Orally active 1,2,4-trioxepanes: Synthesis and antimalarial activity of a series of 7-arylvinyl-1,2,4-trioxepanes against multidrug-resistant Plasmodium yoelii in Swiss mice

Article abstract of DOI:10.1016/j.bmc.2007.11.012

7-Arylvinyl-1,2,4-trioxepanes 7a-d, 8a-d, 9a-d, 10a-d, 11a-c, and 12a-c, prepared by photooxygenation of homoallylic alcohols 5a-d, were evaluated against multi-drug resistant Plasmodium yoelii nigeriensis in Swiss mice by oral and intramuscular routes. Trioxepane 11c, the most active compound of the series, showed more than 98% suppression of parsitaemia at 96 mg/kg by both oral and intramuscular routes. This is the first report on in vivo active 1,2,4-trioxepanes.

Full text of DOI:10.1016/j.bmc.2007.11.012

Available online at www.sciencedirect.com
Bioorganic & Medicinal Chemistry 16 (2008) 1816–1821
Orally active 1,2,4-trioxepanes: Synthesis and antimalarial
activity of a series of 7-arylvinyl-1,2,4-trioxepanes
against multidrug-resistant Plasmodium yoelii in Swiss miceq
Chandan Singh,a,* Shilpi Pandey,a Malvika Sharmaa and Sunil K. Purib
aDivision of Medicinal & Process Chemistry, Central Drug Research Institute, Lucknow, India
bDivision of Parasitology, Central Drug Research Institute, Lucknow, India
Received 4 October 2007; revised 1 November 2007; accepted 2 November 2007
Available online 6 November 2007
Abstract—7-Arylvinyl-1,2,4-trioxepanes 7a–d, 8a–d, 9a–d, 10a–d, 11a–c, and 12a–c, prepared by photooxygenation of homoallylic
alcohols 5a–d, were evaluated against multi-drug resistant Plasmodium yoelii nigeriensis in Swiss mice by oral and intramuscular
routes. Trioxepane 11c, the most active compound of the series, showed more than 98% suppression of parsitaemia at 96 mg/kg
by both oral and intramuscular routes. This is the first report on in vivo active 1,2,4-trioxepanes.
ꢀ 2007 Elsevier Ltd. All rights reserved.
1. Introduction
H
H
H
O
O
O
Malaria is a major threat to the health and economic
prosperity to the people living in tropical and subtropi-
cal areas. Approximately 40% of the world population
lives in areas with the risk of malaria and more than a
million die from this disease.1 The increasing resistance
of causal parasite, Plasmodium to the contemporary
antimalarial drugs, including chloroquine, has further
complicated the malaria problem. Against this scenario,
isolation of artemisinin 1 as the antimalarial principle of
Chinese traditional herb, Artemisia annua, is a major
milestone in the history of malaria chemotherapy. Ever
since its isolation, artemisinin has been a subject of in-
tense structure activity relationship studies.2
O
O
O
O
O
O
H
H
H
O
O
O
OR
O
OCOCH2CH2COOH
1
2 R = Me
3 R = Et
4
Figure 1.
of methods of their synthesis have been reported in re-
cent years.3,4
In contrast, 1,2,4-trioxepanes, the next higher homologs
of 1,2,4-trioxanes and the next obvious candidates for
structure activity relationship (SAR) studies in this area,
have received only limited attention. Only a few meth-
ods of their synthesis have been reported,5–8 the number
of compounds synthesized is small and there is only one
report on their antimalarial activity.8
The antimalarial activity of artemesinin and its clinically
useful derivatives such as artemether 2, arteether 3, and
artesunic acid 4 (Fig. 1) is due to the presence of 1,2,4-
trioxane moiety in their molecular structure. Because
of the limited availability of artemisinin, currently the
focus is on the synthesis and antimalarial assessment
of structurally simplified 1,2,4-trioxanes and a variety
Earlier, we have reported a photooxygenation route for
the preparation of 1,2,4-trioxepanes. The key steps of
this method are (i) preparation of c-hydroxyhydroper-
oxides by photooxygenation of homoallylic alcohols
and (ii) acid catalyzed condensation of these hydrox-
yhydroperoxides with various ketones to furnish 1,2,4-
trioxepanes (Scheme 1).9
Keywords: Malaria chemotherapy; 1,2,4-Trioxane; 1,2,4-Trioxepane;
Multidrug resistant Plasmodium yoelii; Orally active.
q
CDRI communication number: 7188.
*
Corresponding author. Tel.: +91 522 2624273; fax: +91 522
2623405; e-mail: chandancdri@yahoo.com
0968-0896/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2007.11.012

C. Singh et al. / Bioorg. Med. Chem. 16 (2008) 1816–1821
1817
R1
OH
OH
O
1O2
Ar
Ar
R2
H+
O
OH
OH
O
Ar
R1
R2
OOH
6a-d
Ar
Ar
5a-d
OOH
O
O
O
O
O
O
Scheme 1.
O
O
Ar
O
Ar
11a-c
10a-d
Using this methodology we had earlier reported the
preparation of trioxepanes 7a–d, 8a–d and 9a–d
(Fig. 2).9 In this article, we report the preparation of re-
lated 1,2,4-trioxepanes 10a–d, 11a–c, 12a–c and antima-
larial assessment of all these trioxepanes against
multidrug resistant Plasmodium yoelii nigeriensis in
Swiss mice by oral and intramuscular routes. While
the activity of a few 1,2,4-trioxepanes against P. falcipa-
rum in vitro has been reported,8 to the best of our
knowledge this is the first report on in vivo antimalarial
assessment of 1,2,4-trioxepanes.
OH
O
O
Ar
12a-c
Figure 3. a, Ar = phenyl; b, Ar = 4-Cl-phenyl; c, Ar = 4-biphenyl;
d, Ar = 1-naphthyl.
muscular routes. b-Arteether was used as positive con-
trol. The results are summarized in Table 2.
4. Results and discussion
2. Chemistry
As can be seen from Table 2, several of these trioxepanes
exhibited significant suppression of parasitaemia on day
4. Keto trioxepane 11c is the most active compound of
the series. It showed 100% and 98% suppression of para-
sitaemia by intramuscular and oral routes, respectively,
but none of the treated mice survived beyond day 14.
Structurally related keto trioxepanes 11a and 11b are rel-
atively less active. While 11b showed 100% suppression of
parasitaemia by intramuscular route, it exhibited poor
activity by oral route; keto trioxepane 11a showed only
moderate suppression of parasitaemia by oral route. Tri-
oxepanes 7a, 7c and 9c also exhibited significant activity;
while all these compounds showed more than 90% sup-
pression of parasitaemia by oral route, only 7a showed
significant suppression of parasitaemia by i.m. route.
Next in order of activity are trioxepanes 7d, 11a and
12c; all these compounds showed more than 70% suppres-
sion of parasitaemia by oral route. The remainder of the
trioxepanes exhibited poor activity. A comparison of
the activity data of these trioxepanes with our published
data4b,c–l on structurally related trioxanes shows that tri-
oxepanes as a class are less active than the trioxanes.
Trioxepanes 7a–d, 8a–d, and 9a–d were prepared using
the procedure reported earlier.9 c-Hydroxyhydroperox-
ides 6a–d prepared by photooxygenation of homoallylic
alcohols 5a–d according to the published procedure9
were condensed with 2-adamantanone to furnish trioxe-
panes 10a–d in 7–47% yield. A similar reaction of c-
hydroxyhydroperoxide 6a–c with 1,4-cyclohexanedione
furnished keto trioxepanes 11a–c in 40–43% yield (Table
1). LiAlH4 reduction of trioxepanes 11a–c furnished hy-
droxy functionalized trioxepanes 12a–c as inseparable
mixture of diastereomers in 76–79% yields (Fig. 3).
3. Biological activity
Trioxepanes 7a–d, 8a–d, 9a–d, 10a–d, 11a–c, and 12a–c
were evaluated for antimalarial activity against multi-
drug resistant P. yoelii nigeriensis in Swiss mice using
the published protocol.10 All of these compounds were
screened at a dose of 96 mg/kg by both oral and intra-
O
O
O
O
O
O
O
Ar
Ar
Ar
As part of our efforts to understand the mechanism of ac-
tion of 1,2,4-trioxanes, we had earlier reported the Fe (II)
catalyzed chemistry of several 1,2,4-trioxanes structurally
related to the present 1,2,4-trioxepanes.11 Trioxepane 8a
when reacted with FeBr2 in similar reaction conditions,
behaved similarly and furnished diol 13 and bromo deriv-
ative 14 in 29% and 27% yields, respectively (Scheme 2).
Structure of bromo derivative 14 was further confirmed
through its acetyl derivative 15. These observations show
that the difference in the order of antimalarial activity of
these trioxepanes and the related 1,2,4-trioxanes is not
due to their sensitivity towards Fe (II) reagents.
O
O
9a-d
7a-d
8a-d
Figure 2. a, Ar = phenyl; b, Ar = 4-Cl-phenyl; c, Ar = 4-biphenyl; d,
Ar = 1-naphthyl.
Table 1. 1,2,4-Trioxepanes
Compound
Ar
Yielda
%
10a
10b
10c
10d
11a
11b
11c
Phenyl
46
47
39
7
4-Cl-Phenyl
4-Biphenyl
1-Naphthyl
Phenyl
41
43
40
5. Conclusion
4-Cl-Phenyl
4-Biphenyl
We have evaluated a series of 1,2,4-trioxepanes for anti-
malarial activity, several of which exhibited significant
a Yields based on c-hydroxyhydroperoxides.

1818
C. Singh et al. / Bioorg. Med. Chem. 16 (2008) 1816–1821
Table 2. Antimalarial activity of 1,2,4-trioxepanes against P. yoelii in
Swiss mice
O
O
Ar
Compound Dose
(mg/kg/day)
Routea % Suppressionb
on day 4
O
8a
Phenyl
7a
96
96
Oral
i.m.
92.38
87.31
FeBr2, THF, 2h
4-Cl-phenyl 7b
4-Biphenyl 7c
1-Naphthyl 7d
96
96
Oral
i.m.
48.77
57.64
OH
O
Br
96
96
Oral
i.m.
98.22
42. 13
+
OH
OH
O
96
96
Oral
i.m.
70.37
32.10
13
29%
14
27%
Phenyl
8a
96
96
Oral
i.m.
18.21
58.71
DMAP, Ac2O, Et3N
DCM, 2.5h
4-Cl-phenyl 8b
4-Biphenyl 8c
1-Naphthyl 8d
96
96
Oral
i.m.
27.16
6. 17
96
96
Oral
i.m.
64.38
42.36
O
O
15
91%
Br
OAc
96
96
Oral
i.m.
49.75
19.80
Phenyl
9a
96
96
Oral
i.m.
35.80
9.38
Scheme 2.
4-Cl-phenyl 9b
4-Biphenyl 9c
1-Naphthyl 9d
96
96
Oral
i.m.
24.69
46. 91
activity by oral and intramuscular route. Trioxepane
11c, the most active compound of the series, showed
more than 98% suppression of parasitaemia on day 4
both by oral and intramuscular routes. To the best of
our knowledge, this is the first report on in vivo active
1,2,4-trioxepanes.
96
96
Oral
i.m.
91.36
24.69
96
96
Oral
i.m.
17.16
22.25
Phenyl
10a
96
96
Oral
i.m.
57.36
27.41
6. Experimental
4-Cl-phenyl 10b
4-Biphenyl 10c
1-Naphthyl 10d
96
96
Oral
i.m.
58.38
12.18
6.1. General section
96
96
Oral
i.m.
44.78
31.98
All glass apparatus were oven dried prior to use. Melt-
ing points were determined on complab melting point
apparatus and were uncorrected. IR spectra were re-
corded on a Perkin-Elmer FT-IR RX-1 spectrophotom-
96
96
Oral
i.m.
38.27
11.11
1
eter. H NMR and 13C NMR spectra were recorded on
Phenyl
11a
96
96
Oral
i.m.
72.02
36.60
Bruker DPX-200 or Brucker DRX-300 (operating at 200
or 300 MHz) using CDCl3 as solvent. Tetramethylsilane
(d 0.00 ppm) served as an internal standard in 1H NMR
and CDCl3 (d 77.0 ppm) in 13C NMR. Fast Atom Bom-
bardment Mass Spectra (FAB-MS) were obtained on
JEOL SX 102 spectrometer using argon/xenon (6 kv,
10 mA) as the FAB gas. Glycerol or m-nitrobenzyl alco-
hol was used as matrix. Elemental analyses were done
on Perkin-Elmer 2400 C, H, and N analyzer. Reactions
were monitored on silica gel TLC plates (coated with
TLC grade silica gel, obtained from Merck). Detecting
agents used (for TLC) were: iodine vapours and/or
spraying with an aq solution of vanillin in 10% sulfuric
acid followed by heating at 150 ꢁC. Column chroma-
tograpy was performed over silica gel (60–120 mesh)
procured from QualigensTM (India). All chemicals and
reagents were obtained from Aldrich (USA), or Spectro-
chem (India) and were used without further purification.
Anhydrous diethyl ether (ether) used in Grignard reac-
4-Cl-phenyl 11b
4-Biphenyl 11c
96
96
Oral
i.m.
23.36
100.00
96
96
Oral
i.m.
98.49
100.00
Phenyl
12a
96
96
Oral
i.m.
53.59
21.39
4-Cl-phenyl 12b
4-Biphenyl 12c
96
96
Oral
i.m.
54.59
11.47
96
96
Oral
i.m.
84.13
75.47
b-Arteether
3
48
Oral
100
a The drug dilution of compounds were prepared in ground nut oil and
were administered to a group of 5 mice at each dose from day 0–3 in
two divided dose daily.
b Percent suppression = [(C À T)/C] · 100, where C = parasitaemia in
control group and T = parasitaemia in treated group.

C. Singh et al. / Bioorg. Med. Chem. 16 (2008) 1816–1821
1819
tions was obtained from Spectrochem and was kept over
sodium overnight prior to use. c-Hydroxyhydroperox-
ides 6a–d were prepared by published procedure.9
8.02–8.07 (m, 1H); 13C NMR (50 MHz, CDCl3) d
27.58 (2· CH), 30.10 (CH2), 33.49 (CH), 34.34 (CH2),
34.98 (CH2), 35.38 (CH), 37.90 (CH2), 38.02 (CH2),
60.21 (CH2), 86.36 (CH), 108.89 (C), 118.08 (CH2),
125.56 (CH), 126.17 (2· CH), 126.36 (CH), 126.44
(CH), 128.20 (CH), 128.64 (CH), 132.01 (C), 134.08
(C), 138.97 (C), 146.58 (C); MS (m/z) 377 (M+H)+;
Anal. Calcd for C25H28O3: C, 79.75; H, 7.50. Found:
C, 79.29; H, 7.92.
6.2. General procedure and characterization data
6.2.1. General procedure for the preparation of 1,2,4-
trioxepanes from c-hydroxyhydroperoxides (preparation
of 10a as representative). A solution of c-hydroxyhydr-
operoxide 6a (2.0 g), 2-adamantanone (3.1 g, 2 equiv)
and conc HCl (0.5 mL) in dichloromethane (50 mL)
was stirred for 0.5 h at rt. The reaction mixture was con-
centrated on a rotatory evaporator at rt and the crude
product was purified by column chromatography over
silica gel using 0.5% ethyl acetate-hexane as eluent to
6.2.1.4. Compound 11a. Yield 41%, 1H NMR
(200 MHz, CDCl3) d 1.68–2.55 (m, 10H), 3.86 (td, 1H,
J = 12.4, 3.2 Hz), 4.09 (m, 1H), 5.13 (dd, 1H, J = 11.2,
3.2 Hz), 5.38 & 5.46 (2· s, 2H), 7.22–7.49 (m, 5H); 13C
NMR (50 MHz, CDCl3) d; 30.07 (CH2), 30.66 (CH2),
32.92 (CH2), 37.57 (CH2), 53.85 (CH2), 61.41 (CH2),
86.12 (CH), 105.56 (C), 116.56 (CH2), 127.04 (CH),
128.29 (CH), 128.44 (CH), 128.84 (CH), 139.93 (C),
146.34 (C), 210.66 (C). ESMS (m/z) (M)+ 288,
(M+Na)+ 311, (M+K)+ 327; FT-IR (cmÀ1) 1716.9;
Anal. Calcd for C17H20O4: C, 70.81; H, 6.99. Found:
C, 71.23; H, 7.44.
1
furnish 1.56 g (46% yield) of 10a as colourless oil; H
NMR (200 MHz, CDCl3) d 1.60–2.14 (m, 15H), 2.31
(brs, 1H), 3.76 (td, 1H, J = 12.3, 3.3 Hz), 4.02 (t, 1H,
J = 12.1 Hz), 5.05 (dd, 1H, J = 11.2, 3.4 Hz), 5.35 &
5.40 (2· s, 2H), 7.27–7.44 (m, 5H); 13C NMR
(50 MHz, CDCl3) d 27.5 (2· CH), 33.47 (CH), 34.03
(CH2), 34.21 (CH2), 34.33 (CH2), 34.43 (CH2), 35.04
(CH2), 35.47 (CH), 37.95 (CH2), 60.30 (CH2), 85.77
(CH), 108.87 (C), 116.05 (CH2), 127.15 (2· CH),
128.10 (CH), 128.74 (2· CH), 140.14 (C), 146.99 (C);
MS (m/z) 327(M+H)+.
1
6.2.1.5. Compound 11b. Yield 43%, mp 74–80 ꢁC; H
NMR (200 MHz, CDCl3) d 1.70–2.54 (m, 10H), 3.86 (td,
1H, J = 12.4, 3.4 Hz), 4.04–4.15 (m, 1H), 5.08 (dd, 1H,
J = 11.2, 3.2 Hz), 5.40 & 5.46 (2· s, 2H), 7.28–7.38 (m,
4H); 13C NMR (50 MHz, CDCl3) d 30.60 (CH2), 32.90
(CH2), 37.21 (CH2), 37.51 (CH2), 61.31 (CH2), 85.99
(CH), 105.62 (C), 117.62 (CH2), 128.43 (CH), 129.43
(CH), 134.23 (C), 138.30 (C), 145.08 (C), 210.76 (C);
MS (m/z) (M+H)+ 323; FT-IR (cmÀ1) 1717.4.
Compounds 10b–d and 11a–c were also prepared by the
same procedure.
1
6.2.1.1. Compound 10b. Yield 47%, mp 81–85 ꢁC; H
NMR (200 MHz, CDCl3) d 1.60–2.17 (m, 15H), 2.27
(brs, 1H), 3.76 (td, 1H, J = 12.1, 3.4 Hz), 4.01 (t, 1H,
J = 11.8 Hz), 4.99 (dd, 1H, J = 11.5, 3.6 Hz), 5.37 &
5.41 (2· s, 2H), 7.27–7.37 (m, 4H); 13C NMR (50 MHz,
CDCl3) d 27.53 (2· CH), 33.42 (CH), 34.00 (CH2),
34.31 (CH2), 34.39 (CH2), 35.02 (CH2), 35.47 (CH),
37.61 (CH2), 37.82 (CH2), 60.19 (CH2), 85.72 (CH),
108.94 (C), 116.93 (CH2), 128.56 (2· CH), 128.91 (2·
CH), 134.01 (C), 138.44 (C), 145.74 (C); MS (m/z) 361,
363 (M+H)+; Anal. Calcd for C21H25O3Cl + 0.35 H2O:
C, 68.69; H, 7.05. Found: C, 68.40; H, 6.92.
6.2.1.6. Compound 11c. Yield 40%, mp 80–85 ꢁC;1H
NMR (200 MHz, CDCl3) d 1.91–2.57 (m, 10H), 3.87
(td, 1H, J = 12.3, 3.4 Hz), 4.07–4.18 (m, 1H), 5.18 (dd,
1H, J = 11.2, 3.2 Hz), 5.41 & 5.53 (2· s, 2H), 7.25–
7.61 (m, 9H); 13C NMR (50 MHz, CDCl3) d 30.25
(CH2) 32.52 (CH2) 37.12 (CH2), 61.01 (CH2), 85.69
(CH), 105.18 (C), 116.19 (CH2), 127.01 (CH), 127.14
(CH), 27127.41 (CH), 128.79 (CH), 138.32 (C), 140.51
(C), 140.74 (C), 210.38 (C); MS (m/z) 365.0 (M+H)+,
382.1 (M+NH4)+, 387.2 (M+Na)+; FT-IR (cmÀ1
)
6.2.1.2. Compound 10c. Yield 39%, mp 99–102 ꢁC; 1H
NMR (200 MHz, CDCl3) d 1.61–2.12 (m, 15H), 2.32
(brs, 1H), 3.78 (td, 1H, J = 12.3, 3.3 Hz), 4.04 (t, 1H,
J = 12.4 Hz), 5.10 (dd, 1H, J = 11.16, 3.3 Hz), 5.38 &
5.48 (2· s, 2H), 7.40–7.61 (m, 9H); 13C NMR
(50 MHz, CDCl3) d 27.59 (2· CH), 33.50 (CH), 34.05,
(CH2), 34.35 (CH2), 34.45 (CH2), 35.06 (CH2), 35.51
(CH), 37.89 (CH2), 60.31 (CH2), 85.77 (CH), 108.92
(C), 116.08 (CH2), 127.41 (CH), 127.46 (CH), 127.55
(CH), 127.74 (CH), 129.18 (CH), 138.96 (C), 140.95
(C), 141.07 (C), 146.50 (C); MS (m/z) 403 (M+H)+;
HRMS Calcd for C27H30O3: 402.2195. Found:
402.2189.; Anal. Calcd for C27H30O3 + 0.1 H2O: C,
80.20; H, 8.02. Found: C, 80.11; H, 8.04.
1727.4; Anal. Calcd for C23H24O4: C, 75.80; H, 6.64.
Found: C, 75.35; H, 7.07.
6.2.2. General procedure for the LiAlH4 reduction of
trioxepanes 11a–c (preparation of 12a as representative).
To a precooled (0 ꢁC) magnetically stirred slurry of
LiAlH4 (25 mg) in anhydrous ether (10 mL) was added
a solution of ester 11 (500 mg) in anhydrous ether
(10 mL), under nitrogen and stirred at 0 ꢁC for 1 h. Ex-
cess LiAlH4 was quenched by careful addition of cold
water followed by 10% aq NaOH, during which gray
colour changed to white. The ether layer was decanted
off and the white precipitate rinsed with ether
(3 · 5 mL). Combined organic extract was concentrated
and the crude product was purified over a silica gel col-
umn using dichloromethane as eluent to furnish 400 mg
(79% yield) of 12a as a colourless oil; 1H NMR
(200 MHz, CDCl3) d 1.52–2.16 (m, 10H), 3.77–3.83
(m, 2H), 3.96–4.03 (m, 1H), 5.06 (dd, 1H, J = 11.1,
2.2 Hz), 5.36 & 5.43 (2· s, 2H), 7.26–7.42 (m, 5H); 13C
6.2.1.3. Compound 10d. Yield 7%, oil; 1H NMR
(200 MHz, CDCl3) d 1.48–2.01 (m, 15H), 2.31 (brs,
1H), 3.67 (td, 1H, J = 12.3, 3.4 Hz), 3.89 (t, 1H,
J = 12.1 Hz), 4.96 (dd, 1H, J = 10.9, 3.5 Hz), 5.25 &
5.66 (2· s, 2H), 7.29–7.52 (m, 4H), 7.87–7.52 (m, 2H),

1820
C. Singh et al. / Bioorg. Med. Chem. 16 (2008) 1816–1821
NMR (50 MHz, CDCl3) d 27.92 (CH2) 29.13 (CH2)
30.83 (CH2), 30.87 (CH2), 31.08 (CH2), 31.25 (CH2),
31.49 (CH2), 31.64 (CH2), 37.63 (CH2), 37.71 (CH2),
60.82 (CH2), 61.06 (CH2), 68.35 (CH), 69.09 (CH),
85.92 (CH), 106.30 (C), 106.33 (C), 116.44 (CH2),
127.08 (2· CH), 128.21 (CH), 128.81 (2· CH), 140.03
(C), 140.56 (C); MS (m/z) 291.2 (M+H)+; FT-IR
(cmÀ1) 3427.2, Anal. Calcd for C17H22O4 + 0.1H2O: C,
69.88; H, 7.67. Found: C, 69.62; H, 7.88.
2H, J = 7.2 Hz), 3.41 (t, 2H, J = 9.6 Hz), 4.16–4.31 (m,
2H), 4.74–4.77 (m, 1H), 5.35 & 5.41 (2· s, 2H), 7.27–
7.41 (m, 5H); 13C NMR (50 MHz, CDCl3): d 23.89
(CH2), 32.35 (CH2), 33.42 (CH2), 33.68 (CH2), 35.43
(CH2), 62.08 (CH2), 71.10 (CH), 109.95 (C), 113.36
(CH2), 127.24 (2· CH), 125.43 (CH), 128.25 (2· CH),
139.92 (C), 151.59 (C), 173.65 (C); FT-IR: 3020.1,
2928.2, 1728.5 cmÀ1
.
6.2.4. Compound 15. To a solution of compound 14
(50 mg), triethylamine (0.2 ml) and 4-dimethylamino-
pyridine (0.01 g) in dichloromethane (2 ml) was added
Ac2O (0.2 ml) with constant stirring.The reaction mix-
ture was stirred for 2.5 h, concentrated under vacuum
and the crude product was purified by column chroma-
tography over silica gel using 5% ethyl acetate-hexane as
eluent to furnish 50 mg (91% yield) of 15 as a colourless
oil; yield 91%; 1H NMR (300 MHz, CDCl3): d 1.71–2.06
(m, 6H), 2.12 (s, 3H), 2.30 (t, 2H, J = 7.2 Hz), 3.92 (t,
2H, J = 6.6 Hz), 4.06–4.12 (m, 2H), 5.30 & 5.53 (2· s,
2H), 5.80 (dd, 1H, J = 7.2, 5.7 Hz) 7.26–7.43 (m, 5H);
13C NMR (50 MHz, CDCl3): d 21.56 (CH3), 23.80
(CH2), 30.08 (CH2), 32.34 (CH2), 33.37 (CH2), 33.54
(CH2), 61.05 (CH), 72.59 (CH), 114.49 (CH2), 127.35
(2· CH), 128.43 (CH), 128.90 (2· CH), 139.39 (C),
148.21 (C), 170.48 (C), 173.31 (C); FAB-MS: 323, 325,
(M)+–CH3COOH, EIMS: 405.1 (M+Na)+; HRMS:
Cald for C16H20O2Br: 323.06466, found: 323.06458;
Compounds 12b & 12c were also prepared by the same
procedure.
6.2.2.1. Compound 12b. Yield 77%, 1H NMR
(200 MHz, CDCl3) d 1.49–2.09 (m, 10H), 3.71–3.91
(m, 2H), 4.02 (td, 1H, J = 11.4, 2.3 Hz), 5.01 (dd, 1H,
J = 11.1, 2.2 Hz), 5.38 & 5.43 and 5.40 & 5.46 (4· s, to-
gether integrating for 2H), 7.26–7.37 (m, 4H); 13C NMR
(50 MHz, CDCl3) d 27.89 (CH2) 29.00 (CH2) 30.59
(CH2), 30.83 (CH2), 31.04 (CH2), 31.23 (CH2), 31.42
(CH2), 31.58 (CH2), 32.89 (CH2), 37.08 (CH2), 37.39
(CH2), 60.69 (CH2), 60.94 (CH2), 68.30 (CH), 68.94
(CH), 85.79 (CH), 106.36 (C), 117.17 (CH2), 129.02
(2· CH), 130.28 (CH), 134.08 (C), 134.22 (C), 138.39
(C), 145.37 (C); MS (m/z) 325.2 (M + H)+; Anal. Calcd
for C17H21O3Cl + 0.15 H2O: C, 62.34; H, 6.56. Found:
C, 62.20; H, 6.87; FT-IR (cmÀ1) 3424.8.
6.2.2.2. Compound 12c. Yield 76%, mp 123–127 ꢁC,
1H NMR (200 MHz, CDCl3) d 1.51–2.21 (m, 10H),
3.79–3.82 (m, 2H), 3.99–4.11 (m, 1H), 5.11 (dd, 1H,
J = 10.94, 2.1 Hz), 5.39 & 5.51 (2· s, 2H), 7.25-7.61
(m, 9H); 13C NMR (50 MHz, CDCl3) d 27.51 (CH2)
28.64 (CH2) 30.43 (CH2), 30.68 (CH2), 30.85 (CH2),
31.07 (CH2), 31.22 (CH2), 37.18 (CH2), 60.38 (CH2),
67.96 (CH), 68.62 (CH), 85.46 (CH), 105.92 (C),
115.93 (CH2), 126.97 (CH), 127.06 (CH), 127.34 (CH),
128.76 (CH), 138.39 (C), 140.59 (C), 145.64 (C); MS
(m/z) 367.2 (M+H)+; Anal. Calcd for C21H25O3Cl +
0.25 H2O: C, 74.47; H, 7.21. Found: C, 74.11; H, 7.65;
FT-IR (cmÀ1) 3428.8.
FT-IR: 1739.0 cmÀ1
.
6.3. In vivo antimalarial activity
The in vivo efficacy of compounds was evaluated against
Plasmodium yoelii nigeriensis (MDR) in Swiss mice
model. The colony bred Swiss mice (25 1 g) were inoc-
ulated with 106 parasitised RBC on day zero and treat-
ment was administered to a group of five mice at each
dose, from day 0–3, in two divided doses daily. The drug
dilutions were prepared so as to contain the required
amount of the drug (1.2 mg for a dose of 96 mg/kg) in
0.1 ml and administered either intramuscularly or orally
for each dose. Parasitaemia levels were recorded from
thin blood smears from day 4–17 by which time all the
treated mice were dead.
6.2.3. Reaction of 1,2,4-trioxepane 8a with FeBr2. A solu-
tion of compound 8a (500 mg) and FeBr2 (210 mg, 0.5
equiv) in anhydrous THF stirred at rt for 2 h. THF
was evaporated, crude was taken in dichloromethane
and filtered through celite-545, concentrated on a rota-
tory evaporator at rt. The crude product was purified
by column chromatography over silica gel to furnish
compound 13 (0.1 g, yield 29%), and compound 14
(0.18 g, yield 27%).
Acknowledgments
We thank ICMR, New Delhi, for the financial support
and SAIF (CDRI), Lucknow for providing spectral
and analytical data. Shilpi Pandey is thankful to Council
of Scientific and Industrial Research (CSIR), New Del-
hi, for the award of Senior Research Fellowship.
6.2.3.1. Compound 13. Oil; 1H NMR (300 MHz,
CDCl3) d 1.72–1.90 (m, 2H), 2.23 (bs, 1H), 2.72 (bs,
1H), 3.82–3.89 (m, 2H), 4.93–4.95 (m, 1H), 5.37–5.46
(2· s, 2H), 7.31–7.41 (m, 5H); 13C NMR (50 MHz,
CDCl3) d 37.43 (CH2), 61.52 (CH2),73.60 (CH), 112.98
(CH2), 127.21 (2· CH), 128.12 (CH), 128.86 (2· CH),
140.24 (C), 151.75 (C); FAB-MS (m/z) 179 (M+H)+,
161 (M+H ÀH2O)+, 143 (M+H À2 H2O)+.
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