New orally active spiro 1,2,4-trioxanes with high antimalarial potency

Article abstract of DOI:10.1016/j.bmcl.2005.07.013

A new series of functionalized 1,2,4-trioxanes 10-21 have been prepared and assessed for antimalarial activity in mice. Several of these trioxanes show significant activity. Trioxane 16, the most active compound of the series, has shown activity by oral r

Full text of DOI:10.1016/j.bmcl.2005.07.013

Bioorganic & Medicinal Chemistry Letters 15 (2005) 4484–4487
New orally active spiro 1,2,4-trioxanes with high
antimalarial potencyq
Chandan Singh,a,* Heetika Malika 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 17 May 2005; revised 23 June 2005; accepted 7 July 2005
Available online 18 August 2005
Abstract—A new series of functionalized 1,2,4-trioxanes 10–21 have been prepared and assessed for antimalarial activity in mice.
Several of these trioxanes show significant activity. Trioxane 16, the most active compound of the series, has shown activity by oral
route which is comparable with that of the clinically used drug, b-arteether.
ꢀ 2005 Elsevier Ltd. All rights reserved.
1. Introduction
ent in the form of 1,2,4-trioxane is essential for the anti-
malarial activity of artemisinin and its derivatives.
Several synthetic trioxanes originating from different lab-
oratories including our group have shown promising anti-
malarial activity both in vitro and in vivo.4,5
Malaria is a major parasitic disease affecting over 100
countries of the tropical and subtropical regions of the
world including India. Around 300–500 million clinical
cases of malaria are reported every year of which around
2–3 million die due to complicated cases of malaria.1
The situation is getting worse with the emergence of
multi-drug resistant parasites. Against this background,
isolation of artemisinin 1 by the Chinese as the active
principle of their traditional antimalarial drug, Artemi-
sia annua, has been a major breakthrough in malaria
chemotherapy. Artemisinin is active against both chlo-
roquine sensitive and chloroquine resistant malaria.2
Earlier we have shown that b-hydroxyhydroperoxides
6a,b prepared by photooxygenation of allylic alcohols5a
5a,b react with 1,4-cyclohexanedione to give keto-func-
tionalized 1,2,4-trioxanes 7a,b (Scheme 1) and that these
trioxanes undergo facile reductive amination with vari-
ous amines to give amino functionalized 1,2,4-trioxanes
(prototype 8 and 9).6
Some of these amino functionalized 1,2,4-trioxanes
showed high order of activity against chloroquine resis-
tant Plasmodium yoelii in mice.6b
H
H
H
O
O
O
O
O
O
O
O
O O
O
O
O
H
H
H
n
HN
N
NH
O
NHR
O
O
O
Ar
O
Ar
O
O
O
OR
8
OH
9
Cl
1
4
2 R = Me
3 R = Et
O
Several derivatives of artemisinin with better activity pro-
file, for example, artemether 2, arteether 3 and artesunic
acid 4 are being clinically used.3 The peroxide group pres-
OH
O
OH
OH
O O
O
O
Ar
Ar
Ar
Keywords: Artemisinin; Arteether; 1,2,4-Trioxanes; Multi-drug resis-
tant; Antimalarial.
q
5a-b
7a-b
6a-b
Scheme 1. Reagents and conditions: (a) hm (light produced by 500 W
tungsten halogen lamp), O2, methylene blue, MeCN, À10 to 0 ꢁC.
(b) 1,4-Cyclohexanedione, concd HCl, 5 ꢁC.
CDRI Communication No.: 6773.
Corresponding author. Tel.: +91 0522 2224273; fax: +91 0522
2223405; e-mail: chandancdri@yahoo.com
*
0960-894X/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.07.013

C. Singh et al. / Bioorg. Med. Chem. Lett. 15 (2005) 4484–4487
4485
We have further explored the chemistry of the carbonyl
group of these keto-trioxanes and report herein the syn-
thesis of a new series of functionalized 1,2,4-trioxanes
10–21. Several of these trioxanes show better activity
profile than the parent trioxanes 7a,b. Trioxane 16, the
most active compound of the series, has shown activity
by oral route which is comparable with that of the
clinically used drug, b-arteether.
O
O
O
O O
O
O
OH
O
O
OH
Ar
Ar
10-11
12-13
12 Ar = phenyl
13 Ar = 4-biphenyl
10 Ar = phenyl
11 Ar = 4-biphenyl
O O
O O
OH
CH2CO2Et
CCO2Et
R
Ar
O
Ar
O
14a-b and 15a-b
16-19
2. Chemistry
16 Ar = phenyl, R = H
14a Ar = phenyl (higher Rf)
14b Ar = phenyl (lower Rf)
15a Ar = 4-bihenyl (higher Rf)
15b Ar = 4-biphenyl (lower Rf)
17 Ar = phenyl, R = CH3
18 Ar = 4-biphenyl, R = H
19 Ar = 4-biphenyl, R = CH3
Reduction of 7a with NaBH4 in MeOH furnished
alcohol 10 in 96% yield as an inseparable mixture
of diastereomers, which on reaction with succinic
anhydride and Et3N in CH2Cl2 at rt gave hemisucci-
nate 12 in 93% yield, again as an inseparable mixture
of diastereomers. Similarly keto-trioxane 7b on reduc-
tion furnished alcohol 11 in 95% yield as an insepara-
ble mixture of diastereomers, which on reaction with
succinic anhydride and Et3N in CH2Cl2 at rt gave
hemisuccinate 13 in 95% yield, again as an insepara-
ble mixture of diastereomers. Reaction of 7a with
BrCH2COOEt/Zn in dry benzene furnished a mixture
of diastereomers 14a,b in 83% yield. Compounds
14a,b were separated by column chromatography.
Similar reaction of 7b with BrCH2COOEt/Zn in dry
benzene furnished a mixture of diastereomers 15a,b
in 88% yield. The pure isomers were separated by col-
umn chromatography. Keto-trioxane 7a when reacted
with triethylphosphonoacetate in the presence of NaH
as base in dimethoxyethane furnished the Wittig
product 16 in 93% yield as an inseparable mixture
of geometrical isomers. Reaction of keto-trioxane 7a
with triethylphosphono-2-propionate under the same
conditions furnished 17 in 83% yield again as an
inseparable mixture of geometrical isomers. Keto-tri-
oxane 7b on reaction with triethylphosphonoacetate
and triethylphosphono-2-propionate under similar
reaction conditions furnished 18 and 19 as an insepa-
rable mixture of geometrical isomers in 93% and 84%
yields, respectively. Reaction of keto-trioxane 7a with
MeMgBr in diethylether furnished a diastereomeric
mixture of 20a,b in 54% yield which were separated
by column chromatography and characterized as pure
isomers. Similar reaction of 7a with PhMgBr fur-
nished trioxane 21a,b as a diastereomeric mixture in
59% yield, which were separated into pure isomers
by column chromatography and characterized sepa-
rately,7,8 while they were screened as mixture for bio-
logical activity.
O O
OH
R
O
20a-b and 21a-b
20a R = methyl (higher Rf)
20b R = methyl (lower Rf)
21a R = phenyl (higher Rf)
21b R = phenyl (lower Rf)
4. Results and discussion
As can be seen from Table 1, the Wittig product 16, is
the best compound in the series. At 48 mg/kg given
orally, this compound shows complete clearance of
parasitaemia on day 4 and all the animals survive be-
yond day 28. Even at 24 mg/kg, this compound shows
complete clearance of parasitaemia on day 4 though
none of the animals survive beyond day 28. This triox-
ane also shows complete clearance of parasitaemia on
day 4 at 96 mg/kg by im route and 40% of the animals
survive beyond day 28. Surprisingly, Wittig product 17,
which is structurally very close to 16 except that olefin-
ic proton is replaced by a methyl group, is completely
inactive by both the routes. Trioxane 18 is the next best
compound in the series. It shows 100% clearance of
parasitaemia at 96 and 48 mg/kg by oral route and
provides 100% protection at 96 mg/kg in the 28-day
observation period. It also shows 96% clearance of par-
asitaemia on day 4 at 96 mg/kg by im route but none
of the animals survive beyond day 28. Here again the
corresponding methyl substituted derivative 19 is less
active. It provides only 40% protection to the mice
treated at 96 mg/kg by oral route and no protection
when given by im route. Compounds 11 and 20 pro-
vide 100% suppression by im route on day 4 and
40% protection to the treated mice. The rest of the
functionalized trioxanes 10, 12–15 and 21 show only
moderate activity.
3. Antimalarial activity
1,2,4-Trioxanes 10–21 were initially screened for
their antimalarial activity against multi-drug resistant
P. yoelii in Swiss mice at a highest dose of 96 mg/kg9
by oral and intramuscular (im) routes. The trioxanes
showing activity at 96 mg/kg by either route were
further evaluated at 48 and 24 mg/kg. The results are
shown in Table 1.
The moderate order of activity of trioxanes 16 and 18,
the two most orally active compounds of this series,
by im route could be due to their poor solubility in water
which restricts their absorption from the site of injec-
tion.10 We have also observed such difference in activity
between oral and im routes earlier in a related series of
amino functionalized 1,2,4-trioxanes.6b

4486
C. Singh et al. / Bioorg. Med. Chem. Lett. 15 (2005) 4484–4487
Table 1. In vivo antimalarial activity of functionalized 1,2,4-trioxanes
against P. yoelii in Swiss mice
Acknowledgments
Heetika Malik is grateful to the Council of Scientific and
Industrial Research (CSIR), New Delhi, for the award
of a Senior Research Fellowship. Technical help
by Mr. Akhilesh Kumar Srivastava is gratefully
acknowledged.
Compound
Dose
(mg/kg/day)
Route % Suppression Mice alive
on day 4a
on day 28
7a
7b
10
11
96
96
Oral
im
7
99
0/5
0/5
96
96
Oral
im
92
100
0/5
1/5
96
96
Oral
im
78
82
0/5
0/5
References and notes
1. W.H.O. Drug Inf. Bull. 1999, 13, 9.
96
96
Oral
im
91
100
0/5
2/5
2. (a) For reviews on artemisinin and its analogues see:
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.
12
13
96
96
Oral
im
82
14
0/5
0/5
96
96
Oral
im
99
74
0/5
0/5
14a (higher Rf) 96
96
Oral
im
87
30
0/5
0/5
3. For current status of artemisinin derivatives see: Asthana,
O. P.; Srivastava, J. S.; Valecha, N. J. Parasitic Dis. 1997,
211, 1.
14b (lower Rf) 96
96
Oral
im
37
62
0/5
0/5
4. (a) Peters, W.; Robinson, B. L.; Rossier, J. C.; Jefford, C.
W. Ann. Trop. Med. Parasitol. 1993, 87, 1; (b) Posner, G.
H.; Jeon, H. B.; Parker, M. H.; Krasavin, M.; Paik,
I.-H.; Shapiro, T. A. J. Med. Chem. 2001, 44, 3054; (c)
Posner, G. H.; Jeon, H. B.; Polypradith, P.; Paik, I.-H.;
Borstnik, K.; Xie, S.; Shapiro, T. A. J. Med. Chem. 2002,
45, 3824.
5. (a) Singh, C. Tetrahedron Lett. 1990, 31, 6901; (b) Singh, C.;
Misra, D.; Saxena, G.; Chandra, S. Bioorg. Med. Chem.
Lett. 1992, 2, 497; (c) Singh, C.; Misra, D.; Saxena, G.;
Chandra, S. Bioorg. Med. Chem. Lett. 1995, 5, 1913; (d)
Singh, C.; Gupta, N.; Puri, S. K. Bioorg. Med.Chem. 2004,
12, 5553.
15a (higher Rf) 96
96
Oral
im
93
84
0/5
0/5
15b (lower Rf) 96
96
Oral
im
97
86
0/5
0/5
16
96
48
24
96
Oral 100
Oral 100
Oral 100
5/5
5/5
0/5
2/5
im
100
17
18
96
96
Oral
im
39
40
0/5
0/5
96
48
96
Oral 100
Oral 100
5/5
0/5
0/5
6. (a) Singh, C.; Malik, H.; Puri, S. K. Bioorg. Med. Chem.
2004, 12, 1177; (b) Singh, C.; Malik, H.; Puri, S. K.
Bioorg. Med. Chem. Lett. 2004, 14, 459.
im
96
7. Selected data: Trioxane 10. mp 68–70 ꢁC; IR (KBr, cmÀ1
)
19
96
48
96
Oral 100
Oral 100
2/5
0/5
0/5
1
3394; H NMR (200 MHz, CDCl3): d 1.57–1.90 (m, 7H),
1.98–2.12 (m, 1H), 2.36–2.45 and 2.54–2.64 (m, 1H), 3.78
and 3.80 (2 · dd, 1H, J = 11.8, 3.3 Hz, together integrating
for 1H) 3.93 and 3.95 (2 · dd, 1H, J = 11.8, 10.1 Hz,
together integrating for 1H), 5.25 (dd, 1H, J = 10.1,
3.3 Hz), 5.32 and 5.50 (2 · s, 2H), 7.31–7.39 (m, 5H);
13C NMR (50 MHz, CDCl3) d: 25.32 and 25.80 (t), 30.41
and 30.58 (t), 30.83 and 30.95 (t), 31.17 and 31.85 (t), 63.17
and 63.53 (t), 68.28 and 68.79 (d), 80.72 and 80.77 (d),
102.26 and 102.37 (s), 116.84 and 116.88 (t), 126.79 (d,
integrating for 2 carbons), 128.60 (d), 128.99 (d, integrat-
ing for 2 carbons), 139.00 (s), 143.79 (s); FAB-MS (m/z)
277 [M+H]+; Anal. Calcd for C16H20O4: C, 69.54%; H,
7.30%. Found: C, 69.47%; H, 7.36%. Trioxane 15a. mp
140–141ꢁC; IR (KBr, cmÀ1) 1713, 3510; 1H NMR
(200 MHz, CDCl3) d: 1.27 (t, 3H, J = 7.1 Hz), 1.49–1.78
(m, 5H), 1.90–2.15 (m, 2H), 2.45 (s, 2H), 2.49–2.57 (m,
1H), 3.44 (s, 1H, OH), 3.80 (dd, 1H, J = 11.9, 3.5 Hz), 3.90
(dd, 1H, J = 11.9, 9.7 Hz), 4.17 (q, 2H, J = 7.1 Hz), 5.29
(dd, 1H, J = 9.7, 3.5 Hz), 5.35 and 5.56 (2 · s, 2H), 7.34–
7.60 (m, 9H); 13C NMR (50 MHz, CDCl3) d: 14.60 (q),
24.31 (t), 29.96 (t), 33.40 (t), 33.67 (t), 45.60 (t), 61.15 (t),
63.35 (t), 69.49 (s), 80.69 (d), 102.67 (s), 116.79 (t), 127.22
(d, integrating for 2 carbons), 127.41 (d, integrating for 2
carbons), 127.66 (d, integrating for 2 carbons), 127.92 (d),
129.24 (d, integrating for 2 carbons), 137.84 (s), 140.82 (s),
141.43 (s), 143.40 (s), 173.20 (s); FAB-MS (m/z) 439
[M+H]+; Anal. Calcd for C26H30O6: C, 71.21%; H, 6.90%.
im
78
20a and 20b
21a and 21b
b-Arteether
96
96
Oral
im
92
100
0/5
2/5
96
96
Oral
im
95
93
0/5
0/5
48
24
Oral 100
Oral 100
5/5
1/5
Vehicle control
—
—
—
0/15
a Percent suppression = [(C À T)/C] · 100, where C is parasitaemia in
control group and T is parasitaemia in treated group.
5. Conclusion
A new series of functionalized trioxanes have been
prepared using the chemistry of carbonyl group of
trioxanes 7a,b. Several of these trioxanes show bet-
ter activity profiles than the parent trioxanes 7a,b.
Trioxane 16, the most active compound of the ser-
ies, has shown activity by oral route which is
comparable with that of the clinically used drug,
b-arteether.

C. Singh et al. / Bioorg. Med. Chem. Lett. 15 (2005) 4484–4487
4487
Found: C, 71.43%; H, 6.94%. Trioxane 15b. mp 124–
3H), 1.63–1.93 (m, 6H), 2.03–2.18 (m, 1H), 2.37–2.44 (m,
1H), 3.76 (dd, 1H, J = 11.6, 3.1 Hz), 3.88 (dd, 1H,
J = 11.6, 10.1 Hz), 5.25 (dd, 1H, J = 10.1, 3.1 Hz), 5.33
and 5.50 (2 · s, 2H), 7.31–7.36 (m, 5H); 13C NMR
(50 MHz, CDCl3) d: 24.94 (t), 29.94 (q), 30.68 (t), 35.31
(t), 35.60 (t), 63.36 (t), 69.56 (s), 80.76 (d), 102.73 (s),
116.83 (t), 126.43 (d, integrating for 2 carbons), 127.65 (d),
128.57 (d, integrating for 2 carbons), 139.02 (s), 143.87 (s);
ES-MS (ES++Na) 313; Anal. calcd for C17H22O4: C,
70.32; H, 7.64. Found: C, 70.37; H, 7.24. Trioxane 20b. An
oil: IR (neat, cmÀ1) 3381; 1H NMR (200 MHz, CDCl3) d:
1.25 (s, 3H), 1.58–2.03 (m, 7H), 2.58 (dd, 1H, J = 6.2,
2.2 Hz), 3.77 (dd, 1H, J = 11.9, 2.9 Hz), 4.01 (dd, 1H,
J = 11.9, 10.3 Hz), 5.25 (dd, 1H, J = 10.3, 2.9 Hz), 5.31
and 5.50 (2 · s, 2H), 7.29–7.48 (m, 5H); 13C NMR
(50 MHz, CDCl3) d: 25.04 (t), 30.48 (q), 31.13 (t), 35.35
(t), 35.51 (t), 63.27 (t), 69.44 (s), 80.72 (d), 102.71 (s),
116.79 (t), 126.78 (d, integrating for 2 carbons), 128.58 (d),
128.98 (d, integrating for 2 carbons), 139.04 (s), 143.82 (s);
ES-MS (ES++Na) 313; Anal. calcd for C17H22O4: C,
70.32; H, 7.64. Found: C, 70.76; H, 7.36. Trioxane 21a. mp
96–98 ꢁC; IR (KBr, cmÀ1) 3448; 1H NMR (300 MHz,
CDCl3) d: 1.70–1.78 (m, 4H), 1.95–2.26 (m, 3H), 2.71 (d,
1H, J = 12.0 Hz), 3.80 (dd, 1H, J = 12.0, 3.0 Hz), 3.91
(dd,1H, J = 12.0, 9.9 Hz), 5.28 (dd, 1H, J = 9.9, 3.0 Hz),
5.34 and 5.50 (2 · s, 2H), 7.23–7.50 (m, 10H); 13C NMR
(75 MHz, CDCl3) d: 24.3 (t), 29.9 (t), 34.5 (t), 35.0 (t), 62.9
(t), 72.5 (s), 80.3 (d), 102.1 (s), 116.4 (t), 124.5 (d,
integrating for 2 carbons), 126.4 (d, integrating for 2
carbons), 127.0 (d), 128.1 (d), 128.3 (d, integrating for 2
carbons), 128.5 (d, integrating for 2 carbons), 138.5 (s),
143.3 (s), 148.0 (s); FAB-MS (m/z) 353 [M+H]+; Anal.
calcd for C22H24O4: C, 74.98%; H, 6.86%. Found: C,
74.66%; H, 6.71%. Trioxane 21b. mp 104–106 ꢁC; IR
1
125ꢁC; IR (KBr, cmÀ1) 1700, 3515; H NMR (200 MHz,
CDCl3) d: 1.27 (t, 3H, J = 7.1 Hz), 1.54–1.72 (m, 5H),
1.85–2.09 (m, 2H), 2.46 (s, 2H), 2.67 (dd, 1H, J = 13.4,
2.4 Hz), 3.51 (s, 1H, OH), 3.82 (dd, 1H, J = 11.9, 2.9 Hz),
4.06 (dd, 1H, J = 11.9, 10.2 Hz), 4.17 (q, 2H, J = 7.1 Hz),
5.28 (dd, 1H, J = 10.2, 2.9 Hz), 5.33 and 5.56 (2 · s, 2H),
7.34–7.61 (m, 9H); 13C NMR (50 MHz, CDCl3) d: 14.57
(q), 24.50 (t), 30.57 (t), 33.50 (t), 33.73 (t), 45.69 (t), 61.16
(t), 63.29 (t), 69.37 (s), 80.63 (d), 102.64 (s), 116.69 (t),
127.15 (d, integrating for 2 carbons), 127.43 (d, integrating
for 2 carbons), 127.69 (d, integrating for 2 carbons),
127.91 (d), 129.23 (d, integrating for 2 carbons), 137.85 (s),
140.83 (s), 141.47 (s), 143.31 (s), 173.40 (s); FAB-MS (m/z)
439 [M+H]+; Anal. Calcd for C26H30O6: C, 71.21%; H,
6.90%. Found: C, 70.89%; H, 6.97%. Trioxane 16. An oil:
IR (neat, cmÀ1) 1711; 1H NMR (200 MHz, CDCl3) d: 1.26
(t, 3H, J = 7.1 Hz), 1.77–1.84 (m, 2H), 2.08–2.19 (m, 1H),
2.27–2.45 (m, 3H), 2.84–3.13 (m, 2H), 3.79 (dd, 1H,
J = 12.1, 2.9 Hz), 3.94 and 3.96 (2 · dd, 1H, J = 12.1,
10.0 Hz, together integrating for 1H), 4.14 (q, 2H,
J = 7.1 Hz), 5.28 (dd, 1H, J = 10.0, 2.9 Hz), 5.33 and
5.50 (2 · s, 2H), 5.68 (s, 1H), 7.30–7.38 (m, 5H); 13C NMR
(50 MHz, CDCl3) d 14.69 (q), 24.82 and 24.97 (t), 29.18
and 29.90 (t), 33.06 and 33.28 (t), 34.82 and 35.46 (t), 60.04
(t), 63.41 (t), 80.77 (d), 102.14 (s), 115.08 (d), 116.85 and
117.00 (t), 126.80 (d, integrating for 2 carbons), 128.62 (d),
128.99 (d, integrating for 2 carbons), 138.96 (s), 143.78 (s),
159.97 (s), 166.78 (s); FAB-MS (m/z) 345 [M+H]+; HR-
EIMS calcd for C20H24O5, 344.1625; found: 344.1624.
Trioxane 17. An oil: IR (neat, cmÀ1) 1709; 1H NMR
(300 MHz, CDCl3) d: 1.29 and 1.30 (2 · t, 3H, J = 7.2 Hz,
together integrating for 3H), 1.72–1.78 (m, 3H), 1.89 (s,
3H), 2.00–2.16 (m, 1H), 2.28–2.43 (m, 2H), 2.51–2.71 (m,
2H), 3.79 (dd, 1H, J = 11.7, 3.1 Hz), 3.96 (dd, 1H,
J = 11.7, 10.8 Hz), 4.19 and 4.20 (2 · q, 2H, J = 7.2 Hz,
together integrating for 2H), 5.28 (dd, 1H, J = 10.8,
3.1 Hz), 5.33 and 5.50 (2 · s, 2H), 7.28–7.37 (m, 5H);
FAB-MS (m/z) 359 [M+H]+; HR-EIMS calcd for
C21H26O5, 358.1780; found, 358.1780. Trioxane 18. mp
143–145ꢁC; IR (KBr, cmÀ1) 1707; 1H NMR (200 MHz,
CDCl3) d: 1.27 (t, 3H, J = 7.1 Hz), 1.79–1.86 (m, 2H),
2.08–2.45 (m, 4H), 2.81–2.95 (m, 1H), 3.04–3.14 (m, 1H),
3.84 (dd, 1H, J = 11.7, 3.3 Hz), 3.97 and 3.99 (2 · dd, 1H,
J = 11.7, 10.2 Hz, together integrating for 1H), 4.15 (q,
2H, J = 7.1 Hz), 5.32 (dd, 1H, J = 10.2, 3.3 Hz), 5.35 and
5.57 (2 · s, 2H), 5.69 (s, 1H), 7.34–7.60 (m, 9H); FAB-MS
(m/z) 421 [M+H]+; Anal. calcd for C26H28O5: C, 74.26%;
H, 6.71%. Found: C, 74.37%; H, 6.82%. Trioxane 19. mp
68–70ꢁC; IR (KBr, cmÀ1) 1705; 1H NMR (200 MHz,
CDCl3) d: 1.29 and 1.30 (2 · t, 3H,J = 7.0 Hz, together
integrating for 3H), 1.75–1.82 (m, 3H), 1.89 (s, 3H), 2.06–
2.13 (m, 1H), 2.33–2.46 (m, 2H), 2.56–2.68 (m, 2H), 3.83
(dd, 1H, J = 11.7, 3.1 Hz), 4.00 (dd, 1H, J = 11.7,
10.3 Hz), 4.19 and 4.20 (2 · q, 2H, J = 7.0 Hz, together
integrating for 2H), 5.30 (dd, 1H, J = 10.3, 3.1 Hz), 5.35
and 5.57 (2 · s, 2H), 7.30–7.60 (m, 9H); 13C NMR
(50 MHz, CDCl3) d: 14.71 (q), 15.80 (q), 26.46 and 26.64
(t), 27.23 and 27.43 (t), 29.22 and 29.76 (t), 34.83 and 35.34
(t), 60.72 (t), 63.46 (t), 80.69 and 80.73 (d), 102.65 (s),
116.82 and 116.90 (t), 122.09 (s), 127.22 (d, integrating for
2 carbons), 127.43 (d, integrating for 2 carbons), 127.70 (d,
integrating for 2 carbons), 127.95 (d), 129.27 (d, integrat-
ing for 2 carbons), 137.81 (s), 140.81 (s), 141.47 (s), 143.31
(s), 145.11 and 145.24 (s), 170.40 (s); FAB-MS (m/z) 435
[M+H]+; Anal. calcd for C27H30O5: C, 74.63%; H, 6.96%.
Found: C, 74.84%; H, 6.82%. Trioxane 20a. An oil: IR
(neat, cmÀ1) 3419; 1H NMR (200 MHz, CDCl3) d: 1.26 (s,
1
(KBr, cmÀ1) 3449; H NMR (200 MHz, CDCl3) d: 1.69–
2.21 (m, 7H), 2.84 (d, 1H, J = 12.5 Hz), 3.81 (dd, 1H,
J = 11.9, 2.8 Hz), 4.07 (dd, 1H, J = 11.9, 10.4 Hz), 5.29
(dd, 1H, J = 10.4, 2.8 Hz), 5.34 and 5.52 (2 · s, 2H), 7.28–
7.52 (m, 10H); 13C NMR (50 MHz, CDCl3) d: 25.11 (t),
31.25 (t), 35.49 (2 · t), 63.39 (t), 73.46 (s), 80.78 (d), 102.50
(s), 116.92 (t), 124.91 (d, integrating for 2 carbons), 126.81
(d, integrating for 2 carbons), 127.46 (d), 128.67 (d),
128.76 (d, integrating for 2 carbons), 129.05 (d, integrating
for 2 carbons), 139.04 (s), 143.78 (s), 148.66 (s); FAB-MS
(m/z) 353 [M+H]+; Anal. calcd for C22H24O4: C, 74.98%;
H, 6.86%. Found: C, 74.72%; H, 6.53%.
8. In all cases ratio of the diastereomers and geometrical
isomers, as assessed by 1H NMR and 13C NMR, is around
50:50.
9. The in vivo efficacy of compounds was evaluated against P.
yoelii (MDR) in Swiss mice model. The colony bred Swiss
mice (25 1 g) were inoculated with 1 · 106 parasitized
RBC on day zero and treatment was administered to a
group of five mice at each dose, from day 0 to 3, in two
divided doses daily. The drug dilutions of compounds 10
and 11, 14–21 were prepared in groundnut oil while
hemisuccinates 12 and 13 were dissolved in 5% NaHCO3
so as 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 and
0.3 mg for a dose of 24 mg/kg) in 0.1 ml and administered
either intramuscularly or orally for each dose. Parasitaemia
level was recorded from thin blood smears between days 4
and 28.11 Mice treated with b-arteether served as positive
controls.
10. Belpaire, F.; Bogaert, M. G.. In Wermuth, C. G., Ed.,
Second ed.; The Practice of Medicinal Chemistry; Aca-
demic Press: Oxford, 2003, pp 501–515.
11. Puri, S. K.; Singh, N. Exp. Parasitol. 2000, 94, 8.