Synthesis of a series of promising isobenzofuranones for the treatment of acute mucositis caused by chemo- and radiotherapy

Article abstract of DOI:10.1055/s-0033-1340060

A small series of 3,5-dihydroxy-7-methoxy-3,6-dimethylshyisobenzofuran- 1(3H)-one analogues of the immunosuppressant, mycophenolate mofelite (MMF), has been identified during a screening campaign as possible mediators to prevent mucositis. Herein, we pres

Full text of DOI:10.1055/s-0033-1340060

LETTER
▌2397
lSetyternthesis of a Series of Promising Isobenzofuranones for the Treatment of
Acute Mucositis Caused by Chemo- and Radiotherapy
Promising Isobenzofuranones for Treatment of Acute Mucositis
Maude Patoor, Philippe Neuner, Heinz Ruffner, Carsten Spanka, Laure C. Bouchez*
Novartis Institutes for BioMedical Research, Fabrikstrasse 22-1.051.17, 4054 Basel, Switzerland
Fax +41(61)3248001; E-mail: laure.bouchez@novartis.com
Received: 27.08.2013; Accepted after revision: 08.10.2013
Abstract: A small series of 3,5-dihydroxy-7-methoxy-3,6-dimethyl-
isobenzofuran-1(3H)-one analogues of the immunosuppressant,
mycophenolate mofelite (MMF), has been identified during a
screening campaign as possible mediators to prevent mucositis.
Herein, we present a general seven-step approach for the prepara-
tion of small molecule mycophenolate mofelite analogues, which
are readily available for further biological evaluation in our muco-
sitis model.
Key words: isobenzofuranones, mycophenolic acid, Alder–Rickert
reaction, acute mucositis
Chemotherapy agents continue to be the mainstay of can-
cer treatment, but unwanted deleterious effects on highly
proliferative tissues remain a significant drawback. Fur-
thermore, as radiation also affects rapidly dividing cells,
patients receiving combined therapies are at even greater
risk for treatment-related side-effects. Among these
belongs the manifestation of mucositis, a general term
that describes the damage of mucosal epithelial cells as a
result of the cytotoxic effects of chemo- or radiation
therapy.
Laure Bouchez was born in Orleans (France) in 1976. She graduated
from the École Nationale Supérieure de Chimie Mulhouse in 2000. In
November 2004, she received her PhD in Organic Chemistry from the
EPFL (Lausanne, Switzerland) working with Prof. Pierre Vogel on
sulfur dioxide mediated syntheses of polyene natural products. In
February 2005, she joined the group of Prof. Alois Fürstner at the
Max-Planck-Institüt für Kohlenforschung (Mülheim-an-der-Ruhr,
Germany) where she was part of the team who accomplished the total
synthesis of amphidinolides H, G and B. In April 2008, she worked in
the group of Prof. Peter G. Schultz at the Scripps Research Institute
(La Jolla, San Diego, USA) on the identification of chemical and bi-
ological modulators of human stem cell fates. Since November 2010,
she is a Research Investigator at the Novartis Institute for BioMedical
Research in Basel.
The occurrence of oral mucositis constitutes a significant
burden for patients undergoing chemo- or radiotherapy
for solid tumors. Almost all patients treated with radiation
therapy for head and neck cancer will develop some de-
gree of oral mucositis, while patients treated with both ra-
diation and chemotherapy have been found to present with
more severe mucositis and increased morbidity.1 Despite
the prevalence of side-effects related to these treatments,
clinically approved approaches to minimize epithelial
damage caused by these invasive therapies are very re-
stricted. Current treatments for mucositis are limited to
palliative care, such as good oral care, or moderate thera-
peutic remediation.2
cover new classes of chemical modulators that could be
used in the context of radio- and chemotherapy to prevent
the development of severe oral mucositis, and thus reduc-
ing peritransplant morbidity.
During our screening campaign, using the HEK293T cell
line stably expressing a β-catenin/TCF luciferase reporter
construct (STF),4 a series of small molecule isobenzofura-
nones possessing a pentasubstituted aromatic ring were
identified. All the compounds from this series yielded sig-
nificant STF activity values [EC50 (compound 2) = 800
nM and EC50 (compound 4) = 2 μM].5 Structurally, these
isobenzofuranones resemble mycophenolate mofetil
(MMF), a pro-drug of mycophenolic acid (MPA), ap-
proved by the Food and Drug Administration (FDA) (Fig-
ure 1),6 suggesting a role for this recurring motif in the
mechanism of mucositis alleviation.
It has become clear that a mucositis-specific pain protocol
addressing all elements of pain reduction including tissue
damage, sensitization of pain receptors, and elaboration of
inflammatory and pain mediators, has yet to be devel-
oped.3 The identification of drugs further minimizing, or
ideally preventing the development of mucositis would
mark a major leap forward in anticancer therapy. To this
end, we established a series of cellular assays4 that are
amenable for high-throughput screening in order to dis-
To assist in future studies investigating the role of isoben-
zofuranone moieties as post-chemotherapeutic modula-
tors of gastrointestinal side effects, the following
SYNLETT 2013, 24, 2397–2400
Advanced online publication: 23.10.2013
DOI: 10.1055/s-0033-1340060; Art ID: ST-2013-B0827-L
© Georg Thieme Verlag Stuttgart · New York
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6

2398
M. Patoor et al.
LETTER
allowing for the completion of the synthesis of our small
collection of isobenzofuranone derivatives.
O
N
Mitsunobu reaction
O
OH
R = isoprenoid residue
Gilman organo-
cadmium
R
OH
HO
O
O
O
O
OMe
O
+
OH
O
OH
O
O
OMe
O
O
OH
O
O
Alder–Rickert reaction
MeO
MeO
Scheme 1 Retrosynthetic approach for the synthesis of a small col-
lection of isobenzofuranones
MPA
MMF
Inexpensive 2-methylcyclohexane-1,3-dione (5) served as
the point of departure, which was advanced to the enol
ether 6 by a previously reported procedure.8 The interme-
diate enol silyl ether 7 underwent a [4+2] cycloaddition in
presence of dimethyl acetylenedicarboxylate, at –10 °C,
followed by a thermal elimination at 120 °C to give
dimethyl 5-hydroxy-3-methoxy-4-methylphthalate (8)
Figure 1 Structures of mycophenolic acid (MPA) and its pro-drug,
mycophenolate mofetil (MMF)
communication reports a general strategy to access a
small selection of highly substituted isobenzofuranones
containing isoprenoid residues (Figure 2, analogues 1–4).7
OMe
OMe
O
O
O
O
O
OMe
O
O
(i)
OH
OH
O
O
6
5
OMe
O
TMSO
OMe
(ii)
(iii, iv)
HO
OMe
OMe
1
O
O
8
7
2
OMe
O
O
OMe
(v)
a) RX
OMe
OMe
(vi)
O
O
O
O
OMe
OMe
OH
OH
b) ROH
RO
RO
OH
OH
O
O
O
9a–c (see Table 1)
10a–c
OMe
O
OMe
O
1
(vii)
(viii)
O
O
2
RO
3
RO
O
Me
OH
H
O
H
OH
11a: 56%
11b: 53%
11c: 40%
3
4
NOE
NOE
Figure 2 A small selection of 3,5-dihydroxy-7-methoxy-3,6-dime-
thylisobenzofuran-1(3H)-ones containing terpenoid residues
1: 58%
2: 41%
3: 40%
Scheme 2 Reagents and conditions: (i) MeOH, PTSA, r.t., 16 h,
69%; (ii) LDA, TMSCl, THF, –78 °C, 2 h; (iii) DMAD, xylene, –10 °C,
2 h; (iv) 120 °C, 2 h, 36% over 3 steps; (v) see Table 1; alkylation un-
der conditions (a) R–X, K2CO3, DMF, 85 °C, 3 h; under conditions
(b) ROH, DIAD, PPh3, THF, r.t., 16 h; (vi) KOH (15% in MeOH),
reflux, 5 h, quant.; (vii) Ac2O, 105 °C, 3 h; (viii) (a) MeMgBr (3 M
in Et2O), CdCl2, Et2O, 40 °C, reflux, 1 h; (b) 11, Et2O, 40 °C, reflux,
4 h; (c) (1) HCl (1 M), (2) TBAF (1 M in THF), r.t., 4 h in the case
of 3. LDA = lithium diisopropylamide, DIAD = diisopropyl azodi-
carboxylate.
The proposed retrosynthesis of the corresponding myco-
phenolic acid analogues is depicted in Scheme 1. We en-
visioned a flexible approach based on the Alder–Rickert
sequence, involving a suitably substituted cyclohexadiene
(7) and dimethyl acetylenedicarboxylate (DMAD). A va-
riety of terpenoid residues will be introduced by standard
alkylation or under Mitsunobu reaction conditions, thus
Synlett 2013, 24, 2397–2400
© Georg Thieme Verlag Stuttgart · New York

LETTER
Promising Isobenzofuranones for Treatment of Acute Mucositis
2399
(Scheme 2).9 Alkylation proceeded smoothly to enable the
incorporation of the corresponding side chain10 (Table 1,
entries 1–3). The coupling partners a and b were commer-
cially available, whereas c was prepared in a three-step
operation (Scheme 3). Riley’s oxidation of geranyl ace-
tate,11 followed by protection of the resulting alcohol to
give the corresponding tert-butyldiphenylsilyl ether and
saponification of the acetate moiety delivered coupling
partner c, readily available for the synthesis of intermedi-
ate 9c.
OMe
OMe
O
O
O
O
OH
O
OH
O
(i), (ii)
OH
2
4
O
OH
O
Scheme 4 Reagents and conditions: (i) (PhSe)2, BAIB, KSCN,
MeCN, 5 min, r.t., then 2, MeCN, 3 h, r.t., 34%; (ii) NaHCO3, NaIO4
in H2O, 1,4-dioxane, 16 h, r.t., 55%.
(i)–(iii)
In summary, we have successfully developed an efficient
methodology for the synthesis of a small collection of iso-
benzofuranone compounds containing terpenoid motifs.
These first lead compounds will be tested in our rodent
models for radiotherapy-induced intestinal and oral mu-
cositis. This experimental concept will be subject to fur-
ther scrutiny using other disease models in order to allow
potential therapeutic applications in the context of other
gastrointestinal diseases. Biological data concerning the
protective properties of our lead compounds against
mucositis will be reported in due course.
TBDPSO
coupling partner c
geranyl acetate
Scheme 3 Reagents and conditions: (i) geranyl acetate, salicylic
acid, H2SeO3, t-BuOOH (70% in H2O), CH2Cl2, 16 h, r.t., 73%; (ii)
TBDPSCl, imidazole, 16 h, r.t., 94%; (iii) K2CO3, 4 h, r.t., 94%.
Subsequent hydrolysis by potassium hydroxide (KOH)
(15% in MeOH) was slow but effective, and provided the
required trisubstituted phthalic acid building blocks 10a–
c in essentially quantitative yields. These three intermedi-
ates were then subjected to a solution of refluxing acetic
anhydride to yield the corresponding anhydrides 11a–c.
Gratifyingly, addition of the Gilman cadmium reagent,
formed after addition of one equivalent of anhydrous cad-
mium chloride to a cold solution of two equivalents of
methylmagnesium bromide12,13 furnished the desired
products 1, 2 and 3 in moderate to good yields (Scheme 2,
Table 1).14
Acknowledgment
This work was supported by the Developmental and Molecular Pa-
thways (DMP) and the Global Discovery Chemistry (GDC) depart-
ments at the Novartis Institutes for BioMedical Research (NIBR).
We would like to thank specifically the teams of Dr. Heinz Ruffner,
Dr. Florian Fuchs, Dr. Juerg Hunziker and Prof. Mary J. Sever for
extensive discussions and constructive suggestions.
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synlett.SnuIpofoiprmntgirStanoIuifpog
r
t
iornat
For the preparation of compound 4, we adapted a protocol
from Piancatelli et al.15 where a hypervalent iodine(III) re-
agent, [bis(acetoxy)iodo]benzene (BAIB or PhI(OAc)2],
was involved in a multicomponent reaction to facilitate
the formation of the desired allylic alcohol. As predicted,
the necessary tertiary alcohol motif was attained by oxida-
tive removal of the phenylselenium group with aqueous
sodium periodate in 1,4-dioxane (Scheme 4).16,17
References and Notes
(1) Recombinant human KGF (Palifermin, Amgen) has been
approved for the prevention of oral mucositis in patients
undergoing hematology stem cell transplantation. For
example, see: (a) Murphy, B. A.; Beaumont, J. L.; Isitt, J.;
Garden, A. S.; Gwede, C. K.; Trotti, A. M.; Meredith, R. F.;
Epstein, J. B.; Le, Q.-T.; Brizel, D. M.; Bellm, L. A.; Wells,
Table 1 Incorporation of Coupling Partners 9a–c
Entry
1
Substrate
Coupling partner
Conditions
(v) a
Time
8 h
Yield
51%
9a
Br
2
3
9b
9c
(v) b
(v) b
13 h
16 h
53%
87%
Br
TBDPSO
OH
© Georg Thieme Verlag Stuttgart · New York
Synlett 2013, 24, 2397–2400

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M. Patoor et al.
LETTER
N.; Cella, D. J. Pain Symptom Manag. 2009, 38, 522.
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collected analytical data were in perfect agreement with the
data reported in this preparation.
(12) (a) Yang, H.; Hu, G.-Y.; Chen, J.; Wang, Y.; Wang, Z.-H.
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(13) Reactions carried out without cadmium led to a mixture of
compounds presenting the double addition of the methyl
moiety and the expected mono-alkylated product 11.
(14) The structures of the final compounds were fully
characterized by NMR spectroscopy. They presented NOEs
between H-3 and the methyl and between the methyl and the
hydroxy function as depicted in the isobenzofuran-(3H)-one
model (see Scheme 2).
(15) Margarita, R.; Mercanti, C.; Parlanti, L.; Piancatelli, G.
Eur. J. Org. Chem. 2000, 1865.
(16) See the Supporting Information for the preparation of
compound 3.
(17) 3-Hydroxy-5-{[(2E,5E)-7-hydroxy-3,7-dimethylocta-2,5-
dien-1-yl]oxy}-7-methoxy-3,6-dimethylisobenzofuran-
1(3H)-one (4)
(2) (a) Faccini, L.; Martino, R.; Ferrari, A.; Piñana, J. L.;
Valcárel, D.; Barba, P.; Granell, M.; Delgado, J.; Briones, J.;
Sureda, A.; Brunet, S.; Sierra, J. Eur. J. Haematol. 2012, 88,
46. (b) Qiu, W.; Carson-Walter, E. B.; Liu, H.; Epperly, M.;
Greenberger, J. S.; Zambetti, G. P.; Zhang, L.; Yu, J. Cell
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2001, 27, S3. (f) de Koning, B. A.; Philipsen-Geerling, B.;
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Transpl. 2011, 46, 740. (b) Uharek, L.; Gassmann, W.;
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Ruchholtz, W. Bone Marrow Transpl. 1991, 7, 17.
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Grosshans, B.; Salathe, A.; Zietzling, S.; Beck, V.; Therier,
M.; Isken, A.; Xie, Y.; Zhang, Y.; Hao, H.; Shi, X.; Liu, D.;
Song, Q.; Clay, I.; Hintzen, G.; Tchorz, J.; Bouchez, L. C.;
Michaud, G.; Finan, P.; Myer, V. E.; Bouwmeester, T.;
Porter, J.; Hild, M.; Bassilana, F.; Parker, C. N.; Cong, F.
PLoS One 2012, 7, e40976.
To a stirring suspension of KSCN (84 mg, 0.866 mmol) in
MeCN (1 mL), (PhSe)2 (108 mg, 0.346 mmol) followed by
BAIB (139 mg, 0.433 mmol) were added. The cloudy yellow
mixture was stirred at r.t. for 10 min before the addition of a
solution of compound 2 (104 mg, 0.289 mmol) in MeCN (1
mL). The resulting mixture was stirred at r.t. for 16 h. After
completion of the reaction, the mixture was washed with sat.
NaHCO3–10% Na2S2O3 solution (5 mL) and extracted with
EtOAc (2 × 50 mL). The organic layer was washed with
brine (2 × 50 mL), dried over Na2SO4, filtered and the
volatiles evaporated under reduced pressure to afford the
expected intermediate, (E)-3-hydroxy-5-{[7-isothiocyanato-
3,7-dimethyl-6-(phenylselanyl)oct-2-en-1-yl]oxy}-7-
methoxy-3,6-dimethylisobenzofuran-1(3H)-one as a yellow
oil. Next, to a stirring mixture of NaHCO3 (10.97 mg, 0.131
mmol) and NaIO4 (55.8 mg, 0.261 mmol) in H2O (4 mL) was
added a solution of the phenylselenyl intermediate (50 mg,
0.087 mmol) in 1,4-dioxane (8 mL). The cloudy mixture was
stirred overnight at r.t. Upon completion, the mixture was
washed with sat. NH4Cl solution (2 mL) and extracted with
EtOAc (2 × 25 mL). The organic layer was washed with
brine (2 × 50 mL), dried over Na2SO4, filtered and
concentrated under reduced pressure. The crude residue was
purified on silica gel (FC ISCO, gradient elution: 0–70%
EtOAc in heptane) to afford compound 4 as a colorless oil
(18 mg, 0.048 mmol, 55% yield). 1H NMR (400 MHz,
DMSO-d6): δ = 7.57 (s, 1 H, exchangeable with D2O), 7.02
(s, 1 H), 5.59 (d, J = 14.95 Hz, 1 H), 5.51–5.49 (m, 2 H),
4.73–4.70 (m, 2 H), 4.48 (s, 1 H, exchangeable with D2O),
3.90 (s, 3 H), 2.72 (d, J = 6.35 Hz, 2 H), 2.05 (s, 3 H), 1.71
(s, 3 H), 1.70 (s, 3 H), 1.16 (s, 6 H, 2 × CH3). 13C NMR (100
MHz, CDCl3): δ = 166.4, 163.9, 157.7, 151.7, 141.1, 140.0,
124.6, 122.6, 120.4, 109.7, 104.2, 100.6, 71.4, 66.1, 62.5,
42.2, 30.4, 30.0, 26.6, 17.4, 9.3. LC–MS: m/z = 377 [ M +
H]+; tR = 1.03 min (>99% by LC–MS, UV). ROESY
correlation data are reported in the Supporting Information.
(5) Compounds were tested in an 8-point-dilution manner.
Values are given for the EC50 corresponding to the
maximum relative luciferase activity. Data related to
compounds 1 and 3 are not shown.
(6) (a) Neuman, F.; Graef, T.; Tapprich, C.; Vaupel, M.; Steidl,
U.; Germing, U. Bone Marrow Transpl. 2005, 35, 1089.
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Marrow Transpl. 2006, 37, 235.
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Korean Chem. Soc. 2008, 29, 863.
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J. Antibiot. 2011, 64, 723. (b) Gamboa-Angulo, M. M.;
Escalente-Erosa, F.; Garcia-Sosa, K.; Alejo-Gonzalez, F.;
Delgado-Lamas, G.; Pena-Rodriguez, L. M. J. Agric. Food
Chem. 2002, 50, 1053. (c) Hariprakasha, H. K.; Rao, G. S. S.
Indian J. Chem., Sect. B: Org. Chem. Incl. Med. Chem.
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(10) Paz, J. L.; Rodrigues, J. A. R. J. Braz. Chem. Soc. 2003, 14,
975.
(11) The synthesis of the side chain corresponding to compound
9c was reported in the following patent: Skattebol, L.;
Aukrust, I. R.; Sandberg, M. WO2011117324 A2, 2011. The
Synlett 2013, 24, 2397–2400
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