Effect of functional group polarity on the antimalarial activity of spiro and dispiro-1,2,4-trioxolanes

Article abstract of DOI:10.1016/j.bmc.2006.05.041

Based on the structures of several lipophilic trioxolane antimalarial prototypes, we set out to determine which functional groups were associated with good antimalarial profiles and identify more polar (lower Log P/Log D) lead compounds with good physicoc

Full text of DOI:10.1016/j.bmc.2006.05.041

Bioorganic & Medicinal Chemistry 14 (2006) 6368–6382
Effect of functional group polarity on the antimalarial activity
of spiro and dispiro-1,2,4-trioxolanes
Yuxiang Dong,a Yuanqing Tang,a Jacques Chollet,b Hugues Matile,c Sergio Wittlin,b
Susan A. Charman,d William N. Charman,d Josefina Santo Tomas,b Christian Scheurer,b
Christopher Snyder,b Bernard Scorneaux,b Saroj Bajpai,a Scott A. Alexander,a
Xiaofang Wang,a Maniyan Padmanilayam,a Srinivasa R. Cheruku,a
Reto Brunb and Jonathan L. Vennerstroma,*
aCollege of Pharmacy, University of Nebraska Medical Center, 986025 Nebraska Medical Center, Omaha, NE, USA
bSwiss Tropical Institute, Socinstrasse 57, CH-4002 Basel, Switzerland
cF. Hoffmann-La Roche Ltd, Grenzacherstrasse 124, CH-4070 Basel, Switzerland
dCentre for Drug Candidate Optimisation, Victorian College of Pharmacy, Monash University,
381 Royal Parade, Parkville, Vic. 3052, Australia
Received 30 March 2006; accepted 23 May 2006
Available online 8 June 2006
Abstract—Based on the structures of several lipophilic trioxolane antimalarial prototypes, we set out to determine which functional
groups were associated with good antimalarial profiles and identify more polar (lower LogP/LogD) lead compounds with good
physicochemical properties. More lipophilic trioxolanes tended to have better oral activities than their more polar counterparts. Tri-
oxolanes with a wide range of neutral and basic, but not acidic, functional groups had good antimalarial profiles.
ꢀ 2006 Elsevier Ltd. All rights reserved.
H
The semisynthetic artemisinins artemether and artesu-
nate are important drugs in malaria chemotherapy;1
O
H
H
O
O
however, the artemisinins have relatively poor biophar-
maceutical properties that limit their therapeutic poten-
tial.2 Many potent semisynthetic artemisinins and
synthetic antimalarial peroxides have been prepared3
but it has been difficult4 to identify peroxide structures
which maintain optimal activity and at the same time
have the requisite physicochemical and metabolic proper-
ties to ensure good absorption and bioavailability follow-
ing oral administration. It is well accepted that oral
absorption requires a balance between good aqueous sol-
ubility, which is enhanced for more polar structures, and
good membrane permeability, which is favored for less
polar compounds.5–7 Another factor that often limits oral
bioavailability is extensive first-pass metabolism which
typically increases for more lipophilic substrates.8,9
O
O
H
O
O
O
O
O
H
H
O
O
O
O
COOH
O
CH3
O
COOH
Artemether
Artesunate
Artelinate
We recently described10 the discovery of spiro and dispi-
ro-1,2,4-trioxolanes (secondary ozonides) as a promising
class of synthetic antimalarial peroxides, but most of
these early lead compounds (1–6) were highly lipophilic
and had limited oral bioavailability due to poor aqueous
solubility and high metabolic lability.
Keywords: 1,2,4-Trioxolane; Secondary ozonide; Antimalarial;
Artemisinin.
In this paper, we describe the synthesis, physicochemical
and antimalarial properties of 43 diversely functional-
ized derivatives of these early trioxolane prototypes with
*
Corresponding author. Tel.: +1 402 559 5362; fax: +1 402 559
9543; e-mail: jvenners@unmc.edu
0968-0896/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2006.05.041

Y. Dong et al. / Bioorg. Med. Chem. 14 (2006) 6368–6382
6369
O
O
O
O
O
O
O O
O
O
R
O
O
O
O
O
1, R = OH, log P 3.9
2, R = n-propyl, log P 8.1
3, R = phenyl, log P 8.6
5, log P 6.1
6, log P 7.3
4, log P 3.8
a wide polarity spectrum. Our intent was to identify
which functional groups were associated with good anti-
malarial profiles and identify lead compounds with an
appropriate balance between lipophilicity (LogP/LogD)
and aqueous solubility. Our emphasis was on the car-
boxylic acid functional group, not only because of its
potential to form water-soluble salts, but because of
the precedent set with the carboxylic acid-containing
semisynthetic artemisinins, artesunate, and artelinate.11
O
O
16-26, 31, 32
O
O
4
Scheme 2.
Unsaturated ketal 16 (63%) was obtained by transke-
talization of 4 dimethyl ketal. Ketal ketone 17 (57%)
was obtained by ozonolysis of 16 at ꢀ78 ꢁC followed
by a reductive (triphenylphosphine) workup. Oxime
19 and oxime ethers 20–22 were obtained by reaction
of 4 with the appropriate hydroxylamine or O-alkyl
hydroxylamine in yields ranging from 73% to 86%.
Semicarbazone 23 (90%), tosylhydrazone 24 (58%),
N-pyridiniumhydrazone 25 (31%), and guanidinehyd-
razone 26 (64%) were obtained by reaction of 4 with
1. Chemistry
Trioxolanes 46 (50%), 47 (18%), 49 (25%), 51 (45%), and
54 (49%) were obtained directly by Griesbaum coozon-
olysis12,13 reactions between O-methyl 2-adamantanone
oxime 7 and the appropriate 4-substituted cyclohexa-
nones 8 or benzophenones 9 (Scheme 1). Symmetrical
oxime ethers such as 7 preclude the syn-anti isomerism
of the resulting carbonyl oxide intermediates, and ensure
that the stereochemistry of the cycloaddition is only a
function of the starting material ketones. For achiral
benzophenones, the trioxolane products are achiral;
for 4-substituted cyclohexanones, the major trioxolane
isomers are uniformly cis with the substituent and per-
oxo groups at the equatorial and axial positions, respec-
tively.10,14 Assuming that the stereochemistry of the
cycloaddition follows the same course for other 4-substi-
tuted cyclohexanones, we have assigned cis configura-
tions for the new trioxolanes described herein.
Trioxolane carboxylic acids 15 (58%), 48 (84%), 52
(90%), diol 14 (46%), alcohol 30 (87%), and diamine
53 (29% overall) were obtained by aq KOH hydrolysis
of their precursor trioxolane esters;15 the latter were
obtained directly by coozonolysis (25–63%). The synthe-
sis of 53 required three additional post-ozonolysis trans-
4-phenylsemicarbazide,
4-toluenesulfonylhydrazide,
Girard’s reagent P, and aminoguanidine bicarbonate,
respectively. C@N containing trioxolanes 19–26 with
chiral axes were isolated as their racemates. Carbinols
31 (37%) and 32 (41%) were obtained by addition of
the lithium salts of thiazole and 2-picoline to 4. Carbi-
nol 31 was formed and isolated as a 1:1 mixture of
achiral diastereomers; 32 was formed as a mixture of
achiral diastereomers, but was isolated as a single achi-
ral diastereomer. In the absence of X-ray data, the cis
and trans configurations of 31 and 32 could not be
assigned.
Trioxolane alcohol 10, mesylate 11, aldehyde 12, and
carboxylic acid 1314 provided the means to synthesize
the remaining target trioxolanes (Scheme 3). Sodium
sulfate 33 (41%) was obtained by treatment of 10 with
sulfur trioxide pyridine complex in pyridine17 to form
the pyridinium sulfate of 10 that, in turn, was converted
to 33 with aq sodium carbonate. Carbamate 35 (91%)
was obtained by treatment of 10 and carbonyldiimidaz-
ole.18 Acid 34 (75%) was obtained by hydrolysis of its
corresponding ethyl ester.14 Ethers 36 (37%) and 37
(57%) were formed via Mitsunobu reactions with 10.
Sulfones 38 (23%) and 41 (15%) were obtained in a
formations
(lithium
borohydride/lithium
triethylborohydride16 reduction, phthalimide formation
(Mitsunobu), and hydrazine deprotection).
The ketone functional group of 4 provided a convenient
means for functional group transformation (Scheme 2).
Ketal 18 (56%) was obtained by ketalization of 4.
R
OCH3
O3
O
or
R
14, 15, 30, 46-49, 51-54
+
O
N
8
7
R
9
Scheme 1. Griesbaum Coozonolysis.

6370
Y. Dong et al. / Bioorg. Med. Chem. 14 (2006) 6368–6382
O
O
Relative to prototype ketal 5, the more polar ketal diol 14
R
had an antimalarial profile similar to 5, whereas the ketal
diacid 15 was completely inactive following oral dosing
(Table 1). In contrast, 16–18, three similarly lipophilic ke-
tals, had antimalarial profiles similar to prototype 5.
Oxime 19 and oxime ethers 20 and 21 were as potent as
their parent ketone 4 in vitro (Table 2), whereas in vivo
activities improved for 19 and 20, but weakened for the
more lipophilic 21. We note that 22, a carboxylic acid ana-
log of 20, was much less active than its parent oxime ether.
Similarly, the relatively polar carbon–nitrogen double
bond derivatives 23–26 were quite potent in vitro, but
had poor to minimal activities in vivo.
O
33-37, 40
38, 41
50
10, R = CH2OH
11, R = CH2OMs
12, R = CHO
27, 28
13, R = COOH
Scheme 3.
two-step procedure by treatment of 11 with sodium thio-
methoxide and 2-mercapto-1-methylimidazole to form
the sulfides; the latter were oxidized to the sulfones with
m-CPBA. Imidazole 50 (73%) was formed by treatment
of 12 with glyoxal and ammonia. Hydroxamic acid 27
(36%) was obtained from 13 by way of the mixed anhy-
dride (ethyl chloroformate followed by hydroxylamine);
hydroxy amide 28 (46%) was obtained from the HOBt
active ester of 13. Trioxolanes 1, 3, 4, 6, 10–13, 29,
and 42–45 were obtained as previously described.10,14
Carboxylic acid 13 and its more lipophilic hydroxamic
acid (27) and hydroxyethyl amide (28) derivatives are
shown in Table 3. Although 13 was not very potent in vi-
tro, it had quite good activity in vivo; the more weakly
acidic 27 was similarly active in vivo and was 3-fold
more potent in vitro. The in vitro potency for amide
28 was midway between that of 13 and 27 but it was
much less active in vivo.
Values for polar surface area (PSA)19 and LogP/
LogDpH 7.4 were calculated for each of the trioxolanes.
Experimental LogP/LogDpH 7.4 values for 11 selected
trioxolanes were determined by a rapid chromatograph-
ic method.20
Analogs of 1, the potent secondary alcohol metabolite
of ketone 4, are shown in Table 4. Primary alcohol 10
was as potent as 1, but it had much higher activity in vi-
vo. Tertiary carbinols 29 and 30 were designed as ana-
2. Antimalarial activity
logs of
1
with potentially enhanced metabolic
stabilities;21 29 and 1 had very similar antimalarial pro-
files, and although 30 had good potency in vitro, it was
much less active than 1 in vivo. The antimalarial profiles
of heterocyclic weak-base carbinols 31 and 32 were no
better than that of the more lipophilic 4-fluorophenyl
carbinol 30.
In vitro and in vivo antimalarial activities were
measured using the chloroquine-resistant K1 and
chloroquine-sensitive NF54 strains of Plasmodium
falciparum, and Plasmodium berghei-infected mice,
respectively. In vivo data were obtained using single
10 mg/kg oral doses of the trioxolanes administered on
day 1 post-infection in a non-solubilizing, standard sus-
pension vehicle (SSV) formulation comprising 0.5% w/v
carboxymethyl cellulose, 0.5% v/v benzyl alcohol, 0.4%
v/v Tween 80, and 0.9% w/v sodium chloride in water.
As 10 had a much better antimalarial profile than did 1,
and as it is readily synthesized14 as a single cis isomer
(unlike 1), this alcohol was the logical choice for further
derivatization (Table 5). Sodium sulfonate 33, a poten-
Table 1. Activity of trioxolane ketals against Plasmodium falciparum in vitro and Plasmodium berghei in vivo
O
O
O
O
O
O
O O
O
O
R
R
O
O
R
O
O
O
5, 14, 15
16, 17
18
2
PSA (A )
a
IC50 (ng/ml) K1/NF54
Activityb (%)
˚
Compound
R
LogP/LogDpH 7.4
NONE
4
—
—
—
—
—
0
74
3.8c
6.1c
3.6
0.18
6.5
5.3
7.4
3.3c
3.5
49.3
38.4
100.3
142.1
42.8
66.3
42.2
62.2
111.5
0.48/0.73d
1.5/2.7d
0.96/0.41
>100/>100
0.59/1.1
0.62/0.94
3.0/3.0
5
14
CH3
CH2OH
COOH
CH2
O
98
98
15
16
3
99.95
98.9
90
17
18
—
—
AM
AS
0.74/1.2
1.3/1.6
99.36
67
—
a Mean from n = 2–3.
b Groups of three P. berghei-infected MORO mice were treated orally 1 day post-infection with trioxolanes dissolved or suspended in SSV.
Antimalarial activity was measured by percent reduction in parasitemia on day 3 post-infection compared to an untreated control group.
c Measured eLogP value.
d Data from Dong et al.10

Y. Dong et al. / Bioorg. Med. Chem. 14 (2006) 6368–6382
6371
Table 2. Activity of trioxolane oxime ethers and C@N derivatives against Plasmodium falciparum in vitro and Plasmodium berghei in vivo
O
O
O O
N
N
OR
O
O
N
H
R
23-26
19-22
2
PSA (A )
˚
Compound
R
LogP/LogDpH 7.4
IC50 (ng/ml) K1/NF54
Activity (%)
19
20
21
22
23
24
25d
26e
H
CH3
4.1a
5.1a
7.2a
3.1b
3.5
70.6
50.2
0.45/0.67
0.60/1.0
1.3/2.7
83
88
CH2C6H5
CH2COOH
CONHC6H5
Tosyl
48.1
56
103.6
91.7
93.0
32/35
0.65/1.3
1.4/1.8
85c
0c
4.0
1.7
61c
45c
82
COCH2N-pyridinium
C@NH (NH2)
89.6
121.2
0.49/0.60
3.5/5.0
ꢀ1.0
a Measured eLogP value.
b Measured eLogD value.
c
In vivo data from administration in a 3% ethanol and 7% Tween 80 vehicle.
d Chloride salt.
e Hydrochloride salt.
Table 3. Activity of trioxolane acid 13 and its derivatives against Plasmodium falciparum in vitro and Plasmodium berghei in vivo
O
O
O
R
O
2
PSA (A )
˚
Compound
R
LogP/LogDpH 7.4
IC50 (ng/ml) K1/NF54
Activity (%)
13
27
28
OH
NHOH
NH(CH2)2OH
2.8
4.3
4.3
71.2
98.2
87.3
15/13
4.2/3.3
8.0/6.2
97a
96
53
a In vivo data from administration in a 3% ethanol and 7% Tween 80 vehicle.
Table 4. Activity of trioxolane alcohols against Plasmodium falciparum in vitro and Plasmodium berghei in vivo
O
O
OH
R
O
29-32
2
PSA (A )
˚
Compound
R
LogP/LogDpH 7.4
IC50 (ng/ml) K1/NF54
Activity (%)
1
10
29
30
31
32
—
—
3.9a
5.1
4.5
6.6
5.1
5.2
52.9
58.4
50.5
46.4
62.5
57.3
0.25/0.51b
0.83/0.20
0.44/0.84
1.7/3.0
93
99.15
95
CH3
4-FC6H5
2-Thiazolyl
2-Picolyl
49c
1.8/2.3
0.66/0.74
27
68
a Measured eLogP value.
b Data from Dong et al.10
.
c In vivo data from administration in a 3% ethanol and 7% Tween 80 vehicle.
Table 5. Activity of derivatives of trioxolane alcohol 10 against Plasmodium falciparum in vitro and Plasmodium berghei in vivo
O
O
O
OR
2
PSA (A )
˚
Compound
R
LogDpH 7.4
IC50 (ng/ml) K1/NF54
Activity (%)
33
34
35
36
37
SO3Na
1.8
4.8
5.6
6.7
6.0
99.7
85.7
71.9
50.1
62.9
100/110
25/35
0
18
4-COOHC6H5
COIma
4-Pyridyl
1.7/1.9
2.1/2.8
0.62/1.4
97
>99.99
99.43
2-Pyrimidinyl
a Carbonylimidazole.

6372
Y. Dong et al. / Bioorg. Med. Chem. 14 (2006) 6368–6382
Table 6. Activity of trioxolane sulfides and sulfones against Plasmodium falciparum in vitro and Plasmodium berghei in vivo
O
O
O O
O
O
S
R
S
R
O
O
44, 45
38-43
2
˚
Compound
R
LogP/LogDpH 7.4
PSA (A )
IC50 (ng/ml) K1/NF54
Activity (%)
38
39
40
41
42
43
44
45
CH3
C6H5
2-Pyridinyl
4.6
6.3
4.9
5.2
2.9
5.8
5.1
6.0
65.3
61.5
89.3
78.7
84.2
111.5
51.5
79.0
0.62/0.88
1.4/1.6
6.8/6.3
0.82/1.1
2.4/3.4
1.7/2.5
1.4/3.0
0.50/1.2
98
77
36
81
1-Me-2-imidazole
2-Pyridyl N-oxide
1-Me-2-tetrazolyl
2-Pyridyl N-oxide
1-Me-2-tetrazolyl
60
8
99.77
99.47
Table 7. Activity of aryl trioxolanes against Plasmodium falciparum in vitro and Plasmodium berghei in vivo
O
O
O
O
N
R
O
O
N
H
50
3, 46-49
2
PSA (A )
˚
Compound
R
LogP/LogDpH 7.4
IC50 (ng/ml) K1/NF54
Activity (%)
3
46
47
48
49c
50
H
8.6a
8.2a
6.7
5.0
8.1
5.1
19.9
26.2
66.3
74.6
45.7
55.2
2.2/4.8b
3.5/4.6
21/27
96
81
23
3
F
SO2CH3
COOH
4,4-Dimethyl-2-oxazyl
—
36/38
3.7/2.8
0.60/0.35
97
6
a Measured eLogP value.
b Data from Dong et al.10
c Hydrochloride salt.
.
tial phase II metabolite of 10, was two-orders of magni-
tude less potent than the parent alcohol and it was com-
pletely inactive in vivo. The phenyl ether carboxylic acid
34 was similarly inactive. Imidazole carbamate 35 had
good potency in vitro, but its oral activity was substan-
tially less than that of 10. The relatively lipophilic weak-
base ethers 36 and 37 had the best antimalarial profiles
of this group of derivatives of 10.
more polar dicarboxylic acid 5222 and dipyridine 54,
both of which were completely inactive in vivo. The
more lipophilic difluoro 51 had much better activity
in vivo than its unsubstituted parent 6 suggesting that
the latter may be converted to inactive hydroxylated
metabolites although this was not investigated. The dia-
mine 53, while 2- to 3-fold less potent than 6, is consid-
erably less lipophilic (LogD 2.4) and had good activity
in vivo.
As shown in Table 6, we explored trioxolanes containing
the metabolically stable and relatively polar sulfone
functional group. These sulfones (and two sulfide
analogs) had IC50s between 0.50 and 6.8 ng/mL, but
their in vivo activities varied widely. This was especially
evident in the dramatic increase in activity seen for sul-
fides 44 and 45 versus their more polar sulfone counter-
parts 42 and 43.
3. Discussion
Most of the new trioxolanes depicted in Tables 1–8
were quite potent against P. falciparum with IC50s
less than 5 ng/ml. Of the 26 most potent trioxolanes
with IC50s (against K1) < 2 ng/mL, only five had
LogP/LogD values < 4 consistent with the previous
observation4 that moderately high lipophilicity is re-
quired for good antimalarial potency. Of the 10 tri-
Analogs of 3 functionalized at the para position are
shown in Table 7. In vitro potencies decreased signifi-
cantly for the more polar sulfone 47 and carboxylic acid
48. Only the weak-base oxazoline 49 (a potential pro-
drug of 48) was as active in vivo as 3. Unlike the similar-
ly polar 48, weak-base imidazole 50 was the most potent
compound of this group of trioxolanes, although it was
nearly inactive in vivo.
oxolanes
with
IC50s > 10 ng/mL,
seven
were
carboxylic or sulfonic acids; conversely, with two
exceptions (53 and 54), weak-base trioxolanes had
good potency.
Far fewer trioxolanes had good oral activities in the
P. berghei model. Consistent with the trends for in vi-
tro potency, those with oral activities P99% (10, 16,
36, 37, 44, 45, 51) were quite lipophilic with LogP/
Symmetrically substituted analogs of 6 are shown in Ta-
ble 8. In vitro potencies decreased significantly for the

Y. Dong et al. / Bioorg. Med. Chem. 14 (2006) 6368–6382
6373
Table 8. Activity of diaryl trioxolanes against Plasmodium falciparum in vitro and Plasmodium berghei in vivo
R
O
O
O O
N
N
O
O
R
6, 51-53
54
2
PSA (A )
˚
Compound
R
LogP/LogDpH 7.4
IC50 (ng/ml) K1/NF54
Activity (%)
6
H
7.3b
8.1b
2.7
22.9
22.9
2.3/2.6c
2.5/2.3
68a
99.3a
0
51
52
53d
54
F
COOH
CH2NH2
—
124.2
79.7
48.4
>100/>100
11/5.6
>100/>100
2.4
2.4
98
0a
a In vivo data from administration in a 3% ethanol and 7% Tween 80 vehicle.
b Measured eLogP value.
c Data from Dong et al.10
d Dimesylate salt.
.
LogD values ranging from 5.1 to 8.1. Of the 20 triox-
olanes with activities P90%, only six (diol ketal 14,
alcohols 1 and 29, carboxylic acid 13, hydroxamic
acid 27, and diamine 53) had LogP/LogD values be-
low 5. For compounds with good in vitro potency
(IC50 < 2 ng/mL) but with reduced oral efficacy (activ-
ity < 90%), it is likely that poor aqueous solubility
and/or high metabolic lability resulted in low oral bio-
availability since each of these compounds had physi-
cochemical properties consistent with good membrane
permeability.
5. Experimental
5.1. General
Melting points are uncorrected. Using CDCl3,
CD3OD, or DMSO-d6 as solvents, 1H and 13C
NMR spectra were recorded on a 300 MHz spectro-
meter for 19–21 and on a 500 MHz spectrometer for
the remaining compounds. All chemical shifts are
reported in parts per million (ppm) and are relative
to internal (CH3)4Si (0 ppm) for 1H and CDCl3
(77.0 ppm), CD3OD (49.0 ppm), or DMSO-d6
(39.7 ppm) for 13C NMR.
During this work, we made the transition from a solubi-
lizing 3% ethanol and 7% Tween 80 (T/A) vehicle to a
non-solubilizing SSV vehicle for oral dosing. We
observed that the activity of 7/30 trioxolanes was signi-
ficantly lower (25- to 1000-fold)23 in the SSV versus T/A
vehicle (data not shown); significantly these seven triox-
olanes were the highly lipophilic (LogP/LogD 5.1–8.6)
compounds 3, 5, 18, 20, 21, 46, and 49, all of which
had good in vitro potency. These data supported the
hypothesis that poor solubility and dissolution severely
restricted the oral absorption of these lipophilic trioxol-
anes. In addition, these data showed that the use of the
non-solubilizing SSV vehicle for assessment of oral
activity kept the focus on those trioxolanes that might
be expected to have reasonable oral bioavailability and
made certain that our SAR would not be skewed by
the very high oral activities seen for highly lipophilic
trioxolanes in the solubilizing T/A vehicle.
5.2. Starting material synthesis
4,40-Benzophenonedicarboxylic acid was obtained in
80% yield by KMnO4 oxidation of 4,40-dimethylbenz-
ophenone; esterification of the diacid in refluxing tol-
uene/EtOH with concd H2SO4 catalyst afforded
diethyl 4,40-benzophenonedicarboxylate in 90% yield.24
4-[4-(methylsulfonyl)phenyl]cyclohexanone was ob-
tained in a five-step sequence.24 The first step was
addition of the Grignard reagent formed from 4-
bromothioanisole to the monoethylene ketal of 1,4-
cyclohexanedione to produce the tertiary benzylic
alcohol. Oxidation to the sulfone alcohol with oxone25
followed by dehydration with methanesulfonyl chlo-
ride/triethylamine26 cleanly afforded the corresponding
olefin. Hydrogenation of the olefin over Pd–C and
deprotection with TFA afforded the desired keto sul-
fone. As indicated below, the remaining starting mate-
rials cyclohexanones and benzophenones were
commercially available or were prepared according
to known procedures.
4. Summary
From these data, it is evident that in vitro potency is not
a reliable predictor of in vivo activity and that the more
lipophilic trioxolanes tend to have better oral activities
than their more polar counterparts, an outcome consis-
tent with that seen for other classes of synthetic perox-
ides.4 Trioxolanes with a wide range of neutral and
basic, but not acidic, functional groups had good anti-
malarial profiles.
5.2.1. Diethyl 4,40-benzophenonedicarboxylate. 1H NMR
(CDCl3)
d
1.42 (t, J = 7.5 Hz, 6H), 4.43 (q,
J = 7.0 Hz, 4H), 7.84 (d, J = 8.5 Hz, 4H), 8.18 (d,
J = 8.5 Hz, 4H). 13C NMR (125.7 MHz, CDCl3) d
14.26, 61.45, 129.89, 129.74, 134.18, 140.63, 165.66,
195.25.

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Y. Dong et al. / Bioorg. Med. Chem. 14 (2006) 6368–6382
5.3. 4-[4-(Methylsulfonyl)phenyl]cyclohexanone
35.77, 36.13, 39.07, 60.69, 61.44, 61.48, 96.00, 108.15,
110.84. Anal. Calcd for C21H32O7Æ0.077 CHCl3: C,
62.40; H, 7.97. Found: C, 62.76; H, 7.77.
1H NMR (CDCl3) d 1.92–2.02 (m, 2H), 2.22–2.28 (m,
2H), 2.52–2.56 (m, 4H), 3.06 (s, 3H), 3.10–3.18 (m,
1H), 7.46 (d, J = 8.5 Hz, 2H), 7.91 (d, J = 8.5 Hz, 2H).
5.6. Adamantane-2-spiro-30-110,110-dicarboxy-
10,20,40,90,130-pentaoxadispiro[4.2.5.2]pentadecane (15)
5.4. General procedure for the preparation of
1,2,4-trioxolanes
A solution of adamantane-2-spiro-30-110, 110-bis(eth-
oxycarbonyl)-10,20,40,90,130-pentaoxadispiro[4.2.5.2]pen-
tadecane (0.73 g, 1.5 mmol), 15% aq KOH (4.2 ml) in
methanol (30 ml) was heated at 50 ꢁC for 2 h. After
being cooled to rt, the reaction mixture was concentrat-
ed to 5 ml, acidified with concd HCl, and extracted with
CHCl3 (5· 50 ml). The combined organic layers were
washed with water (2· 50 ml) and brine (50 ml), dried
over MgSO4, filtered, and concentrated to afford 15
(0.38 g, 58%) as a colorless solid. Mp 151–153 ꢁC
(water). 1H NMR (DMSO-d6) d 1.51–2.14 (m, 22H),
4.13 (s, 2H), 4.15 (s, 2H). 13C NMR (DMSO-d6) d
25.86, 26.26, 29.16, 30.16, 34.27, 34.37, 35.77, 36.13,
52.89, 61.65, 96.49, 107.99, 110.92, 169.11. Anal. Calcd
for C21H28O9: C, 59.43; H, 6.65. Found: C, 59.42; H,
6.66.
Ozone was produced with an OREC ozone generator
(0.6 L/min O2, 60 V), passed through an empty gas
washing bottle that was cooled to ꢀ78 ꢁC, and bubbled
through a solution of an 2-adamantanone O-methyl
oxime and a ketone in pentane or pentane/CH2Cl2 at
0 ꢁC. The oxime ether was consumed within 3 min. After
completion, the solution was flushed with oxygen for
5 min before being concentrated in vacuo at rt to give
a residue that was purified by flash chromatography.
Although we encountered no difficulties in working with
these 1,2,4-trioxolanes (secondary ozonides), routine
precautions such as the use of shields, fume hoods,
and avoidance of metal salts should be observed when-
ever possible. Differential scanning calorimetry experi-
ments revealed that these 1,2,4-trioxolanes had good
thermal stabilities; decomposition occurred at 127–
175 ꢁC with enthalpies ranging from 300 to 650 J/g.
5.7. Adamantane-2-spiro-30-110-methylene-10, 20,40,90,130-
pentaoxadispiro[4.2.5.2]pentadecane (16)
5.5. Adamantane-2-spiro-30-110,110-bis(hydroxymethyl)-
10,20,40,90,130-pentaoxadispiro[4.2.5.2]pentadecane (14)
Step 1. A mixture of 410 (1.12 g, 4 mmol), TFA
(0.70 ml), CH2Cl2 (10 ml), and methanol (70 ml) was
stirred at rt for 16 h. The reaction was quenched with
NaHCO3 (2.0 g) and stirred for an additional 1 h before
evaporation to dryness. The residue was dissolved in
CH2Cl2 (20 ml), washed with water and brine, dried
over MgSO4, filtered, and concentrated to afford
Step 1. A solution of O-methyl 2-adamantanone oxime27
(2.69 g, 15 mmol) and 3,3-bis(ethoxycarbonyl)-1,5-
dioxaspiro[5.5]undecan-9-one28 (4.71 g, 15 mmol) in
pentane (100 ml) and CH2Cl2 (50 ml) was treated with
ozone according to the general procedure. The crude
product was purified by flash chromatography (silica
gel, 10% ether in petroleum ether) to afford adaman-
tane-2-spiro-30-110,110-bis(ethoxycarbonyl)-10,20,40,90,
130-pentaoxadispiro[4.2.5. 2]pentadecane (3.60 g, 50%)
1
dimethyl ketal of 4 (1.31 g, 100%) as a colorless oil. H
NMR (CDCl3) d 1.66–2.02 (m, 22H), 3.18 (s, 3H),
3.19 (s, 3H).
Step 2. A mixture of the above ketal (1.30 g, 4 mmol),
2-methylene-1,3-propanediol (0.70 g, 8 mmol), and p-
TsOH (0.5 g) in CH2Cl2 (70 ml) and THF (10 ml) was
stirred at rt for 16 h. The reaction was quenched with
NaHCO3 (1.0 g), stirred for an additional 1 h, and
diluted with water (70 ml). After separation of the
organic layer, the aqueous layer was extracted with
CH2Cl2 (2· 50 ml). The combined organic layers were
washed with water and brine, dried over MgSO4, fil-
tered, and concentrated. The crude product was puri-
fied by flash chromatography (silica gel, 8% ether in
hexanes) to afford 16 (0.87 g, 63%) as a colorless solid.
1
as a colorless solid. Mp 74–77 ꢁC (ethanol). H NMR
(CDCl3) d 1.27 (t, J = 7.1 Hz, 6H), 1.61–2.18 (m,
22H), 4.24 (q, J = 7.2 Hz, 4H), 4.28 (s, 4H).
Step 2. A solution of adamantane-2-spiro-30-110,110-
bis(ethoxycarbonyl)-
10,20,40,90,130-pentaoxadispi-
ro[4.2.5. 2]pentadecane (1.00 g, 2.18 mmol), lithium
borohydride (2.10 ml, 4.20 mmol, 2 M in THF), and
lithium triethylborohydride (0.42 ml, 0.42 mmol, 1 M
in THF) in ether (5 ml) was stirred at rt for 3 h. The
reaction mixture was diluted with ether (10 ml) and
washed with 3 M aq NaOH (2· 10 ml), water
(2· 10 ml), and brine (10 ml). The combined aqueous
layers were extracted with CHCl3 (3· 50 ml), and the
chloroform extract was washed with water (2· 50 ml)
and brine (50 ml). The ether extract and chloroform ex-
tract were combined, dried over MgSO4, filtered, and
concentrated. The residue was purified by flash chroma-
tography (silica gel, 5% methanol in chloroform) to af-
ford 14 (0.40 g, 46%) as a colorless solid. Mp 146–
148 ꢁC (ethanol/H2O 3:2). 1H NMR (DMSO-d6) d
1.60–2.15 (m, 22H), 3.36 (d, J = 4.9 Hz, 4H), 3.61 (s,
2H), 3.62 (s, 2H), 4.49 (t, J = 5.4 Hz, 2H). 13C NMR
(DMSO-d6) d 25.86, 26.26, 29.34, 30.21, 34.27, 34.36,
1
Mp 58–59 ꢁC (hexanes). H NMR (CDCl3) d 1.59–2.21
(m, 22H), 4.31 (s, 4H), 4.86 (s, 2H). 13C NMR (CDCl3)
d 26.60, 27.02, 29.97, 30.69, 34.84, 34.94, 36.49, 36.90,
63.63, 97.60, 107.92, 108.38, 111.59, 141.15. Anal.
Calcd for C20H28O5: C, 68.94; H, 8.10. Found: C,
68.77; H, 7.93.
5.8. Adamantane-2-spiro-30-110-oxo-10,20,40,90,130-pen-
taoxadispiro[4.2.5.2]pentadecane (17)
A solution of 16 (0.65 g, 1.9 mmol) in CH2Cl2 (80 ml) at
ꢀ78 ꢁC was treated with ozone for 10 min, flashed with
oxygen for 5 min before addition of triphenylphosphine

Y. Dong et al. / Bioorg. Med. Chem. 14 (2006) 6368–6382
6375
(0.49 g, 1.9 mmol). The reaction mixture was warmed up
to rt and stirred at rt for 1 h before evaporation to dry-
ness. The crude product was purified by flash chroma-
tography (silica gel, 10% ether in hexanes) to afford 17
(0.37 g, 57%) as a colorless solid. Mp 76–79 ꢁC (hex-
anes). 1H NMR (CDCl3) d 1.61–2.21 (m, 22H), 4.17
(s, 4H). 13C NMR (CDCl3) d 26.61, 27.03, 29.80,
30.81, 34.85, 34.96, 36.52, 36.89, 66.92, 66.94, 99.14,
107.96, 111.82, 207.00. Anal. Calcd for C19H26O6: C,
65.13; H, 7.48. Found: C, 65.38; H, 7.58.
4H), 3.84 (s, 3H). 13C NMR (CDCl3) d 21.54, 26.40,
26.81, 28.74, 32.59, 33.85, 34.72, 34.77, 34.84, 36.28,
36.70, 61.15, 107.92, 112.00, 156.93. Anal. Calcd for
C17H25NO4: C, 66.43; H, 8.20; N, 4.56. Found: C,
66.58; H, 8.29; N, 4.41.
5.12. Adamantane-2-spiro-30-80-benzyloxyimino-10,20,40-
trioxaspiro[4.5]decane (21)
To a solution of 410 (0.56 g, 2.0 mmol) in CH2Cl2 (5 ml)
and methanol (5 ml) were added pyridine (0.30 ml) and
5.9. Adamantane-2-spiro-30-110,120-benzo-10,20,40,90,140-
pentaoxadispiro[4.2.6.2]hexadecane (18)
O-benzylhydroxylamine
hydrochloride
(0.48 g,
3.0 mmol), and the reaction mixture was stirred at rt
for 24 h. The reaction mixture was concentrated in vac-
uo to provide a crude residue that was purified by
recrystallizations from ethanol/H2O (20 ml, 1:1) and
from ethanol/H2O (15 ml, 2:1) to give 21 (0.66 g, 86%)
as a colorless solid. Mp 62–64 ꢁC (ethanol/H2O 2:1).
1H NMR (CDCl3) d 1.60–2.10 (m, 18H), 2.32–2.50 (m,
2H), 2.53–2.67 (m, 1H), 2.72–2.86 (m, 1H), 5.08 (s,
2H), 7.25–7.42 (m, 5H). 13C NMR (CDCl3) d 21.87,
26.41, 26.81, 28.76, 32.61, 33.87, 34.72, 34.74, 34.79,
34.85, 36.29, 36.70, 75.36, 107.94, 111.99, 127.67,
127.90, 128.31, 137.99, 157.57. Anal. Calcd for
C23H29NO4: C, 72.04; H, 7.62; N, 3.65. Found: C,
72.30; H, 7.49; N, 3.77.
To a solution of 410 (0.28 g, 1.0 mmol) in 1,2-dimethoxy-
ethane (10 ml) were added 1,5-dihydro-3-methoxy-2,4-
benzodioxepin (0.20 g, 1.1 mmol) and p-toluenesulfonic
acid monohydrate (38 mg), and the reaction mixture
was stirred at rt for 30 min before being quenched by
addition of saturated NaHCO3 solution (1.0 ml). The
reaction mixture was concentrated in vacuo to provide
a crude residue that was purified by recrystallizations
from ethanol/H2O (15 ml, 2:1) and from ethanol
(10 ml) to give 18 (0.22 g, 56%) as a colorless solid. Mp
149–151 ꢁC (ethanol). 1H NMR (CDCl3) d 1.60–2.20
(m, 22H), 4.80–4.94 (m, 4H), 7.02–7.09 (m, 2H), 7.13–
7.22 (m, 2H). 13C NMR (CDCl3) d 26.53, 26.94, 29.46,
31.12, 34.81, 34.91, 36.42, 36.84, 64.65, 101.38, 108.42,
111.65, 126.09, 126.15, 126.75, 138.01, 138.09. Anal.
Calcd for C24H30O5: C, 72.34; H, 7.59. Found: C,
72.51; H, 7.70.
5.13. Adamantane-2-spiro-30-80-carboxymethoxyimino-
10,20,40-trioxaspiro[4.5]decane (22)
To a solution of 410 (0.278 g, 1.0 mmol) in methanol
(5 ml) were added pyridine (0.16 g, 2.0 mmol) and carb-
5.10. Adamantane-2-spiro-30-80-hydroxyimino-10,20,40-
trioxaspiro[4.5]decane (19)
oxymethoxylamine
hemihydrochloride
(0.262 g,
1.2 mmol). The reaction was stirred at rt for 4 h. After
the solvent was removed in vacuo, the crude residue
was acidified with 2 M HCl (25 ml) and extracted with
CH2Cl2 (3· 20 ml). The combined extracts were dried
over Na2SO4 and concentrated to give a residue that
was triturated in hexanes to afford 22 (0.30 g, 85%) as
To a solution of 410 (0.557 g, 2.0 mmol) in CH2Cl2
(5 ml) and methanol (5 ml) were added pyridine
(0.30 ml) and hydroxylamine hydrochloride (0.210 g,
3.0 mmol), and the reaction mixture was stirred at rt
for 24 h. The reaction mixture was concentrated in vac-
uo to provide a crude residue that was purified by
recrystallization from ethanol/H2O (20 ml, 1:1) to give
19 (0.43 g, 73%) as a colorless solid. Mp 137–139 ꢁC
1
a colorless solid. Mp 126–128 ꢁC (hexanes). H NMR
(CDCl3) d 1.60–2.10 (m, 18H), 2.33–2.50 (m, 2H),
2.59–2.70 (m, 1H), 2.72–2.90 (m, 1H), 4.62 (s, 2H). 13C
NMR (CDCl3) d 22.08, 26.52, 26.92, 28.55, 32.54,
33.76, 34.80, 34.87, 34.92, 36.41, 36.79, 69.71, 107.77,
112.15, 160.04, 174.84. Anal. Calcd for C18H25NO6: C,
61.52; H, 7.17; N, 3.99. Found: C, 61.48; H, 7.16; N,
3.84.
1
(ethanol/H2O 1:1). H NMR (CDCl3) d 1.62–2.10 (m,
18H), 2.32–2.88 (m, 4H), 8.60–8.95 (br s, 1H). 13C
NMR (CDCl3) d 20.97, 26.41, 26.81, 28.72, 32.48,
33.74, 34.74, 34.80, 34.84, 36.29, 36.70, 107.91, 112.06,
157.94. Anal. Calcd for C16H23NO4: C, 65.51; H, 7.90;
N, 4.77. Found: C, 65.65; H, 7.96; N, 4.75.
5.14. Adamantane-2-spiro-30-10,20,40-trioxaspiro[4.5]dec-
an-80-one 4-phenylsemicarbazone (23)
5.11. Adamantane-2-spiro-30-80-methoxyimino-10,20,40-
trioxaspiro[4.5]decane (20)
To a solution of 410 (0.28 g, 1.0 mmol) in ethanol (5 ml)
and CH2Cl2 (1.5 ml) was added a solution of 4-phenylse-
micarbazide (0.17 g, 1.1 mmol) in ethanol (5 ml) and
CH2Cl2 (2 ml), and the reaction mixture was stirred at
rt for 1 h before being heated to 50 ꢁC for 30 min. The
solution was cooled to rt and the resulting precipitate
was filtered, washed with ethanol, and dried to afford
23 (0.37 g, 90%) as a colorless solid. Mp 161–163 ꢁC
dec (ethanol). 1H NMR (CDCl3) d 1.62–2.10 (m,
18H), 2.48–2.61 (m, 3H), 2.62–2.69 (m, 1H), 7.02–7.09
(m, 1H), 7.23–7.35 (m, 2H), 7.48–7.54 (m, 2H), 8.24 (s,
1H), 9.11 (s, 1H). 13C NMR (CDCl3) d 23.17, 26.46,
To a solution of 410 (0.557 g, 2.0 mmol) in CH2Cl2
(5 ml) and methanol (5 ml) were added pyridine
(0.30 ml) and methoxylamine hydrochloride (0.250 g,
3.0 mmol), and the reaction mixture was stirred at rt
for 24 h. The reaction mixture was concentrated in vac-
uo to provide a crude residue that was purified by
recrystallizations from ethanol/H2O (20 ml, 1:1) and
from ethanol/H2O (15 ml, 2:1) to give 20 (0.51 g, 83%)
as a colorless solid. Mp 97–99 ꢁC (ethanol/H2O 2:1).
1H NMR (CDCl3) d 1.60–2.10 (m, 18H), 2.30–2.81 (m,

6376
Y. Dong et al. / Bioorg. Med. Chem. 14 (2006) 6368–6382
26.87, 31.88, 32.57, 33.92, 34.75, 34.79, 34.93, 36.35,
36.37, 36.75, 107.75, 112.17, 119.33, 123.10, 128.84,
138.26, 150.83, 154.31. Anal. Calcd for C23H29N3O4:
C, 67.13; H, 7.10; N, 10.21. Found: C, 66.86; H, 6.92;
N, 10.04.
34.70, 34.74, 34.84, 36.23, 36.26, 36.65, 107.26, 112.27,
156.57, 157.93. Anal. Calcd for C17H27ClN4O3: C,
55.05; H, 7.34; N, 15.11. Found: C, 55.14; H, 7.51; N,
15.30.
5.18. cis-Adamantane-2-spiro-30-80-[(hydroxyamino)car-
bonyl]-10,20,40-trioxaspiro[4.5]decane (27)
5.15. Adamantane-2-spiro-30-10,20,40-trioxaspiro[4.5]dec-
an-80-one tosylhydrazone (24)
A solution of ethyl chloroformate (0.26 g, 2.4 mmol),
1314 (0.62 g, 2.0 mmol), and triethylamine (0.27 g,
2.6 mmol) in ether (6 ml) was stirred at 0 ꢁC for 10
min. The solid was removed by filtration, and the filtrate
was added to a freshly prepared solution of hydroxyl-
amine. (To a suspension of KOH (168 mg, 3.0 mmol)
in methanol (1 ml) at 0 ꢁC was added a solution of
hydroxylamine hydrochloride (0.20 g, 3 mmol) in meth-
anol (3 ml). The reaction mixture was stirred at 0 ꢁC for
15 min and filtered to remove solid by-products. The fil-
trate was used as such.) The resulting mixture was stir-
red at rt for 1 h and concentrated. The crude product
was purified by flash chromatography (silica gel, 8%
methanol in chloroform) to afford 27 (0.23 g, 36%) as
a colorless solid. Mp 130–132 ꢁC (ethanol/water 1:2).
1H NMR (DMSO-d6) d 1.40–2.19 (m, 23H), 8.60 (s,
1H), 10.35 (s, 1H). 13C NMR (DMSO-d6) d 25.87,
26.27, 26.50, 33.03, 34.28, 34.30, 35.84, 36.15, 39.04,
107.85, 110.64, 171.30. Anal. Calcd for C17H25NO5: C,
63.14; H, 7.79; N, 4.33. Found: C, 62.97; H, 7.57; N,
4.26.
To a solution of 410 (0.28 g, 1.0 mmol) and p-toluene-
sulfonhydrazide (0.21 g, 1.1 mmol) in CH2Cl2 (5 ml)
and ethanol (5 ml) was added acetic acid (0.5 ml), and
the reaction mixture was heated to 50 ꢁC for 2 h. The
reaction mixture was cooled to rt and concentrated in
vacuo. The residue was purified by recrystallization
from ethanol/H2O (15 ml, 2:1) to give 24 (0.26 g, 58%)
as a colorless solid. Mp 137 ꢁC dec (ethanol/H2O 2:1).
1H NMR (DMSO-d6) d 1.52–2.10 (m, 18H), 2.15–2.65
(m, 4H), 2.38 (s, 3H), 7.39 (d, J = 7.8 Hz, 2H), 7.72 (d,
J = 7.8 Hz, 2H), 10.23 (s, 1H). 13C NMR (DMSO-d6)
d 20.92, 23.84, 25.72, 26.12, 31.05, 31.80, 33.09, 34.17,
34.29, 35.58, 35.97, 107.55, 111.19, 127.44, 129.31,
136.28, 143.01, 158.63. Anal. Calcd for C23H30N2O5S:
C, 61.86; H, 6.77; N, 6.27. Found: C, 61.71; H, 6.81;
N, 6.53.
5.16. Adamantane-2-spiro-30-10,20,40-trioxaspiro[4.5]dec-
an-80-one pyridinioacetylhydrazone chloride (25)
To a solution of 410 (278 mg, 1 mmol) in ethanol (10 ml)
and acetic acid (1 ml) was added Girard’s reagent P
(190 mg, 1 mmol). The mixture was stirred at 25 ꢁC for
24 h. The solvent was removed in vacuo, and the residue
was purified by recrystallization from ether/methanol
(95:5) to afford 25 (140 mg, 31%, 2:1 mixture of two tau-
tomers) as a yellowish solid. Mp 88–90 ꢁC (ether/metha-
nol 9:1). 1H NMR (CD3OD) d 1.58–2.39 (m, 18H),
2.43–2.92 (m, 4H), 5.72 (s, minor isomer), 5.94 (s, major
isomer), 8.10–8.28 (m, 2H), 8.61–8.78 (m, 1H), 8.90–9.14
(m, 2H). 13C NMR (CD3OD) d 21.36, 24.51, 25.72,
27.88, 28.29, 29.00, 29.08, 31.93, 32.59, 32.80, 32.87,
33.58, 33.68, 33.89, 34.83, 35.73, 35.77, 35.92, 36.63,
37.22, 37.72, 38.78, 39.02, 40.18, 40.25, 41.08, 61.72
(m), 62.77 (m), 108.80, 108.92, 113.21, 128.86, 129.00,
129.20, 147.46, 147.66, 157.71, 163.30, 167.86, 175.75.
Anal. Calcd for C23H30ClN3O4ÆH2O: C, 59.28; H, 6.92;
N, 9.02. Found: C, 58.88; H, 7.24; N, 8.83.
5.19. cis-Adamantane-2-spiro-30-80-[[(20-hydroxyeth-
yl)amino]carbonyl]-10,20,40-trioxaspiro[4.5]decane (28)
A solution of 1314 (0.31 g, 1.0 mmol), 1-[3-(dimethylami-
no)propyl]-3-ethylcarbodiimide hydrochloride (0.29 g,
1.5 mmol), HOBT (0.20 g, 1.5 mmol), and 2-aminoetha-
nol (0.09 g, 1.5 mmol) in DMF (10 ml) was stirred at rt
for 18 h before being quenched with 2 M aq HCl
(30 ml). The mixture was extracted with ethyl acetate
(4· 30 ml), and the combined extracts were washed with
water (2· 30 ml) and brine (30 ml), dried over MgSO4,
and concentrated. The residue was purified by flash
chromatography (silica gel, 5% methanol in CH2Cl2)
to afford 28 (0.16 g, 46%) as a colorless solid. Mp 114–
1
116 ꢁC (ether/CH2Cl2 2:1). H NMR (CDCl3) d 1.59–
2.08 (m, 22H), 2.17 (br s, 1H), 3.38–3.45 (m, 2H), 3.71
(t, J = 4.8 Hz, 2H), 6.13 (s, 1H). 13C NMR (CDCl3) d
26.44, 26.84, 26.99, 33.58, 34.75, 34.78, 36.35, 36.75,
42.27, 43.58, 62.31, 107.77, 111.53, 176.04. Anal. Calcd
for C19H29NO5: C, 64.93; H, 8.32; N, 3.99. Found: C,
64.68; H, 8.11; N, 3.93.
5.17. Adamantane-2-spiro-30-80-oxo-10,20,40-trioxaspi-
ro[4.5]decaneamidinohydrazone hydrochloride (26)
To a solution of 410 (555 mg, 2 mmol) in THF (11 ml),
water (3 ml), and ethanol (3.5 ml) were added 2 M aq
HCl (1.5 ml) and aminoguanidine bicarbonate
(299 mg, 2.2 mmol). The mixture was stirred at rt for
30 h before removal of solvents. The residue was tritu-
rated with ethanol (10 ml) and the resulting precipitate
was collected by filtration and washed with THF to give
26 (476 mg, 64%) as a colorless solid. Mp 150 ꢁC dec
(ethanol). 1H NMR (CDCl3) d 1.46–2.27 (m, 18H),
2.42–2.61 (m, 2H), 2.62–2.83 (m, 2H), 6.34 (s, 1H),
7.63 (br s, 2H), 7.91 (s, 1H), 10.95 (s, 1H). 13C NMR
(CDCl3) d 24.83, 26.37, 26.77, 31.72, 32.49, 33.62,
5.20. Adamantane-2-spiro-30-80-(40-fluorophenyl)-80-
hydroxy-10,20,40-trioxaspiro[4.5]decane (30)
Step 1. A solution of O-methyl 2-adamantanone oxime27
(0.36 g, 2 mmol) and 4-acetoxy-4-(4-fluorophenyl)cyclo-
hexanone24,29 (0.50 g, 2 mmol) in pentane (100 ml) and
CH2Cl2 (10 ml) was treated with ozone according to
the general procedure. The crude product was purified
by flash chromatography (silica gel, 5% ether in petro-
leum ether) to afford adamantane-2-spiro-30-80-acet-
oxy-80-(40- fluorophenyl)-10,20,40-trioxaspiro[4.5]decane

Y. Dong et al. / Bioorg. Med. Chem. 14 (2006) 6368–6382
6377
(0.44 g, 53%) as a colorless solid. Mp 147–149 ꢁC (etha-
bined organic extracts were washed with brine (50 ml),
dried over MgSO4, and concentrated. The purification
of the crude product by flash chromatography (silica
gel, 70% EtOAc in hexanes) followed by recrystalliza-
tion from ethanol afforded 32 (385 mg, 41%) as a
colorless solid. Mp 128–130 ꢁC. 1H NMR (CDCl3) d
1.41–2.25 (m, 22H), 2.88 (s, 2H), 5.82 (s, 1H), 7.11 (d,
J = 7.7 Hz, 1H), 7.17 (dd, J = 7.3, 4.6 Hz, 1H), 7.63
(ddd, J = 7.7, 7.7, 1.9 Hz, 1H), 8.49 (d, J = 4.1 Hz,
1H). 13C NMR (CDCl3) d 26.51, 26.89, 29.93, 34.80,
35.03, 36.43, 36.83, 47.30, 70.09, 109.01, 111.30,
121.53, 124.42, 136.89, 148.40, 159.55. Anal. Calcd for
C22H29NO4: C, 71.13; H, 7.87; N, 3.77. Found: C,
71.31; H, 7.94; N, 3.93.
1
nol/H2O 1:1). H NMR (CDCl3) d 1.62–2.19 (m, 20H),
2.07 (s, 3H), 2.53 (app d, J = 12.2 Hz, 2H), 6.96–7.04
(m, 2H), 7.27–7.33 (m, 2H).
Step 2. A mixture of adamantane-2-spiro-30-80-acetoxy-
80-(40-
fluorophenyl)-10,20,40-trioxaspiro[4.5]decane
(2.40 g, 5.76 mmol), methanol (56 ml), and 17 % aq
KOH (5.6 ml) was heated at 50 ꢁC for 2 h. The reaction
mixture was cooled to rt, concentrated to 10 ml, diluted
with water (40 ml), and extracted with chloroform
(40· 3 ml). The combined organic layers were dried over
MgSO4, filtered, and concentrated in vacuo. The residue
was purified by crystallization from ethanol/H2O (1:1) to
give 30 (1.87 g, 87%) as a colorless solid. Mp 122–124 ꢁC
1
(ethanol/H2O 1:1). H NMR (CDCl3) d 1.60–2.18 (m,
5.23. (cis-Adamantane-2-spiro-30-10,20,40-trioxaspi-
ro[4.5]decan-80-yl)methyl sodium sulfate (33)
20H), 2.25 (td, J = 13.7, 4.4 Hz, 2H), 6.98–7.14 (m,
2H), 7.38–7.56 (m, 2H). 13C NMR (CDCl3) d 26.54,
26.94, 30.25, 34.84, 36.49, 36.53, 36.84, 71.85, 108.22,
111.62, 115.02 (d, J = 21.1 Hz), 126.17 (d, J = 7.8 Hz),
144.03 (d, J = 3.2 Hz), 161.87 (d, J = 245.4 Hz). Anal.
Calcd for C22H27FO4: C, 70.57; H, 7.27. Found: C,
70.37; H, 7.27.
To a stirred suspension of sulfur trioxide pyridine com-
plex (1.62 g, 10 mmol) in dry pyridine (5 ml) was added
1014 (1 g, 3.4 mmol) in portions. Stirring was continued
for 24 h at rt. After removal of the pyridine under re-
duced pressure, a saturated Na2CO3 solution (10 ml)
was added. The mixture was kept at ꢀ20 ꢁC for 4 h, then
at 0 ꢁC overnight. The precipitate was filtered, washed
with cold water (5 ml), and dried in a vacuum oven to
give trioxolane 33 as a colorless solid (0.55 g, 41%).
5.21. Adamantane-2-spiro-30-80-hydroxy-80-(20-thiazolyl)-
10,20,40-trioxaspiro[4.5]decane (31)
1
To a stirred solution of 2-bromothiazole (246 mg,
1.5 mmol) in dry THF (4 ml) under N2 at ꢀ78 ꢁC was
added n-BuLi (1.6 M in hexanes, 1 ml, 1.5 mmol). The
resulting bright yellow solution was stirred for 1 h at
the same temperature, and then a solution of 410
(415 mg, 1.5 mmol) in dry THF (10 ml) was added.
The mixture was allowed to reach 0 ꢁC, poured into
ice-water mixture (15 ml), and extracted with ether
(3· 25 ml). The combined organic extracts were washed
with brine (25 ml), dried over MgSO4, and concentrated.
The crude product was purified by flash chromatogra-
phy (silica gel, 10% EtOAc in hexanes) followed by
recrystallization from hexanes/ether (9:1) to afford 31
(202 mg, 37%, 1:1 mixture of 2 diastereomers) as a col-
orless solid. Mp 64–66 ꢁC (hexanes/ether 9:1). 1H
NMR (CDCl3) d 1.60–2.42 (m, 22H), 3.18 (s, 0.5H),
3.40 (s, 0.5H), 7.28 (d, J = 3.0 Hz, 0.5 H), 7.30 (d,
J = 3.0 Hz, 0.5H), 7.69 (d, J = 3.3 Hz, 0.5H), 7.72 (d,
J = 3.0 Hz, 0.5H). 13C NMR (CDCl3) d 26.45, 26.46,
26.85, 29.98, 30.09, 34.73, 34.77, 34.79, 34.86, 36.34,
36.40, 36.48, 36.75, 36.77, 72.44, 73.00, 107.91, 107.97,
111.61, 111.84, 119.02, 141.95, 142.16, 177.99, 178.23.
Anal. Calcd for C19H25NO4S: C, 62.78; H, 6.93; N,
3.85. Found: C, 62.94; H, 7.01; N, 3.89.
Mp 156–157 ꢁC. H NMR (DMSO-d6) d 1.01–1.12 (m,
2H), 1.51–1.95 (m, 21H), 3.52 (d, J = 6.3 Hz, 2H). 13C
NMR (DMSO-d6) d 26.01, 26.41, 26.68, 33.39, 34.44,
34.46, 35.64, 35.96, 36.29, 69.96, 108.80, 110.60. Anal.
Calcd for C17H25NaO7S: C, 51.51; H, 6.36. Found: C,
51.47; H, 6.31.
5.24. cis-Adamantane-2-spiro-30-80-[(40-carboxyphen-
oxy)methyl]-10,20,40-trioxaspiro[4.5]decane (34)
A mixture of cis-adamantane-2-spiro-30-80-[[40-(ethoxy-
carbonyl)phenoxy]methyl]-10,20,40-trioxaspiro[4.5]dec-
ane14 (0.30 g, 0.68 mmol), KOH (0.38 g), THF (10 ml),
methanol (10 ml), and water (2 ml) was heated at
50 ꢁC for 3 h. The mixture was concentrated to 5 ml,
diluted with water (15 ml), and acidified with 1 M aq
HCl (1 ml). The resulting solid was collected by filtra-
tion to give 34 (0.21 g, 75%) as a colorless solid. Mp
165–168 ꢁC. 1H NMR (DMSO-d6) d 1.15–1.27 (m,
2H), 1.50–2.17 (m, 21H), 3.88 (d, J = 6.2 Hz, 2H), 7.00
(d, J = 8.8 Hz, 2H), 7.87 (d, J = 8.3 Hz, 2H). 13C
NMR (DMSO-d6) d 25.99, 26.40, 26.53, 33.27, 34.45,
35.35, 35.95, 36.26, 72.09, 108.70, 110.71, 114.41,
123.04, 131.50, 162.47, 167.15. Anal. Calcd for
C24H30O6: C, 69.54; H, 7.30. Found: C, 69.67; H, 7.21.
5.22. Adamantane-2-spiro-30-80-hydroxy-80-(20-pyridi-
nylmethyl)-10,20,40-trioxaspiro[4.5]decane (32)
5.25. cis-Adamantane-2-spiro-30-10,20,40-trioxaspi-
ro[4.5]decane-80-methyl imidazole-1-carboxylate (35)
To a stirred solution of 2-picoline (279 mg, 3.0 mmol) in
dry THF (10 ml) under N2 at ꢀ78 ꢁC was added n-BuLi
(1.6 M in hexanes, 1.9 ml, 3.0 mmol). The resulting
bright yellow solution was stirred at the same tempera-
ture for 1 h before a solution of 410 (690 mg, 2.5 mmol)
in dry THF (15 ml) was added slowly. The mixture was
allowed to reach 0 ꢁC, then poured into ice water
(50 ml), and extracted with ether (3· 50 ml). The com-
To a solution of 1014 (0.29 g, 1 mmol) in CH3CN (10 ml)
and THF (3 ml) was added 1,10-carbonyldiimidazole
(0.21 g, 1.3 mmol). The mixture was stirred at rt for
2 h before being quenched with cold water (50 ml).
The resulting precipitate was collected by filtration,
washed with water, and dried to afford trioxolane 35
(0.34 g, 91%) as a colorless solid. Mp 110–112 ꢁC

6378
Y. Dong et al. / Bioorg. Med. Chem. 14 (2006) 6368–6382
1
(water). H NMR (CDCl3) d 1.25–1.50 (m, 2H), 1.51–
2.21 (m, 21H), 4.25 (d, J = 6.3 Hz, 2H), 7.07 (s, 1H),
7.42 (s, 1H), 8.13 (s, 1H). 13C NMR (CDCl3) d 26.61,
27.02, 33.54, 34.86, 34.88, 35.66, 36.57, 36.90, 72.07,
108.17, 111.59, 117.03, 130.76, 137.07, 148.71. Anal.
Calcd for C21H28N2O5: C, 64.93; H, 7.27; N, 7.21.
Found: C, 65.12; H, 7.12; N, 7.25.
5.28. cis-Adamantane-2-spiro-30-80-[(methylsulfo-
nyl)methyl]-10,20,40-trioxaspiro[4.5]decane (38)
Step 1. To a solution of sodium thiomethoxide (0.42 g,
6 mmol) in DMF (30 ml) was added dropwise a solution
of 1114 (1.11 g, 3 mmol) in DMF (10 ml). The mixture
was heated at 55 ꢁC for 6 h before removal of the sol-
vent. The residue was dissolved in CH2Cl2 (30 ml) and
washed with water and brine, dried over MgSO4, fil-
tered, and concentrated. The crude product was purified
by flash chromatography (silica gel, 90% ethyl acetate in
hexanes) to afford cis-adamantane-2-spiro-30-80-[(meth-
ylthio)methyl]- 10,20,40-trioxaspiro[4.5]decane (0.35 g,
5.26. cis-Adamantane-2-spiro-30-80-[(40-pyridinyl-
oxy)methyl]-10,20,40-trioxaspiro[4.5]decane mesylate (36)
A mixture of diisopropyl azodicarboxylate (243 mg,
1.2 mmol) and triphenylphosphine (315 mg, 1.2 mmol)
in THF (5 ml) under argon was stirred at 0 ꢁC for
30 min before 1014 (294 mg, 1 mmol) and 4-hydroxy-
pyridine (114 mg, 1.2 mmol) were added. The resulting
mixture was stirred at rt for 5 h. After concentration,
the crude product was purified by flash chromatogra-
phy (silica gel, 40% ethyl acetate in hexanes, then 2%
to 6% MeOH in CH2Cl2) to give the crude free base
of 36 (eluted first) and pure cis-adamantane-2-spiro-
30-80-[(40-oxo-10(40H)-pyridinyl)methyl]-10,20,40-trioxa-
spiro[4.5]decane (85 mg, 23%, eluted second) as a
colorless solid. Mp 138–140 ꢁC. 1H NMR (CDCl3) d
1.17–1.35 (m, 2H), 1.59–2.03 (m, 21H), 3.60 (d,
J = 7.3 Hz, 2H), 6.39 (d, J = 7.8 Hz, 2H), 7.22 (d,
J = 7.3 Hz, 2H). The crude free base of 36 was dis-
solved in CH2Cl2/ether (1:3, 8 ml) and treated with a
solution of methanesulfonic acid (77 mg, 0.8 mmol) in
ether (2 ml). The precipitate was collected by filtration
to afford 36 (172 mg, 37%) as a colorless solid. Mp
153–155 ꢁC. 1H NMR (CDCl3) d 1.34–1.49 (m, 2H),
1.61–2.09 (m, 21H), 2.88 (s, 3H), 4.08 (d, J = 6.3 Hz,
2H), 7.29 (d, J = 7.3 Hz, 2H), 8.72 (d, J = 6.8 Hz,
2H). 13C NMR (CDCl3) d 26.41, 26.48, 26.81, 33.46,
34.76, 35.60, 36.36, 36.71, 39.34, 74.77, 108.08,
111.66, 112.64, 143.28, 171.01. Anal. Calcd for
C23H33NO7S: C, 59.08; H, 7.11; N, 3.00. Found: C,
58.89; H, 7.15; N, 3.09.
1
36%) as a colorless oil. H NMR (CDCl3) d 1.15–1.37
(m, 2H), 1.50–2.02 (m, 21H), 2.10 (s, 3H), 2.40 (d,
J = 7.0 Hz, 2H).
Step 2. To a solution of the above thioether (350 mg,
1.08 mmol) in CH2Cl2 (5 ml) at 0 ꢁC was added drop-
wise a solution of 3-chloroperoxybenzoic acid (70 % re-
agent, 790 mg, 3.2 mmol) in CHCl3/CH2Cl2 (1:1, 16 ml).
After 2 h, the mixture was allowed to warm up to rt and
stirred overnight before being quenched with saturated
aq NaHCO3 (50 ml). The resulting mixture was concen-
trated to 50 ml and filtered. The collected precipitate
was purified by flash chromatography (silica gel, 25%
ethyl acetate in hexanes; then 5% MeOH in CH2Cl2)
to afford 38 (245 mg, 64%) as a colorless solid. Mp
118–121 ꢁC. 1H NMR (CDCl3) d 1.33–1.52 (m, 2H),
1.59–2.03 (m, 20H), 2.04–2.25 (m, 1H), 2.92 (s, 3H),
2.94 (d, J = 6.4 Hz, 2H). 13C NMR (CDCl3) d 26.43,
26.81, 30.15, 30.78, 33.66, 34.75, 36.35, 36.73, 42.16,
60.13, 107.72, 111.61. Anal. Calcd for C18H28O5S: C,
60.65; H, 7.92. Found: C, 60.70; H, 7.75.
5.29. cis-Adamantane-2-spiro-30-80-[(phenylsulfo-
nyl)methyl]-10,20,40-trioxa-80-azaspiro[4.5]decane (39)
A solution of O-methyl 2-adamantanone oxime27
(1.79 g, 10 mmol) and 4-[(phenylsulfonyl)methyl]cyclo-
hexanone14 (1.20 g, 4.76 mmol) in pentane (50 ml) and
CH2Cl2 (25 ml) was treated with ozone according to
the general procedure. The crude product was purified
by flash chromatography (silica gel, 33% ether in hex-
anes) to afford 39 (0.78 g, 39%) as a colorless solid.
5.27. cis-Adamantane-2-spiro-30-80-[(20-pyrimidinyl-
oxy)methyl]-10,20,40-trioxaspiro[4.5]decane mesylate (37)
To a suspension of 60% NaH (80 mg, 2 mmol) in DMF
(10 ml) under N2 at 0 ꢁC was added dropwise a solution
of 1014 (588 mg, 2 mmol) in DMF (20 ml). The mixture
was stirred at rt for 1 h and cooled down to 0 ꢁC. After
2-chloropyrimidine (241 mg, 2 mmol) was added, the
resulting mixture was stirred at rt overnight. Water
(70 ml) was added, and the precipitate was collected
by filtration. The crude product was dissolved in ether
(20 ml) and added to a solution of methanesulfonic acid
(170 mg, 1.77 mmol) in ether/CH2Cl2 (1:1, 4 ml). The
solid was collected by filtration and dried to afford 37
1
Mp 120–122 ꢁC (ether/hexanes 1:1). H NMR (CDCl3)
d 1.25–1.46 (m, 2H), 1.60–2.21 (m, 21H), 2.99 (d,
J = 6.3 Hz, 2H), 7.54–7.62 (m, 2H), 7.63–7.70 (m, 1H),
7.88–7.96 (m, 2H). 13C NMR (CDCl3) d 26.44, 26.83,
30.11, 31.19, 33.69, 34.75, 34.76, 36.35, 36.75, 61.79,
107.77, 111.53, 127.73, 129.32, 133.63, 140.21. Anal.
Calcd for C23H30O5S: C, 66.00; H, 7.22. Found: C,
66.15; H, 7.10.
1
(530 mg, 57%) as a colorless solid. Mp 133–135 ꢁC. H
5.30. cis-Adamantane-2-spiro-30-80-[(20-pyrimidinylsulfo-
nyl)methyl]-10,20,40-trioxaspiro[4.5]decane (40)
NMR (CDCl3) d 1.27–1.41 (m, 2H), 1.62–2.04 (m,
21H), 2.93 (s, 3H), 4.42 (d, J = 7.4 Hz, 2H), 7.31–7.36
(m, 1H), 8.94 (d, J = 5.4 Hz, 2H), 11.28 (br s, 1H); 13C
NMR (CDCl3) d 26.45, 26.51, 26.84, 33.40, 34.77,
35.29, 36.37, 36.75, 39.28, 74.65, 108.31, 111.55,
115.16, 159.43, 160.34. Anal. Calcd for C22H32N2O7S:
C, 56.39; H, 6.88; N, 5.98. Found: C, 56.16; H, 6.72;
N, 5.89.
Step 1. To a mixture of 1014 (588 mg, 2 mmol) and tri-
phenylphosphine (628 mg, 2.4 mmol) in benzene
(10 ml) at rt under N2 was added dropwise a solution
of DIPAD (486 mg, 2.4 mmol) in benzene (2 ml). After
5 min, 2-pyrimidinethiol (224 mg, 2 mmol) in benzene
(5 ml) was added slowly over a period of 20 min. The

Y. Dong et al. / Bioorg. Med. Chem. 14 (2006) 6368–6382
6379
stirring was continued for 24 h before removal of the
solvent. The crude product was purified by flash chro-
matography (silica gel, 15% ethyl acetate in hexanes)
to give cis-adamantane-2-spiro-30-80-[(20- pyrimidinyl-
tered, and concentrated. The crude product was purified
by flash chromatography (silica gel, 10–50% ethyl ace-
tate in hexanes) to afford 41 (130 mg, 51%) as a colorless
solid. Mp 151–152 ꢁC. H NMR (CDCl3) d 1.31–1.51
(m, 2H), 1.59–2.04 (m, 20H), 2.06–2.25 (m, 1H), 3.41
(d, J = 6.3 Hz, 2H), 3.99 (s, 3H), 6.98 (s, 1H), 7.12 (s,
1H). 13C NMR (125.7 MHz, CDCl3) d 26.44, 26.84,
29.96, 30.89, 33.68, 34.76, 35.08, 36.35, 36.75, 59.99,
107.77, 111.55, 125.39, 128.96, 142.61. Anal. Calcd for
C21H30N2O5S/ C, 59.69; H, 7.16; N, 6.63. Found: C,
59.56; H, 7.10; N, 6.47.
1
thio)methyl]-10,20,40-trioxaspiro[4.5]decane
(420 mg,
54%) as a colorless solid. Mp 140–142 ꢁC. 1H NMR
(CDCl3) d 1.21–1.42 (m, 2H), 1.60–2.11 (m, 21H), 3.09
(d, J = 6.9 Hz, 2H), 6.95 (t, J = 4.8 Hz, 1H), 8.50 (d,
J = 4.7 Hz, 2H).
Step 2. To a solution of the above thioether (396 mg,
1.0 mmol) in CH2Cl2 (5 ml) at 0 ꢁC was added dropwise
a solution of 3-chloroperoxybenzoic acid (70% reagent,
790 mg, 3.2 mmol) in CHCl3/CH2Cl2 (1:1, 16 ml). After
2 h, the mixture was allowed to warm up to rt and stir-
red overnight before being quenched with saturated aq
NaHCO3 (40 ml). The organic layer was separated,
and the aqueous layer was extracted with CHCl3
(2· 20 ml). The combined organic extracts were washed
with water and brine, dried over MgSO4, and concen-
trated. The crude product was purified by flash chroma-
tography (silica gel, 20–50% ethyl acetate in hexanes) to
afford 40 (315 mg, 73%) as a colorless solid. Mp 152–
5.32. Adamantane-2-spiro-30-80-(40-fluorophenyl)-10,20,40-
trioxaspiro[4.5]decane (46)
A solution of O-methyl 2-adamantanone oxime27
(0.36 g, 2 mmol) and 4-(4-fluorophenyl)cyclohexa-
none30 (0.38 g, 2 mmol) in pentane (50 ml) was treated
with ozone according to the general procedure. The
crude product was purified by flash chromatography
(silica gel, 2% ether in petroleum ether) to afford 46
(0.36 g, 50%) as a colorless solid. Mp 103–106 ꢁC (eth-
anol/H2O 1:1). 1H NMR (CDCl3) d 1.58–2.25 (m,
22H), 2.43–2.70 (m, 1H), 6.90–7.02 (m, 2H), 7.11–
7.22 (m, 2H). 13C NMR (CDCl3) d 26.43, 26.84,
31.57, 34.63, 34.76, 36.36, 36.75, 42.15, 108.24,
111.41, 115.06 (d, J = 21.4 Hz), 128.03 (d, J = 7.4 Hz),
141.75 (d, J = 3.0 Hz), 161.26 (d, J = 244.1 Hz). Anal.
Calcd for C22H27FO3: C, 73.72; H, 7.59. Found: C,
73.65; H, 7.66.
1
154 ꢁC. H NMR (CDCl3) d 1.32–1.49 (m, 2H), 1.61–
2.07 (m, 20H), 2.12–2.29 (m, 1H), 3.47 (d, J = 6.8 Hz,
2H), 7.57 (dd, J = 4.9, 4.9 Hz, 1H), 8.96 (d, J = 4.9 Hz,
2H). 13C NMR (125.7 MHz, CDCl3) d 26.44, 26.82,
30.04, 30.87, 33.66, 34.76, 36.35, 36.75, 56.34, 107.78,
111.59, 123.71, 158.66, 166.30. Anal. Calcd for
C21H28N2O5S: C, 59.98; H, 6.71; N, 6.66. Found: C,
60.16; H, 6.78; N, 6.77.
5.33. cis-Adamantane-2-spiro-30-80-[(40-methylsulfo-
nyl)phenyl]-10,20,40-trioxaspiro[4.5]decane (47)
5.31. cis-Adamantane-2-spiro-30-80-[[(10-methyl-10H-imi-
dazol-20-yl)sulfonyl]methyl]-10,20,40-trioxaspiro[4.5]dec-
ane (41)
A solution of O-methyl 2-adamantanone oxime27
(0.54 g, 3 mmol) and 4-[4-(methylsulfonyl)phenyl]cyclo-
hexanone (0.75 g, 3 mmol) in pentane (50 ml) and
CH2Cl2 (50 ml) was treated with ozone according to
the general procedure. The crude product was purified
by flash chromatography (silica gel, 30% ethyl acetate
in hexanes) to afford 47 (0.22 g, 18%) as a colorless solid.
Mp 132–135 ꢁC (hexanes/CH2Cl2 4:1). 1H NMR
(CDCl3) d 1.62–2.19 (m, 22H), 2.60–2.74 (m, 1H), 3.04
(s, 3H), 7.40 (d, J = 8.3 Hz, 2H), 7.86 (d, J = 8.0 Hz,
2H). 13C NMR (CDCl3) d 26.48, 26.88, 31.14, 34.48,
34.80, 36.43, 36.78, 42.94, 44.53, 107.95, 111.64,
127.59, 127.80, 138.45, 152.59. Anal. Calcd for
C23H30O5S: C, 66.00; H, 7.22. Found: C, 66.08; H, 7.16.
Step 1. To a suspension of 60% NaH (160 mg, 4 mmol)
in DMF (5 ml) under N2 at 0 ꢁC was added dropwise a
solution of 2-mercapto-1-methylimidazole (456 mg,
4.0 mmol) in DMF (10 ml). The mixture was stirred
for 1 h before a solution of 1114 (744 mg, 2 mmol) in
DMF (4 ml) was added dropwise. The mixture was stir-
red at rt overnight and concentrated. The residue was
dissolved in CH2Cl2 (30 ml), washed with water and
brine, dried over MgSO4, filtered, and concentrated.
The crude product was purified by flash chromatogra-
phy (silica gel, 25% ethyl acetate in hexanes) to afford
cis-adamantane-2-spiro-30-80-[[(10-methyl-10H-imidazol-
20-yl)thio]methyl]-10,20,40-trioxaspiro[4.5]decane (0.24 g,
30%) as a colorless solid. Mp 140–142 ꢁC. 1H NMR
(CDCl3) d 1.20–1.35 (m, 2H), 1.60–2.00 (m, 21H), 3.00
(d, J = 6.8 Hz, 2H), 3.60 (s, 3H), 6.90 (s, 1H), 7.03 (s,
1H).
5.34. cis-Adamantane-2-spiro-30-80-(40-carboxyphenyl)-
10,20,40-trioxaspiro[4.5]decane (48)
Step 1. A solution of O-methyl 2-adamantanone oxime27
(1.10 g, 6.2 mmol) and 4-[4-(ethoxycarbonyl)phenyl]cy-
clohexanone31 (1.70 g, 6.2 mmol) in pentane (100 ml)
and CH2Cl2 (50 ml) was treated with ozone according
to the general procedure. The crude product was puri-
fied by flash chromatography (silica gel, 10% ether in
hexanes) to afford cis-adamantane-2-spiro-30-80-[40-
(ethoxycarbonyl)phenyl]-10,20,40-trioxaspiro[4.5]decane
(1.60 g, 63%) as a colorless solid. Mp 129–132 ꢁC (hex-
Step 2. To a solution of the above thioether (250 mg,
0.6 mmol) in CH2Cl2 (5 ml) at 0 ꢁC was added dropwise
a solution of 3-chloroperoxybenzoic acid (70% reagent,
400 mg, 1.6 mmol) in CHCl3/CH2Cl2 (1:1, 8 ml). After
2 h, the mixture was allowed to warm up to rt, stirred
overnight, and concentrated to 3 ml. The residue was
diluted with saturated aq NaHCO3 (20 ml) and extract-
ed with CH2Cl2 (2· 20 ml). The combined extracts were
washed with water and brine, dried over MgSO4, fil-
anes/ether 9:1). 1H NMR (CDCl3)
d
1.38 (t,
J = 7.2 Hz, 3H), 1.63–2.22 (m, 22H), 2.56–2.71 (m,

6380
Y. Dong et al. / Bioorg. Med. Chem. 14 (2006) 6368–6382
1
1H), 4.36 (q, J = 7.2 Hz, 2H), 7.27 (d, J = 7.8 Hz, 2H),
7.96 (d, J = 8.0 Hz, 2H).
CH2Cl2, 3:2). H NMR (CDCl3) d 1.58–2.23 (m, 22H),
2.75–2.98 (m, 1H), 6.96 (s, 2H). 13C NMR (CDCl3) d
26.54, 26.94, 29.11, 33.92, 34.82, 34.86, 36.23, 36.47,
36.84, 108.00, 111.54, 121.10 (br s), 151.00. Anal. Calcd
for C19H26N2O3: C, 69.06; H, 7.93; N, 8.48. Found: C,
69.04; H, 7.93; N, 8.60.
Step 2. A mixture of cis-adamantane-2-spiro-30-80-[40-
(ethoxycarbonyl)phenyl]-10,20,40-trioxaspiro[4.5]decane
(1.38 g, 3.35 mmol), KOH (1.13 g), THF (30 ml), meth-
anol (30 ml), and water (6 ml) was heated at 50 ꢁC for
2 h. The mixture was concentrated to 10 ml, diluted with
water (50 ml), and extracted with ethyl acetate. The
aqueous layer was acidified with 1 M aq HCl to pH 2,
and the resulting solid was collected by filtration to give
5.37. Adamantane-2-spiro-30-50,50-bis(40-fluorophenyl)-
10,20,40-trioxolane (51)
A solution of O-methyl 2-adamantanone oxime27
(0.90 g, 5 mmol) and 4,40-difluorobenzophenone
(1.09 g, 5 mmol) in pentane (90 ml) and CH2Cl2
(10 ml) was treated with ozone according to the general
procedure. The crude product was purified by flash
chromatography (silica gel, 2% ether in petroleum ether)
to afford 51 (0.87 g, 45%) as a colorless solid. mp 86–
89 ꢁC (ethanol/H2O 1:1). 1H NMR (CDCl3) d 1.60–
2.05 (m, 12H), 2.06–2.40 (m, 2H), 6.90–7.20 (m, 4H),
7.35–7.65 (m, 4H). 13C NMR (CDCl3) d 26.41, 26.84,
34.77, 34.96, 36.17, 36.71, 108.95, 114.21, 115.06 (d,
J = 21.3 Hz), 128.96 (d, J = 8.4 Hz), 135.56, 162.95 (d,
J = 248.0 Hz). Anal. Calcd for C23H22F2O3/ C, 71.86;
H, 5.77. Found: C, 71.78; H, 5.87.
1
48 (1.08 g, 84%) as a colorless solid. Mp 157 ꢁC dec. H
NMR (CDCl3) d 1.63–2.22 (m, 22H), 2.57–2.72 (m, 1H),
7.31 (d, J = 8.3 Hz, 2H), 8.03 (d, J = 8.1 Hz, 2H). 13C
NMR (CDCl3) d 26.49, 26.90, 31.14, 34.58, 34.81,
36.43, 36.80, 43.10, 108.14, 111.54, 126.99, 127.23,
130.46, 152.54, 171.45. Anal. Calcd for C23H28O5: C,
71.85; H, 7.34. Found: C, 71.68; H, 7.33.
5.35. cis-Adamantane-2-spiro-30-80-[40-(40,50-dihydro-
40,40-dimethyl-20-oxazolyl)phenyl]-10,20,40-trioxaspi-
ro[4.5]decane hydrochloride (49)
Step 1. A solution of O-methyl 2-adamantanone oxime27
(1.32 g, 7.4 mmol) and 4-[4-(4,5-dihydro-4,4-dimethyl-2-
oxazolyl)phenyl]cyclohexanone31,32 (2.00 g, 7.4 mmol)
in pentane (100 ml) and CH2Cl2 (50 ml) was treated with
ozone according to the general procedure. The crude
product was purified by flash chromatography (silica
gel, 10–30% ether in hexanes) to afford cis-adaman-
tane-2-spiro-30-80-[40-(40,50-dihydro-40,40-dimethyl-20-
oxazolyl)phenyl]-10,20,40-trioxaspiro[4.5]decane (0.80 g,
5.38. Adamantane-2-spiro-30-50,50-bis(40-carboxyphenyl)-
10,20,40-trioxolane (52)
Step 1. A solution of O-methyl 2-adamantanone oxime27
(1.79 g, 10 mmol) and 4,40-bis(ethoxycarbonyl)benzo-
phenone (3.26 g, 10 mmol) in pentane (60 ml) and
CH2Cl2 (40 ml) was treated with ozone according to
the general procedure. The crude product was purified
by flash chromatography (silica gel, 10% ether in hex-
anes) to afford adamantane-2-spiro-30-50,50-bis[40-(eth-
oxycarbonyl)phenyl]-10,20,40-trioxolane (1.77 g, 36%) as
a colorless solid. Mp 143–145 ꢁC (ether). 1H NMR
(CDCl3) d 1.38 (t, J = 7.1 Hz, 6H), 1.60–2.07 (m,
12H), 2.20 (app d, J = 12.2 Hz, 2H), 4.37 (q,
J = 7.2 Hz, 4H), 7.58 (d, J = 8.3 Hz, 4H), 8.03 (d,
J = 8.3 Hz, 4H).
1
25%) as a colorless solid. Mp 138–140 ꢁC (ethanol). H
NMR (CDCl3) d 1.37 (s, 6H), 1.59–2.16 (m, 22H),
2.51–2.68 (m, 1H), 4.08 (s, 2H), 7.24 (d, J = 8.0 Hz,
2H), 7.85 (d, J = 8.0 Hz, 2H).
Step 2. To a solution of cis-adamantane-2-spiro-30-80-
[40-(40, 50-dihydro-40,40-dimethyl-20- oxazolyl)phenyl]-
10,20,40-trioxaspiro[4.5]decane (0.21 g, 0.48 mmol) in
ether (9 ml) and CH2Cl2 (1 ml) was added 1 M ethereal
HCl (0.5 ml). The resulting precipitate was collected by
filtration to afford 49 (0.20 g, 88%) as a colorless solid.
Mp 143–145 ꢁC. 1H NMR (CDCl3) d 1.58–2.25 (m,
28H), 2.58–2.80 (m, 1H), 4.69 (br s, 2H), 7.44 (br s,
2H), 8.40 (br s, 2H). 13C NMR (CDCl3) d 26.44,
26.84, 27.19, 30.87, 34.37, 34.76, 36.39, 36.74, 43.21,
63.92, 83.36, 107.83, 111.59, 117.60, 128.16, 131.38,
156.27, 168.98. Anal. Calcd for C27H36ClNO4: C,
68.41; H, 7.65; N, 2.95. Found: C, 68.26; H, 7.80; N,
2.90.
Step 2. A mixture of adamantane-2-spiro-30-50,50-bis[40-
(ethoxycarbonyl)phenyl]-10,20,40-trioxolane
(0.44 g,
0.89 mmol), THF (7 ml), and 40% aq KOH (4.5 ml)
was heated at 50 ꢁC for 5 days. The reaction mixture
was cooled to rt and extracted with ether (5· 20 ml).
The aqueous layer was acidified to pH 3 with concd
HCl. The resulting precipitate was filtered and recrystal-
lized from ethanol/water (2:1) to afford 52 (0.35 g, 90%)
1
as a colorless solid. Mp 170 ꢁC (EtOAc) dec. H NMR
(DMSO-d6) d 1.60–2.05 (m, 12H), 2.13 (app d,
J = 11.7 Hz, 2H), 7.60 (d, J = 8.8 Hz, 4H), 7.98 (d,
J = 8.8 Hz, 4H). 13C NMR (DMSO-d6) d 25.79, 26.19,
34.25, 34.42, 35.56, 35.99, 108.40, 113.95, 126.42,
129.46, 131.47, 143.44, 166.69. Anal. Calcd for
C25H24O7: C, 68.80; H, 5.54. Found: C, 68.64; H, 5.34.
5.36. cis-Adamantane-2-spiro-30-80-(10H-imidazol-20-yl)-
10,20,40-trioxaspiro[4.5]decane (50)
To a solution of cis-adamantane-2-spiro-30-80-formyl-
10,20, 40-trioxaspiro[4.5]decane14 (292 mg, 1 mmol) and
40% glyoxal (145 mg, 1 mmol) in methanol (12 ml) at
0 ꢁC was added ammonia (0.45 ml, 7 N in methanol).
The resulting mixture was stirred at rt overnight and
concentrated. The crude product was crystallized from
hexanes/CH2Cl2 (3:2) to afford trioxolane 50 (240 mg,
73%) as a colorless solid. Mp 138–140 ꢁC (hexanes/
5.39. Adamantane-2-spiro-30-50,50-bis[40-(aminometh-
yl)phenyl]-10,20,40-trioxolane dimesylate (53)
Step 1. To a solution of adamantane-2-spiro-30-50,50-
bis[40- (ethoxycarbonyl)phenyl]-10,20,40- trioxolane14

Y. Dong et al. / Bioorg. Med. Chem. 14 (2006) 6368–6382
6381
(1.0 g, 2.00 mmol) in ether (5 ml) and THF (2 ml) was
Acknowledgment
added dropwise 2 M lithium borohydride in THF
(2.00 ml, 4 mmol) followed by 1 M lithium triethylboro-
hydride in THF (0.4 ml, 0.4 mmol). The resulting mix-
ture was stirred at rt for 24 h and then diluted with
ether (30 ml). The mixture was washed with 1 M aque-
ous NaOH (2· 5 ml), water (2· 5 ml), and brine (5 ml),
dried over MgSO4, filtered, and concentrated to afford
the diol (0.80 g, 96%) as a colorless solid.
This investigation received financial support from the
UNDP/WORLD BANK/WHO Special Programme
for Research and Training in Tropical Diseases (TDR
ID No. 960275) and Medicines for Malaria Venture
(MMV).
References and notes
Step 2. Diisopropyl azodicarboxylate (0.70 ml,
3.53 mmol) was added dropwise to a mixture of the diol
(0.80 g, 1.96 mmol), phthalimide (0.57 g, 3.87 mmol),
and triphenylphosphine (1.31 g, 5 mmol) in THF
(20 ml) at 0 ꢁC under N2. The resulting mixture was stir-
red at rt for 24 h and then quenched with 5% aqueous
NaHCO3 (20 ml). The solid was collected by filtration
and washed with water, THF, and ether to afford the
bisphthalimide (1.06 g, 81%) as a white solid.
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Step 3. A mixture of the bisphthalimide (0.73 g,
1.10 mmol) and hydrazine monohydrate (1 ml) in chlo-
roform (30 ml) and methanol (4 ml) was heated at
50 ꢁC for 24 h. The reaction mixture was cooled to
rt, filtered to remove the solid by-product, and concen-
trated. The residue was dissolved in CHCl3, washed
with brine, dried over MgSO4, filtered, and treated
with a solution of methanesulfonic acid (0.21 g) in
CHCl3 (10 ml). After removal of the solvent, the crude
product was purified by crystallization from EtOH/
CHCl3 (1:4) to afford 53 (0.20 g, 37%) as a colorless
solid. Mp 147–148 ꢁC. 1H NMR (CD3OD) d 1.62–
1.94 (m, 12H), 2.18–2.25 (m, 2H), 2.68 (s, 6H), 4.13
(s, 4H), 7.47 (d, J = 8.3 Hz, 4H), 7.57 (d, J = 8.3 Hz,
4H). 13C NMR (CD3OD) d 27.85, 28.28, 35.70,
35.94, 37.59, 37.64, 39.48, 43.88, 110.22, 115.35,
128.61, 129.94, 135.26, 142.17. Anal. Calcd for
C27H38N2O9S2: C, 54.16; H, 6.40; N, 4.68. Found: C,
53.96; H, 6.29; N, 4.80.
12. Griesbaum, K.; Liu, X.; Kassiaris, A.; Scherer, M. Libigs
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15. Trioxolane ester precursors were obtained in 25–63%
yields.
5.40. Adamantane-2-spiro-30-50,50-bis(20-pyridyl)-10,20,40-
trioxolane (54)
16. Brown, H. C.; Narasimhan, S. J. Org. Chem. 1982, 47,
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day 3 post-infection compared to an untreated control
group. For example, a compound with an activity of
99.99% is 10-fold more active than one with an activity of
99.90% and 100-fold more active than one with an activity
of 99.0%.
A solution of O-methyl 2-adamantanone oxime27 (716 g,
4.0 mmol) and di-2-pyridyl ketone (777 mg, 4.2 mmol)
in pentane (70 ml) and CH2Cl2 (30 ml) was treated with
ozone according to the general procedure. The crude
product was purified by flash chromatography (silica
gel, 4% ethanol in ether) to afford 54 (620 mg, 44%) as
a colorless solid. Mp 135–136 ꢁC (ether). 1H NMR
(CDCl3) d 1.60–2.10 (m, 12H), 2.27 (app d, J = 12 Hz,
2H), 7.21 (ddd, J = 8.5, 5.0, 1.0 Hz, 2H), 7.76 (ddd,
J = 8.0, 8.0, 2.0 Hz, 2H), 7.95 (d, J = 8.0 Hz, 2H), 8.55
(dd, J = 4.5, 1.0 Hz, 2H). 13C NMR (CDCl3) d 26.50,
26.86, 34.81, 34.88, 35.93, 36.74, 107.92, 114.58,
121.16, 123.16, 136.38, 149.12, 158.20. Anal. Calcd for
C21H22N2O3: C, 71.98; H, 6.33; N, 7.99. Found: C,
71.94; H, 6.30; N, 7.91.
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Padmanilayam, M.; Tang, Y.; Charman, W. N. U.S.
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5.41. Antimalarial screens
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