In vitro and in vivo antimalarial evaluation of semi-synthetic derivatives of gomphostenin

Article abstract of DOI:10.1016/j.bmcl.2010.05.035

A novel series of semi-synthetic gomphostenin derivatives (1-9) were prepared utilizing C-14 hydroxyl group for the first time and studied for their antimalarial properties. In vitro antiplasmodial activity was evaluated against both the chloroquine sensitive and resistant strains of Plasmodium falciparum. Most of the compounds exhibited superior or comparable antiplasmodial activity compared to parent compound, that is, gomphostenin (GN). Based upon in vitro antiplasmodial activity, compounds with IC₅₀ values less than 10 μM were selected for in vivo antiplasmodial evaluation against Plasmodium berghei infection in mice model. GN derivatives 3 and 5 were found to have curative activity with moderate chemosuppression of 65% and 69%, respectively, at the dose level of 150 mg/kg/day.

Full text of DOI:10.1016/j.bmcl.2010.05.035

Bioorganic & Medicinal Chemistry Letters 20 (2010) 4233–4236
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
In vitro and in vivo antimalarial evaluation of semi-synthetic derivatives
of gomphostenin
*
Manisha Sathe, M. P. Kaushik
Discovery Center, Process Technology Development Division, Defence R&D Establishment, Jhansi Road, Gwalior 474 002, MP, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel series of semi-synthetic gomphostenin derivatives (1–9) were prepared utilizing C-14 hydroxyl
group for the first time and studied for their antimalarial properties. In vitro antiplasmodial activity was
evaluated against both the chloroquine sensitive and resistant strains of Plasmodium falciparum. Most of
the compounds exhibited superior or comparable antiplasmodial activity compared to parent compound,
that is, gomphostenin (GN). Based upon in vitro antiplasmodial activity, compounds with IC50 values less
Received 9 February 2010
Revised 22 April 2010
Accepted 12 May 2010
Available online 15 May 2010
than 10 lM were selected for in vivo antiplasmodial evaluation against Plasmodium berghei infection in
Keywords:
mice model. GN derivatives 3 and 5 were found to have curative activity with moderate chemosuppres-
sion of 65% and 69%, respectively, at the dose level of 150 mg/kg/day.
Ó 2010 Elsevier Ltd. All rights reserved.
Antimalarials
Gomphostemma niveum
In vitro
In vivo
Clerodane
Semi-synthesis
Malaria is one of the most important parasitic infections1 of hu-
mans due to its high morbidity and mortality, a threat to over 2 bil-
lion people living in areas of high incidence. Plasmodium
falciparum, the causative agent of the malignant form of malaria,
has high adaptability by mutation and is resistant to various types
of antimalarial drugs, a serious setback to antimalarial programs,
essentially because it precludes the use of cheap and previously
effective drugs like chloroquine. Therefore, in order to decrease
the risk of resistance,2 new families of active compounds are
needed with independent mechanism of action.3 The success of
the antimalarial drug quinine and the discovery of artemisinin,
the most potent antimalarial drug both from plant source have
lead to the study of plants to find out novel antimalarial agents.4
In order to improve the efficacy and pharmaceutical profile, much
attention has been given to the chemical modification5 of bioactive
compounds. Chemical modification of artemisinin6 has resulted
into new derivatives that combine higher antimalarial activity
and bio-availability. For instance, derivatization of artemisinin at
C10 has yielded compounds such as artemether and sodium
artesunate that have already entered the clinics,7 Another impor-
tant derivative, in clinical use, is dihydroartemisinin.8 All these
drugs are characterized for important antiplasmocidal activities
with IC50 values falling in the micro molar range.9 As a result, it
is always necessary to carry out extensive evaluations to determine
the consequences of modifying a structure. As a part of our ongoing
research activities on biologically active compounds, we have re-
cently reported10 the isolation and identification of Gomphoste-
nins (Fig. 1) from the plant Gomphostemma niveum and their
in vitro antimalarial evaluation against P. falciparum.
Gomphostenin (GN) is a clerodane class of diterpene with a
a,b-
unsaturated -lactone ring. From our initial in vitro studies, GN
c
was found to have potential antiplasmodial properties; however,
inhibition of malaria parasite was not comparable to that of
standard antimalarial drug, that is, chloroquine and artemisinin.
Consequently, in search of more effective derivative of GN, we syn-
thesized several derivatives of GN through semi-synthetic route
and herein, we report the synthesis and in vitro as well as
in vivo antiplasmodial evaluation of semi-synthetic GN derivatives
for the first time. The isolation of GN was achieved by the reported
method.10 Further by utilizing the C-14 hydroxyl group of GN, var-
ious derivatives were synthesized (Scheme 1) and characterized.11
The antiplasmodial efficacy of the GN derivatives (1–9) was
evaluated by conventional12in vitro parasite culture method, using
H
O
O
H
O
HO
* Corresponding author. Tel.: +91 751 2343972; fax: +91 751 2340042.
E-mail addresses: mpkaushik@rediffmail.com, kaushik12@sancharnet.in (M.P.
Kaushik).
Figure 1. Gomphostenin (GN).
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.05.035

4234
M. Sathe, M. P. Kaushik / Bioorg. Med. Chem. Lett. 20 (2010) 4233–4236
H
H
O
O
O
O
H
O
H
O
O
H
O
O
O
O
H
F3C
O
O
O
Cl
4
3
H
O
H
O
c
d
F
2
5
b
e
H
H
H
O
O
O
O
O
O
O
O
O
O
S
O
H
O
a
H
H
f
O
O
O
HO
1
6
i
H
g
O
O
H
h
O
O
O
9
O
H
O
O
S
O
H
O
H
O
O
O
O
7
O
H
O
O
H3CO
8
Scheme 1. Reagents and conditions: (a) Cbz-Cl, Et3N, CH2Cl2; (b) CH2N2 (in Et2O), dry DMSO; (c) p-CF3C6H4CH2Br, NaH, DMF; (d) p-ClC6H4CH2Br, NaH, DMF;
(e) p-FC6H4CH2Br, NaH, DMF; (f) MsCl, Et3N, CH2Cl2; (g) (BOC)2O, Et3N, CH2Cl2; (h) p-OCH3C6H4CH2Br, NaH, DMF; (i) TsCl, Et3N, CH2Cl2.
chloroquine sensitive (MRC-2) and chloroquine resistant strain
(RKL9) of P. falciparum. Parasites were cultured in human B (+)
erythrocytes in Rosewell Park Memorial Institute (RPMI)-1640
media (GIBCO-BRL, Paisely, Scotland) supplemented with 25 mM
4-(2-hydroxyethyl)-1-piperazine ethane sulfonic acid (HEPES)
buffer, 10% human AB (+) serum, and 0.2% sodium bicarbonate
(Sigma), and maintained at 5% CO2. Cultures containing predomi-
nantly early ring stages were synchronized by addition of 5%
the test and control. In vitro antimalarial activities of GN deriva-
tives (1–9) as IC50 values for the inhibition of chloroquine sensitive
and resistant strains are summarized in Table 1.
It is evident from the Table 1 that most of the derivatives were
more potent than the parent compound. The introduction of phe-
nyl ring at C-14 position had substantial effect on the inhibition
of malarial parasite. Additionally when the phenyl group was
substituted at 4 positions with Cl or F the activity increased with
D
-sorbitol (Sigma) lysis, used for testing. Initial culture was main-
tained in small vials with 10% hematocrit, that is, 10 L erythro-
cytes containing 1.0% ring-stage parasite in 100 L complete
media. The culture volume per well for the assay was 100 L.
IC50 14 lM and 8.3 lM, respectively. The activity was highest
l
when tri-fluoro substituted methyl was used at 4 position of phe-
nyl group. This emphasizes the fact that presence of fluorine group
and phenyl ring favor the activity. Of the nine compounds, 3 and 5
demonstrated maximum in vitro antiplasmodial activity against
l
l
The number of parasites for the assay was adjusted to 1–1.5% by
diluting with fresh human B (+) red blood cells (RBC). Assays were
carried out in 96-well microtitre flat-bottomed tissue culture
plates incubated at 37 °C for 24 h in the presence of twofold serial
dilutions of compounds and chloroquine diphosphate (CQ) for their
effect on schizont maturation. All the GN derivatives 1–9 were dis-
solved in ethanol and further diluted with RPMI-1640 medium (the
final ethanol concentration did not exceed 0.5%, which did not af-
fect parasite growth). Chloroquine diphosphate was dissolved in
aqueous medium. Tests were carried out in duplicate wells for each
dose of the drugs. Solvent control cultures containing the same
concentrations of the solvent present in the test wells were carried
out with RPMI-1640 containing 10% AB (+) serum. Parasite growth
was found to be unaffected by the solvent concentrations. Growth
of the parasites from duplicate wells of each concentration was
monitored in Giemsa-stained blood smears by counting the num-
ber of schizonts per 100 asexual parasites. Percentage schizont
maturation inhibition was calculated by the formula: (1 À Nt/
Nc) Â 100, where Nt and Nc represent the number of schizonts in
Table 1
IC50 values of GN derivatives (1–9) and chloroquine diphosphate (CQ) against
P. falciparum
Compound
IC50 SD (
l
M) CQ-S
IC50 SD (lM) CQ-R
GN
1
2
3
4
5
6
7
8
115.0 0.018
42.2 0.023
94.4 0.031
4.8 0.012
14.0 0.016
8.3 0.014
69.9 0.011
78.5 0.017
37.6 0.013
26.1 0.018
0.024 0.011
113.5 0.011
43.9 0.017
88.9 0.025
4.4 0.022
18.8 0.028
8.1 0.017
73.3 0.011
84.9 0.021
47.7 0.017
45.8 0.012
0.038 0.017
9
CQ
IC50 values are expressed in micro molar concentrations (
tions. All experiments were realized in triplicate.
lM) standard devia-

M. Sathe, M. P. Kaushik / Bioorg. Med. Chem. Lett. 20 (2010) 4233–4236
4235
Table 2
References and notes
Blood schizonticidal activity of GN derivatives 3 and 5 against P. berghei in mice
during 4-day test
1. Ridley, R. G. Nature 2003, 424, 887.
2. Kano, S. Prog. Med. 2001, 21, 319.
3. Olliaro, P. L.; Yuthavong, Y. Pharmacol. Ther. 1999, 81, 91.
GN derivative
Concentrations
(mg/kg/day)
Average %*
parasitemia
Average %
suppression
4. (a) Bjorkman, A.; Willcox, M.; Marbiah, N.; Payne, D. Bull. WHO 1991, 69, 456;
(b) Bruchfeld, J.; Dias, F.; Hellgren, U.; Eriksson, O.; Andreasson, P. A.; Crato, J.;
Rombo, L. Trop. Med. Parasitol. 1991, 42, 153; (c) Olliaro, P. L. Pharmacol. Ther.
2001, 89, 207; (d) Pandey, A. V.; Tekwani, B. L.; Singh, R. L.; Chauhan, V. S. J. Biol.
Chem. 1999, 274, 19383; (e) Newman, D. J.; Cragg, G. M. J. Nat. Prod. 2007, 70,
461.
3
150
100
50
150
100
50
11.5 0.3
12.4 1.8
17.5 0.6
10.3 2.3
22.3 2.3
26.4 3.4
1.07 0.02
33.7 3.7
65.87 0.6
63.20 2.1
48.40 1.1
69.44 1.3
33.21 1.4
21.66 3.2
96.82 0.3
0
5
5. Avery, M. A.; Muraleedharan, K. M.; Desai, P. V.; Bandyopadhyaya, A. K.;
Furtado, M. M.; Tekwani, B. L. J. Med. Chem. 2003, 46, 4244.
CQ
5
6. (a) Klayman, D. L. Science 1985, 228, 1049; (b) Luo, X. D.; Shen, C. C. Med. Res.
Rev. 1987, 7, 29; (c) Zaman, S. S.; Sharma, R. P. Heterocycles 1991, 32, 1593; (d)
Cumming, J. N.; Ploypradith, P.; Posner, G. H. Adv. Pharmacol. 1997, 37, 253; (e)
Zhou, W. S.; Xu, X. X. Acc. Chem. Res. 1994, 27, 211; (f) Bhattacharya, A. K.;
Sharma, R. P. Heterocycles 1999, 51, 1681.
Negative control
*
P <0.01, values are expressed as mean S.D (n = 3); negative control = saline plus
0.5% Tween-80.
7. (a) Sowunmi, A.; Oduola, A. M. J. Acta Trop. 1996, 61, 57; (b) Adams, P. A.;
Barman, P. A. J. Pharm. Pharmacol. 1996, 48, 183.
8. De Vries, P. J.; Dien, T. K. Drugs 1996, 52, 818.
9. Balint, G. A. Pharmacol. Ther. 2001, 90, 261.
CQ sensitive and CQ resistant parasitic strain. In vitro studies
revealed that all the semi-synthetic derivatives of GN are more ac-
tive than the parent molecule however, less active than chloro-
quine. Based upon in vitro antiplasmodial activity, compounds
10. Sathe, M.; Kaushik, M. P. Bioorg. Med. Chem. Lett. 2010, 20, 1312.
11. Spectroscopic data for GN derivatives 1: viscous colorless liquid, IR (KBr): 1774,
1755, 1660, 1170, 1293 cmÀ1 1H NMR (CDCl3, 400 MHz) d 0.91 (m, 3H), 1.23
.
(m, 1H), 1.39 (m, 3H), 1.41 (m, 2H), 1.47 (m, 2H), 1.66 (m, 2H), 1.8 (m, 3H), 1.85
(m, 1H), 1.89 (m, 2H), 2.23 (m, 2H), 3.80–3.86 (dd, J = 7.5, 7.5 1H), 4.20–4.24
(dd, J = 4.0, 4.0 1H), 5.17 (s, 2H), 5.73 (s, 1H), 4.7 (s, 2H), 7.2 (s, 1H), 7.32–7.47
(m, 5H). 13C NMR (CDCl3, 100 MHz) d 18.2, 18.4, 18.7, 18.8, 21.7, 34.2, 34.7,
34.8, 38.0, 39.5, 40.5, 45.3, 50.2, 65.4, 70.7, 71.2, 125.6, 127.1, 127.3, 127.6,
128.8, 128.9, 134.0, 136, 143.8, 171.2, 171.9, 199.4. ESI-MS 467 (M+H)+; Anal.
Calcd for C28H34O6: C, 72.08; H, 7.35. Found: C, 72.14; H, 7.30. 2: viscous
with IC50 value less than 10 lM were selected for in vivo antiplas-
modial activity evaluation against chloroquine sensitive P. berghei
(ANKA strain) infection in mice model (Table 2) using the classical
4-day suppressive test.13 Each swiss albino mice was inoculated on
day 0, intraperitoneally with 0.2 ml of infected blood containing
about 1 Â 107 P. berghei parasitized red blood cells. Different dilu-
tions of test compounds were prepared by suspending the com-
pound in saline containing 0.5% Tween-80. The animal were
divided into three groups of five mice each and orally adminis-
trated shortly after inoculation with 3 and 5, respectively (50,
100, and 150 mg/kg/day), chloroquine (5 mg/kg/day), and an equal
volume of saline plus 0.5% Tween-80 (negative control) for four
consecutive days (day 0 to day 3), respectively. On the fifth day
(day 4), thin films were made from the tail blood of each mouse
and the parasitemia level was determined by counting the number
of parasitized erythrocytes out of 600 erythrocytes in random
fields of the microscope. Average percentage suppression was cal-
culated as 100 (A À B/A), where A is the average percentage para-
sitemia in the negative control group and B is the average
percentage parasitemia in the test group.
colorless liquid, IR (KBr): 1750, 1735, 1663, 1170, 1333 cmÀ1 1H NMR (CDCl3,
.
400 MHz) d 0.92 (m, 3H), 1.25 (m, 1H), 1.40 (m, 3H), 1.42 (m, 2H), 1.48 (m, 2H),
1.69 (m, 2H), 1.8 (m, 3H), 1.83 (s, 3H), 1.86 (m, 1H), 1.9 (m, 2H), 2.24 (m, 2H),
3.80–3.86 (dd, J = 7.5, 7.5 1H), 4.20–4.25 (dd, J = 4.0, 4.0 1H), 5.74 (s, 1H), 4.7 (s,
2H), 7.1 (s, 1H). 13C NMR (CDCl3, 100 MHz) d 18.3, 18.6, 18.7, 18.9, 21.7, 34.3,
34.7, 34.8, 38.0, 39.5, 40.5, 45.3, 59.6, 65.3, 70.3, 125.6, 134.0, 143.8, 171.2,
171.9, 199.4. ESI-MS 347 (M+H)+. Anal. Calcd for C21H30O4: C, 72.80; H, 8.73.
Found: C, 72.84; H, 8.76. For 3: viscous colorless liquid, IR (KBr): 1750, 1735,
1663, 1400 cmÀ1 1H NMR (CDCl3, 400 MHz) d 0.92 (m, 3H), 1.25 (m, 1H), 1.40
.
(m, 3H), 1.42 (m, 2H), 1.48 (m, 2H), 1.69 (m, 2H), 1.8 (m, 3H), 1.86 (m, 1H), 1.9
(m, 2H), 2.24 (m, 2H), 3.80–3.86 (dd, J = 7.5, 7.5 1H), 4.20–4.25 (dd, J = 4.0, 4.0
1H), 4.71 (s, 2H), 5.74 (s, 1H), 4.7 (s, 2H), 7.1 (s, 1H), 7.35 (t, J = 7.69 1H), 7.54 (t,
J = 7.56 1H), 7.62 (d, J = 8.1 1H), 7.73 (d, J = 7.69 1H). 13C NMR (CDCl3, 100 MHz)
d 18.3, 18.5, 18.7, 18.9, 21.7, 34.3, 34.7, 34.8, 38.0, 39.6, 40.5, 45.3, 65.3, 70.3,
72.2, 122.1, 124.4, 125.2, 125.5, 125.6, 127.2, 127.4, 134.0, 140, 143.8, 171.2,
171.9, 199.4. ESI-MS 491 (M+H)+. Anal. Calcd for C28H33F3O4: C, 68.56; H, 6.78.
Found: C, 68.50; H, 6.72. 4: viscous colorless liquid, IR (KBr): 1770, 1749, 1650,
1170, 980 cmÀ1 1H NMR (CDCl3, 400 MHz) d 0.91 (m, 3H), 1.23 (m, 1H), 1.39
.
(m, 3H), 1.41 (m, 2H), 1.47 (m, 2H), 1.66 (m, 2H), 1.8 (m, 3H), 1.85 (m, 1H), 1.89
(m, 2H), 2.23 (m, 2H), 3.80–3.86 (dd, J = 7.5, 7.5 1H), 4.20–4.24 (dd, J = 4.0, 4.0
1H), 4.63 (s, 2H), 5.73 (s, 1H), 4.7 (s, 2H), 7.2 (s, 1H), 7.34–7.57 (m, 4H). 13C
NMR (CDCl3, 100 MHz) d 18.2, 18.6, 18.7, 18.8, 21.7, 34.2, 34.7, 34.8, 38.0, 39.5,
40.5, 45.3, 50.1, 65.4, 70.7, 73.2, 125.6, 128.7, 128.8, 130, 134.2, 135, 136.6,
143.8, 171.2, 171.9, 199.2. ESI-MS 457 (M+H)+. Anal. Calcd for C27H33ClO4: C,
70.96; H, 7.28. Found: C, 70.92; H, 7.21. 5: viscous colorless liquid, IR (KBr):
In case of in vivo experiment although chemosuppression of
69% and 65% was observed at the highest dose level of 150 mg/
kg/day with GN derivative 3 and 5 however, both the compounds
were found to possess curative activity for more then 28 days as
none of the mice died before D +28. In summary, new semi-syn-
thetic derivatives of GN were prepared and evaluated for antiplas-
1778, 1749, 1640, 1165, 1100 cmÀ1 1H NMR (CDCl3, 400 MHz) d 0.91 (m, 3H),
.
1.23 (m, 1H), 1.36 (m, 3H), 1.43 (m, 2H), 1.45 (m, 2H), 1.62 (m, 2H), 1.8 (m, 3H),
1.85 (m, 1H), 1.89 (m, 2H), 2.23 (m, 2H), 3.81–3.85 (dd, J = 7.5, 7.5 1H), 4.20–
4.24 (dd, J = 4.0, 4.0 1H), 4.60 (s, 2H), 5.73 (s, 1H), 4.7 (s, 2H), 7.2 (s, 1H), 7.17–
7.37 (m, 4H). 13C NMR (CDCl3, 100 MHz) d 18.2, 18.62, 18.7, 18.8, 21.7, 34.2,
34.7, 34.8, 38.0, 39.5, 40.5, 45.3, 52.2, 65.4, 70.7, 73.5, 115.3, 115.4, 129.2,
129.3, 133, 162.1 125.6, 143.6, 171.2, 171.7, 199.3. ESI-MS 441 (M+H)+. Anal.
Calcd for C27H33FO4: C, 73.61; H, 7.55. Found: C, 73.64; H, 7.50. 6: white solid,
modial properties. Compounds with IC50 value less than 10 lM
were selected for in vivo antiplasmodial evaluation against P. berg-
hei infection in mice model. GN derivative 3 and 5 were found to
have curative activity with moderate chemosuppression. It can
be concluded that chemical modification of GN certainly holds
great promise, and that further exploration in this field may lead
to potent antimalarial agents.
mp 62 °C, IR (KBr): 1758, 1733, 1667, 1330 cmÀ1 1H NMR (CDCl3, 400 MHz) d
.
0.92 (m, 3H), 1.25 (m, 1H), 1.40 (m, 3H), 1.42 (m, 2H), 1.48 (m, 2H), 1.69 (m,
2H), 1.8 (m, 3H), 1.86 (m, 1H), 1.9 (m, 2H), 2.24 (m, 2H), 3.16 (s, 3H), 3.80–3.85
(dd, J = 7.4, 7.4 1H), 4.20–4.25 (dd, J = 4.2, 4.2 1H), 5.74 (s, 1H), 4.7 (s, 2H), 7.1
(s, 1H). 13C NMR (CDCl3, 100 MHz) d 18.3, 18.6, 18.7, 18.9, 21.7, 34.3, 34.7, 34.8,
37.9, 38.0, 39.6, 40.5, 45.3, 65.3, 70.3, 125.2, 134.3, 143.1, 171.1, 171.7, 199.4.
ESI-MS 411 (M+H)+. Anal. Calcd for C21H30O6S: C, 61.44; H, 7.37; S, 7.81. Found:
C, 61.40; H, 7.33; S, 7.84. 7: white solid, mp 85 °C, IR (KBr): 1756, 1743, 1735,
Acknowledgments
1664, 1050 cmÀ1 1H NMR (CDCl3, 400 MHz) d 0.92 (m, 3H), 1.25 (m, 1H), 1.40
.
(m, 3H), 1.42 (m, 2H), 1.48 (m, 2H), 1.54 (s, 9H), 1.69 (m, 2H), 1.8 (m, 3H), 1.86
(m, 1H), 1.9 (m, 2H), 2.24 (m, 2H), 3.80–3.86 (dd, J = 7.4, 7.4 1H), 4.20–4.25 (dd,
J = 4.5, 4.5 1H), 5.72 (s, 1H), 4.3 (s, 2H), 7.1 (s, 1H). 13C NMR (CDCl3, 100 MHz) d
18.1, 18.4, 18.9, 19.1, 21.7, 28.7, 34.3, 35.1, 35.6, 38.6, 39.7, 45.9, 52, 63.2, 70.4,
77.3, 127.4, 128.2. 128.3, 133.9, 144.4, 151.2, 172.6, 174.6, 199.5. ESI-MS 417
(M+H)+. Anal. Calcd for C25H36O5: C, 72.08; H, 8.71. Found C, 72.11; H, 8.60. 8:
viscous colorless liquid, IR (KBr): 1753, 1743, 1735, 1550, 1664, 1260,
The authors are thankful to late Dr. C. Usha Devi for in vitro
evaluation studies and Haffkin Institute, Parel Mumbai for the
in vivo studies.
Supplementary data
1050 cmÀ1 1H NMR (CDCl3, 400 MHz) d 0.91 (m, 3H), 1.22 (m, 1H), 1.40 (m,
.
3H), 1.38 (m, 2H), 1.46 (m, 2H), 1.67 (m, 2H), 1.8 (m, 3H), 1.86 (m, 1H), 1.9 (m,
2H), 2.23 (m, 2H), 3.78 (s, 3H), 3.82–3.86 (dd, J = 7.5, 7.5 1H), 4.20–4.25 (dd,
J = 4.0, 4.0 1H), 4.73 (s, 2H), 5.74 (s, 1H), 4.7 (s, 2H), 7.1 (s, 1H), 7.3–7.6 (m, 4H).
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2010.05.035.

4236
M. Sathe, M. P. Kaushik / Bioorg. Med. Chem. Lett. 20 (2010) 4233–4236
13C NMR (CDCl3, 100 MHz) d 18.1, 18.5, 18.6, 18.9, 21.7, 34.3, 34.7, 34.8, 38.0,
39.53, 40.5, 45.3, 55.8, 65.3, 70.3, 72.2, 124.1, 125.3, 125.5, 125.8, 127.2, 127.6,
134.4, 140.2, 143.9, 171.3, 171.8, 199.2. ESI-MS 453 (M+H)+. Anal. Calcd for
2H), 7.2 (s, 1H), 7.47–7.75 (m, 4H). 13C NMR (CDCl3, 100 MHz) d 18.2, 18.6,
18.7, 18.8, 21.2, 21.7, 34.2, 34.7, 34.8, 38.0, 39.5, 40.5, 45.3, 50.2, 65.4, 70.7,
128.2, 128.3, 130.3, 131.5, 133, 140.2, 143.6, 144.4, 171.2, 171.7, 199.3; ESI-MS
487 (M+H); Anal. Calcd for C27H34O6S: C, 66.64; H, 7.04. Found: C, 66.60; H,
7.09.
C
28H36O5: C, 74.31; H, 8.02. Found: C, 74.34; H, 8.02. 9: brown solid, mp 123–
125 °C. IR (KBr): 1772, 1741, 1646, 1400, 1380, 1170 cmÀ1 1H NMR (CDCl3,
.
400 MHz) d 0.93 (m, 3H), 1.22 (m, 1H), 1.31 (m, 3H), 1.42 (m, 2H), 1.43 (m, 2H),
1.60 (m, 2H), 1.81 (m, 3H), 1.83 (m, 1H), 1.89 (m, 2H), 2.21 (m, 2H), 2.34 (s, 3H),
3.82–3.85 (dd, J = 7.5, 7.5 1H), 4.20–4.24 (dd, J = 4.0, 4.0 1H), 5.73 (s, 1H), 4.7 (s,
12. Trager, W.; Jensen, J. B. Science 1976, 193, 673.
13. Knight, D. J.; Peters, W. Ann. Trop. Med. Parasitol. 1980, 74, 393.