FR290581, a novel sordarin derivative: Synthesis and antifungal activity

Article abstract of DOI:10.1016/j.bmcl.2009.01.051

Sordarin is a unique natural product antifungal agent that is an inhibitor of elongation factor 2. To improve biological activity, we synthesized various compounds by novel modification of the aglycone, sordaricin. As a result, we have discovered the nove

Full text of DOI:10.1016/j.bmcl.2009.01.051

Bioorganic & Medicinal Chemistry Letters 19 (2009) 1465–1468
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Bioorganic & Medicinal Chemistry Letters
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FR290581, a novel sordarin derivative: Synthesis and antifungal activity
a
a
a
a
Tadaatsu Hanadate a, , Masaki Tomishima , Nobuyuki Shiraishi , Daisuke Tanabe , Hiroshi Morikawa ,
*
David Barrett a, Satoru Matsumoto b, Kazumi Ohtomo b, Katsuyuki Maki b
a Chemistry Research Labs., Astellas Pharma Inc., 2-1-6 Kashima, Yodogawa-ku, Osaka 532-8514, Japan
b Pharmacology Research Labs., Astellas Pharma Inc., 2-1-6 Kashima, Yodogawa-ku, Osaka 532-8514, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Sordarin is a unique natural product antifungal agent that is an inhibitor of elongation factor 2. To
improve biological activity, we synthesized various compounds by novel modification of the aglycone,
sordaricin. As a result, we have discovered the novel sordarin derivative FR290581. This compound
exhibited superior activity and a good pharmacokinetic profile, and also displayed good in vivo activity
against Candida albicans.
Received 14 November 2008
Revised 17 December 2008
Accepted 9 January 2009
Available online 22 January 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Antifungal
Sordarin
Candida albicans
In recent years, with the growing number of immunosup-
pressed patients (transplants, cancer, AIDS, etc.), invasive mycoses
have become an increasingly serious problem. A number of anti-
fungal agents are used commonly, for example, azoles, polyenes,
and echinocandins, and although treatment of fungal diseases
has been vastly improved, there is still room for improvement.
For example, azoles and polyenes often have side effects and/or
drug–drug interactions, and some organisms are resistant to these
antifungals, whereas echinocandins are not oral agents, and are
only available as a parenteral formulation. Therefore, there is a
need for orally antifungal agents with a novel mode of action and
good oral actvity.1
Sordarin (1) is an antifungal antibiotic that was discovered in
1971 as a metabolite of Sordaria araneosa.2 A number of related
natural products having the sordarin skeleton have also been re-
ported3–5 as antifungal agents such as zofimarin (2)3 and
FR231956 (3)4 (Fig. 1). Semi-synthetic sordarin derivatives which
have improved antifungal activity have also been reported by
several groups (Fig. 2).6 Sordarin and related compounds inhibit
protein synthesis by a mechanism involving selective binding to
the elongation factor 2 (EF-2) and ribosome complex in fungi.7
Sordarin (1) has activity against Candida species, however be-
cause of the weak antifungal activity and poor pharmacokinetic
profile of sordarin itself, in vivo activity is not observed, hence
synthetic efforts reported to date have focused on increasing
antifungal activity and improving pharmacokinetic profile. While
some semi-synthetic sordarin derivatives display good antifungal
activity against Candida species (Fig. 2), the activity in serum and
the pharmacokinetic profile are not sufficiently high.
Herein, we describe the discovery of the novel sordarin deriva-
tive FR290581 (8). To find a more potent antifungal agent, we fo-
cused on modification of sordaricin (7) and synthesized various
novel derivatives. We speculated that the conformation between
the alcohol oxygen of sordaricin (7) and the amino group nitrogen
of the above derivatives (4, 5, and 6)6 was important to the anti-
fungal activity, and that the antifungal activity in serum could be
improved by optimization of the amino group. Moreover, it was
thought that poor stability that originated in the acetal structure
led to a poor PK profile, and we aimed to discover a non-acetal
structure. As a result, we discovered the novel sordarin derivative
FR290581 (8), bearing a unique tri-substituted tetrahydrofuran
ring (Fig. 3).
The synthesis of FR290581 (8) is outlined in Scheme 1. Sor-
daricin (7) was prepared from sordarin according to the reported
method.8 Aldehyde (13) was prepared from sordaricin (7) by
protection of the carboxyl group with diphenyl diazomethane,
protection of the formyl group with ethylene glycol, and oxida-
tion of the alcohol (12) to aldehyde (13) with catalytic TPAP.
Alcohol (14) was obtained by nucleophilic addition reaction9
with the lithium naphthalenide derivative derived from (11).
Bromide (11) was prepared from butyl crotonate according to
Uchida’s general method10 (enolate alkylation with the appropri-
ate iodide, reduction with LAH and mesylation followed by bro-
mination with LiBr). In this addition reaction step, when the
Grignard reagent (Mg) was used instead, the yield was very
low. The R selectivity of this addition reaction to the alcohol
was about 6:1 (ratio determined by NMR). This selectivity is
* Corresponding author. Tel.: +81 6 6390 1143.
E-mail address: tadaatsu.hanadate@jp.astellas.com (T. Hanadate).
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.01.051

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T. Hanadate et al. / Bioorg. Med. Chem. Lett. 19 (2009) 1465–1468
O
O
OH
O
O
O
O
OMe
O
O
O
OMe
OMe
HO
O
HO
O
HO
O
HO
H
HO
H
HO
H
O
O
O
O
O
O
Sordarin (1)
Zofimarin (2)
Hypoxysordarin/FR231956 (3)
Figure 1. Natural sordarin derivatives.
Cl
Cl
N
N
N
HO
O
OH
O
O
O
O
O
HO
H
HO
H
HO
H
O
O
O
O
O
O
GW531920 (4)
R-135853 (5)
Figure 2. Semi-synthetic sordarin derivatives.
6
erate activity against non-Candida albicans pathogens and C. neo-
formans, although no activity against Aspergillus species was
displayed. This result suggested that there may be a possibility to
discover a broad-spectrum oral antifungal agent by further modifi-
cation of FR290581 (8).
Table 2 shows the in vitro antifungal activity against C. albicans
in mouse serum, pharmacokinetics profile and in vivo activity of
FR290581 (8) along with sordarin (1). FR290581 (8) displayed po-
tent in vivo activity, and activity was 100-fold superior against C.
albicans as compared with sordarin (1) in mouse serum.
FR290581 (8) also showed 50-fold higher Cmax and significantly
longer half-life as compared with sordarin (1). The good in vivo
activity reflected the good in vitro activity in serum and good phar-
macokinetic profile.
OH
O
N
HO
H
HO
H
N
O
O
O
O
O
Sordaricin (7)
FR290581 (8)
Figure 3.
Table 3 shows kidney burden in a mouse systemic candidiasis
model of C. albicans. In this model, FR290581 (8) exhibited good
efficacy. Although FLCZ exhibited only
a fungistatic effect,
speculated to be due to the steric hindrance of the i-Pr group
and/or benzhydryl group. The R/S configuration of the major iso-
mer was determined after subsequent transformation to the io-
dide (15). Whilst all diastereomers were present, alcohol (14)
was used for the following step. The key intermediate (15) was
prepared by iodoetherification of alcohol (14) with deprotection.
Fortunately, this reaction progressed in a trans-selective manner.
The diastereomers of iodide were separable by crystallization
with MeOH. The configuration of the major isomer of iodide
(15) was established by X-ray crystallography. In the final step,
amination of iodide (15) furnished the desired product
FR290581 (8).11
Table 1 shows the in vitro antifungal activity of FR290581 (8)
along with sordarin and the clinically used antifungal agent fluco-
nazole (FLCZ). FR290581 (8) is clearly more potent than sordarin
(1) against all fungi. FR290581 (8) exhibited good activity against
Candida species including azole-resistant C. albicans as well as
azole-susceptible strains. Moreover FR290581 (8) exhibited mod-
FR290581 (8) displayed fungicidal activity against kidney fungal
burden. This result suggests that FR290581 (8) may be useful for
prophylaxis and also as a promising treatment.
In conclusion, we have discovered a novel sordarin derivative
FR290581 (8) bearing a unique tri-substituted tetrahydrofuran
ring.12 This tetrahydrofuran ring was prepared by the key reac-
tion of nucleophilic addition and trans-selective iodoetherifica-
tion. FR290581 (8) shows good in vitro activity against Candida
species including azole-resistant C. albicans and moderate activ-
ity against C. neoformans. FR290581 (8) also displayed good
in vivo activity resulting from potent serum MIC and a good
PK profile. Additionally, in a mouse systemic C. albicans infection
model, FR290581 displayed fungicidal activity. These results sug-
gest that FR290581 may be a promising orally antifungal agent.
Further evaluation of FR290581 (8) as a candidate and structure–
activity relationships (SAR) of a series of FR290581-analogs will
be published elsewhere.

T. Hanadate et al. / Bioorg. Med. Chem. Lett. 19 (2009) 1465–1468
1467
iii, iv
i, ii
O
HO
Br
O
9
10
11
R/S=6/1
Br
H
OH
R
11
OH
OH
O
vii
viii
v, vi
HO
BzhO
O
BzhO
O
BzhO
O
O
O
O
O
O
O
O
O
H
Sordaricin (7)
14
12
13
X
ix
O
O
I
N
HO
HO
H
N
O
O
O
O
H
O
15
FR290581 (8)
Scheme 1. Reagents and conditions: (i) n-butyl iodide, LDA, HMPA, THF, À78 °C; (ii) LAH, THF, 0 °C, 55% from 9; (iii) MsCl, DIPEA, CH2Cl2, 0 °C, 82%; (iv) LiBr, acetone, 86%;
(v) diphenyl diazomethane, CH2Cl2, 60%; (vi) TsOH, ethylene glycol, 89%; (vii) TPAP, NMO, CH2Cl2, 85%; (viii) Li, naphthalene, 11, THF, À78 °C, then 13, THF, 44%; (ix) I2,
NaHCO3, CH3CN, crystallization from MeOH, 48%; (x) (2R,6S)-2,6-dimethyl-4-(4-piperidinyl) morpholine, CH2Cl2, 54%.
Acknowledgment
Table 1
MICa of FR290581 (8) against clinical isolates of fungi
We thank our Fermentation research laboratories for supply of
sordarin materials.
Organism
FR290581
Sordarin
FLCZ
C. albicans ATCC90028
C. albicans 22009 (FLCZ-R)
C. glabrata ATCC90030
C. tropicalis 21005
0.5
0.5
1
0.5
8
32
64
64
64
0.125
128
16
0.25
1
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2009.01.051.
C. parapsilosis ATCC22019
>128
C. neoformans TIMM0354
A. fumigatus ATCC204305
4
128
>128
>128
0.25
>128
References and notes
a
Minimum inhibitory concentration (lg/mL).
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Table 2
Serum MIC, PK profiles and in vivo efficacy of FR290581 (8)
FR290581
Sordarin
Serum MICa
Cmax
g/mL)b
T1/2 (h)
0.25
1.0
3.4
32
0.02
0.33
(
l
ED50 (mg/kg)c
2
>40
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a
Minimum inhibitory concentration in mouse serum (
Mouse, 2 mg/kg, po.
Mouse systemic candidiasis model, po.
lg/mL).
b
c
Table 3
Kidney burden in mouse systemic C. albicans infection
D
log cfu/g kidneya
FR290581b
FLCZb
À1.09*
À0.19
a
D
logarithm of kidney burden subtracted from inoculation after 24 h.
b
20 mg/kg, po, n = 5.
p < 0.01 significant to control 0 h (Dunnett comparison).
*

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(50 mg, 0.3 mmol) at room temperature. The mixture was stirred at the same
temperature for 12 h and diluted with AcOEt. The solution was washed with
1.0 M aqueous sodium hydroxide, water, and brine, dried over sodium sulfate,
then concentrated. The residue was purified by HPLC (C18, 20–100%
acetonitrile in water (+0.2% formic acid)). The desired fraction was
concentrated. The residue was diluted with saturated aqueous sodium
hydrogen carbonate and extracted with AcOEt three times. The combined
organic layer was washed with 1.0 M aqueous sodium hydroxide and brine,
dried over sodium sulfate, and concentrated to give the compound of
FR290581 (8) (19.1 mg) as a colorless oil. FABMS (m/z): 637.5 [MÀH]À; IR
(ATR): 2954, 2929, 2866, 2812, 1710, 1452, 1375, 1144, 1074; 1H NMR (CDCl3,
d): 0.77–1.09 (14H, m), 1.11–2.58 (37H, m), 268–3.02 (4H, m), 3.58–3.87 (3H,
m), 4.44–4.60 (1H, m), 5.91–5.99 (1H, m), 9.91 (1H, s).
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ORTEP plot of the key intermediate iodide (15). Details will be provided in a
subsequent publication from these laboratories.
11. Representative synthetic procedure and spectral data for title compound
FR290581 (8). Under a nitrogen atmosphere, to a solution of naphthalene
(8.5 g, 67 mmol) in THF (100 mL) was added lithium turnings (0.4 g, 62 mmol)
at room temperature, and the mixture was stirred at the same temperature for
1 h then cooled to À78 °C. To the cooled mixture was added dropwise 11
(10.0 g, 52 mmol) in THF (15 mL) at the same temperature, and stirring was
continued for 1.5 h. To the mixture was added dropwise 13 (20.0 g, 37 mmol)
in THF (15 mL) at À78 °C, and stirring was continued at the same temperature
for 2 h. The reaction was quenched via addition of water at À78 °C. After being
allowed to warm to room temperature, the mixture was extracted three times
with AcOEt. The combined extract was washed with brine, dried over
magnesium sulfate, and concentrated. The residue was purified by silica gel
column chromatography to give compound 14 (5.3 g) as a white amorphous
solid. To
a
suspension of iodine (2.8 g, 10.3 mmol) and sodium
hydrogencarbonate (3.7 g, 44.0 mmol) in acetonitrile (20 mL) was added a
solution of 14 (3.7 g, 5.7 mmol) in acetonitrile (20 mL) at room temperature.
The mixture was stirred for 1 h. The resulting mixture was quenched by
saturated aqueous sodium thiosulfate solution. The color turned to a white
suspension. After evaporation of acetonitrile, the aqueous layer was extracted
with ethyl acetate three times. The combined organic layer was washed with
saturated aqueous ammonium chloride solution, and brine, dried over
magnesium sulfate, then concentrated. The residue was purified by silica gel
column (hexane/ethyl acetate = 100:0–85:15). The obtained white amorphous
solid was purified by recrystallization from methanol to give 15 (1.9 g).To a
solution of the compound of 15 (38.0 mg, 0.1 mmol) in dichloromethane
(0.2 mL) was added (2R,6S)-2,6-dimethyl-4-(4-piperidinyl) morpholine
12. A tri-substituted tetrahydrofuran ring was optimal for PK properties. Further
details will be disclosed in the full paper.