) was added dropwise. After stirring for
9 h, the reaction was complete as evidenced by TLC (10%
MeOH–DCM). Aqueous methanol was added then the
pH adjusted to 7.0 by addition of glacial AcOH. After
evaporation, the residue was purified on a Lichroprep
RP-18 column using a gradient of 50–95% MeOH in
water to provide 17-b-glucosylfulvestrant 3 (0.50 g, 65%).
dH (400 MHz, DMSO-d6) 9.00 (br s, 1H), 7.05 (d, 1H,
J ¼ 9.1 Hz), 6.50 (dd, 1H, J ¼ 9.1 Hz, 2.5 Hz), 6.41 (d,
1H, J ¼ 2.5 Hz), 4.96–4.82 (br m, 3H), 4.50–4.44 (br t,
1H), 4.21 (d, 1H, J ¼ 7.5 Hz), 3.75 (t, 1H, J ¼ 6.9 Hz),
3.69–3.62 (m, 1H), 3.48–3.38 (m, 1H), 3.15–3.07 (m, 1H),
3.07–2.99 (m, 2H), 2.95–2.54 (m, 7H), 2.47–2.27 (m, 2H),
2.27–2.11 (m, 2H), 2.01–1.83 (m, 4H), 1.69–1.41 (m, 5H),
1.41–1.08 (m, 18H), 0.96–0.82 (br m, 1H), 0.78 (s, 3H).
HRMS (FAB+), calcd for C38H58O8F5S M+H 769.3773,
found 769.3765 (MHþ). HPLC (Luna-ODS column;
1 ml minꢀ1; MeCN KClaq (30 mM), pH 2.2, 60:40; k
275 nm), rt 2.88 min, purity 99.7%.
b-glycosides were isolated in every case described (e.g.,
3
0
0
0
in 14, dH1 ¼ 4.62, d, JH1 –H2 ¼ 7.2 Hz).
2. Experimental
2.1. Representative procedure for glycosylation
Boron trifluoride diethyl etherate (0.65 ml, 1.5 equiv)
was added to a solution of 3-benzoylfulvestrant 13
(2.36 g, 3.32 mmol) in dry 1,2-DCE (16 ml) at )20 °C
(ice–salt cooling) under Ar. After 45 min, a solution of

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M. J. Thompson et al. / Tetrahedron Letters 45 (2004) 1207–1210
3. Sim, M. M.; Kondo, H.; Wong, C.-H. J. Am. Chem. Soc.
1993, 115, 2260–2267.
Acknowledgements
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K. W.; Scheinmann, F.; Stachulski, A. V. J. Chem. Soc.,
Perkin Trans. 1 2001, 3037–3041.
We thank AstraZeneca UK Ltd. for supplying fulve-
strant for use in this work and for funding the project.
We would particularly like to acknowledge the help of
Dr. Shampa Das and Dr. Paul Gellert at AstraZeneca
UK Ltd.
7. Illi, V. O. Tetrahedron Lett. 1979, 26, 2431–2432.
8. Becker, D.; Galili, N. Tetrahedron Lett. 1992, 33, 4775–
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