Orally active antimalarials: Synthesis and bioevaluation of a new series of steroid-based 1,2,4-trioxanes against multi-drug resistant malaria in mice

Article abstract of DOI:10.1016/j.bmcl.2007.05.055

A new series of steroid-based 1,2,4-trioxanes 7a-f, 8a-f and 9b-e have been synthesized and evaluated for their antimalarial activity against multi-drug resistant Plasmodium yoelii in Swiss mice by oral route. The biological activity shows a strong depend

Full text of DOI:10.1016/j.bmcl.2007.05.055

Bioorganic & Medicinal Chemistry Letters 17 (2007) 4097–4101
Orally active antimalarials: Synthesis and bioevaluation
of a new series of steroid-based 1,2,4-trioxanes
against multi-drug resistant malaria in miceq
Chandan Singh,a,* Upasana Sharma,a Gunjan Saxenaa and Sunil. K. Purib
aDivision of Medicinal and Process Chemistry, Central Drug Research Institute, Lucknow 226001, India
bDivision of Parasitology, Central Drug Research Institute, Lucknow 226001, India
Received 24 March 2007; revised 9 May 2007; accepted 18 May 2007
Available online 23 May 2007
Abstract—A new series of steroid-based 1,2,4-trioxanes 7a–f, 8a–f and 9b–e have been synthesized and evaluated for their antima-
larial activity against multi-drug resistant Plasmodium yoelii in Swiss mice by oral route. The biological activity shows a strong
dependence on the size and the nature of the steroidal side chain. Pregnane-based trioxanes 8a–f show better activity profile than
trioxanes 7a–f and 9b–e, derived from cholesterol and tigogenine, respectively.
ꢀ 2007 Elsevier Ltd. All rights reserved.
Malaria is a major parasitic disease prevalent in many
countries in Africa, Asia and South America.1 Out of
R1
R2
+
O
OH
O OH
OH
/ H
O O
O
R1
R2
1O2
the four species of Plasmodium that affect humans, Plas-
modium falciparum is the most dangerous and its resis-
tance to contemporary antimalarial drugs has further
compounded the problem. Against this background,
artemisinin 1, the active principle of Artemisia annua,
and its semisynthetic derivatives, e.g., artemether 2,
arteether 3 and artesunic acid 4, are the only class of
antimalarials which are effective against multi-drug
resistant malaria2,3 (Fig. 1). The peroxide bond in the
form of 1,2,4-trioxane is essential for the antimalarial
activity of this class of drugs. Several 1,2,4-trioxanes
originating from different laboratories have shown
promising antimalarial activity both in vitro and
in vivo.4 But the search for structurally simpler, cheaper
and more effective synthetic trioxanes remains an area of
hot pursuit.
Ar
Ar
Ar
From this detailed SAR studies, adamantane-based tri-
oxanes were found to be more active than the other
spiro-1,2,4-trioxanes. Considering the high cost of ada-
mantane derivatives, currently we are focusing on the
easily accessible steroidal ketones as substitute for
2-adamantanone. In the present communication, we re-
port on the synthesis of steroid-based spiro-1,2,4-triox-
anes and their bioevaluation against multi-drug
resistant Plasmodium yoelii in mice by oral route. While
synthesis of several steroid-based tetraoxanes with
Earlier we have reported a photooxygenation route for
the preparation of 1,2,4-trioxanes.5 Several of the triox-
anes prepared by this method have shown promising
antimalarial activity.6
H
H
H
O
O
O
O
O
O
O
O
O
O
H
H
H
O
O
O
O
O
OR
OH
Keywords: Malaria; Artemisinin; 1,2,4-Trioxanes; Steroid-based.
q
1
2 R = Me
3 R = Et
O
4
CDRI Communication No. 7151.
Corresponding author. Tel.: +91 522 2624273; fax: +91 522
2623405; e-mail: chandancdri@yahoo.com
*
Figure 1.
0960-894X/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2007.05.055

4098
C. Singh et al. / Bioorg. Med. Chem. Lett. 17 (2007) 4097–4101
modest antimalarial activity has been reported,7 to our
knowledge this is the first report on steroid-based
1,2,4-trioxanes.8
pounds showed 100% clearance of parasitaemia on day
4 and 40% of the treated mice survived beyond day 28.
Trioxane 8c was the next best compound of the series. It
showed 60% protection at 96 mg/kg · 4 days and 20%
protection at 48 mg/kg · 4 days. Trioxanes 8a and 8d
showed 40% protection at 96 mg/kg · 4 days and 20%
protection at 48 mg/kg · 4 days. Trioxane 8e showed
20% protection at 96 mg/kg · 4 days. At 48 mg/kg, it
showed 100% suppression on day 4 and none of the trea-
ted mice survived until day 28.
b-Hydroxyhydroperoxides 6a–f were prepared by the
photooxygenation of allylic alcohols 5a–f according
to our reported procedure and were reacted in situ with
cholestanone 9 to furnish trioxanes 7a–f in 23–69%
overall yields.6,10 A similar condensation of 6a–f with
3,20-pregnanedione 10 furnished trioxanes 8a–f in 40–
87% overall yields. b-Hydroxyhydroperoxides 6b–e
were also reacted under similar conditions with tigoge-
nine derived ketone 11 to furnish trioxanes 9b–e in
35–55% overall yields9,10 (Fig. 2). Cholestanone 9,
3,20-pregnanedione 10 and ketone 11 were prepared
from cholesterol, 16-dehydro-pregnanolone-3-acetate
and diosgenin using standard procedures, respectively.
All these trioxanes were obtained as inseparable
mixture of diastereomers. Compounds 7a–f, 8a–f and
9b–e were initially screened against multi-drug resistant
P. yoelii in Swiss mice at 96 mg/kg · 4 days by oral
route.11–14 Trioxanes 8a–f, which showed significant
activity at 96 mg/kg, were further screened at 48 mg/
kg · 4 days. Arteether which showed 100% protection
at 48 mg/kg · 4 days was used as positive control.
Results are summarized in Table 1.
Trioxanes 7a–f and 9b–e showed weak activity. Com-
pounds 7a–f showed 15–73% suppression of parasita-
emia on day 4 at 96 mg/kg · 4 days and none of the
treated mice survived until day 28. Similarly, com-
pounds 9b–e showed only 36–71% suppression on day
4 at 96 mg/kg and none of the mice survived until 28.
From the limited SAR data, it appears that the steroidal
side chain has a strong bearing on the biological activity.
Trioxanes 8a–f which have shorter side chain as com-
pared with that of 7a–f and 9b–e are significantly more
active. The data can also be rationalized in terms of lipo-
philicity of these compounds. The active compounds
(8a–f), all pregnane-based, are comparatively less hydro-
phobic (logP = 7.07–8.03) than the weakly active triox-
anes 7a–f and 9b–e (logP = 10.61–11.43 and 8.26–8.95).
In this context, it is worth noting that pregnane moiety
has earlier been identified as a biologically privileged
substructure (supporting moiety) for a series of antiviral
compounds.15 More SAR data is needed to resolve the
question whether the side chain per se is important or
overall lipophilicity of the compound. Our current ef-
forts are directed to answer this question.
As can be seen from Table 1, cholestane-based trioxanes
7a–f and tigogenine-based trioxanes 9b–e were less ac-
tive than pregnane-based trioxanes 8a–f. All the preg-
nane-based trioxanes 8a–f showed 100% suppression
on day 4 with 40–100% protection to the treated mice
when administered at 96 mg/kg · 4 days (twice the
effective dose of arteether) by oral route. Among preg-
nane-based trioxanes, 8b and 8f were the most active
compounds of the series. Both these trioxanes showed
100% clearance of parasitaemia on day 4 at 96 mg/
kg · 4 days and all the treated mice survived beyond
day 28. Even at 48 mg/kg · 4 days, both these com-
In conclusion, we have prepared a new series of steroid-
based 1,2,4-trioxanes some of which show very signifi-
cant activity against multi-drug resistant P. yoelii in
Swiss mice by oral route.
O
O
OH
OH
O
H
H
O OH
H
H
H
H
O
O
O
X
X
9
5a-f
10
6a-f
11
O
O
O
O
O
O
O
O
O
O
O
O
X
X
9b-e
X
7a-f
8a-f
X: [a] H; [b] OMe; [c] Me; [d] F; [e] Cl; [f] Br
Figure 2.

C. Singh et al. / Bioorg. Med. Chem. Lett. 17 (2007) 4097–4101
4099
Table 1. In vivo antimalarial activity of compounds 7a–f, 8a–f and 9b–e against multi-drug resistant P. yoelii in Swiss mice by oral route
General Structure
X
Compound logPb Dose (mg/kg/day) % Suppression on day-4a Mice alive on day-28
H 7a
OMe 7b
10.61
—
96
96
96
96
96
96
73.0
53.5
27.4
14.8
43.4
26.1
0/5
0/5
0/5
0/5
0/5
0/5
O
O
Me
F
7c
7d
7e
7f
11.09
10.76
11.16
11.43
O
Cl
Br
X
H
8a
7.20
7.07
7.69
7.36
7.76
8.03
96
48
96
48
96
48
96
48
96
48
96
48
100.0
100.0
100.0
100.0
100.0
100.0
100.0
100.0
100.0
100.0
100.0
100.0
2/5
1/5
5/5
2/5
3/5
2/5
2/5
1/5
1/5
0/5
5/5
2/5
O
OMe 8b
Me
F
8c
8d
8e
8f
O
O
O
Cl
Br
X
O
O
OMe 9b
8.26
8.87
8.55
8.95
96
96
96
96
36.1
50.7
45.1
71.7
0/5
0/5
0/5
0/5
O
O
Me
F
9c
9d
9e
O
Cl
X
Arteether
—
—
3.84
48
24
100.0
100.0
5/5
1/5
a Percent suppression = [(C À T)/C] · 100, where C is parasitaemia in control group and T is parasitaemia in treated group.
b logP values have been calculated from Chemdraw ultra 7.0. logP value of compound 7b could not be calculated by Chemdraw ultra 7.0.
3. (a) Asthana, O. P.; Srivastava, J. S.; Valecha, N. J.
Parasitic Diseases 1997, 211, 1; (b) WHO: Facts on ACTs
(Artemisinin-based Combination Therapies), http://
www.rbm.who.int/cmc; (c) Posner, G. H.; Paik, I-H.;
Chang, W.; Borstnik, K.; Sinishtaj, S.; Rosenthal, A. S.;
Shapiro, T. A. J. Med. Chem. 2007, ASAP article, web
release date 17-04-2007.
Acknowledgments
Upasana Sharma is thankful to the Council of Scientific
and Industrial Research, New Delhi, for the award of
Senior Research Fellowship. We also thank Department
of Science & Technology, New Delhi, and IPCA Labo-
ratories, Mumbai, for financial support.
4. (a) Kepler, J. A.; Philip, A.; Lee, Y. W.; Matthew, C.;
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Jefford, C. W. Ann. Trop. Med. Parasitol 1993, 87, 9; (d)
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Posner, G. H.; Maxwell, J. P.; O’Dowd, H.; Krasavin, M.;
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I.-H.; Borstnik, K.; Xie, S.; Shapiro, T. A. J. Med. Chem.
2002, 45, 3824; (h) Griesbeck, A. G.; El-Idreesy, T. T.;
References and notes
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Shen, C. C. Med. Res. Rev. 1987, 7, 29; (c) Cumming, J.
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cycles 1999, 51, 1681; (e) Borstnik, K.; Paik, I.; Shapiro, T.
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Ploypradith, P. Acta Trop. 2004, 89, 329; (g) O’Neill, P.
M.; Posner, G. H. J. Med. Chem. 2004, 47, 2945.

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C. Singh et al. / Bioorg. Med. Chem. Lett. 17 (2007) 4097–4101
Fiege, M.; Brun, R. Org. Lett. 2002, 24, 4193; (i) O’Neill,
P. M.; Mukhtar, A.; Ward, S. A.; Bickley, J. F.; Davies, J.;
J = 12.1 and 10.1 MHz), 5.21–5.23 (m, 1H), 5.32 and 5.49
(2· s, 2H), 7.27–7.36 (m, 5H); 13C NMR (CDCl3,
75 MHz) d: 11.45 (CH3), 12.01 (CH3), 18.68 (CH3),
21.27 (CH2), 22.56 (CH3), 22.81 (CH3), 23.84 (CH2),
24.21 (CH2), 24.67 (CH2), 28.01 (CH), 28.23 (CH2), 28.54
(CH2), 31.88 (CH2), 34.60 (CH2), 35.49 (CH), 35.79 (CH),
36.19 (CH2), 36.23 (CH2), 39.53 (CH2), 40.03 (CH2), 41.77
(CH), 42.60 (C · 2), 53.98 (CH), 56.29 (CH), 56.42 (CH),
62.80 (CH2), 80.34 and 80.36 (CH), 102.91 and 103.15 (C),
116.26 (CH2), 126.40 (2· CH), 128.12 (CH), 128.53 (2·
CH), 138.70 (C), 143.61 (CH); FAB-MS (m/z): 549
Bachi, M. D.; Stocks, P. A. Org. Lett. 2004, 18, 3035.
5. Singh, C. Tetrahedron Lett. 1990, 31, 6901.
6. (a) Singh, C.; Misra, D.; Saxena, G.; Chandra, S. Bioorg.
Med. Chem. Lett. 1992, 2, 497; (b) Singh, C.; Misra, D.;
Saxena, G.; Chandra, S. Bioorg. Med. Chem. Lett. 1995, 5,
1913; (c) Singh, C.; Gupta, N.; Puri, S. K. Bioorg. Med.
Chem. Lett. 2003, 13, 3447; (d) Singh, C.; Malik, H.; Puri,
S. K. Bioorg. Med. Chem. 2004, 12, 1177; (e) Singh, C.;
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4484; (i) Singh, C.; Kanchan, R.; Srivastava, D.; Puri, S.
K. Bioorg. Med.Chem. Lett. 2006, 16, 584; (j) Singh, C.;
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7. (a) Todorovic, N. M.; Stefanovic, M.; Tinant, B.; Decl-
ercq, J. P.; Makler, M. T.; Solaja, B. A. Steroids 1996, 61,
688; (b) Opsenica, D.; Pocsfalvi, G.; Juranic, Z.; Tinant,
B.; Declercq, J. P.; Kyle, P. E.; Milhous, W. K.; Solaja, B.
A. J. Med. Chem. 2000, 43, 3274; (c) Solaja, B. A.; Terzic,
N.; Pocsfalvi, G.; Gerena, L.; Tinant, B.; Opsenica, D.;
Milhous, W. K. K. J. Med. Chem. 2002, 45, 3331; (d)
Opsenica, D.; Angelovski, G.; Pocsfalvi, G.; Juranic, Z.;
Zizak, Z.; Kyle, D.; Milhous, W. K.; Solaja, B. A. Bioorg.
Med. Chem. 2003, 11, 2761; (e) Opsenica, I.; Terzik, N.;
Opsenica, D.; Angelovsky, G.; Lehnig, M.; Eilbracht, P.;
Tinant, B.; Zizak, Z.; Smith, K. S.; Yang, Y. S.; Diaz, D.
S.; Smith, P. L.; Milhous, W. K.; Dokovic, D.; Solaja, B.
A. J. Med. Chem. 2006, 49, 3790.
[M+H]+; Anal. Calcd for C37H56O3:
10.28%; Found C 80.61%, H 9.76%.
C 80.97%, H
Compound 7b. 1H NMR (CDCl3, 200 MHz) d: 0.65 (s,
3H), 0.82 (d, 3H, J = 6.4 MHz), 0.87 (s, 3H), 0.90–1.99 (m,
37H), 3.72–3.80 (m, 1H), 3.81 (s, 3H), 3.82–3.88 (m, 1H),
5.19–5.20 (m, 1H), 5.22 and 5.42 (2· s, 2H), 6.86 (d, 2H,
J = 8.5 MHz), 7.32 (d, 2H, J = 8.5 MHz); 13C NMR
(CDCl3, 75 MHz) d: 11.52 (CH3), 12.08 (CH3), 18.68
(CH3), 21.26 (CH2), 22.56 (CH3), 22.81 (CH3), 23.83
(CH2), 24.20 (CH2), 24.64 (CH2), 28.01 (CH), 28.23
(CH2), 28.32 (CH2), 31.72 (CH2), 31.91 (CH2), 34.33
(CH2), 35.47 (CH), 35.79 (CH), 36.17 (CH2), 36.62 (CH2),
39.52 (CH2), 40.01 (CH2), 41.76 (CH), 42.56 (C · 2), 53.95
(CH), 55.30 (CH3), 56.27 (CH), 56.45 (CH), 62.86 (CH2),
80.49 and 80.51 (CH), 101.60 and 101.73 (C), 113.91 (2·
CH), 114.85 (CH2), 127.57 (2· CH), 131.00 (C), 142.88
(C), 159.56 (C); FAB-MS (m/z): 579 [M+H]+; Anal. Calcd
for C38H58O4: C 78.85%, H 10.10%; Found C 78.63%, H
10.36%.
Compound 7c. 1H NMR (CDCl3, 200 MHz) d: 0.64 (s,
3H), 0.82 (d, 3H, J = 6.7 MHz), 0.87 (s, 3H), 0.91–1.93 (m,
37H), 2.33 (s, 3H),3.69–3.74 (m, 1H), 3.84 and 4.00 (2· dd,
1H, J = 11.8 and 10.3 MHz), 5.20–5.22 (m, 1H), 5.26 and
5.46 (2· s, 2H), 7.13 (d, 2H, J = 7.7 MHz), 7.28 (d, 2H,
J = 7.7 MHz); 13C NMR (CDCl3, 50 MHz) d: 11.90
(CH3), 12.54 (CH3), 19.14 (CH3), 21.58 (CH3), 21.62
(CH2), 23.05 (CH3), 23.29 (CH3), 23.84 (CH2), 24.23
(CH2), 24.76 (CH2), 28.47 (CH), 28.52 (CH2) 28.98 (CH2),
34.68 (CH2), 34.77 (CH2), 35.91 (CH), 36.27 (CH), 37.21
(CH2), 37.78 (CH2), 38.56 (CH2), 39.91 (CH2), 42.10
(CH), 43.03 (C · 2), 54.37 (CH), 56.45 (CH), 56.71 (CH),
62.64 and 62.86 (CH2), 80.70 and 80.84 (CH), 103.27 and
103.41 (C), 115.77 (CH2), 126.65 (2· CH), 129.67 (2· CH),
136.17 (C), 138.36 (C), 143.81 (C); FAB-MS (m/z): 563
[M]+; Anal. Calcd for C38H58O3: C 81.09%, H 10.36%;
Found C 80.87%, H 10.58%.
8. For the preparation of a cholesterol-derived artemisinin-
like 1,2,4-trioxane, see: Rong, Y.-J.; Wu, Y. J. Chem. Soc.,
Perkin Trans 1 1993, 2149.
9. General procedure for the preparation of steroid-based
1,2,4-trioxanes 7a–f, 8a–f and 9b–e: (compound 8a is taken
as representative example). A solution of 3-phenyl-but-2-
en-1-ol 5a (1 g, 6.75 mmol) and methylene blue (10 mg) in
CH3CN (75 mL) was irradiated with 500 W tungsten-
halogen lamp at À10 to 0 ꢁC while oxygen gas was
bubbled slowly into the reaction mixture for 5 h. Com-
pound 3,20-Pregnanedione 10 (3.2 g, 1.5 equiv,
10.1 mmol) and HCl (0.1 mL) were added and the reaction
mixture was stirred at room temperature for 3 h. Usual
workup followed by column chromatography over silica
gel furnished trioxane 8a (1.3 g, 45% yield) as an insep-
arable mixture of diastereomers. Mp 124–126 ꢁC; FT-IR
(KBr, cmÀ1): 1715; 1H NMR (CDCl3, 200 MHz) d: 0.59 (s,
3H), 0.82 (s, 3H), 0.89–1.97 (m, 21H), 2.10 (s, 3H), 2.20–
2.52 (m, 2H), 3.73 (dd, 1 H, J = 11.7 and 2.1 MHz), 3.89
and 4.02 (2· dd, 1 H, J = 11.7 and 10.6 MHz), 5.23 (dd,
1H, J = 10.6 and 2.1), 5.32 and 5.49 (2· s, 2H), 7.30–7.36
(m, 5H); 13C NMR (CDCl3, 50 MHz) d: 11.86 (CH3),
13.88 (CH3), 21.66 (CH2), 23.18 (CH2), 24.81 (CH2), 28.40
(CH2), 28.79 (CH2), 31.96 (CH3), 32.18 (CH2), 34.98
(CH2), 35.84 (CH), 36.46 (CH2), 39.44 (CH2), 42.11 (CH),
42.65 (C · 2), 54.09 (CH), 57.02 (CH), 63.22 (CH2), 64.19
(CH), 80.71 (CH), 103.22 (C), 116.75 (CH2), 126.78
(CH · 2), 128.58 (CH), 128.98 (CH · 2), 139.09 (C),
146.23 (C), 210.08 (C); ES-MS (m/z): 501 [M + Na]+;
Anal. Calcd for C31H42O4: C 77.79%, H 8.84%; found C
77.47, H 9.21%.
Compound 8b. FT-IR (KBr, cmÀ1): 1711; 1H NMR
(CDCl3, 200 MHz) d: 0.59 (s, 3H), 0.82 (s, 3H), 0.89–
2.02 (m, 21H), 2.10 (s, 3H), 2.46–2.52 (m, 2H), 3.70–3.76
(m, 1H), 3.79 (s, 3H), 3.83–3.88 (m, 1H), 5.19–5.20 (m,
1H); 5.22 and 5.42 (2· s, 2H), 6.86 (d, 2H, J = 8.6 MHz),
7.32 (d, 2H, J = 8.6Hz); 13C NMR (CDCl3, 50 MHz) d:
11.93 (CH3), 13.84 (CH3), 21.65 (CH2), 23.18 (CH2), 24.79
(CH2), 28.40 (CH2), 28.79 (CH2), 31.88 (CH3), 32.21
(CH2), 34.98 (CH2), 35.82 (CH), 36.43 (CH2), 39.40
(CH2), 42.27 (CH), 44.57 (C · 2), 54.08 and 54.19 (CH),
55.64 (CH3), 56.98 (CH) 63.23 (CH2) 64.13 (CH), 80.71
and 80.75 (CH), 103.10 and 103.22 (C), 114.31 (CH · 2),
115.01 (CH2), 127.89 (CH · 2), 131.36 (C), 143.13 and
143.23 (C), 159.99 (C), 209.77 (C); ES-MS (m/z): 531
[M+Na]+; Anal. Calcd for C32H44O5: C 75.56%, H 8.72%;
Found C 75.23%, H 9.21%.
Compound 8c. FT-IR (KBr, cmÀ1): 1714; 1H NMR
(CDCl3, 200 MHz) d: 0.59 (s, 3H), 0.82 (s, 3H), 0.89–
2.02 (m, 21H), 2.09 (s, 3H), 2.33 (s, 3H), 2.47–2.54 (m,
2H), 3.74 (dd, 1H, J = 11.8 and 2.7 MHz), 3.85 and 3.90
(2· dd, 1H, J = 11.8 and 10.3 MHz), 5.20 (dd, 1H,
J = 10.3 and 2.7 MHz); 5.22 and 5.42 (2· s, 2H), 7.13(d,
10. Selected spectral data:
Compound 7a. 1H NMR (CDCl3, 200 MHz) d: 0.64 (s,
3H), 0.83 (d, 3H, J = 6.6 MHz), 0.85 (s, 3H), 0.90–1.98 (m,
37H), 3.71–3.74 (m, 1H), 3.88 and 4.02 (2· dd, 1H,

C. Singh et al. / Bioorg. Med. Chem. Lett. 17 (2007) 4097–4101
4101
2H, J = 7.8 MHz), 7.28 (d, 2H, J = 7.8 MHz); 13C NMR
(CDCl3, 50 MHz) d: 11.95 (CH3), 13.86 (CH3), 21.55
(CH2), 21.58 (CH3), 23.17 (CH2), 24.81 (CH2), 28.54
(CH2), 28.79 (CH2), 31.89 (CH3), 32.20 (CH2), 34.98
(CH2), 35.82 (CH), 36.43 (CH2), 39.39 (CH2), 42.32 (CH),
44.57 (C · 2), 54.11 (CH), 56.98 (CH), 63.26 (CH2) 64.11
(CH), 80.65 (CH), 103.08 and 103.21 (C), 115.75 (CH2),
126.57 (CH · 2), 129.66 (CH · 2), 136.06 (C), 138.33 (C),
143.68 (C), 209.76 (C); ES-MS (m/z): 515 [M+Na]+; Anal.
Calcd for C32H44O4: C 78.01%, H 9.00%; Found C
77.85%, H 8.55%.
3.90 and 3.99–4.08 (2· m, 1H), 4.37–4.45 (m, 1H), 5.24–
5.26 (m, 1H), 5.28 and 5.43 (2· s, 2H), 6.88 and 6.96 (2· d,
2H, J = 9.0 MHz), 7.34 and 7.36 (2· d, 2H, J = 9.0 MHz);
13C NMR (CDCl3, 75 MHz) d: 11.29 (CH3), 14.23 (CH3),
16.91 (CH3), 17.03 (CH3), 21.38 (CH2), 27.54 (CH2), 29.02
(CH2), 30.11 (CH2), 31.50 (CH2), 32.71 (CH), 34.86
(CH2), 35.14 (CH2), 37.15 (CH2), 38.76 (CH2), 40.04
(CH2), 42.82 (CH), 43.13 (CH), 44.08 (C · 2), 54.18
(CH),55.24 (CH), 55.65 (CH3), 62.56 (CH), 63.24 (CH2),
65.55 (CH2), 67.18 (CH2), 79.94 (CH), 81.24 (CH), 101.52
and 101.59 (C), 108.65 (C), 112.65 (CH2), 126.28 (CH · 2),
129.79 (CH · 2), 136.10 (C), 138.43 (C), 158.33 (C); ES-
MS (m/z) 606 [M+H]+; Anal. Calcd for C38H54O6: C
75.28%, H 8.97%; Found C 75.01%, H 9.26%.
Compound 8d. FT-IR (KBr, cmÀ1): 1716; 1H NMR
(CDCl3, 200 MHz) d: 0.60 (s, 3H), 0.82 (s, 3H), 0.87–
2.02 (m, 21H), 2.10 (s, 3H), 2.51–2.55 (m, 2H), 3.73 (dd,
1H, J = 11.9 and 2.9 MHz), 3.83 and 4.10 (2· dd, 1H,
J = 10.3 and 11.9 MHz), 5.18 (dd, 1H, J = 10.3 and
2.9 MHz); 5.31 and 5.45 (2· s, 2H), 7.02 (t, 2H, J = 8.6),
7.30–7.39 (m, 2H); 13C NMR (CDCl3, 50 MHz) d: 11.90
(CH3), 13.84 (CH3), 21.64 (CH2), 23.18 (CH2), 24.78
(CH2), 28.56 (CH2), 28.63 (CH2), 31.88 (CH3), 32.23
(CH2), 34.96 (CH2), 35.82 (CH), 36.43 (CH2), 39.41
(CH2), 42.07 (CH), 44.59 (C · 2), 54.20 (CH), 57.00
(CH), 62.89 (CH2), 64.15 (CH), 80.66 and 80.79 (CH),
103.34 and 103.44 (C), 115.63 (CH), 116.05 (CH), 116.86
(CH2), 128.51 (CH), 128.67 (CH), 135.10 (C), 142.91 (C),
160.58 (C), 209.86 (C); ES-MS (m/z): 519 [M+Na]+.
Compound 8e. FT-IR (KBr, cmÀ1): 1719; 1H NMR
(CDCl3, 200 MHz) d: 0.59 (s, 3H), 0.82 (s, 3H), 0.84–
2.02 (m, 21H), 2.10 (s, 3H), 2.51–2.55 (m, 2H), 3.73 (dd,
1H, J = 11.9 & 2.7 MHz), 3.88 and 4.02 (2· dd, 1H,
J = 11.9 and 10.1 MHz), 5.15 (dd, 1H, J = 10.1 and
2.7 MHz), 5.34 and 5.49 (2· s, 2H), 7.29–7.31 (m, 4H);
13C NMR (CDCl3, 50 MHz) d: 11.92 (CH3), 13.84 (CH3),
21.63 (CH2), 23.17 (CH2), 24.83 (CH2), 28.76 (CH2), 28.77
(CH2), 31.87 (CH3), 32.20 (CH2), 34.95(CH2), 35.79 (CH),
36.41 (CH2), 39.38 (CH2), 42.25 (CH), 44.55 (C · 2), 54.17
(CH), 56.97 (CH), 62.83 (CH2), 64.11 (CH), 80.43 and
80.56 (CH), 103.21 and 103.33 (C), 117.36 (CH2), 128.13
(CH · 2), 129.10 (CH · 2), 134.46 (C), 137.46 (C), 142.68
(C), 209.76 (C). ES-MS (m/z) 512 [M+Na]+. Anal. Calcd
for C31H41ClO4: C 72.56%, H 8.05%; Found C 72.45%, H
8.33%.
Compound 9c. 1H NMR (CDCl3, 300 MHz) d: 0.78 (s,
3H), 0.80 (d, 3H, J = 6.3 MHz), 0.85 (s, 3H), 0.97 (d, 3H,
J = 6.8 MHz), 1.10–1.88 (m, 27H), 2.36 (s, 3H), 3.87 (t,
1H, J = 10.7 MHz), 3.47 (dd, 1H, J = 10.4 and 3.3 MHz),
3.73 and 3.77 (2· dd, 1H, J = 11.9 and 3.0 MHz), 3.89 and
4.02 (2· dd, 1H, J = 11.9 and 10.3 MHz), 4.36–4.44 (m,
1H), 5.22 and 5.25 (2· dd, 1H, J = 10.3 and 3.0 MHz),
5.28 and 5.47 (2· s, 2H), 7.15 and 7.16 (2· d, 2H,
J = 8.0 MHz), 7.28 and 7.30 (2· d, 2H, J = 8.0 MHz); 13
C
NMR (CDCl3, 75 MHz) d: 11.90 (CH3), 14.93 (CH3),
16.91 (CH3), 17.57 (CH3), 21.38 (CH2), 21.55 (CH3), 27.12
(CH2), 28.42 (CH2), 31.11 (CH2), 32.50 (CH2), 32.71
(CH), 34.86 (CH2), 35.14 (CH2), 37.15 (CH2), 39.48
(CH2), 40.04 (CH2), 42.82 (CH), 43.13 (CH), 44.03
(C · 2), 54.21 (CH), 56.64 (CH), 62.56 (CH), 63.24
(CH2), 64.11 (CH2), 67.18 (CH2), 80.74 (CH), 81.24
(CH), 103.21 and 103.35 (C), 109.64 (C), 115.85 (CH2),
126.65 (CH · 2), 129.65 (CH · 2), 136.10 (C), 138.43 (C),
143.56 (C); FAB-MS (m/z): 591 [M+H]+; Anal. Calcd for
C38H54O5: C 77.25%, H 9.21%; Found C 76.81%, H
8.88%.
11. In vivo test procedure. The colony-bred Swiss mice
(25 1 g) were inoculated with 1 · 106 parasitized RBC
on day 0 and treatment was administered to a group of
five mice at each dose, from day 0 to day 3, in two divided
doses daily. The drug dilutions of compounds 7a–f, 8a–f
and 9b–e were prepared in groundnut oil to contain the
required amount of the drug (1.2 mg for a dose of 96 mg/
kg, 0.6 mg for a dose of 48 mg/kg) in 0.1 ml and
administered orally. Parasitaemia level was recorded from
thin blood smears between day 4 and 28.13 The treated
mice surviving beyond day 28 were recorded as the mice
protected by the drug. Mice treated with b-Arteether
served as positive controls.
12. (a) One hundred percent suppression of parasitaemia
means number of parasites below the detection limit; (b)
One hundred percent protection means all the treated mice
survive until day 28. Similarly 50% and 20% protection
mean only 50% and 20% of the treated mice survive until
day 28.
Compound 8f. FT-IR (KBr, cmÀ1): 1712; 1H NMR
(CDCl3, 200 MHz) d: 0.60 (s, 3H), 0.82 (s, 3H), 1.21–
2.02 (m, 21H), 2.10 (s, 3H), 2.51–2.55 (m, 2H), 3.73 (dd,
1H, J = 11.5 and 2.7 MHz), 3.88 and 4.02 (2· dd, 1H,
J = 10.0
& 11.5 MHz), 5.15 (dd, 1H, J = 10.0 and
2.7 MHz), 5.34 and 5.50 (2· s, 2H), 7.24–7.48 (m, 4H);
13C NMR (CDCl3, 50 MHz) d: 11.84 (CH3), 13.86 (CH3),
21.65 (CH2), 23.21 (CH2), 24.80 (CH2), 28.41 (CH2), 28.79
(CH2), 31.91 (CH3), 32.20 (CH2), 34.99 (CH2), 35.85
(CH), 36.46 (CH2), 39.44 (CH2), 42.09 (CH), 44.62 (C · 2),
54.22 (CH), 57.02 (CH), 62.86 (CH2), 64.19 (CH), 80.46
and 80.50 (CH), 103.93 and 103.31 (C), 117.48 (CH2),
122.70 (C), 128.48 (CH · 2), 129.10 (CH · 2), 137.97 (C),
143.79 (C), 209.97 (C); ES-MS (m/z) 579 [M+Na]+; Anal.
Calcd for C31H41BrO4: C 66.78%, H 7.41%; Found C
66.43%, H 7.98%. 9b. 1H NMR (CDCl3, 300 MHz) d: 0.78
(s, 3H), 0.80 (d, 3H, J = 6.3 MHz), 0.89 (s, 3H), 0.97 (d,
3H, J = 6.9 MHz), 1.11–2.01 (m, 27H), 3.37 (t, 1H,
J = 12.0 MHz), 3.48 (dd, 1H, J = 12.0 and 6.0 MHz),
3.75 (dd, 1H, J = 12.0 and 2.1 MHz), 3.83 (s, 3H), 3.86–
13. Puri, S. K.; Singh, N. Exp. Parasitol 2000, 94, 8.
14. Most researchers in this field use the Plasmodium berghei
mouse-model for the antimalarial screening. But we find
multi-drug resistant P. yoelii mouse-model is a more
reliable model for the discovery of new compounds to
combat drug-resistant malaria.
15. Cavallini, G.; Massarani, E.; Nardi, D. J. Med. Chem.
1964, 7, 673.