First total synthesis of 5-hydroxy-3-methyl-4-propylsulfanyl-5 h -furan-2-one: A cancer chemopreventive agent

Article abstract of DOI:10.1055/s-0030-1260004

The first total synthesis of 5-hydroxy-3-methyl-4-propylsulfanyl-5H-furan- 2-one, a newly discovered natural product with anticancer property is described by two different routes. A sequence involving an incorporation of a methyl group via a Gilman reagent and a chemoselective reduction of a cyclic anhydride functionality are the key steps. The methods proposed start from easily available starting materials and allow ready preparation of the final compound in good overall yield. Georg Thieme Verlag Stuttgart · New York.

Full text of DOI:10.1055/s-0030-1260004

PAPER
1595
First Total Synthesis of 5-Hydroxy-3-methyl-4-propylsulfanyl-5H-furan-2-
one: A Cancer Chemopreventive Agent
Total
S
ynthesi
a
s
of 5-Hydr
n
oxy-3-meth
j
a
pylsulfanyl
y
-5
H
-furan-2-one P. Borikar,a Vincent Paul,*a Vedavati G. Puranik,a Vilas T. Sathe,a Selene Lagunas-Rivera,b Mario Ordónez*b
a
Division of Organic Chemistry, National Chemical Laboratory, Pune 411008, India
Fax +91(20)25902629; E-mail: vp.swamy@ncl.res.in; E-mail: palacios@ciq.uaem.mx
b
Centro de Investigaciones Quimicas, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, 62209 Cuernavaca, Morelos,
México
Received 2 March 2011; revised 24 March 2011
OH
Abstract: The first total synthesis of 5-hydroxy-3-methyl-4-pro-
pylsulfanyl-5H-furan-2-one, a newly discovered natural product
with anticancer property is described by two different routes. A se-
quence involving an incorporation of a methyl group via a Gilman
reagent and a chemoselective reduction of a cyclic anhydride func-
tionality are the key steps. The methods proposed start from easily
available starting materials and allow ready preparation of the final
compound in good overall yield.
S
O
O
1
Figure 1 Structure of 5-hydroxy-3-methyl-4-propylsulfanyl-5H-
furan-2-one (1)
Key words: Allium cepa, synthesis, Gilman reagent, chemopreven-
tive, selective
cule 1, which could be useful for structure–activity rela-
tionship study.
In our retrosynthetic analysis (Scheme 1), we envisioned
that the target molecule 1 could be obtained from com-
mercially available maleic anhydride (4). The 5-hydroxy
functionality in 1 could be prepared from cyclic anhydride
2 via selective reduction of carbonyl group. Cyclic anhy-
dride 2 could be attained from bromomaleimide 3 as a key
intermediate in path A, which could be obtained from ma-
leic anhydride (4). In our other approach, cyclic anhydride
2 could be prepared from bromomethylmaleimide (5),
which could be obtained from citraconic anhydride (6).
Cancer chemoprevention involves prevention, delay, or
reversal of the process of carcinogenesis through inges-
tion of dietary or pharmaceutical agents.1,2 It also involves
suppression of carcinogen metabolic activation.3 In par-
ticular, the induction of phase II enzymes can offer protec-
tion against toxic and reactive chemical species.4 Many
recent studies have shown that elevation of phase II en-
zymes, such as NAD(P)H:quinone reductase (QR) and
glutathione S-transferase (GST), correlates with protec-
tion against chemically induced carcinogenesis in animal
models,5,6 in the stage of promotion7 as well as initation.5
OH
O
S
S
5-Hydroxy-3-methyl-4-propylsulfanyl-5H-furan-2-one (1)
(Figure 1), a g-hydroxybutenolide derivative was first iso-
lated from Allium cepa (green onion) by Xiao and Parkin
in 2007.8 The g-hydroxybutenolide [5-hydroxy-2-(5H)-
furanone] is an important moiety, found in many bioactive
natural products.9 The preliminary biological evaluation
revealed that the target molecule 1 induced phase II drug
metabolizing enzyme, QR up to 5.55-fold compared to the
control (CD = 15.6 mg/ml). Moreover, compound 1 dou-
bled GST activity at the upper end of the dose range.
However, to the best of our knowledge, the synthesis of
compound 1 has not been reported in the literature and
taking into account the important biological activities, we
initiated the development of a flexible strategy for the
synthesis of this molecule.
O
O
O
O
1
2
path B
O
path A
O
Br
Br
N
N
O
O
5
3
O
O
Herein, we describe a concise and an efficient approach,
designed to afford the first total synthesis of target mole-
O
O
O
O
4
6
Scheme 1 Retrosynthetic analysis of 1
SYNTHESIS 2011, No. 10, pp 1595–1598
x
x.
x
x
.
2
0
1
1
Advanced online publication: 15.04.2011
DOI: 10.1055/s-0030-1260004; Art ID: Z24011SS
© Georg Thieme Verlag Stuttgart · New York

1596
S. P. Borikar et al.
PAPER
As illustrated in Scheme 2, the total synthesis of target HRMS and 13C NMR spectral data in full agreement with
1
molecule 1 commenced with the known compound 3, those reported in the literature.8 In the H NMR data for
which can be easily prepared from maleic anhydride 4 compound 1, the hydroxyl proton appeared as a broad sin-
(path A).10 Reaction of bromomaleimide 3 with propane- glet at 4.27 ppm, instead of the reported doublet at 3.3
1-thiol in N,N-dimethylformamide at 90 °C afforded thio- ppm. Also, H-5 proton of compound 1 appeared as a sin-
maleimide 7 in 61% yield, as a consequence of a nucleo- glet instead of the reported doublet. Its structure was fur-
philic substitution. Subsequently, bromination of 7 with ther confirmed by X-ray crystal structure analysis. The
molecular bromine in the presence of triethylamine in ORTEP diagram of 1 is given in Figure 2.
dichloromethane at 0 °C to room temperature furnished
the bromide 8 in 92% yield. The next step was the incor-
poration of the methyl group at the C-3 position, which
was the key step for the synthesis of 1. The displacement
of the bromo group by a methyl group using Grignard re-
agent (MeMgCl) in anhydrous tetrahydrofuran afforded a
complex reaction mixture and isolation of the desired
product was difficult. Hence, we planned to introduce the
methyl group using Gilman reagent. Freshly prepared
Me2CuLi11 from copper(I) iodide and 1.6 M methyllithium
in hexane at –78 °C in anhydrous tetrahydrofuran reacted
with 8 to afford the key intermediate methyl thiomaleim-
ide 9 in 63% yield. Alkaline hydrolysis of 9 with aqueous
5 M potassium hydroxide in absolute ethanol under reflux
furnished the cyclic anhydride 2 in 60% yield.12 Finally,
the selective reduction of carbonyl group at C-5 position
in cyclic anhydride 2 with 0.5 equivalent of sodium boro-
hydride in anhydrous methanol gave a mixture of two re-
gioisomers 1 (64%) and 10 (28%), which were separated
by flash column chromatography. Compound 1 exhibited
Figure 2 ORTEP plot of the X-ray crystal structure of 1
O
O
S
Br
Further, the confirmation of synthetic 5-hydroxy-4-meth-
N
a
N
yl-3-proplysulfanyl-5H-furan-2-one (10) was accom-
plished on the basis of 1H NMR, 13C NMR, 13C DEPT, and
HMBC spectral data. In the HMBC spectrum (Figure 3),
the H-6 proton of the methyl group is strongly correlated
with the C-3, C-4 and C-5 carbons through two or three
bonds. The H-5 proton is strongly correlated with C-2 and
C-4 and weakly correlated with the C-6 carbon. Hence,
we conclude that the methyl group is placed in between
the hydroxy and sulfur groups with strong bonding.
O
O
7
3
O
S
c
N
b
Br
O
8
O
O
S
S
d
N
O
O
S
3
O
2
O
8
7
1
O
5
9
9
2
4
OH
H3C6
S
OH
H
O
10
e
O
Figure 3 Significant 1H–13C long-range correlations observed from
HMBC spectra of compound 10
1
+
O
S
In retrosynthetic path B, bromomethylmaleimide (5) was
prepared from commercially available citraconic anhy-
dride (6) by simple bromination reaction followed by nu-
cleophilic substitution reaction with propane-1-thiol
affording methyl thiomaleimide 9 in good yield. Further
alkaline hydrolysis of 9 and selective reduction of cyclic
anhydride 2 gave final molecule 1 (Scheme 3). In this ap-
proach, we designed an alternative route, avoiding the use
of a Gilman reagent.
O
OH
10
70:30
Scheme 2 Reagents and conditions: (a) propane-1-thiol, DMF,
90 °C, 61%; (b) Br2, Et3N, CH2Cl2, 0 °C to r.t., 92%; (c) Me2CuLi,
THF, –78 °C, 63%; (d) aq 5 M KOH, EtOH, reflux, 2 h, 60%; (e)
NaBH4, MeOH, 0 °C to r.t. (64% for 1, 28% for 10).
Synthesis 2011, No. 10, 1595–1598 © Thieme Stuttgart · New York

PAPER
Synthesis of 5-Hydroxy-3-methyl-4-propylsulfanyl-5H-furan-2-one
1-Benzyl-3-(propylthio)-1H-pyrrole-2,5-dione (7)
1597
O
O
O
Br
To a stirred solution of 3 (5.0 g, 18.8 mmol) in DMF (50 mL) was
added propane-1-thiol (2.55 mL, 28.2 mmol). The resulting mixture
was then heated at 90 °C for 4 h. H2O (20 mL) was added to the re-
action mixture and extracted with EtOAc (3 × 30 mL). The organic
layer was separated, washed with H2O (2 × 10 mL), dried (Na2SO4),
and then concentrated in vacuo. The residue was purified by silica
gel column chromatography using 2% EtOAc in hexane to afford
compound 7 as a pale yellow crystal; yield: 3.0 g (61%).
a
N
O
O
6
5
b
IR (CHCl3): 3143, 3032, 2926, 2873, 1762, 1556, 1497, 1433, 1397,
1354, 1241, 1141, 1054 cm–1.
O
S
1H NMR (200 MHz, CDCl3): d = 1.07 (t, J = 7.32 Hz, 3 H), 1.76 (m,
2 H), 2.88 (t, J = 7.20 Hz, 2 H), 4.67 (s, 2 H), 6.05 (s, 1 H), 7.28–
7.37 (m, 5 H).
N
O
13C NMR (50 MHz, CDCl3): d = 13.38, 21.10, 33.62, 41.59, 117.15,
9
127.73, 128.40, 128.57, 136.18, 151.64, 167.62, 169.26.
Scheme 3 Reagents and conditions: (a) i. BnNH2, AcOH, reflux, 3
h, NaOAc, ii. Br2, 0 °C to r.t., 86%; (b) propane-1-thiol, DMF, 90 °C,
3 h, 92%.
MS (ESI): m/z = 261 (M)+.
1-Benzyl-3-bromo-4-(propylthio)-1H-pyrrole-2,5-dione (8)
To a stirred solution of 7 (2.69 g, 10.3 mmol) in CH2Cl2 (30 mL) at
0 °C was added Br2 (0.63 mL, 12.4 mmol) dropwise. The resulting
solution was stirred for 5 min at 0 °C, and Et3N (1.72 mL, 12.4
mmol) was added. Then, the reaction mixture was brought to r.t. and
In summary, we have achieved two facile routes for the
first total synthesis of 5-hydroxy-3-methyl-4-propylsulfa-
nyl-5H-furan-2-one (1) from readily available starting
materials, in good overall yields. This methodology can stirred for an additional 1 h. The progress of the reaction was mon-
itored by TLC (10% EtOAc in hexane). H2O (15 mL) was added to
be applied for the synthesis of new analogues of com-
the mixture and extracted with CH2Cl2 (3 × 20 mL). The combined
pound 1.
organic layers washed with H2O (2 × 15 mL), dried (Na2SO4), and
concentrated. The residue was purified by silica gel column chro-
All chemicals were purchased from commercial sources (Sigma-
Aldrich, Lancaster, and Merck) and used without further purification.
Solvents used as reaction media were purchased from local sources
and used after distillation. Petroleum ether (PE) used refers to the
fraction boiling in the range 40–60 °C. Reactions were monitored
using analytical TLC plates (Merck, silica get 60 F254, 0.25 mm),
and compounds were visualized with ultraviolet light. Silica gel
(60–120 and 230–400 mesh) was used for column chromatography.
1H and 13C NMR spectra were recorded on a Bruker Avance DPX
300 and DPX 400 instrument operating at 300 MHz (1H), and 75
MHz (13C) and 400 MHz. Chemical shifts (d) are reported in ppm
using TMS as an internal standard. Mass spectra were obtained on
a Shimadzu GCMS-QP5050 instrument. IR spectra were recorded
on a Perkin-Elmer FTIR 16PC spectrometer. Melting points were
determined on a Büchi instrument and are uncorrected.
matography using 1% EtOAc in hexane to afford compound 8 as a
yellow solid; yield: 3.2 g (92%).
IR (CHCl3): 2900, 1750, 1715, 1530, 1432, 1391, 1200, 1177, 1080,
1040, 759, 665 cm–1.
1H NMR (200 MHz, CDCl3): d = 1.04 (t, J = 7.20 Hz, 3 H), 1.70 (m,
2 H), 3.36 (t, J = 7.46 Hz, 2 H), 4.69 (s, 2 H), 7.26–7.36 (m, 5 H).
13C NMR (50 MHz, CDCl3): d = 12.98, 23.84, 32.69, 42.56, 116.51,
128.00, 128.56, 128.70, 135.70, 143.54, 164.02, 165.65.
MS (ESI): m/z = 341 (M + 1).
1-Benzyl-3-methyl-4-(propylthio)-1H-pyrrole-2,5-dione (9)
Path A: The following reaction was carried out under an inert atmo-
sphere. To a stirred solution of CuI (0.7 g, 3.68 mmol) in anhyd
THF (20 mL) at –78 °C was added a 1.6 M solution of MeLi in hex-
ane (5.75 mL, 9.2 mmol). The solution became dark black. The re-
sulting mixture was stirred for 1 h. To the above solution,
compound 8 (1.0 g, 3.06 mmol) in anhyd THF (5 mL) was added
dropwise and stirred for 4 h at –78 °C. The progress of the reaction
was monitored by TLC (10% EtOAc in hexane). The reaction mix-
ture was quenched by the addition of sat. aq NH4Cl (20 mL) and ex-
tracted with Et2O (3 × 25 mL). The combined organic layers were
washed with H2O (2 × 10 mL), dried (Na2SO4), and concentrated in
vacuo to afford a yellow residue. purification of the residue by silica
gel flash column chromatography using 1% EtOAc in hexane af-
forded compound 9 as a yellow oil; yield: 0.51 g (63%).
3-Bromo-1-benzyl-1H-pyrrole-2,5-dione (3)
A stirred mixture of maleic anhydride (4; 5.0 g, 51.0 mmol) and
benzylamine (5.55 mL, 51.0 mmol) in glacial AcOH (50 mL) was
refluxed for 2 h. After the solution was cooled to 0 °C, Br2 (2.6 mL,
51 mmol) and NaOAc (4.18 g, 51.0 mmol) were added and the re-
action mixture was stirred for 2 h at 0 °C to r.t. Then ice-water (100
g) was added and the mixture was extracted with CH2Cl2 (3 × 30
mL). The combined organic layers were separated and washed with
H2O (20 mL). The combined organic layers were dried (Na2SO4)
and concentrated in vacuo. The residue was purified by column
chromatography on silica gel using 2% EtOAc in hexane to afford
compound 3 as a yellow solid; yield: 4.9 g (36%).
Path B: To a stirred solution of 5 (5.0 g, 17.8 mmol) in DMF (40
mL) was added propane-1-thiol (2.42 mL, 26.7 mmol). The result-
ing mixture was then heated at 90 °C for 3 h. H2O (20 mL) was add-
ed to the reaction mixture and extracted with EtOAc (3 × 30 mL).
The combined organic layers were washed with H2O (2 × 10 mL),
dried (Na2SO4), and concentrated in vacuo. The residue was puri-
fied by silica gel column chromatography using 2% EtOAc in hex-
ane to afford compound 9 as pale yellow crystals; yield: 4.52 g
(92%).
IR (CHCl3): 3059, 2938, 2848, 1955, 1907, 1776, 1651, 1600, 1494,
1402, 1288, 925 cm–1.
1H NMR (200 MHz, CDCl3): d = 4.63 (s, 2 H), 6.79 (s, 1 H), 7.18–
7.28 (m, 5 H).
13C NMR (50 MHz, CDCl3): d = 42.27, 128.03, 128.51, 128.70,
131.36, 131.84, 135.56, 164.93, 168.09.
MS (ESI): m/z = 266 (M + 1).
IR (CHCl3): 3367, 2932, 1704, 1603, 1400, 1348, 1070 cm–1.
Synthesis 2011, No. 10, 1595–1598 © Thieme Stuttgart · New York

1598
S. P. Borikar et al.
PAPER
1H NMR (200 MHz, CDCl3): d = 0.93 (t, J = 7.33 Hz, 3 H), 1.56 (m,
2 H), 1.92 (s, 3 H), 3.16 (t, J = 7.45 Hz, 2 H), 4.57 (s, 2 H), 7.19–
7.28 (m, 5 H).
13C NMR (50 MHz, CDCl3): d = 9.56, 13.04, 23.91, 33.28, 41.77,
127.73, 128.38, 128.61, 135.92, 136.42, 138.29, 167.90, 169.70.
1H NMR (200 MHz, CDCl3): d = 0.99 (t, J = 7.34 Hz, 3 H), 1.59 (m,
2 H), 2.11 (s, 3 H), 2.97 (t, J = 7.45 Hz, 2 H), 5.93 (s, 1 H).
13C NMR (50 MHz, CDCl3): d = 12.73, 13.01, 23.51, 33.32, 98.07,
125.22, 160.71, 169.19.
MS (ESI): m/z = 188 (M)+.
MS (ESI): m/z = 275 (M)+.
1-Benzyl-3-methyl-4-bromo-1H-pyrrole-2,5-dione (5)
3-Methyl-4-(propylthio)furan-2,5-dione (2)
To a stirred solution of citraconic anhydride (6; 15.0 mL, 167
mmol) in glacial AcOH (100 mL) was added benzylamine (18.0
mL, 167 mmol) dropwise in an ice-cooled bath. The mixture was
then heated to reflux for 3 h. After cooling, NaOAc (13.7 g, 167
mmol) and Br2 (12.9 mL, 251 mmol) were added at r.t. Then, the
mixture was poured into ice-water (100 mL) and extracted with
EtOAc (3 × 20 mL). The combined organic phases were dried
(Na2SO4) and the solvent was removed to give the crude product,
which was purified by recrystallization from EtOAc to afford com-
pound 5; yield: 40.2 g (86%).
To a stirred solution of 9 (0.1 g, 0.36 mmol) in absolute EtOH (5
mL) was added dropwise aq 5 M KOH (10 mL). The resulting mix-
ture was then refluxed for 2 h with stirring. The mixture was con-
centrated and the residue was cooled to 0 °C and acidified with aq
2 M HCl and extracted with EtOAc (3 × 15 mL). The combined or-
ganic layers were washed with H2O (2 × 5 mL), dried (Na2SO4), fil-
tered, and evaporated. Purification by column chromatography
using 5% EtOAc in hexane afforded 2 as a dark yellow liquid; yield:
0.040 g (60%).
IR (CHCl3): 3342, 2986, 2306, 1825, 1766, 1712, 1600, 1421, 1265,
1021, 896, 739, 705, 665 cm–1.
IR (CHCl3): 3470, 3059, 2938, 2848, 1955, 1907, 1776, 1651, 1600,
1494, 1402, 1288, 925 cm–1.
1H NMR (200 MHz, CDCl3): d = 1.03 (t, J = 7.33 Hz, 3 H), 1.68 (m,
2 H), 2.05 (s, 3 H), 3.31 (t, J = 7.46 Hz, 2 H).
1H NMR (200 MHz, CDCl3): d = 2.02 (s, 3 H), 4.68 (s, 2 H), 7.26–
7.35 (m, 5 H).
13C NMR (50 MHz, CDCl3): d = 9.99, 12.86, 23.76, 33.04, 136.00,
142.43, 161.95, 163.84.
13C NMR (50 MHz, CDCl3): d = 10.55, 42.18, 124.86, 128.45,
128.59, 128.88, 135.76, 142.18, 165.04, 168.88.
MS (ESI): m/z = 187 (M + 1).
MS (ESI): m/z = 280 (M)+.
( )-5-Hydroxy-3-methyl-4-propylsulfanyl-5H-furan-2-one (1)
To a stirred solution of compound 2 (0.05 g, 0.268 mmol) in anhyd
MeOH (1 mL) was added NaBH4 (0.005 g, 0.0134 mmol) at 0 °C
and stirred for 10 min. The reaction was monitored by TLC (30%
EtOAc in hexane). After the reaction was complete, ice-water (5
mL) was added and extracted with EtOAc (3 × 10 mL). The com-
bined organic phases were washed with H2O (2 × 5 mL), dried
(Na2SO4), filtered, and concentrated in vacuo. The crude product
was purified by silica gel flash column chromatography using 10%
EtOAc in hexane to afford racemic 1 (0.032 g, 64%) as a white crys-
talline solid and racemic 10 (0.014 g, 27.5%) as a pale yellow liquid.
IR (CHCl3): 3432, 2984, 1735, 1446, 1374, 1246, 939, 757 cm–1.
1H NMR (200 MHz, CDCl3): d = 1.05 (t, J = 7.3 Hz, 3 H), 1.71 (m,
2 H), 1.84 (s, 3 H), 3.08 (m, 2 H), 4.27 (s, 1 H), 6.06 (s, 1 H).
13C NMR (50 MHz, CDCl3): d = 9.12, 13.16, 23.39, 32.32, 96.49,
122.55, 157.75, 170.94.
HRMS (ESI): m/z (M+) calcd for C8H12O3S: 188.05072; found:
188.05071.
Acknowledgment
The financial support from Department of Science and Technology,
New Delhi (GAP264126, GAP278826) and CONACYT-MEXICO
(62271) is gratefully acknowledged. We are grateful to Dr. Boiko
Oleksandr and Dr. Dmytro Kovalskyy from Kiev National Univer-
sity, Ukraine for their valuable suggestions.
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(14) CCDC 813937 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
at www.ccdc.cam.ac.uk/conts/retrieving.html [or from the
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44(1223)336033, E-mail:
deposit@ccdc.cam.ac.uk].
The X-ray diffraction data of 1 were carried out on a Bruker
SMART APEX single crystal CCD diffractometer using graphite
monochromated Mo Ka radiation with fine focus tube with 50 kV
and 30mA. Data reduction was carried out with SAINTPLUS, and
the structure was solved and refined SHELX-97 (ShelxTL)13 was
used for structure solution and full matrix least squares refinement
on F2.
Crystal Data for 114
C8H12O3S, MW = 188.24, orthorhombic, space group: Pbca,
a = 11.1790(8) Å, b = 8.0910(6) Å, c = 21.1200(15) Å, a = 90°,
b = 90°, g = 90°, V = 1910.3(2) Å3, Z = 8, Dcalcd = 1.309 mg/m3,
m = 0.305 mm–1, l = 0.71073 Å, crystal size 0.38 × 0.21 × 0.03 mm,
T = 273(2) K, full matrix least squares, R1 = 0.0674, wR2 = 0.1570,
for observed 1670 reflections [I > 2s (I)].
( )-5-Hydroxy-4-methyl-3-propylsulfanyl-5H-furan-2-one (10)
IR (CHCl3): 3393, 2965, 2932, 2873, 1746, 1707, 1635, 1456, 1381,
1339, 1294, 1128, 1087, 1009, 946, 755, 699 cm–1.
Synthesis 2011, No. 10, 1595–1598 © Thieme Stuttgart · New York