First synthesis and antiprotozoal activities of divinyl sulfone-modified carbohydrates

Article abstract of DOI:10.1016/j.bmcl.2010.04.056

Divinyl sulfone-modified carbohydrates have been synthesized for the first time by reacting easily available carbohydrate epoxides with thioethanol in a regiospecific fashion. One of the modified divinyl sulfones initiated significant cell death in Entamoeba species and the influence of the anomeric configurations on the biological activities of these sugar-derived divinyl sulfones has been highlighted. The most active compound in this series was found to be devoid of any toxicity.

Full text of DOI:10.1016/j.bmcl.2010.04.056

Bioorganic & Medicinal Chemistry Letters 20 (2010) 3777–3780
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
First synthesis and antiprotozoal activities of divinyl sulfone-modified
carbohydrates
Tarun Kumar Pal a, Tuli Dey b, Arindam Chakrabarty b, Debanjana Dey a, Sudip K. Ghosh b,
,
*
Tanmaya Pathak a,
*
a Department of Chemistry, Indian Institute of Technology Kharagpur, Kharagpur 721 302, India
b Department of Biotechnology, Indian Institute of Technology Kharagpur, Kharagpur 721 302, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Divinyl sulfone-modified carbohydrates have been synthesized for the first time by reacting easily avail-
able carbohydrate epoxides with thioethanol in a regiospecific fashion. One of the modified divinyl sulf-
ones initiated significant cell death in Entamoeba species and the influence of the anomeric configurations
on the biological activities of these sugar-derived divinyl sulfones has been highlighted. The most active
compound in this series was found to be devoid of any toxicity.
Received 1 September 2009
Revised 28 February 2010
Accepted 15 April 2010
Available online 18 April 2010
Ó 2010 Published by Elsevier Ltd.
Keywords:
Divinyl sulfone
Carbohydrates
Antiprotozoal
Entamoeba histolytica
Entamoeba invadens
Along with other socio-economic problems in developing coun-
tries, diarrhoea is one of the major contributors to childhood mor-
tality and morbidity, causing an estimated 2.5 million deaths per
year and long term effect on growth and cognitive functions.1 Pro-
tozoan parasites2 including Entamoeba histolytica are responsible
for 34 million to 50 million symptomatic cases of amoebiasis
worldwide each year, causing 40–100 thousand deaths annu-
ally.1c–e It is well established that cysteine proteases are important
virulence factors of various infectious agents and the main proteo-
lytic enzymes in many protozoan parasites1 including E. histolyti-
ca.3 Entamoeba invadens, the encystation model of parasite
E. histolytica also reported to have multiple cysteine proteases.4,5
Vinyl sulfones in general are known to inhibit cysteine proteases
through Micheal addition of the thiol residue on to electron deficient
double bond.6 Although different classes of organic molecules such
as peptides, proteins, etc. functionalized with vinyl sulfone group
have shown wide-ranging interesting biological compounds, divinyl
sulfone (DVS) or 1,10-sulfonylbisethene (H2C@CHSO2CH@CH2) is
capable of reacting with wide-ranging nucleophiles to afford disub-
stituted or cyclic derivatives. It may be argued therefore that a divi-
nyl sulfone analogue would be more efficient than monovinyl
sulfone analogues such that it would be able to alkylate two biolog-
ical nucleophiles at the same time. Although the biological impor-
tance of DVS was recognized way back in 1940s,7 it was studied
recentlyforitsinhibitorypropertiesagainstglyceraldehyde-3-phos-
phate dehydrogenase,8a inducible VCAM-1 expression,8b SrtA, a
transpeptidase required for cell wall protein anchoring and viru-
lence in Staphylococcus aureus,8c cysteine protease of Plasmodium
falciparum,8d etc. Functionalized divinyl sulfones were screened
as anti-inflammatory9a and tumor cells growth inhibitory9a
agents.9b–d However, the utilization of the DVS functional group in
biology is restricted to a great extent because of the non-availability
of suitable and efficient strategies for the synthesis of functionalized
divinyl sulfones, especially DVS skeleton attached to chiral moieties
such as carbohydrates.
Our study required an easy access to relatively large amount of
divinyl sulfone-modified carbohydrates. A retrosynthetic analysis
of the route to target compounds having divinyl sulfone group in
the five-membered rings necessitated the introduction of
a
ASCH2CH2OH group at the C3 position of a furanosyl carbohydrate
in. After several trial reactions we concluded that the easiest and
general way of forming a CAS bond would be the regioselective
opening of epoxides derived from carbohydrates with the sulfur
nucleophile generated from mercaptoethanol (HSCH2CH2OH). Since
these vinyl sulfones were to be subjected to biological studies, it was
necessary to generate only one regioisomer from these ring opening
reactions. Wethereforetookadvantageoftheregioselectiveopening
of epoxides imparted by the anomeric configuration of the sugar
epoxides. On the other hand, since the reactions of vinyl sulfone-
modified pent-2-enopyranosides are influenced to a great extent
* Corresponding authors. Tel.: +91 322 283342; fax: +91 322 282252.
E-mail addresses: sudip@hijli.iitkgp.ernet.in (S.K. Ghosh), tpathak@chem.
iitkgp.ernet.in (T. Pathak).
0960-894X/$ - see front matter Ó 2010 Published by Elsevier Ltd.
doi:10.1016/j.bmcl.2010.04.056

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T. K. Pal et al. / Bioorg. Med. Chem. Lett. 20 (2010) 3777–3780
by the anomeric configuration10 we planned to study the antipara-
sitic properties of both - and b-anomeric divinyl sulfones.
Thus, the trityl protected
-anomeric lyxo-epoxide 110 was re-
acted with mercaptoethanol in the presence of TMG to generate
3. Compound 3 was oxidized to the sulfone 4 using MMPP. Both
the hydroxyl groups of 4 were mesylated and consequent elimina-
tion of the mesyl groups in the presence of pyridine produced the
desired divinyl sulfone 7 in 64% overall yield. To establish the gen-
eral applicability of the synthetic strategy and compatibility of this
OH
OMe
X
RO
a
RO
RO
OMe
OMe
O
O
O
O
(a)
(c)
a
O2S
OH
9 R = Tr
10 R = Bn
11 R = Tr, X = S
(b)
(b)
15 R = Tr
16 R = Bn
12 R = Tr, X = SO2
13 R = Bn, X = S
14 R = Bn, X = SO2
approach with other protecting groups, the benzyl protected
a-
anomeric epoxide 210 was also reacted with mercaptoethanol in
the presence of TMG to generate 5. Oxidation of 5 to the sulfone
6 and the mesylation of the latter compound afforded the benzyl
protected divinyl sulfone 8 in 52% overall yield (Scheme 1).
In order to synthesize the b-anomeric analogues of 7 and 8, the
trityl protected b-anomeric ribo-epoxide 910 and the benzyl pro-
tected b-anomeric epoxide 1010 were converted to thio derivatives
11 and 13, respectively, following the procedure described in
Scheme 1. Compounds 11 and 13 were oxidized to sulfones 12
and 14 in the usual manner. The sulfones were converted to the
desired vinyl sulfones 15 (53%) and 16 (45%) via mesylation and
elimination (Scheme 2).11 It should be noted that in both cases
(Schemes 1 and 2), only C3-sulfonylated compounds were isolated.
Since compounds 3/5 and 11/13 remained contaminated with
high-boiling mercaptoethanol, these compounds were directly
taken for next synthetic steps and the final vinyl sulfones were ob-
tained as pure materials.
Scheme 2. Synthesis of b-anomeric furanosyl-modified divinyl sulfone. Reagents
and conditions: (a) mercaptoethanol, TMG, DMF, 5 h, 90 °C; (b) MMPP, MeOH, 6 h,
rt; (c) MsCl, py, 0–4 °C, 24 h (for 15, yield 53%; for 16, yield 45%) (in three steps).
Table 1
IC50 values of metronidazole [Mtz], 7, 8, 15, 16 against E .histolytica and E. invadens
Compounds
IC50 (lM) values
E. histolytica
E. invadens
Metronidazole
7
8
15
16
2.5
3.0
25
30.1
17
37.86
24.35
32.93
19.5
9.3
IC50 values were calculated using Prism Graphpad software. IC50 value presented
here is the average of at least three experiments done in triplicate.
We selected four modified divinyl compounds 7/8 and 15/16 to
detect their amoebicidal and growth inhibition effect. E. histolytica
and E. invadens cells were maintained using TYIS-33 medium at 37
and 25 °C, respectively. Stock (10 mM) of 7, 8, 15 and 16 was
prepared by dissolving them in DMSO. Approximately 5 ꢀ 105/mL
cells were incubated in presence of modified compounds at
Cell viability assay for 16, compound showing the best inhibi-
tory property amongst compounds screened (Table 1) was per-
formed with MCF7 (breast cancer) and AH927 (feline fibroblast)
cell lines.14,15 It has been observed (Fig. 1) that the vinyl sulfone
16 has no cytotoxic effect against both cancer cell (MCF7) and nor-
mal cell (AH927).
In summary, the quest for sugar-based antiparasitic new chem-
ical entities has led to the synthesis of densely functionalized divi-
nyl sulfones which are constructed on chiral appendages like
pentofuranosyl carbohydrates using easily accessible 2,3-O-anhy-
dro sugars as starting materials. One of the divinyl sulfones 16 ini-
tiated significant cell death in E. invadens and is devoid of any
notable toxicity. This preliminary study suggests that the anomeric
configuration may have a role in determining the antiparasitic
properties of this new class of compounds which is also in line with
their chemical properties. This first ever report on the biological
properties of a vinyl sulfone-modified carbohydrate in general
and divinyl sulfone-modified carbohydrate in particular is
expected to trigger research on a new line of antiamoebic agents
as well as other antiparasitic drugs.
concentration ranging from 0 to 100 lM. DMSO and metronidazole
were used as negative and positive controls, respectively. After
24 h incubation, cells were washed with 1ꢀ PBS and live cells were
counted using hemocytometer in presence of trypan blue. All the
compounds found to show amoebicidal effect within 12 h. The
IC50 values of each compound were calculated using Prism Graph-
pad software (Table 1).
It should be noted that the b-anomeric vinyl sulfones 15, 16 are
more active than their
a-anomeric analogues 7, 8, respectively
(Table 1). This observation highlights the influence of the anomeric
configurations on the antiparasitic activities of these compounds
which is in line with the reaction patterns of these compounds with
nucleophiles such as primary amines. We observed that the a-ano-
meric vinyl sulfone 7 reacted with one equivalent of benzylamine
to produce the cyclic derivative 17 in 48 h whereas the b-anomeric
vinyl sulfones 15 under similar reaction conditions produced the
cyclic derivative 18 at a much faster rate in 6 h (Scheme 3).12,13
TrO
X
RO
RO
RO
O
OH
O
(c)
O
O
O
(a)
7
15
Y
NBn
OMe
OMe
OMe
O2S
O2S
X
1 R = Tr
2 R = Bn
17 X = H; Y = OMe, Z = Bn
18 X = OMe; Y = H, Z = Bn
OH
7 R = Tr
8 R = Bn
3 R = Tr, X = S
19 X = H, Y = OMe, Z = CH2CH2OCOp-NO2Ph
20 X = OMe, Y = H, Z = CH2CH2OTr
(b)
(b)
4 R = Tr, X = SO2
5 R = Bn, X = S
6 R = Bn, X = SO2
Scheme 3. Reactions of
a- and b-anomeric furanosyl-modified divinyl sulfones.
Reagents and conditions: (17) benzylamine, MeOH, rt, 48 h, 97%; (18) benzylamine,
MeOH, rt, 6 h, 95%; (19) i—ethanolamine, MeOH, rt, 60 h; ii—p-nitrobenzoyl
chloride, py, rt, 2 h, 55% (in two steps); (20) i—ethanolamine, MeOH, rt, 60 h;
ii—trityl chloride, py, rt, 3 days, 58% (in two steps).
Scheme 1. Synthesis of
and conditions: (a) mercaptoethanol, TMG, DMF, 5 h, 90 °C; (b) MMPP, MeOH, 6 h,
rt; (c) MsCl, py, 0–4 °C, 24 h (for 7, yield 64%; for 8, yield 52%) (in three steps).
a-anomeric furanosyl-modified divinyl sulfone. Reagents

T. K. Pal et al. / Bioorg. Med. Chem. Lett. 20 (2010) 3777–3780
3779
A. Supplementary data
MCF 7
AH927
MTT assay
3
2.5
2
Crystallographic data (excluding structure factors) for the struc-
tures in this paper have been deposited with the Cambridge Crys-
tallographic Data Center as supplementary publication numbers
CCDC 682467 and 682468. Copies of the data can be obtained, free
of charge, on application to CCDC, 12 Union Road, Cambridge CB2
1EZ, UK [fax: +44 (0)1223-336033 or e-mail: deposit@ccdc.cam.a-
c.uk]. Experimental details and spectra of all new compounds asso-
ciated with this article can be found, in the online version.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2010.04.056.
1.5
1
0.5
0
0
1
10 20 30 40 50 100
concentration of compound 16 in µM
References and Notes
Figure 1. Cell viability assay for 16 using MCF7 (breast cancer) and AH927 (feline
fibroblast) cell lines.
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9. (a) Fang, S.-H.; Padmavathi, V.; Rao, Y. K.; Venkata, S. D. R. C.; Thriveni, P.;
Geethangili, M.; Padmaja, A.; Tzeng, Y.-M. Int. Immunopharmacol. 2006, 6, 1699;
For reviews on the biological activities of vinyl sulfones, see: (b) Vicik, R.;
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Figure 2. ORTEP diagram of compound 19.
11. Compound 16:
A mixture of mercaptoethanol (2.94 mL, 42.3 mmol) and
TMG (3.90 mL, 33.8 mmol) in DMF (10 mL) was heated at 60 °C for
30 min. Compound 10 (1 g, 4.23 mmol) was added to this mixture and
the mixture was heated at 90–120 °C for 4–5 h with stirring under N2.
After completion (tlc), the reaction mixture was poured into satd.
solution of NaHCO3 (20 mL) and the product was extracted with EtOAc
(3ꢀ 10 mL). The combined organic layers were dried over anhyd.
Na2SO4, filtered and the filtrate was concentrated under reduced
pressure to get
a gummy residue. The residue was purified over silica
gel column (Eluent/EtOAc/pet ether = 1:1) to get the sulfide 13. To
a
well-stirred solution of 13 in dry MeOH (10 mL) was added MMPP
(6.22 g, 12.69 mmol) and the mixture was stirred for 6 h under N2. After
completion of reaction (tlc), MeOH was evaporated to dryness under
reduced pressure and the residue thus obtained was dissolved in satd.
NaHCO3 solution (20 mL). The solution was extracted with EtOAc (3ꢀ
10 mL). The combined organic layers were dried over anhyd. Na2SO4,
filtered and the filtrate was concentrated under reduced pressure to get
a residue. The residue was purified over silica gel column (Eluent/EtOAc/
pet ether = 3:2) to obtain the sulfone 14. To
a well-stirred solution of
14 in pyridine (10 mL) was added solution of MsCl (1.45 mL,
a
12.69 mmol) in pyridine (5 mL) dropwise at 0 °C under N2. After
completion of the addition, the reaction mixture was kept at +4 °C.
After 24 h (tlc), the reaction mixture was poured into ice-cold water
and the solution was extracted with EtOAc (3ꢀ 10 mL). The combined
organic layers were dried over anhyd. Na2SO4, filtered and the filtrate
Figure 3. ORTEP diagram of compound 20.
was concentrated under reduced pressure to get
a residue. The crude
material was stirred at room temperature with Et3N (2 mL) in DCM
(10 mL). After 2 h (tlc), the reaction mixture was concentrated under
Acknowledgments
reduced pressure to get
a residue. The residue was purified over silica
gel column to afford 16 (0.59 g, 45%) in three steps from 10. Eluent/
T.K.P. and T.D. thank the Council of Scientific and Industrial Re-
search (CSIR), New Delhi, India for fellowships. S.K.G. wishes to
thank CSIR for partial financial support. T.P. thanks the Department
of Science and Technology, New Delhi for financial support.
EtOAc/pet ether (1:3). Gummy liquid. ½a D25:5
ꢁ
(–) 42.24 (c 1.50, CHCl3). 1H
NMR (CDCl3): d3.45 (s, 3H), 3.62–3.70 (m, 1H), 3.80–3.86 (m, 1H), 4.59
(s, 2H), 5.05–5.08 (m, 1H), 5.77 (br s, 1H), 6.08 (d, J = 9.6 Hz, 1H), 6.42
(d, J = 16.6 Hz, 1H), 6.61–6.74 (m, 2H), 7.31–7.35 (m, 5H). 13C NMR

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T. K. Pal et al. / Bioorg. Med. Chem. Lett. 20 (2010) 3777–3780
(CDCl3): d55.4, 71.3 (CH2), 73.3 (CH2), 83.1, 107.3, 127.7, 128.3, 130.3
14. Both the cell lines were grown in DMEM supplemented with heat inactivated
FBS and antibiotics. Confluent cell from each culture flask was then trypsinized
and viable cell count was done by trypan blue solution. Numbers of cells
(2 ꢀ 103) were seeded in each well in a 96-well flat bottomed cell culture plate
and kept at 5% CO2 and 37 °C. After 36 h compound 16 was added to both the
(CH2), 136.8, 137.7 (C), 138.5, 145.9 (C). HRMS [ES+, (M+Na)+]: for
C15H18O5NaS Calcd 333.0771, obsd 333.0773.
12. Compounds 8 and 16 also react with benzylamine under similar conditions
following the similar pattern. However, in this case, 16 produced a single cyclic
product whereas 8 generated an inseparable mixture of cyclic compounds.
13. In order to establish the configurations at C2 and C3 of compounds 17 and 18,
it was necessary to synthesize another set of cyclic compounds 19 and 20 (see
Supporting information). The configurations at C2 and C3 of compounds 19 and
20 were unambiguously established with the help of the X-ray analysis of their
single crystals (Figs. 2 and 3).
cells with different concentrations ranging from 0 to 100 lM and kept for 48 h.
Well without 16 was used as control. After 48 h of treatment with 16, MTT
assay was performed using standard protocol.15
15. Mosmann, T. R. J. Immunol. Methods 1983, 65, 55.