Bile acid-based 1,2,4-trioxanes: Synthesis and antimalarial assessment(1)

Article abstract of DOI:10.1021/jm301323k

A new series of bile acid-based trioxanes 23a-d, 24a-d, 25a-d, 26a, 26b, and 26d have been synthesized and assessed for their antimalarial activity against multidrug-resistant Plasmodium yoelii in Swiss mice by oral route. The antimalarial activity of these trioxanes showed a strong dependence on the side-chain length; shortening side-chain length lead to increase in activity. The antimalarial activity also showed even stronger dependence on the stereochemistry at C3 and C6 (C21 in Figure 5) of the trioxane moiety. Of the two diastereomers isolated of each of the trioxanes, more polar one was significantly more active than the less polar one. The more polar diastereomer of the trioxanes 26a, 26b, and 26d, were the most active compounds of the series. All these three trioxanes provided 100% protection at 24 mg/kg × 4 days. In this model β-arteether provided 100% and 20% protection at 48 mg/kg × 4 days and 24 mg/kg × 4 days, respectively.

Full text of DOI:10.1021/jm301323k

Article
pubs.acs.org/jmc
Bile Acid-Based 1,2,4-Trioxanes: Synthesis and Antimalarial
Assessment1
Chandan Singh,*,† Mohammad Hassam,† Ved Prakash Verma,† Ajit Shanker Singh,†
Niraj Krishna Naikade,† Sunil K. Puri,‡ Prakas R. Maulik,§ and Ruchir Kant§
‡
§
†Division of Medicinal & Process Chemistry, Division of Parasitology, and Division of Molecular and Structural Biology,
CSIR-Central Drug Research Institute, Lucknow-226001, India
S
* Supporting Information
ABSTRACT: A new series of bile acid-based trioxanes 23a−d, 24a−d, 25a−d, 26a, 26b,
and 26d have been synthesized and assessed for their antimalarial activity against
multidrug-resistant Plasmodium yoelii in Swiss mice by oral route. The antimalarial activity
of these trioxanes showed a strong dependence on the side-chain length; shortening side-
chain length lead to increase in activity. The antimalarial activity also showed even stronger
dependence on the stereochemistry at C3 and C6 (C21 in Figure 5) of the trioxane
moiety. Of the two diastereomers isolated of each of the trioxanes, more polar one was significantly more active than the less
polar one. The more polar diastereomer of the trioxanes 26a, 26b, and 26d, were the most active compounds of the series. All
these three trioxanes provided 100% protection at 24 mg/kg × 4 days. In this model β-arteether provided 100% and 20%
protection at 48 mg/kg × 4 days and 24 mg/kg × 4 days, respectively.
component plays an important part in the biological activity of
this class of compounds. These results prompted us to
investigate the SAR of the corresponding bile acid-based
trioxanes. Bile acids differ significantly from the sterols in shape,
as unlike sterols, the A/B ring junction in bile acids is cis.
Moreover, commercially available bile acids such as lithocholic
acid, cholic acid, and dehydrocholic acid offer variety in the
functional groups in tetracyclic ring system. Also bile acids have
the advantage of having carboxyl group in the side chain which
allows for a systematic degradation of the side chain. Together
these unique properties of bile acids make them attractive
templates for the preparation of a new series of 1,2,4-trioxanes.
Several bile acid-based tetraoxanes prepared by Solaja et al.,
have shown promising antimalarial activity.7 Using lithocholic
acid and testosterone 20 as the starting materials, we have
prepared ketones 10, 15, 19, and 20a (Figure 3) with
decreasing side chain length. These ketones have been further
elaborated into 1,2,4-trioxanes 23a−d, 24a−d, 25a−d, 26a,
26b, and 26d. Some of these new trioxanes have shown
significant antimalarial activity against multidrug-resistant
Plasmodium yoelii in mice.8,9
INTRODUCTION
■
Malaria affects around 300−500 million people in the tropical
and subtropical areas of the world with an annual death toll of
around two million.2 The malaria situation is further
complicated with the development of resistance against the
standard and affordable drugs such as chloroquine.3 Against this
background, isolation of artemisinin 1 as the active principle of
the Chinese traditional drug against malaria, Artemisia annua,
was a major breakthrough in malaria chemotherapy.4
Artemisinin owes its antimalarial activity due to the presence
of 1,2,4-trioxane moiety and is active against both chloroqui-
nine-sensitive and chloroquinine-resistant malaria. Artemisinin
derivatives, e.g., artemether 2, arteether 3, and artesunic acid 4
(Figure 1), are currently the drugs of choice for the treatment
of malaria caused by multidrug-resistant Plasmodium falcipa-
rum.5
As a part of our endeavor to develop synthetic substitutes for
these drugs, we had recently reported a new series of steroid-
based 1,2,4-trioxanes.6 Of the several prototypes of these
steroid-based trioxanes e.g. 5, 6, and 7 prepared by us (Figure
2), only prototype 7 had shown significant antimalarial activity,
suggesting that the length of the side chain of the steroid
CHEMISTRY
■
Ketones 10, 19, and 20a were prepared using reported
procedures (Schemes 1, 3, and 4).10,11 Ketone 15 was prepared
from lithocholic acid 8 according to Scheme 2. Thus acetylation
of lithocholic acid 8 with acetic anhydride yielded 11, which on
lead tetraacetate mediated oxidative decarboxylation furnished
12. Olefin 12 on reaction with mercuric acetate in aqueous
tetrahydrofuran, followed by addition of alkaline sodium
Received: September 14, 2012
Figure 1. Artemisinin and its derivatives.
© XXXX American Chemical Society
A
dx.doi.org/10.1021/jm301323k | J. Med. Chem. XXXX, XXX, XXX−XXX

Journal of Medicinal Chemistry
Article
Figure 2. Steroid-based 1,2,4-trioxanes.
Figure 3. Bile acid-based ketones.
Scheme 1
Reagents and conditions: (a) MeOH, concd HCl, 65 °C, 4 h; (b) Jones reagent, acetone, 0 °C, 15 min.
Scheme 2
Reagents and conditions: (a) Ac2O, Et3N, DMAP (cat.), rt, 5 h; (b) Pb(OAc)4, Cu(OAc)2, C5H5N, C6H6, reflux, 12 h; (c) Hg(AcO)2, THF-H2O
(1:1), rt, 30 min; (d) NaBH4, NaOH, rt, 30 min; (e) MeOH, KOH, rt, 20 min; (f) Jones reagent, acetone, 0 °C, 15 min.
borohydride, furnished 13, which on reaction with methanolic
potassium hydroxide furnished 14. Diol 14 was further oxidized
with Jones reagent to 15.
TLC homogeneous fractions referred to as less polar fraction
(higher Rf on TLC) and more polar fraction (lower Rf on
TLC). The more polar fraction in all these cases were found to
1
be single compound as shown by H NMR and 13C NMR. A
β-Hydroxyhydroperoxides 22a−d were prepared by photo-
oxygenation of allylic alcohols 21a−d, using the procedure
reported earlier.12 Acid-catalyzed condensation of β-hydrox-
yhydroperoxides 22a−d with ketones 10, 15, 19, and 20a
furnished trioxanes 23a−d, 24a−d, 25a−d, 26a, 26b, and 26d,
respectively, in 36−74% yields (Scheme 5, Table 1). All of
these trioxanes were obtained as a mixture of diastereomers
which were separated by column chromatography into two
typical TLC representation of these fractions shown in Figure
4. Also the more polar fraction in all these cases was found to
be significantly more active than the less polar fraction. The
more polar diastereomer of 26a furnished crystals suitable for
X-ray analysis and were analyzed accordingly.
X-ray Analysis of 26a (More Polar Isomer). The
conformation of compound 26a (more polar isomer) was
B
dx.doi.org/10.1021/jm301323k | J. Med. Chem. XXXX, XXX, XXX−XXX

Journal of Medicinal Chemistry
Article
squares mean plane through atoms O1, O2, O3, and C20 for
ring B, deviations of atom C3 and C10 are −0.596(5) and
0.676(5) Å, respectively, from the least-squares mean plane
through atoms C1, C2, C4, and C5 for ring C, deviations of
atoms C5 and C8 are −0.656(5) and 0.635(5) Å, respectively,
from the least-squares mean plane through atoms C9, C10, C6,
and C7 for ring D, while the deviations of atoms C9 and C13
are −0.616(5) and 0.696(6) Å, respectively, from the least-
squares mean plane through atoms C11, C12, C14, and C8 for
ring E. Ring F has an envelope conformation; deviations of
atom C13 is 0.694(6) Å from the mean plane through atoms
C14, C15, C16, and C17.
Table 1. Yields of Bile Acid-Based 1,2,4-Trioxanes
On the basis of the X-ray result of 26a (more polar isomer),
all more polar isomer of 23a−d, 24a−d, 25a−d, 26b, and 26d
were assigned the same stereochemistry as shown for 26a in
Figure 5.13
None of the compounds corresponding to less polar fraction
of 23a−d, 24a−d, 25a−d, 26a, 26b, and 26d furnished crystals
suitable for X-ray analysis. Also these fractions, although
homogeneous on TLC, showed presence of more than one
compound as shown by 13C NMR. Because these fractions
showed very poor antimalarial activity, no attempt was made to
further purify these fractions.
ANTIMALARIAL ACTIVITY
■
Both the fractions (less polar and more polar) corresponding to
trioxanes 23a−d, 24a−d, 25a−d, 26a, 26b, and 26d were
initially screened for antimalarial activity by oral route against
multidrug-resistant Plasmodium yoelii nigeriensis in Swiss mice at
a dose of 96 mg/kg × 4 days using Peter’s procedure.14
Trioxanes which showed 100% protection at 96 mg/kg × 4
days were further screened at lower doses.15 In this model, β-
arteether provided 100% and 20% protection at 48 mg/kg × 4
days and 24 mg/kg × 4 days, respectively, by oral route. The
results are summarized in Table 2.
Figure 4. TLC representation of trioxane 26a.
confirmed by single crystal X-ray diffraction studies. The
compound 26a (more polar isomer) was crystallized in P21
space group with two molecules in the unit cell. The ORTEP
diagram (Figure 5) showed the molecular structure of
C29H40O4 and its conformation with atomic numbering
scheme. The absolute configuration of the title compound
could not be confirmed with present study. However, on the
basis of the literature precedence,11 the X-ray studies showed
the molecule consists of six rings (A, B, C, D, E, and F) to
which two β-equatorial methyl groups are attached at the C10
and C13 positions and one hydroxyl group at C17 substituted
in ring F. The relative stereochemistry of C3 and C21 are S and
R, respectively. Ring A is almost planar. Rings B, C, D, and E
exist in chair conformations: the deviations of atom C3 and
C21 are 0.681(5) and −0.705(5) Å, respectively, from the least-
RESULT AND DISCUSSION
■
Reaction of β-Hydroxyhydroperoxides 22a−d with
Ketones 10, 15, 19, and 20a: Stereochemical Expect-
ation and Outcome. β-Hydroxyhydroperoxides 22a−d used
in this study were a racemic mixture and their reaction with
each of the ketones 10, 15, 19, and 20a were expected to
furnish trioxanes as a mixtures of four diastereomers. In the
Scheme 3
Reagents and conditions: (a) m-CPBA, NaHCO3, CH2Cl2, 0 °C to rt, 5 h; (b) HIO4·2H2O, THF, 0 °C to rt, 5 h; (c) hν, O2, rose bengal, MeOH,
10% KOH, 0 °C, 6 h; (d) Jones reagent, acetone, 0 °C, 15 min.
C
dx.doi.org/10.1021/jm301323k | J. Med. Chem. XXXX, XXX, XXX−XXX

Journal of Medicinal Chemistry
Article
Scheme 4
Reagents and conditions: (a) Pd−C, H2, THF, rt, 6 h.
Scheme 5
Reagents and conditions: (a) hν, O2, methylene blue, CH3CN, −10 to 0 °C, 4 h; (b) p−TSA, CH3CN, rt, 6 h.
Figure 5. (a) ORTEP diagram of trioxane 26a (more polar isomer) molecular structure of C29H40O4 at 30% probability. (b) Stereostructure of 26a
(more polar isomer).
event, in each case the reaction furnished two TLC
homogeneous fractions referred to as less polar fraction (higher
Rf on TLC) and more polar fraction (lower Rf on TLC). The
more polar fractions (lower Rf on TLC) of these trioxanes
showed the presence of only one diastereomer as judged from
Because none of these less polar fractions showed significant
antimalarial activity, no attempt was made to further purify
these fractions.
These results suggest that the reaction is partly stereospecific;
one of the two enantiomers of β-hydroxyhydroperoxides favors
the formation of a single diastereomer. Keeping the styrenyl
side chain in an equatorial configuration could be the driving
force for the selectivity. For the other enantiomer, an
equatorially placed styrenyl side chain will require the ring
closure from the β face of the bile acid nucleus. This
energetically unfavorable requirement will result in loss of
selectivity, leading to the formation of both the diastereomers
comprising the less polar fraction.
1
their H NMR and 13C NMR data. The more polar fraction
corresponding to trioxane 26a furnished crystals suitable for X-
ray analysis and were analyzed accordingly, and its stereo-
chemistry is depicted in Figure 5. On the basis of the similarity
1
in TLC pattern, H NMR and 13C NMR data all the other
more polar isomer corresponding to trioxane 23a−d, 24a−d,
25a−d, 26b, and 26d were assigned the same stereochemistry.
The corresponding less polar fraction of these trioxanes
though homogeneous on TLC showed the presence of more
than one diastereomer, at least two, as judged by 13C NMR.
Antimalarial Activity. Antimalarial activity of these
trioxanes exhibited strong dependence on two factors (i)
D
dx.doi.org/10.1021/jm301323k | J. Med. Chem. XXXX, XXX, XXX−XXX

Journal of Medicinal Chemistry
Article
Table 2. In Vivo Antimalarial Activity of Trioxanes 23a−d, 24a−d, 25a−d, 26a, 26b, and 26d against Multidrug-Resistant
Plasmodium yoelii nigeriensis in Swiss Mice by Oral Route
a
b
Percent suppression = [(C − T)/C] × 100, where C = parasitaemia in control group and T = parasitaemia in treated group. 100% suppression of
parasitaemia means, number of parasites if present, are below the detection limit.15 (**) Mice that did not develop patent infection until day 28 were
recorded as cured.
stereochemistry around trioxane ring and (ii) length of the side
chain. As can be seen from Table 2, none of the less polar
fractions corresponding to 23a−d, 24a−d, 25a−d, 26a, 26b,
and 26d showed significant antimalarial activity. On the other
hand, several of the trioxanes corresponding to the more polar
fractions showed a high order of antimalarial activity by oral
route and the antimalarial activity showed strong dependence
on the length of the side chain.16
Trioxane 23a−d (more polar isomer) with full length bile
acid side chain showed very poor antimalarial activity; none of
these trioxanes showed 100% clearance of parasitemia on day 4
at 96 mg/kg. Among trioxane 24a−d (more polar isomer), with
side chain shorter by one carbon, trioxane 24a−c showed 100%
clearance of parasitemia on day 4 at 96 mg/kg and two of them
(24a and 24b) provided 60% protection to the treated mice.
Trioxane 25a−d (more polar isomer) with side chain length
shorter by another two carbons, showed high-order antimalarial
activity. Trioxanes 25a−c provided 100% protection both at 96
mg/kg and 48 mg/kg. These trioxanes also provided 60−80%
protection at 24 mg/kg. Trioxanes 26a, 26b, and 26d (more
polar isomer), with no carbon side chain, were the most active
compounds of the series. All these three trioxanes showed
100% protection at 96, 48, and 24 mg/kg.
Thus, trioxane 24a, 24b, and 26d are twice as active as β-
arteether.
CONCLUSION
■
We have prepared a new series of trioxanes using bile acid
derived ketones. The oral antimalarial activity of these trioxanes
showed strong dependence both on stereochemistry around
trioxane ring and length of the side chain. Trioxanes 26a, 26b,
and 26d, with no carbon side chain, were the most active
compound of the series. All these three trioxanes showed 100%
protection at 24 mg/kg and were twice as active as β-arteether.
EXPERIMENTAL SECTION
■
General. All glass apparatus were oven-dried prior to use. Melting
points were determined on COMPLAB melting point apparatus and
are uncorrected. IR spectra were recorded on a Perkin−Elmer FT−IR
RXI spectrophotometer. 1H NMR and 13C NMR spectra were
1
recorded on Bruker DPX−200 (operating at 200 MHz for H and at
50 MHz for 13C) or DRX−300 (operating at 300 MHz for H and at
1
75 MHz for 13C) spectrometers using CDCl3 as solvent.
1
Tetramethylsilane (0.00 ppm) served as an internal standard in H
NMR and CDCl3 (77.0 ppm) in 13C NMR. Chemical shifts are
reported in part per million. Splitting patterns are described as singlet
(s), doublet (d), triplet (t) and multiplet (m). Electrospray mass
spectra (ESMS) were recorded on a Micromass Quattro II triple
quadruple mass spectrometer. Fast atom bombardment mass spectra
(FAB-MS) were obtained on JEOL SX 102 spectrometer using argon/
β-Arteether, the positive control in these studies, provided
100% protection at 48 mg/kg and 20% protection at 24 mg/kg.
E
dx.doi.org/10.1021/jm301323k | J. Med. Chem. XXXX, XXX, XXX−XXX

Journal of Medicinal Chemistry
Article
xenon (6 kV, 10 mA) as the FAB gas. Glycerol or m-nitrobenzyl
alcohol was used as matrix. Reactions were monitored on silica gel
TLC plates (coated with TLC grade silica gel, obtained from Merck).
Detecting agents used (for TLC) were iodine vapors and/or spraying
with an aq solution of vanillin in 10% sulfuric acid followed by heating
at 150 °C. Column chromatography was performed over silica gel
(60−120 Mesh) procured from Qualigens (India), flash silica gel
(230−400 Mesh) procured from Spectrochem (India). All chemicals
and reagents were obtained from Aldrich (USA), Lancaster (England)
or Spectrochem (India) and were used without further purification. log
p values of the compounds were calculated using Chem Draw Ultra 8.0
software. Elemental analyses of all the new compounds were recorded
on Vario EL-III C H N S analyzer (Germany), and values were within
0.5% of the calculated values for all compounds and therefore these
compounds meet the criteria of ≥95% purity.
Methyl-3-oxo-5β-cholan-24-oate (9). Concd hydrochloric acid
(5.00 mL) was added to a suspension of 8 (5.00 g, 13.3 mmol) in
methanol (200 mL), and the reaction mixture was refluxed at 65 °C
for 4 h. Reaction mixture was concentrated in vacuo at rt to furnish
crude product which was recrystallized with DCM−hexane to furnish
9 (4.36 g, 84% yield) as a white solid; mp 173−174 °C. IR (KBr,
cm−1) 1735, 3368. 1H NMR (300 MHz, CDCl3) δ 0.64 (s, 3H), 0.91−
0.92 (m, 6H), 1.07−2.41 (m, 29H), 3.67 (s, 3H), 4.68−4.77 (m, 1H).
ESMS (m/z) 413 [M + Na]+.
using EtOAc−hexane (2:98) to furnish 12 (6.15 g, 69% yield) as a
1
white solid; mp 80−82 °C. FT-IR (KBr, cm−1): 1726. H NMR (200
MHz, CDCl3) δ 0.67 (s, 3H), 0.93 (s, 3H), 1.05 (d, 3H, J = 6.2 Hz),
1.08−1.86 (m, 24H), 2.02 (s, 3H), 4.68−4.93 (m, 3H), 5.60−5.69 (m,
1H). 13C NMR (50 MHz, CDCl3) δ 12.61 (CH3), 20.48 (CH3), 21.22
(CH2), 21.80 (CH3), 23.74 (CH3), 24.60 (CH2), 26.74 (CH2), 27.02
(CH2), 27.42 (CH2), 28.88 (CH2), 32.64 (CH2), 34.97 (C), 35.45
(CH2), 36.19 (CH), 40.47 (CH2), 40.87 (CH), 41.60 (CH), 42.28
(CH), 43.06 (C), 56.04 (CH), 56.94 (CH), 74.69 (CH), 111.96
(CH2), 145.53 (CH), 174.25 (C). ESMS (m/z) 395 [M + Na]+.
3α-Acetyl-24-nor-5β-cholan-22-ol (13). A solution of 12 (5.00
g, 13.4 mmol) in THF (10.0 mL) was added to a solution of mercuric
acetate (10.2 g, 32.1 mmol) in H2O (50.0 mL) and THF (50.0 mL).
The reaction mixture was stirred at rt for 30 min. Then 3 M NaOH
was added followed by the addition of 0.5 M NaBH4 in 3 M NaOH.
The reaction mixture was stirred at rt for another 30 min. The mercury
was allowed to settle; sodium chloride was added to saturate the
aqueous layer and separated. Organic layer was concentrated in vacuo
at rt, and the crude product was purified by column chromatography
over silica gel using EtOAc−hexane (1:9) to furnish 13 (3.16 g, 60%
yield) as a white solid; mp 118−120 °C. FT-IR (KBr, cm−1): 1715,
3416. 1H NMR (200 MHz, CDCl3) δ 0.79 (s, 3H), 1.06 (s, 6H), 1.17
(d, 3H, J = 6.7 Hz), 1.23−2.09 (m, 25H), 2.14 (s, 3H), 4.02 (bs, 1H),
4.83 (bs, 1H). 13C NMR (50 MHz, CDCl3) δ: 11.96 (CH3), 12.37
(CH3), 16.01 (CH3), 21.19 (CH2), 21.73 (CH3), 23.66 (CH3), 24.63
(CH2), 26.69 (CH2), 26.92 (CH2), 27.33 (CH2), 27.75 (CH2), 32.54
(CH2), 34.85 (CH2) 35.33 (C), 36.13 (CH), 40.50 (CH2), 40.81
(CH), 42.15 (CH), 42.30 (CH), 43.27 (C), 54.03 (CH), 56.47 (CH),
69.02 (CH), 74.67 (CH), 170.91 (C). ESMS (m/z) 413 [M + Na]+.
24-Nor-5β-cholan-3,22-diol (14). 10% methanolic KOH (20.0
mL) was added to 13 (3.00 g, 7.68 mmol) and stirred at rt for 20 min.
Reaction mixture was diluted with water and filtered on a sintered
funnel and dried to furnish 14 (2.18 g, 82% yield). ESMS (m/z) 371
[M + Na]+.
24-Nor-5β-cholan-3,22-dione (15). Jones reagent (3.00 mL) was
added to a solution of 14 (2.00 g, 5.74 mmol) in acetone (20.0 mL)
and stirred at 0 °C for 15 min. Reaction mixture was diluted with water
(200 mL) and extracted with EtOAc (2 × 50 mL). The organic layer
was dried over anhyd Na2SO4 and concentrated in vacuo at rt to
furnish crude product which was purified by column chromatography
over silica gel using EtOAc−hexane (1:9) as eluent to furnish 15 (1.68
g, 85%) as an white solid; mp 160−162 °C. FT-IR (KBr, cm−1): 1726,
2931. 1H NMR (200 MHz, CDCl3) δ 0.52 (s, 3H), 0.84 (s, 3H), 0.93
(d, 3H, J = 6.8 Hz), 1.11−1.83 (m, 20H), 1.91 (s, 3H), 1.98−2.32 (m,
3H), 2.52 (t, 1H, J = 14.1 Hz). 13C NMR (50 MHz, CDCl3) δ 12.61
(CH3), 16.65 (CH3), 21.45 (CH2), 22.93 (CH3), 24.70 (CH2), 26.05
(CH2), 26.89 (CH2), 27.76 (CH2), 28.32 (CH3), 35.16 (C), 35.80
(CH), 37.30 (CH2), 37.41 (CH2), 40.22 (CH2), 40.98 (CH), 42.57
(CH2), 43.22 (C), 44.53 (CH), 50.47 (CH), 52.49 (CH), 56.12 (CH),
212.48 (C), 212.85 (C). ESMS (m/z) 367 [M + Na]+.
Methyl-3-oxo-5β-cholan-24-oate (10). Jones reagent (5.00 mL)
was added to a solution of 9 (4.00 g, 10.3 mmol) in acetone (50.0
mL), and the reaction mixture was stirred at 0 °C for 15 min. Reaction
mixture was diluted with water (200 mL) and extracted with ethyl
acetate (2 × 100 mL). The organic layer dried over anhyd Na2SO4 and
concentrated in vacuo at rt to furnish crude product which was
purified by column chromatography over silica gel using EtOAc−
hexane (1:9) as eluent to furnish 10 (3.54 g, 89% yield) as a white
1
solid; mp 145−146 °C. IR (KBr, cm−1) 1714, 1737. H NMR (300
MHz, CDCl3) δ 0.65 (s, 3H), 0.88 (d, 3H, J = 6.3 Hz), 0.98 (s, 3H),
1.07−2.35 (m, 27 H), 2.65 (t, 1H, J = 14.2 Hz), 3.62 (s, 3H). 13C
NMR (50 MHz, CDCl3) δ: 12.19 (CH3), 18.40 (CH3), 21.35 (CH2),
22.75 (CH3), 24.28 (CH2), 25.91 (CH2), 26.77 (CH2), 28.25 (CH2),
31.12 (CH2), 31.16 (CH2), 35.01 (C), 35.45 (CH2), 35.70 (CH),
37.14 (CH), 37.25 (CH2), 40.21 (CH2), 40.94 (CH), 42.43 (CH),
42.92 (C), 44.44 (CH), 51.50 (CH3), 56.16 (CH2), 56.58 (CH),
174.71 (C), 213.26 (C). ESMS (m/z) 411 [M + Na]+.
3α-Acetyl Lithocholic Acid (11). Acetic anhydride (10.00 mL),
triethylamine (14.00 mL), and DMAP (5 mg, 0.04 mmol) were added
to a solution of 8 (20.00 g, 53.11 mmol) in THF (100 mL), and
reaction mixture was stirred at room temperature for 5 h. Reaction
mixture was concentrated in vacuo at rt to furnish crude product which
was purified by column chromatography over silica gel using MeOH−
CHCl3 (1:99) as eluent to furnish 11 (18.56 g, 83%). FT-IR (KBr,
1
cm−1): 1726. H NMR (200 MHz, CDCl3) δ 0.65 (s, 3H), 0.93 (s,
6H), 1.07−1.99 (m, 26H), 2.03 (s, 3H), 2.24−2.40 (m, 2H), 4.65−
4.74 (m, 1H), 9.82 (s, 1H). 13C NMR (50 MHz, CDCl3) δ: 12.45
(CH3), 18.65 (CH3), 21.23 (CH2), 21.86 (CH3), 23.73 (CH3), 24.58
(CH2), 26.72 (CH2), 27.41 (CH2), 28.57 (CH2), 31.16 (CH2), 31.45
(CH2), 32.12 (CH2), 32.62 (CH2), 34.95 (C), 35.42 (CH2), 35.70
(CH), 36.17 (CH), 40.53 (CH2), 40.78 (CH), 42.26 (CH), 43.13 (C),
56.36 (CH), 56.88 (CH), 74.51 (CH), 171.19 (C), 180.73 (C). ESMS
(m/z) 441 [M + Na]+.
3α-Acetyl-24-nor-5β-chol-22-ene (12). Pyridine (50.0 mL) and
cupric acetate (1.66 g, 8.3 mmol) were added to a solution of 11 (10.0
g, 23.9 mmol) in dry benzene (100 mL), and the reaction mixture was
heated to 90 °C under N2 atmosphere. Lead tetraacetate (30.0 g, 67.7
mmol) was added in portions during and the reaction mixture was
refluxed for additional 12 h. It was cooled to room temperature and
filtered through Celite; the residue was washed with benzene (75 mL).
Addition of water (100 mL) and extraction with benzene yielded an
organic layer that was further stirred with 1N HCl (200 mL) for 30
min. The benzene layer was separated and washed with water (100
mL) followed by saturated aq NaHCO3 (100 mL). The organic layer
was dried over anhyd Na2SO4, concentrated in vacuo at rt, and the
crude product was purified by column chromatography over silica gel
3α-Acetyl-24-nor-5β-cholan-22-oxirane (16). m-CPBA (5.52 g,
40.5 mmol) was added to a mixture of 12 (4.00 g, 10.7 mmol) and
NaHCO3 (1.50 g, 17.8 mmol) in DCM (100 mL) at 0 °C over 20 min.
The resulting mixture was stirred for additional 4 h at rt. The mixture
was quenched with saturated aq NaHCO3 solution (40 mL) and
extracted with CH2Cl2 (2 × 50 mL). The organic layer dried over
anhyd Na2SO4 and concentrated in vacuo at rt to furnish crude
product which was purified by column chromatography over silica gel
using EtOAc−hexane (2:98) to furnish 16 (2.92 g, 70% yield). FT-IR
(KBr, cm−1): 1733. 1H NMR (300 MHz, CDCl3) δ 0.62 (s, 3H), 0.84
(s, 3H), 1.02−1.08 (m, 7H), 1.22−1.94 (m, 20H), 2.00 (s, 3H), 2.55−
2.57 (m, 2H), 2.70−2.76 (m, 1H), 4.70 (m, 1H). 13C NMR (75 MHz,
CDCl3) δ 10.82 (CH3), 15.62 (CH3), 19.46 (CH2), 20.05 (CH3),
22.00 (CH3), 22.98 (CH2), 25.02 (CH2), 25.28 (CH2), 25.67 (CH2),
25.98 (CH2), 30.90 (CH2), 33.23 (C), 33.71 (CH2), 34.47 (CH),
38.26 (CH), 38.58 (CH2), 39.17 (CH), 40.52 (CH), 41.59 (C), 47.63
(CH2), 52.74 (CH), 54.74 (CH), 55.98 (CH), 72.88 (CH), 169.03
(C). FAB-MS (m/z): 411 [M + Na]+.
3α-Acetyl-23,24-dinor-5β-cholan-22-al (17). A solution of
periodic acid (1.45 g, 6.38 mmol) in THF (5.00 mL) was added
F
dx.doi.org/10.1021/jm301323k | J. Med. Chem. XXXX, XXX, XXX−XXX

Journal of Medicinal Chemistry
Article
dropwise to an ice-cooled solution of 16 (2.00 g, 5.15 mmol) in THF
(20.0 mL) over a period of 10 min. The resulting mixture was stirred
for additional 4 h at rt. The reaction mixture was neutralized with
saturated aq NaHCO3 (20 mL) and water (50 mL) were extracted
with diethyl ether (3 × 50 mL). The organic layer dried over anhyd
Na2SO4 and concentrated in vacuo at rt to furnish crude product
which was purified by column chromatography over silica gel using
EtOAc−hexane (3:97) to furnish 17 (1.33 g, 69% yield). FT-IR (KBr,
was bubbled into a solution of 21a (500 mg, 3.37 mmol) and
methylene blue (5 mg) in acetonitrile (25 mL) at −10 to 0 °C. The
reaction mixture was irradiated with visible light by means of a
tungsten−halogen lamp (500 W) for 4 h. β-Hydroxyhydroperoxide
22a formed in the reaction was not isolated and reacted in situ with 10
(1.40 g, 3.60 mmol) in the presence of p-TSA (40 mg, 0.23 mmol) for
6 h at rt. Saturated aq NaHCO3 (30 mL) was added. The aq layer was
extracted with diethyl ether (2 × 100 mL), and the combined organic
layer was dried over anhyd Na2SO4 and concentrated under vacuo at
rt. The crude product was purified by column chromatography over
silica gel using EtOAc−hexane (5:95) as eluent to furnish 23a (1.37 g,
74% yield, based on 21a as starting material).
1
cm−1): 1727. H NMR (300 MHz, CDCl3) δ 0.69 (s, 3H), 0.93 (s,
3H), 1.10 (d, 3H, J = 6.6 Hz), 1.21−1.94 (m, 23H), 2.01 (s, 3H),
2.30−2.37 (m, 1H), 4.65−4.76 (m, 1H), 9.55 (d, 1H, J = 3 Hz). 13C
NMR (75 MHz, CDCl3) δ 11.09 (CH3), 12.10 (CH3), 19.19 (CH2),
20.10 (CH3), 21.99 (CH3), 23.26 (CH2), 25.03 (CH2), 25.31 (CH2),
25.65 (CH2), 25.79 (CH2), 30.93 (CH2), 33.29 (C), 33.74 (CH2),
34.50 (CH), 38.53 (CH2), 39.19 (CH), 40.53 (CH), 42.00 (C), 48.12
(CH), 49.94 (CH), 54.46 (CH), 72.94 (CH), 169.20 (C), 203.59 (C);
FAB-MS (m/z): 397 [M + Na]+.
Trioxane 23a. This was obtained in 74% yield as a diastereomeric
mixture which was separated by column chromatography.
Trioxane (23a, Less Polar Isomer). This was obtained as an oil.
1
IR (neat, cm−1) 1630, 1736, 2925. H NMR (300 MHz, CDCl3) δ
0.63 (s, 3H), 0.89 (d, 3H, J = 6.3 Hz), 0.93 (s, 3H), 1.03−2.55 (m,
28H), 3.62 (s, 3H), 3.68−3.74 (m, 1H), 3.79−3.88 (m, 1H), 5.21 (dd,
1H, J = 10.2 and 2.3 Hz), 5.28 (s, 1H), 5.45 (s, 1H), 7.27−7.36 (m,
5H). 13C NMR (75 MHz, CDCl3) δ 12.11 (CH3), 18.32 (CH3), 21.11
(CH2), 23.16 (CH3), 23.69 (CH2), 24.22 (CH2), 26.18 (CH2), 26.54
(CH2), 28.22 (CH2), 31.01 (2 × CH2), 32.63 (CH2), 34.48 (CH2),
35.08 (C), 35.38 (CH), 35.67 (CH), 39.15 (CH), 39.92 (CH), 40.13
(CH2), 42.74 (C), 51.43 (CH3), 55.93 (CH), 56.43 (CH), 62.70
(CH2), 80.40 (CH), 103.72 (C), 116.28 (CH2), 126.40 (2 × CH),
128.15 (CH), 128.56 (2 × CH), 138.60 (C), 143.61 (C), 174.59 (C).
ESMS (m/z) 551 [M + H]+. Anal. C for C35H50O5: C, 76.33%, H,
9.15%. Found: C, 76.24%, H, 9.00%.
Trioxane (23a, More Polar Isomer). This was obtained as a solid;
mp 80−81 °C. IR (KBr, cm−1) 1630, 1735, 2920. 1H NMR (300 MHz,
CDCl3) δ 0.65 (s, 3H), 0.91 (d, 3H, J = 6.2 Hz), 0.96 (s, 3H), 1.07−
2.70 (m, 28H), 3.67 (s, 3H), 3.75 (dd, 1H, J = 11.6 and 2.7 Hz), 4.03
(dd, 1H, J = 11.6 and 10.6 Hz), 5.25 (dd, 1H, J = 10.6 and 2.7 Hz),
5.32 (s, 1H), 5.51 (s, 1H), 7.27−7.42 (m, 5H). 13C NMR (75 MHz,
CDCl3) δ 12.25 (CH3), 18.49 (CH3), 21.23 (CH2), 23.16 (CH3),
24.20 (CH2), 24.37 (CH2), 26.10 (CH2), 26.43 (CH2), 28.37 (CH2),
31.21 (CH2), 31.26 (CH2), 32.97 (CH2), 35.10 (C), 35.56 (CH),
35.82 (CH), 35.87 (CH2), 39.37 (CH), 40.04 (CH), 40.34 (CH2),
42.94 (C), 51.64 (CH3), 56.19 (CH), 56.68 (CH), 63.12 (CH2), 80.44
(CH), 103.81 (C), 116.52 (CH2), 126.58 (2 × CH), 128.35 (CH),
128.76 (2 × CH), 138.86 (C), 143.67 (C), 174.89 (C). ESMS (m/z)
551 [M + H]+. Anal. Calcd for C35H50O5: C, 76.33%, H, 9.15%.
Found: C, 76.19%, H, 9.37%.
5β-pregnanolone (18). A slow stream of oxygen was bubbled into
a solution of 17 (1.00 g, 2.67 mmol) and rose bengal (8 mg) in 10%
methanolic KOH (50 mL) in a 200 mL double-jacketed round-bottom
flask, maintained below 0 °C by circulating cold ethanol. The reaction
mixture was irradiated with visible light by means of a tungsten−
halogen lamp (500 W) for 6 h. The reaction mixture was poured into
H2O (50 mL), extracted with ether, and washed successively with 10%
HCl (20 mL), saturated aq NaHCO3 (20 mL), and H2O (20 mL).
The organic layer was dried over anhyd Na2SO4 and concentrated in
vacuo at rt to furnish crude product which was purified by column
chromatography over silica gel using EtOAc−hexane (15:85) to
furnish 18 (0.660 g, 78% yield) as a solid; mp 126−128 °C. FT-IR
(KBr, cm−1): 1720, 3415. 1H NMR (300 MHz, CDCl3) δ 0.58 (s, 3H),
0.91 (s, 3H), 1.22−2.04 (m, 23H), 2.12 (s, 3H), 3.55−3.71 (m, 2H).
13C NMR (50 MHz, CDCl3) δ 13.66 (CH3), 21.14 (CH2), 23.17
(CH2), 23.64 (CH3), 24.73 (CH2), 26.72 (CH2), 27.41 (CH2), 30.46
(CH2), 31.76 (CH3) 34.92 (C), 35.67 (CH2), 36.17 (CH), 36.35
(CH2), 39.52 (CH2), 40.76 (CH), 42.33 (CH), 44.76 (C), 57.05
(CH), 64.23 (CH), 71.69 (CH), 211.14 (C). ESMS (m/z) 341 [M +
Na]+.
5β-Pregna-3,20-dione (19). Jones reagent (2.00 mL) was added
to a solution of 18 (660 mg, 2.07 mmol) in acetone (10.0 mL) at 0 °C
for 15 min. Reaction mixture was diluted with water (100 mL) and
extracted with EtOAc (2 × 25 mL). The organic layer was dried over
anhyd Na2SO4 and concentrated in vacuo at rt to furnish crude
product which was purified by column chromatography over silica gel
using EtOAc−hexane (1:9) as eluent to furnish 19 (591 mg, 90%
Trioxane 23b. This was obtained in 55% yield as a diastereomeric
mixture which was separated by column chromatography.
1
yield) as a white solid; mp 102−104 °C. IR (KBr, cm−1): 1715. H
Trioxane (23b, Less Polar Isomer). This was obtained as an oil.
NMR (300 MHz, CDCl3) δ 0.59 (s, 3H), 0.98 (s, 3H), 1.06−2.15 (m,
20H), 2.08 (s, 3H), 2.24−2.36 (m, 1H), 2.50 (t, 1H, J = 9.0 Hz), 2.64
(t, 1H, J = 14.2 Hz). 13C NMR (50 MHz, CDCl3) δ 13.51 (CH3),
21.29 (CH2), 22.70 (CH3), 23.02 (CH2), 24.47 (CH2), 25.84 (CH2),
26.62 (CH2), 31.56 (CH3) 35.00 (CH), 35.62 (C), 37.05 (CH2),
37.21 (CH2), 39.18 (CH2), 40.83 (CH), 42.36 (CH2), 44.26 (CH),
44.33 (C), 56.68 (CH), 63.81 (CH), 209.34 (C), 212.93 (C); ESMS
(m/z) 339 [M + Na]+.
1
IR (Neat, cm−1) 1629, 1736, 2930. H NMR (300 MHz, CDCl3) δ
0.59 (s, 3H), 0.86 (d, 3H, J = 6.2 Hz), 0.89 (s, 3H), 1.00−2.49 (m,
28H), 3.58 (s, 3H), 3.63−3.69 (m, 1H), 3.75−3.85 (m, 1H), 5.10−
5.13 (m, 1H), 5.24 (s, 1H), 5.37 (s, 1H), 6.94 (t, 2H, J = 8.5 Hz),
7.28−7.32 (m, 2H). 13C NMR (75 MHz, CDCl3) δ 12.01 (CH3),
18.24 (CH3), 21.06 (CH2), 22.64 (CH2), 23.07 (CH3), 23.12 (CH3),
24.15 (CH2), 26.14 (CH2), 26.32 (CH2), 26.50 (CH2), 28.14 (CH2),
30.91 (CH2), 30.95 (CH2), 31.57 (CH2), 32.58 (CH2), 34.38 (CH2),
35.01 (C), 35.32 (CH), 35.64 (CH), 39.09 (CH), 39.27 (CH), 39.92
(CH), 40.09 (CH2), 42.68 (C), 51.25 (CH3), 55.93 (CH), 56.39
(CH), 62.36 (CH2), 80.17 (CH), 80.33 (CH), 103.50 (C), 103.65
(C), 115.23 (CH), 115.51 (CH), 116.16 (CH2), 116.31 (CH2),
128.10 (CH), 128.21 (CH), 134.73 (C), 142.64 (C), 162.60 (C, JC−F
= 247.6 Hz), 174.35 (C). ESMS (m/z) 569 [M + H]+. Anal. Calcd for
C35H49FO5: C, 73.91%, H, 8.68%. Found: C, 73.54%, H, 8.92%.
Trioxane (23b, More Polar Isomer). This was obtained as a
17β-Hydroxy-5β-androstan-3-one (20a). Palladium charcoal
(500 mg) was added to a solution of testosterone 20 (5.00 g, 17.3
mmol) in THF (25.0 mL) and hydrogenation was carried out at rt for
6 h.11 The catalyst was filtered through Celite, solvent was removed
under reduced pressure, and the crude product obtained as the mixture
of 5α and 5β form was separated by column chromatography using
EtOAc−benzene (2:98) as eluent to furnish 20a (1.98 g, 39%) as a
white solid; mp 120−122 °C. IR (KBr, cm−1) 1708, 2862, 2927, 3421.
1H NMR (300 MHz, CDCl3) δ 0.76 (s, 3H), 1.03 (s, 3H), 1.07−2.36
1
white solid; mp 90−92 °C. IR (KBr, cm−1) 1600, 1737, 2935. H
(m, 22H), 2.67 (t, 1H, J = 14.2 Hz), 3.65 (t, 1H, J = 8.6 Hz). 13C
NMR (75 MHz, CDCl3) δ 11.34 (CH3), 20.97 (CH3), 22.84 (CH2),
23.54 (CH2), 25.55 (CH2), 26.64 (CH2), 30.68 (CH2), 35.15 (C),
35.77 (CH), 37.01 (CH2), 37.21 (CH2), 37.35 (CH2), 41.10 (CH),
42.48 (CH2), 43.29 (C), 44.48 (CH), 51.18 (CH), 81.93 (CH),
213.58 (C). ESMS (m/z) 313 [M + Na]+.
NMR (300 MHz, CDCl3) δ 0.64 (s, 3H), 0.91 (d, 3H, J = 6.2 Hz),
0.94 (s, 3H), 1.04−2.67 (m, 28H), 3.66 (s, 3H), 3.74 (dd, 1H, J = 11.6
and 2.4 Hz), 4.03 (dd, 1H, J = 11.6 and 10.6 Hz), 5.18 (dd, 1H, J =
10.6 and 2.4 Hz), 5.30 (s, 1H), 5.45 (s, 1H), 7.03 (t, 2H, J = 8.6 Hz),
7.34−7.39 (m, 2H). 13C NMR (75 MHz, CDCl3) δ 12.22 (CH3),
18.45 (CH3), 21.20 (CH2), 23.13 (CH3), 24.17 (CH2), 24.34 (CH2),
26.07 (CH2), 26.39 (CH2), 28.35 (CH2), 31.18 (CH2), 31.21 (2 ×
General Procedure for Preparation of Bile Acid-Based 1,2,4-
Trioxanes: Synthesis of Trioxane 23a. A slow stream of oxygen
G
dx.doi.org/10.1021/jm301323k | J. Med. Chem. XXXX, XXX, XXX−XXX

Journal of Medicinal Chemistry
Article
CH2), 32.91 (CH2), 35.06 (C), 35.54 (CH), 35.77 (CH), 39.33 (CH),
40.00 (CH), 40.30 (CH2), 42.90 (C), 51.64 (CH3), 56.15 (CH), 56.64
(CH), 62.82 (CH2), 80.38 (CH), 103.83 (C), 115.51 (CH), 115.79
(CH), 116.66 (CH2), 128.28 (CH), 128.38 (CH), 134.89 (C), 142.58
(C), 162.84 (C, JC−F = 246.1 Hz), 174.89 (C). ESMS (m/z) 569 [M +
H]+; Anal. Calcd for C35H49FO5: C, 73.91%, H, 8.68%. Found: C,
73.69%, H, 8.79%.
Anal. Calcd for C35H49BrO5: C, 66.76%, H, 7.84%. Found: C, 67.08%,
H, 8.05%.
Trioxane 24a. This was obtained in 44% yield as a diastereomeric
mixture which was separated by column chromatography.
Trioxane (24a, Less Polar Isomer). This was obtained as semi
solid. IR (neat, cm−1) 1708, 2933. 1H NMR (300 MHz, CDCl3) δ 0.67
(s, 3H), 0.95 (s, 3H), 1.11−1.93 (m, 25H), 2.09 (s, 3H), 2.44−2.57
(m, 2H), 3.71−3.78 (m, 1H), 3.82−3.90 (m, 1H), 5.22−5.26 (m, 1H),
5.32 (s, 1H), 5.49 (s, 1H), 7.31−7.37 (m, 5H). 13C NMR (50 MHz,
CDCl3) δ 12.76 (CH3), 16.80 (CH3), 21.45 (CH2), 23.51 (CH3),
23.56 (CH3), 24.07 (CH2), 24.86 (CH2), 26.56 (CH2), 26.75 (CH2),
26.86 (CH2), 27.88 (CH2), 28.18 (CH3), 33.02 (CH2), 34.86 (CH2),
35.51 (C), 36.07 (CH), 39.53 (CH), 39.67 (CH), 40.38 (CH), 40.46
(CH2), 43.40 (C), 50.87 (CH), 52.64 (CH), 56.33 (CH), 63.12
(CH2), 63.18 (CH2), 80.74 (CH), 80.88 (CH), 104.00 (C), 104.16
(C), 116.68 (CH2), 116.82 (CH2), 126.83 (2 × CH), 128.57 (CH),
128.97 (2 × CH), 139.01 (C), 143.94 (C), 143.98 (C), 213.19 (C).
ESMS (m/z) 529 [M + Na]+. Anal. Calcd for C33H46O4: C, 78.22%,
H, 9.15%. Found: C, 78.47%, H, 9.60%.
Trioxane (24a, More Polar Isomer). This was obtained as semi
solid. IR (neat, cm−1) 1709, 2931. 1H NMR (300 MHz, CDCl3) δ 0.67
(s, 3H), 0.95 (s, 3H), 1.09−1.94 (m, 25H), 2.09 (s, 3H), 2.45−2.70
(m, 2H), 3.74−3.79 (m, 1H), 4.05 (dd, 1H, = 11.5 and 10.5 Hz), 5.24
(dd, 1H, J = 10.2 and 2.1 Hz), 5.33 (s, 1H), 5.51 (s, 1H), 7.31−7.38
(m, 5H). 13C NMR (50 MHz, CDCl3) δ 12.75 (CH3), 16.79 (CH3),
21.40 (CH2), 23.52 (CH3), 24.86 (CH2), 26.32 (CH2), 26.72 (CH2),
27.11 (CH2), 27.91 (CH2), 28.40 (CH3), 30.31 (CH2), 32.81 (CH2),
35.37 (C), 36.06 (CH), 39.57 (CH), 40.31 (CH), 40.46 (CH2), 43.40
(C), 50.78 (CH), 52.67 (CH), 56.39 (CH), 63.29 (CH2), 80.67 (CH),
103.78 (C), 116.76 (CH2), 126.79 (2 × CH), 128.58 (CH), 128.98 (2
× CH), 139.06 (C), 143.82 (C), 213.20 (C). ESMS (m/z) 529 [M +
Na]+. Anal. Calcd for C33H46O4: C, 78.22%, H, 9.15%. Found: C,
77.90%, H, 8.95%.
Trioxane 23c. This was obtained in 45% yield as a diastereomeric
mixture which was separated by column chromatography.
Trioxane (23c, Less Polar Isomer). This was obtained as an oil.
1
IR (neat, cm−1) 1589, 1735, 2938.1. H NMR (300 MHz, CDCl3) δ
0.64 (s, 3H), 0.90 (d, 3H, J = 6.1 Hz), 0.94 (s, 3H), 1.05−2.53 (m,
28H), 3.65 (s, 3H), 3.69−3.77 (m, 1H), 3.82−3.91 (m, 1H), 5.16−
5.19 (m, 1H), 5.34 (s, 1H), 5.47 and 5.48 (2 × s, together integrating
for 1H), 7.31 (s, 4H). 13C NMR (75 MHz, CDCl3) δ 12.20 (CH3),
18.42 (CH3), 21.21 (CH2), 23.25 (CH3), 23.29 (CH2), 24.32 (CH2),
26.28 (CH2), 26.46 (CH2), 26.63 (CH2), 27.06 (CH2), 28.32 (CH2),
29.16 (CH2), 29.73 (CH2), 31.15 (CH2), 32.24 (CH2), 32.72 (CH2),
34.52 (CH2), 35.20 (C), 35.50 (CH), 35.78 (CH), 39.29 (CH), 39.43
(CH), 40.05 (CH), 40.24 (CH2), 42.86 (C), 51.60 (CH3), 56.05
(CH), 56.57 (CH), 62.53 (CH2), 80.26 (CH), 80.44 (CH), 103.84
(C), 103.99 (C), 117.07 (CH2), 117.25 (CH2), 127.94 (2 × CH),
128.86 (2 × CH), 134.24 (C), 137.18 (C), 142.64 (C), 174.84 (C).
ESMS (m/z) 585 [M + H]+. Anal. Calcd for C35H49ClO5: C, 71.83%,
H, 8.44%. Found: C, 71.88%, H, 8.03%.
Trioxane (23c, More Polar Isomer). This was obtained as a white
1
solid; mp 105−106 °C. IR (KBr, cm−1) 1591, 1738, 2936. H NMR
(300 MHz, CDCl3) δ 0.65 (s, 3H), 0.91 (d, 3H, J = 6.2 Hz), 0.96 (s,
3H), 1.05−2.66 (m, 28H), 3.67 (s, 3H), 3.73−3.77 (m, 1H), 4.03 (dd,
1H, J = 11.4 and 10.8 Hz), 5.16−5.20 (m, 1H), 5.34 (s, 1H), 5.50 (s
1H), 7.33 (s, 4H). 13C NMR (75 MHz, CDCl3) δ 12.25 (CH3), 18.48
(CH3), 21.22 (CH2), 23.16 (CH3), 24.37 (CH2), 26.09 (CH2), 26.42
(CH2), 26.92 (CH2), 28.39 (CH2), 30.14 (CH2), 31.21 (CH2), 31.26
(CH2), 32.93 (CH2), 35.10 (C), 35.57 (CH), 35.80 (CH), 39.36
(CH), 40.03 (CH), 40.32 (CH2), 42.94 (C), 51.70 (CH3), 56.17
(CH), 56.67 (CH), 62.81 (CH2), 80.25 (CH), 103.92 (C), 117.23
(CH2), 127.96 (2 × CH), 128.95 (2 × CH), 134.33 (C), 137.28 (C),
142.52 (C), 174.98 (C). ESMS (m/z) 585 [M + H]+. Anal. Calcd for
C35H49ClO5: C, 71.83%, H, 8.44%. Found: C, 71.38%, H, 8.85%.
Trioxane 23d. This was obtained in 51% yield as a diastereomeric
mixture which was separated by column chromatography.
Trioxane 24b. This was obtained in 67% yield as a diastereomeric
mixture which was separated by column chromatography.
Trioxane (24b, Less Polar Isomer). This was obtained as a white
solid; mp 65−67 oC. IR (KBr, cm−1) 1708, 2932. 1H NMR (300 MHz,
CDCl3) δ 0.66 (s, 3H), 0.94 (s, 3H), 1.10 (d, 3H, J = 6.8 Hz), 1.14−
1.97 (m, 22H), 2.08 (s, 3H), 2.31−2.53 (m, 2H), 3.68−3.76 (m, 1H),
3.81−3.89 (m, 1H), 5.15−5.19 (m, 1H), 5.29 (s, 1H), 5.42−5.43 (m,
1H), 7.01 (t, 2H, J = 8.6 Hz), 7.31−7.36 (m, 2H). 13C NMR (50
MHz, CDCl3) δ 12.74 (CH3), 16.78 (CH3), 21.43 (CH2), 23.49
(CH3), 23.54 (CH3), 24.09 (CH2), 24.85 (CH2), 26.54 (CH2), 26.73
(CH2), 26.84 (CH2), 27.27 (CH2), 27.87 (CH2), 28.18 (CH3), 29.45
(CH2), 29.98 (CH2), 32.51 (CH2), 32.99 (CH2), 34.80 (CH2), 35.50
(C), 36.06 (CH), 39.53 (CH), 39.66 (CH), 40.38 (CH), 40.45 (CH2),
43.40 (C), 50.86 (CH), 52.64 (CH), 56.33 (CH), 62.85 (CH2), 62.91
(CH2), 80.74 (CH), 104.06 (C), 104.21 (C), 115.65 (CH), 116.07
(CH), 116.88 (CH2), 117.06 (CH2), 128.54 (CH), 128.71 (CH),
135.13 (C), 142.93 (C), 142.98 (C), 163.07 (C, JC−F = 246 Hz),
213.20 (C). ESMS (m/z) 547 [M + Na]+. Anal. Calcd for C33H45FO4:
C, 75.54%, H, 8.64%. Found: C, 75.09%, H, 8.76%.
Trioxane (24b, More Polar Isomer). This was obtained as a
white solid; mp 76−77 oC. IR (KBr, cm−1) 1709, 2933. 1H NMR (300
MHz, CDCl3) δ 0.67 (s, 3H), 0.95 (s, 3H), 1.11 (d, 3H, J = 6.8 Hz),
1.26−1.94 (m, 22H), 2.09 (s, 3H), 2.45−2.67 (m, 2H), 3.74−3.79 (m,
1H), 4.05 (dd, 1H, J = 11.2 and 10.6 Hz), 5.16−5.19 (m, 1H), 5.31 (s,
1H), 5.46 (s, 1H), 7.02 (t, 2H, J = 8.6 Hz), 7.34−7.39 (m, 2H). 13C
NMR (50 MHz, CDCl3) δ 12.73 (CH3), 16.77 (CH3), 21.38 (CH2),
23.49 (CH3), 24.85 (CH2), 26.30 (CH2), 26.70 (CH2), 27.08 (CH2),
27.90 (CH2), 28.42 (CH3), 30.34 (CH2), 32.78 (CH2), 35.34 (C),
36.04 (CH), 39.55 (CH), 40.29 (CH), 40.44 (CH2), 43.39 (C), 50.75
(CH), 52.65 (CH), 56.37 (CH), 63.00 (CH2), 80.63 (CH), 103.82
(C), 115.66 (CH), 116.09 (CH), 116.92 (CH2), 128.49 (CH), 128.64
(CH), 135.13 (C), 142.77 (C), 163.07 (C, JC−F = 246 Hz), 213.22
(C). ESMS (m/z) 547 [M + Na]+. Anal. Calcd for C33H45FO4: C,
75.54%, H, 8.64%. Found: C, 75.17%, H, 8.54%.
Trioxane (23d, Less Polar Isomer). This was obtained as an oil.
1
IR (Neat, cm−1) 1735, 2938. H NMR (300 MHz, CDCl3) δ 0.64 (s,
3H), 0.90 (d, 3H, J = 5.8 Hz), 0.94 (s, 3H), 1.04−2.51 (m, 28H), 3.65
(s, 3H), 3.68−3.76 (m, 1H), 3.80−3.89 (m, 1H), 5.14−5.18 (m, 1H),
5.34 (s, 1H), 5.47 and 5.48 (2 × s, together integrating for 1H), 7.24
(d, 2H, J = 8.3 Hz), 7.45 (d, 2H, J = 8.3 Hz). 13C NMR (75 MHz,
CDCl3) δ 12.25 (CH3), 18.47 (CH3), 21.27 (CH2), 23.29 (CH3),
23.34 (CH3), 23.90 (CH2), 24.37 (CH2), 26.33 (CH2), 26.51 (CH2),
26.68 (CH2), 27.11 (CH2), 28.36 (CH2), 29.80 (CH2), 31.23 (CH2),
32.30 (CH2), 32.78 (CH2), 34.57 (CH2), 35.26 (C), 35.55 (CH),
35.85 (CH), 39.36 (CH), 39.49 (CH), 40.12 (CH), 40.31 (CH2),
42.93 (C), 51.64 (CH3), 56.12 (CH), 56.64 (CH), 62.58 (CH2), 80.30
(CH), 80.48 (CH), 103.92 (C), 104.07 (C), 117.21 (CH2), 117.40
(CH2), 122.48 (C), 128.32 (2 × CH), 131.87 (2 × CH), 137.74 (C),
142.79 (C), 174.90 (C). ESMS (m/z) 629 [M + H]+. Anal. Calcd for
C35H49BrO5: C, 66.76%, H, 7.84%. Found: C, 66.28%, H, 7.54%.
Trioxane (23d, More Polar Isomer). This was obtained as a
white solid; mp 120−121 °C. IR (KBr, cm−1) 1735.4, 2938.1. 1H
NMR (300 MHz, CDCl3) δ 0.64 (s, 3H), 0.90 (d, 3H, J = 5.8 Hz),
0.94 (s, 3H), 1.06−2.64 (m, 28H), 3.65 (s, 3H), 3.73−3.77 (m, 1H),
4.00−4.07 (m, 1H), 5.14−5.18 (m, 1H), 5.35 (s, 1H), 5.49 (s, 1H),
7.26 (d, 2H, J = 8.3 Hz), 7.45 (d, 2H, J = 8.3 Hz). 13C NMR (75 MHz,
CDCl3) δ 12.23 (CH3), 18.44 (CH3), 21.18 (CH2), 23.27 (CH3),
24.33 (CH2), 26.06 (CH2), 26.45 (CH2), 26.89 (CH2), 28.34 (CH2),
30.12 (CH2), 31.20 (2 × CH2), 32.54 (CH2), 35.07 (C), 35.52 (CH),
35.79 (CH), 39.34 (CH), 40.03 (CH), 40.29 (CH2), 42.90 (C), 51.60
(CH3), 56.15 (CH), 56.68 (CH), 62.68 (CH2), 80.14 (CH), 103.63
(C), 117.19 (CH2), 122.46 (C), 128.22 (2 × CH), 131.85 (2 × CH),
137.74 (C), 142.55 (C), 174.81 (C). ESMS (m/z) 629 [M + H]+.
Trioxane 24c. This was obtained in 50% yield as a diastereomeric
mixture which was separated by column chromatography.
H
dx.doi.org/10.1021/jm301323k | J. Med. Chem. XXXX, XXX, XXX−XXX

Journal of Medicinal Chemistry
Article
Trioxane (24c, Less Polar Isomer). This was obtained as a white
solid; mp 74−75 °C. IR (KBr, cm−1) 1709, 2933. 1H NMR (300 MHz,
CDCl3) δ 0.67 (s, 3H), 0.95 (s, 3H), 1.11 (d, 3H, J = 6.7 Hz), 1.19−
1.99 (m, 22H), 2.09 (s, 3H), 2.30−2.50 (m, 2H), 3.69−3.77 (m, 1H),
3.82−3.91 (m, 1H), 5.16−5.19 (m, 1H), 5.34 (s, 1H), 5.48 (s, 1H),
7.31 (s, 4H). 13C NMR (75 MHz, CDCl3) δ 12.41 (CH3), 16.45
(CH3), 21.11 (CH2), 23.17 (CH3), 23.22 (CH3), 24.52 (CH2), 26.23
(CH2), 26.41 (CH2), 26.53 (CH2), 27.00 (CH2), 27.55 (CH2), 27.86
(CH3), 29.09 (CH2), 29.67 (CH2), 32.18 (CH2), 32.67 (CH2), 34.45
(CH2), 35.15 (C), 35.72 (CH), 39.17 (CH), 39.32 (CH), 40.05 (CH),
40.10 (CH2), 43.04 (C), 50.48 (CH), 52.30 (CH), 55.98 (CH), 62.46
(CH2), 80.17 (CH), 80.35 (CH), 103.69 (C), 103.84 (C), 116.97
(CH2), 117.16 (CH2), 127.85 (CH), 127.88 (CH), 128.79 (2 × CH),
134.16 (C), 137.11 (C), 142.50 (C), 142.56 (C), 212.62 (C). ESMS
(m/z) 563 [M + Na]+. Anal. Calcd for C33H45ClO4: C, 73.24%, H,
8.38%. Found: C, 73.43%, H, 8.31%.
Trioxane (24c, More Polar Isomer). This was obtained as white
solid; mp 90−91 °C. IR (KBr, cm−1) 1709, 2934. 1H NMR (300 MHz,
CDCl3) δ 0.67 (s, 3H), 0.95 (s, 3H), 1.11 (d, 3H, J = 6.7 Hz), 1.25−
1.94 (m, 22H), 2.09 (s, 3H), 2.45−2.66 (m, 2H), 3.74−3.79 (m, 1H),
4.05 (dd, 1H, J = 11.3 and 10.6 Hz), 5.16−5.19 (m, 1H), 5.35 (s, 1H),
5.50 (s, 1H), 7.32 (s, 4H). 13C NMR (75 MHz, CDCl3) δ 12.31
(CH3), 16.36 (CH3), 20.97 (CH2), 23.08 (CH3), 24.43 (CH2), 25.89
(CH2), 26.29 (CH2), 26.67 (CH2), 27.49 (CH2), 28.00 (CH2), 29.93
(CH3), 32.37 (CH2), 34.93 (C), 35.62 (CH), 39.14 (CH), 39.89
(CH), 40.03 (CH2), 42.97 (C), 50.33 (CH), 52.24 (CH), 55.96 (CH),
62.53 (CH2), 80.04 (CH), 103.44 (C), 117.01 (CH2), 127.75 (2 ×
CH), 128.73 (2 × CH), 134.11 (C), 137.09 (C), 142.29 (C), 212.76
(C). ESMS (m/z) 563 [M + Na]+. Anal. Calcd for C33H45ClO4: C,
73.24%, H, 8.38%. Found: C, 73.15%, H, 8.39%.
1H, J = 11.9 and 10.3 Hz), 5.23 (dd, 1H, J = 10.3 and 2.6 Hz), 5.32 (s,
1H), 5.49 (s, 1H), 7.29−7.39 (m, 5H). 13C NMR (75 MHz, CDCl3) δ
13.63 (CH3), 21.27 (CH2), 23.10 (CH2), 23.24 (CH3), 23.89 (CH2),
24.61 (CH2), 26.32 (CH2), 26.57 (CH2), 31.73 (CH3), 32.81 (CH2),
34.64 (CH2), 35.14 (CH2), 35.32 (C), 35.85 (CH), 39.30 (CH), 39.39
(CH2), 40.14 (CH), 44.50 (C), 56.89 (CH), 62.90 (CH2), 64.02
(CH), 80.71 (CH), 103.75 (C), 103.90 (C), 116.64 (CH2), 126.58
(CH), 126.63 (CH), 128.35 (CH), 128.75 (2 × CH), 138.80 (C),
143.78 (C), 209.77 (C). ESMS (m/z) 496 [M + NH4]+. Anal. Calcd
for C31H42O4: C, 77.79%, H, 8.84%. Found: C, 77.98%, H, 8.72%.
Trioxane (25a, More Polar Isomer). This was obtained as a white
solid; mp 89−91 °C. IR (KBr, cm−1) 1702, 2934. 1H NMR (300 MHz,
CDCl3) δ 0.60 (s, 3H), 0.95 (s, 3H), 1.19−2.21 (m, 22H), 2.11 (s,
3H), 2.49−2.55 (m, 1H), 3.77 (dd, 1H, J = 11.6 and 2.8 Hz), 4.04 (dd,
1H, J = 11.66 and 10.3 Hz), 5.24 (dd, 1H, J = 10.3 and 2.8 Hz), 5.33
(s, 1H), 5.51 (s, 1H), 7.30−7.40 (m, 5H). 13C NMR (75 MHz,
CDCl3) δ 13.67 (CH3), 21.27 (CH2), 23.13 (CH2), 23.29 (CH3),
24.65 (CH2), 26.52 (CH2), 26.86 (CH2), 30.28 (2 × CH2), 31.75
(CH3), 32.64 (CH2), 35.22 (C), 35.89 (CH), 39.38 (CH), 39.47
(CH2), 40.12 (CH), 44.57 (C), 57.04 (CH), 63.14 (CH2), 64.13
(CH), 80.53 (CH), 103.57 (C), 116.60 (CH2), 126.64 (2 × CH),
128.42 (CH), 128.81 (2 × CH), 138.90 (C), 143.65 (C), 209.82 (C).
ESMS (m/z) 496 [M + NH4]+. Anal. Calcd for C31H42O4: C, 77.79%,
H, 8.84%. Found: C, 77.62%, H, 8.91%.
Trioxane 25b. This was obtained in 69% yield as a diastereomeric
mixture which was separated by column chromatography.
Trioxane (25b, Less Polar Isomer). This was obtained as a white
solid; mp 65−66 °C. IR (KBr, cm−1) 1702, 2934. 1H NMR (300 MHz,
CDCl3) δ 0.60 (s, 3H), 0.95 (s, 3H), 1.21−2.03 (m, 22H), 2.11 (s,
3H), 2.50−2.56 (m, 1H), 3.70−3.78 (m, 1H), 3.83−3.92 (m, 1H),
5.18 (dd, 1H, J = 10.2 and 2.8 Hz), 5.31 (s, 1H), 5.45 (s, 1H), 7.02 (t,
2H, J = 8.4 Hz), 7.33−7.38 (m, 2H). 13C NMR (75 MHz, CDCl3) δ
13.65 (CH3), 21.28 (CH2), 23.25 (CH2), 23.30 (CH3), 24.61 (CH2),
26.51 (CH2), 26.57 (CH2), 27.00 (CH2), 29.25 (CH2), 29.77 (CH2),
31.76 (CH3), 32.31 (CH2), 35.32 (C), 35.86 (CH), 39.38 (CH2),
39.43 (CH), 40.10 (CH), 44.52 (C), 56.92 (CH), 62.71 (CH2), 64.02
(CH), 80.56 (CH), 103.81 (C), 115.53 (CH), 115.81 (CH), 116.71
(CH2), 128.35 (CH), 128.46 (CH), 134.89 (C), 134.93 (C), 142.71
(C), 142.76 (C), 163.03 (C, JC−F = 246.7 Hz), 209.83 (C). ESMS (m/
z) 519 [M + Na]+. Anal. Calcd for C31H41FO4: C, 74.97%, H, 8.32%.
Found: C, 74.61%, H, 8.79%.
Trioxane (25b, More Polar Isomer). This was obtained as a
white solid; mp 78−80 °C. IR (KBr, cm−1) 1694, 2936. 1H NMR (300
MHz, CDCl3) δ 0.59 (s, 3H), 0.94 (s, 3H), 1.20−1.89 (m, 22H), 2.10
(s, 3H), 2.45−2.54 (m, 1H), 3.75 (dd, 1H, J = 11.4 and 2.3 Hz), 4.04
(dd, 1H, J = 114 and 10.4 Hz), 5.17 (dd, 1H, J = 10.4 and 2.3 Hz),
5.31 (s, 1H), 5.46 (s, 1H), 7.02 (t, 2H, J = 8.5 Hz), 7.33−7.38 (m,
2H). 13C NMR (75 MHz, CDCl3) δ 13.42 (CH3), 21.02 (CH2), 22.89
(CH2), 23.04 (CH3), 24.40 (CH2), 26.27 (CH2), 26.61 (CH2), 29.96
(2 × CH2), 31.49 (CH3), 32.38 (CH2), 34.96 (C), 35.63 (CH), 39.13
(CH2), 39.21 (CH), 39.88 (CH), 44.31 (C), 56.78 (CH), 62.61
(CH2), 63.87 (CH), 80.25 (CH), 103.37 (C), 115.32 (CH), 115.61
(CH), 116.51 (CH2), 128.12 (CH), 128.22 (CH), 134.77 (C), 142.39
(C), 162.69 (C, JC−F = 246 Hz), 209.53 (C). ESMS (m/z) 519 [M +
Na]+. Anal. Calcd for C31H41FO4: C, 74.97%, H, 8.32%. Found: C,
74.52%, H, 8.88%.
Trioxane 24d. This was obtained in 46% yield as a diastereomeric
mixture which was separated by column chromatography.
Trioxane (24d, Less Polar Isomer). This was obtained as a white
solid; mp 78−79 °C. IR (KBr, cm−1) 1708, 2933. 1H NMR (300 MHz,
CDCl3) δ 0.59 (s, 3H), 0.88 (s, 3H), 1.04 (d, 3H, J = 6.8 Hz), 1.18−
1.91 (m, 22H), 2.02 (s, 3H), 2.24−2.45 (m, 2H), 3.62−3.70 (m, 1H),
3.74−3.83 (m, 1H), 5.09−5.12 (m, 1H), 5.27 (s, 1H), 5.41 and 5.42 (2
× s, together integrating for 1H), 7.18 (d, 2H, J = 8.4 Hz), 7.39 (d, 2H,
J = 8.4 Hz). 13C NMR (50 MHz, CDCl3) δ 12.55 (CH3), 16.59
(CH3), 21.23 (CH2), 23.29 (CH3), 23.34 (CH3), 23.89 (CH2), 24.65
(CH2), 26.34 (CH2), 26.53 (CH2), 26.64 (CH2), 27.07 (CH2), 27.67
(CH2), 27.99 (CH3), 29.22 (CH2), 29.78 (CH2), 32.30 (CH2), 32.78
(CH2), 34.56 (CH2), 35.30 (C), 35.85 (CH), 39.33 (CH), 39.45
(CH), 40.16 (CH), 40.24 (CH2), 43.20 (C), 50.68 (CH), 52.43 (CH),
56.12 (CH), 62.61 (CH2), 62.68 (CH2), 80.51 (CH), 103.91 (C),
104.06 (C), 117.29 (CH2), 117.49 (CH2), 122.51 (C), 128.31 (CH),
128.34 (CH), 131.90 (2 × CH), 137.70 (C), 142.67 (C), 142.73 (C),
213.08 (C). ESMS (m/z) 586 [M + H]+. Anal. Calcd for C33H45BrO4:
C, 67.68%, H, 7.75%. Found: C, 67.61%, H, 8.06%.
Trioxane (24d, More Polar Isomer). This was obtained as a
white solid; mp 91−93 °C. IR (KBr, cm−1) 1709, 2934. 1H NMR (300
MHz, CDCl3) δ: 0.66 (s, 3H), 0.94 (s, 3H), 1.10 (d, 3H, J = 6.8 Hz),
1.19−1.93 (m, 22H), 2.09 (s, 3H), 2.42−2.65 (m, 2H), 3.73−3.78 (m,
1H), 4.04 (dd, 1H, J = 11.5 and 10.3 Hz), 5.15−5.18 (m, 1H), 5.34 (s,
1H), 5.50 (s, 1H), 7.25 (d, 2H, J = 8.2 Hz), 7.45 (d, 2H, J = 8.2 Hz).
13C NMR (50 MHz, CDCl3) δ: 12.74 (CH3), 16.80 (CH3), 21.39
(CH2), 23.51 (CH3), 24.86 (CH2), 26.71 (CH2), 27.10 (CH2), 27.91
(CH2), 28.45 (CH3), 30.35 (CH2), 32.79 (CH2), 33.15 (CH2), 35.36
(C), 36.04 (CH), 39.56 (CH), 40.29 (CH), 40.45 (CH2), 43.40 (C),
50.77 (CH), 52.65 (CH), 56.37 (CH), 62.96 (CH2), 80.41 (CH),
103.89 (C), 117.53 (CH2), 122.73 (C), 128.49 (2 × CH), 132.13 (2 ×
CH), 137.98 (C), 142.74 (C), 213.33 (C). ESMS (m/z) 586 [M +
H]+. Anal. Calcd for C33H45BrO4: C, 67.68%, H, 7.75%. Found: C,
67.28%, H, 7.91%.
Trioxane 25c. This was obtained in 55% yield as a diastereomeric
mixture which was separated by column chromatography.
Trioxane (25c, Less Polar Isomer). This was obtained as a white
solid; mp 72−73 °C. IR (KBr, cm−1) 1705, 2933. 1H NMR (300 MHz,
CDCl3) δ 0.59 (s, 3H), 0.94 (s, 3H), 1.01−2.03 (m, 22H), 2.11 (s,
3H), 2.50−2.56 (m, 1H), 3.70−3.77 (m, 1H), 3.82−3.91 (m, 1H),
5.17−5.19 (m, 1H), 5.34 (s, 1H), 5.48−5.49 (m, 1H), 7.28−7.34 (s,
4H). 13C NMR (50 MHz, CDCl3) δ 13.83 (CH3), 21.48 (CH2), 23.30
(CH2), 23.46 (CH3), 23.50 (CH3), 24.81 (CH2), 26.53 (CH2), 26.72
(CH2), 26.78 (CH2), 29.42 (CH2), 30.01 (CH2), 31.93 (CH3), 32.51
(CH2), 33.00 (CH2), 34.77 (CH2), 35.51 (C), 36.04 (CH), 39.49
(CH), 39.58 (CH2), 40.34 (CH), 44.68 (C), 57.08 (CH), 62.79
(CH2), 62.85 (CH2), 64.20 (CH), 80.55 (CH), 80.73 (CH), 104.01
(C), 104.16 (C), 117.39 (CH2), 117.58 (CH2), 128.21 (2 × CH),
Trioxane 25a. This was obtained in 55% yield as a diastereomeric
mixture which was separated by column chromatography.
Trioxane (25a, Less Polar Isomer). This was obtained as a white
solid; mp 62−63 °C. IR (KBr, cm−1) 1702, 2934. 1H NMR (300 MHz,
CDCl3) δ 0.59 (s, 3H), 0.95 (s, 3H), 1.12−2.16 (m, 22H), 2.12 (s,
3H), 2.51−2.59 (m, 1H), 3.73 (dd, 1H, J = 11.9 and 2.9 Hz), 3.86 (dd,
I
dx.doi.org/10.1021/jm301323k | J. Med. Chem. XXXX, XXX, XXX−XXX

Journal of Medicinal Chemistry
Article
129.13 (2 × CH), 134.52 (C), 137.44 (C), 142.83 (C), 142.89 (C),
209.86 (C). ESMS (m/z) 535 [M + Na]+. Anal. Calcd for
C31H41ClO4: C, 72.56%, H, 8.05%. Found: C, 72.57%, H, 7.89%.
Trioxane (25c, More Polar Isomer). This was obtained as a white
11.6 and 10.5 Hz), 5.23 (dd, 1H, J = 10.8 and 2.7 Hz), 5.32 (s, 1H),
5.50 (s, 1H), 7.31−7.37 (m, 5H). 13C NMR (75 MHz, CDCl3) δ
11.44 (CH3), 20.90 (CH2), 23.40 (CH3), 23.67 (CH2), 26.20 (CH2),
26.87 (CH2), 30.21 (CH2), 30.31 (CH2), 30.85 (CH2), 32.75 (CH2),
35.33 (C), 36.00 (CH), 37.20 (CH2), 39.52 (CH), 40.41 (CH), 43.39
(C), 51.42 (CH), 63.16 (CH2), 80.54 (CH), 82.17 (CH), 103.65 (C),
116.60 (CH2), 126.67 (2 × CH), 128.45 (CH), 128.85 (2 × CH),
138.93 (C), 143.69 (C). ESMS (m/z) 475 [M + Na]+. Anal. Calcd for
C29H40O4: C, 76.95%, H, 8.91%. Found: C, 76.91%, H, 9.22%. Crystal
data: C29 H40 O4, M = 452.61, monoclinic, P2(1), a = 7.008(4) Å, b =
18.623(11) Å, c = 9.550(6) Å, β = 97.63(1)°, V = 1235.38 Å3, Z = 2,
Dc = 1.217 g cm−3, μ (Mo Kα) = 0.08 mm−1, F(000) = 492,
rectangular block, colorless, size = 0.20 mm × 0.225 mm × 0.30 mm,
7830 reflections measured (Rint = 0.0572), 5654 unique, wR2 = 0.2261
for all data, conventional R1 = 0.0675 for 3215 F0 > 4σ(F0) and 0.1175
for all 5654 data, S = 0.990 for all data and 302 parameters. Unit cell
determination and X-ray intensity data collection were performed on
Bruker SMART APEX CCD area-detector instruments. Structure
solutions by direct methods and refinements by full-matrix least-
squares methods on F2. Programs: SMART (Bruker, 2001), SMART
32(Bruker), SAINT (Bruker, 2001), SHELXTL-NT [Bruker AXS Inc.:
Madison, Wisconsin, USA 1997]. CCDC (deposit no.: CCDC
871201) contains the supplementary crystallographic data. These
data can be obtained free of charge from www.ccdc.cam.uk/conts/
retrieving.html [or from the Cambridge Crystallographic Data Center,
12 Union Road, Cambridge, CB2 1EZ, UK; fax (Internet), +44-1223/
336-033; E-mail: deposit@ccdc.cam.ac.uk.
1
solid; mp 145−147 °C. IR (KBr, cm−1) 1705, 2933. H NMR (300
MHz, CDCl3) δ 0.59 (s, 3H), 0.94 (s, 3H), 1.07−2.04 (m, 22H), 2.10
(s, 3H), 2.45−2.55 (m, 1H), 3.77 (dd, 1H, J = 11.5 and 2.3 Hz), 4.04
(dd, 1H, J = 11.5 and 10.3 Hz), 5.18 (dd, 1H, J = 10.3 and 2.3 Hz),
5.35 (s, 1H), 5.51 (s, 1H), 7.29−7.36 (m, 4H). 13C NMR (50 MHz,
CDCl3) δ 13.59 (CH3), 21.18 (CH2), 23.04 (CH2), 23.21 (CH3),
24.56 (CH2), 26.43 (CH2), 26.76 (CH2), 30.10 (2 × CH2), 31.68
(CH3), 32.54 (CH2), 35.12 (C), 35.78 (CH), 39.28 (CH), 39.36
(CH2), 40.02 (CH), 44.47 (C), 56.93 (CH), 62.72 (CH2), 64.01
(CH), 80.22 (CH), 103.55 (C), 117.19 (CH2), 127.92 (2 × CH),
128.90 (2 × CH), 134.30 (C), 137.24 (C), 142.43 (C), 209.65 (C).
ESMS (m/z) 535 [M + Na]+. Anal. Calcd for C31H41ClO4: C, 72.56%,
H, 8.05%. Found: C, 72.94%, H, 8.32%.
Trioxane 25d. This was obtained in 36% yield as a diastereomeric
mixture which was separated by column chromatography.
Trioxane (25d, Less Polar Isomer). This was obtained as a white
solid; mp 79−80 °C. IR (KBr, cm−1) 1703, 2931. 1H NMR (300 MHz,
CDCl3) δ 0.60 (s, 3H), 0.96 (s, 3H), 1.07−2.05 (m, 22H), 2.12 (s,
3H), 2.52−2.58 (m, 1H), 3.71−3.79 (m, 1H), 3.83−3.92 (m, 1H),
5.17−5.21 (m, 1H), 5.36 (s, 1H), 5.50 and 5.51 (2 × s, together
integrating for 1H), 7.25−7.28 (m, 2H), 7.46−7.49 (m, 2H). 13C
NMR (75 MHz, CDCl3) δ 13.45 (CH3), 21.07 (CH2), 22.87 (CH2),
23.05 (CH3), 23.10 (CH3), 23.71 (CH2), 24.41 (CH2), 26.12 (CH2),
26.30 (CH2), 26.36 (CH2), 26.79 (CH2), 26.92 (CH2), 29.85 (CH2),
30.18 (CH2), 31.57 (CH3), 32.09 (CH2), 32.58 (CH2), 34.35 (CH2),
35.11 (C), 35.63 (CH), 39.08 (CH), 39.17 (CH2), 39.21 (CH2), 39.91
(CH), 44.30 (C), 56.67 (CH), 56.70 (CH2), 62.36 (CH2), 63.81
(CH), 80.29 (CH), 103.64 (C), 103.78 (C), 117.09 (CH2), 117.30
(CH2), 122.31 (C), 128.09 (CH), 128.13 (CH), 131.70 (2 × CH),
137.47 (C), 142.45 (C), 142.51 (C), 209.63 (C). ESMS (m/z) 579
[M + Na]+. Anal. Calcd for C31H41BrO4: C, 66.78%, H, 7.41%. Found:
C, 67.19%, H, 7.88%.
Trioxane 26b. This was obtained in 63% yield as a diastereomeric
mixture which was separated by column chromatography.
Trioxane (26b, Less Polar Isomer). This was obtained as a white
1
solid; mp 64−65 °C. IR (KBr, cm−1) 2932, 3399. H NMR (300 Hz,
CDCl3) δ 0.72 (s, 3H), 0.95 (s, 3H), 1.05−2.54 (m, 23H), 3.62 (t, 1H,
J = 8.4 Hz), 3.72−3.77 (m, 1H), 3.81−3.90 (m, 1H), 5.16−5.19 (m,
1H), 5.30 (s, 1H), 5.43 and 5.44 (2 × s, together integrating for 1H),
7.01 (t, 2H, J = 8.4 Hz), 7.32−7.37 (m, 2H). 13C NMR (75 MHz,
CDCl3) δ 11.36 (CH3), 20.86 (CH2), 23.31 (CH2), 23.36 (CH3),
23.58 (CH2), 23.90 (CH2), 25.94 (CH2), 26.15 (CH2), 26.54 (CH2),
26.99 (CH2), 29.25 (CH2), 29.80 (CH2), 30.70 (CH2), 32.37 (CH2),
32.85 (C), 34.60 (CH2), 35.39 (CH2), 35.92 (CH), 37.09 (CH2),
39.40 (CH), 39.54 (CH), 40.36 (CH), 43.28 (C), 51.23 (CH), 62.64
(CH2), 62.69 (CH2), 80.53 (CH), 80.72 (CH), 82.02 (CH), 103.86
(C), 104.01 (C), 115.52 (CH), 115.80 (CH), 116.69 (CH2), 116.89
(CH2), 128.37 (CH), 128.47 (CH), 134.90 (C), 142.71 (C), 162.79
(C, JC−F = 248 Hz). ESMS (m/z) 493 [M + Na]+. HRMS calcd for
C29H39FO4, 470.2832; found, 470.2808. Anal. Calcd for C29H39FO4:
C, 74.01%, H, 8.35%. Found: C, 73.84%, H, 8.81%.
Trioxane (25d, More Polar Isomer). This was obtained as a
1
white solid; mp 154−155 °C. IR (KBr, cm−1) 1704, 2930. H NMR
(300 MHz, CDCl3) δ 0.61 (s, 3H), 0.95 (s, 3H), 1.21−2.04 (m, 22H),
2.11 (s, 3H), 2.45−2.56 (m, 1H), 3.77 (dd, 1H, J = 11.5 and 2.4 Hz),
4.05 (dd, 1H, J = 11.5 and 10.3 Hz), 5.18 (dd, 1H, J = 10.3 and 2.4
Hz), 5.36 (s, 1H), 5.52 (s, 1H), 7.27 (d, 2H, J = 8.3 Hz), 7.47 (d, 2H, J
= 8.3 Hz). 13C NMR (75 MHz, CDCl3) δ 13.45 (CH3), 21.02 (CH2),
22.87 (CH2), 23.06 (CH3), 24.41 (CH2), 26.27 (CH2), 26.60 (CH2),
29.93 (2 × CH2), 31.55 (CH3), 32.37 (CH2), 34.96 (C), 35.61 (CH),
39.12 (CH), 39.20 (CH2), 39.84 (CH), 44.32 (C), 56.76 (CH), 62.55
(CH2), 63.86 (CH), 80.00 (CH), 103.40 (C), 117.12 (CH2), 122.32
(C), 128.07 (2 × CH), 131.71 (2 × CH), 137.54 (C), 142.30 (C),
209.58 (C). ESMS (m/z) 579 [M + Na]+. Anal. Calcd for
C31H41BrO4: C, 66.78%, H, 7.41%. Found: C, 67.25%, H, 7.87%.
Trioxane 26a. This was obtained in 39% yield as a diastereomeric
mixture which was separated by column chromatography.
Trioxane (26b, More Polar Isomer). This was obtained as a
1
white solid; mp 161−162 °C. IR (KBr, cm−1) 2932, 3407. H NMR
(300 Hz, CDCl3) δ 0.72 (s, 3H), 0.95 (s, 3H), 1.01−2.66 (m, 23H),
3.61 (t, 1H, J = 8.4 Hz), 3.70−3.77 (m, 1H), 3.97−4.07 (m, 1H), 5.17
(dd, 1H, J = 10.2 and 2.3 Hz), 5.31 (s, 1H), 5.45 (s, 1H), 7.01 (t, 2H, J
= 8.4 Hz), 7.32−7.38 (m, 2H). 13C NMR (75 MHz, CDCl3) δ 11.28
(CH3), 20.73 (CH2), 23.23 (CH2), 23.50 (CH3), 26.03 (CH2), 26.70
(CH2), 30.07 (CH2), 30.65 (CH2), 32.57 (CH2), 32.93 (C), 35.15
(CH2), 35.82 (CH), 37.06 (CH2), 39.34 (CH), 40.24 (CH), 43.22
(C), 51.25 (CH), 62.71 (CH2), 80.34 (CH), 81.95 (CH), 103.54 (C),
115.44 (CH), 115.73 (CH), 116.60 (CH2), 128.23 (CH), 128.34
(CH), 134.84 (C), 142.50 (C), 162.86 (C, JC−F = 248 Hz). ESMS (m/
z) 493 [M + Na]+. HRMS calcd for C29H39FO4, 470.2832; found,
470.2827. Anal. Calcd for C29H39FO4: C, 74.01%, H, 8.35%. Found: C,
74.09%, H, 8.67%.
Trioxane (26a, Less Polar Isomer). This was obtained as a white
1
solid; mp 65−67 °C. IR (KBr, cm−1) 2931, 3400. H NMR (300 Hz,
CDCl3) δ 0.72 (s, 3H), 0.96 (s, 3H), 1.04−2.56 (m, 23H), 3.62 (t, 1H,
J = 8.4 Hz), 3.69−3.77 (m, 1H), 3.81−3.90 (m, 1H), 5.23 (dd, 1H, J =
10.2 and 2.4 Hz), 5.31 (s, 1H), 5.48 (s, 1H), 7.30−7.36 (m, 5H). 13C
NMR (75 MHz, CDCl3) δ 11.32 (CH3), 20.83 (CH2), 23.27 (CH3),
23.55 (CH2), 23.85 (CH2), 25.92 (CH2), 26.52 (CH2), 30.70 (2 ×
CH2), 32.84 (CH2), 34.61 (CH2), 35.35 (C), 35.89 (CH), 37.07
(CH2), 39.36 (CH), 40.34 (CH), 43.25 (C), 51.21 (CH), 62.86
(CH2), 80.67 (CH), 81.99 (CH), 103.76 (C), 103.91 (C), 116.63
(CH2), 126.56 (2 × CH), 128.31 (CH), 128.71 (2 × CH), 138.76
(C), 143.76 (C). ESMS (m/z) 475 [M + Na]+. HRMS calcd for
C29H40O4, 452.2927; found, 452.2953. Anal. Calcd for C29H40O4: C,
76.95%, H, 8.91%. Found: C, 76.68%, H, 9.08%.
Trioxane 26d. This was obtained in 62% yield as a diastereomeric
mixture which was separated by column chromatography.
Trioxane (26d, Less Polar Isomer). This was obtained as a white
1
solid; mp 68−69 °C. IR (KBr, cm−1) 2929, 3435. H NMR (300 Hz,
CDCl3) δ 0.72 (s, 3H), 0.96 (s, 3H), 1.01−2.52 (m, 23H), 3.62 (t, 1H,
J = 8.4 Hz), 3.69−3.76 (m, 1H), 3.81−3.90 (m, 1H), 5.15−5.18 (m,
1H), 5.33 (s, 1H), 5.47−5.48 (m, 1H), 7.23−7.26 (m, 2H), 7.43−7.46
(m, 2H). 13C NMR (75 MHz, CDCl3) δ 11.27 (CH3), 20.77 (CH2),
23.22 (CH3), 23.28 (CH2), 23.50 (CH2), 25.86 (CH2), 26.05 (CH2),
Trioxane (26a, More Polar Isomer). This was obtained as a white
1
solid; mp 145−147 °C. IR (KBr, cm−1) 29626, 3433. H NMR (300
Hz, CDCl3) δ 0.72 (s, 3H), 0.96 (s, 3H), 1.02−2.52 (m, 23H), 3.61 (t,
1H, J = 8.4 Hz), 3.75 (dd, 1H, J = 11.6 and 2.7 Hz), 4.03 (dd, 1H, J =
J
dx.doi.org/10.1021/jm301323k | J. Med. Chem. XXXX, XXX, XXX−XXX

Journal of Medicinal Chemistry
Article
26.46 (CH2), 26.89 (CH2), 29.73 (CH2), 30.65 (CH2), 32.28 (CH2),
32.77 (CH2), 34.48 (CH), 35.30 (C), 35.83 (CH2), 35.94 (CH), 37.01
(CH2), 39.31 (CH), 40.28 (CH), 43.19 (C), 51.15 (CH), 62.50
(CH2), 80.42 (CH), 81.94 (CH), 103.80 (C), 103.95 (C), 117.18
(CH2), 117.41 (CH2), 122.41 (C), 128.25 (2 × CH), 131.80 (2 ×
CH), 137.64 (C), 142.64 (C). ESMS (m/z) 553 [M + Na]+. Anal.
Calcd for C29H39BrO4: C, 65.53%, H, 7.40%. Found: C, 65.42%, H,
7.28%.
therapy. Microbiol. Rev. 1996, 60, 301−315. (d) Cumming, J. N.;
Ploypradith, P.; Posner, G. H. Antimalarial activity of artemisinin
(qinghaosu) and related trioxanes. Adv. Pharmacol. 1997, 37, 253−
297. (e) Bhattacharya, A. K.; Sharma, R. P. Recent developments on
the chemistry and biological activity of artemisinin and related
antimalarials. Heterocycles 1999, 51, 1681−1745. (f) Borstnik, K.; Paik,
I.; Shapiro, T. A.; Posner, G. H. Antimalarial chemotherapeutic
peroxides: Artemisinin, Yingzhaosu A and related compounds. Int. J.
Parasitol. 2002, 32, 1661−1667. (g) Ploypradith, P. Development of
artemisinin and its structurally simplified trioxane derivatives as
antimalarial drugs. Acta Trop. 2004, 89, 329−342. (h) O’Neill, P. M.;
Posner, G. H. A Medicinal chemistry perspective on artemisinin and
related endoperoxides. J. Med. Chem. 2004, 47, 2945−2964. (i) Tang,
Y.; Dong, Y.; Vennerstrom, J. L. Synthetic Peroxides as Antimalarials.
Med. Res. Rev. 2004, 24, 425−448. (j) Jefford, C. W. New development
in synthetic peroxidic drugs as artemisinin mimics. Drug Discovery
Today 2007, 12, 487−494. (k) Muraleedharan, K. M.; Avery, M. A.
Progress in the development of peroxide-based antiparasitic agents.
Drug Discovery Today 2009, 14, 793−803. (l) Chaturvedi, D.;
Goswami, A.; Pratim Saikia, P.; Barua, N. C.; Rao, P. G. Artemisinin
and its derivatives: a novel class of anti-malarial and anti-cancer agents.
Chem. Soc. Rev. 2010, 39, 435−454. (m) Dondrop, A. M.; Yeung, S.;
White, L.; Nguon, C.; Day, N. P. J.; Socheat, D.; Seidlein, L. V.
Artemisinin resistance: current status and scenarios for containment.
Nature Rev. Microbiol. 2010, 8, 272−280. (n) O’ Brien, C.; Henrich, P.
P.; Passi, N.; Fidlock, D. Recent clinical and molecular insight into
emerging artemisinin resistance in Plasmodium falciparum. Curr. Opin.
Infect. Dis. 2011, 24, 570−577. (o) Slack, R. D.; Jacobine, A. M.;
Posner, G. P. Antimalarial peroxides: advances in drug discovery and
design. Med. Chem. Commun. 2012, 3, 281−297.
(5) (a) Asthana, O. P.; Srivastava, J. S.; Valecha, N. Current status of
the artemisinin derivatives in the treatment of malaria with focus on
arteether. J. Paras. Dis. 1997, 211, 1−12. (b) Jambou., R.; Legrand, E.;
Niang, M.; Khim, N.; Lim, P.; Volney, B.; Therese Ekala, M.; Bouchier,
C.; Esterre, P.; Fandeur, T.; Mercereau-Puijalon, O. Resistance of
Plasmodium falciparum field isolates to in-vitro artemether and point
mutations of the SERCA-type PfATPase6. Res. Lett. 2005, 366, 1960−
1963.
(6) Singh, C.; Sharma, U.; Saxena, G.; Puri, S. K. Orally active
antimalarials: Synthesis and bioevaluation of a new series of steroid-
based 1,2,4-trioxanes against multidrug-resistant malaria in mice.
Bioorg. Med. Chem. Lett. 2007, 17, 4097−4101.
(7) (a) Todorovic, N. M.; Stefanovic, M.; Tinant, B.; Declercq, J. P.;
Makler, M. T.; Solaja, B. A. Steroidal geminal dihydroperoxides and
1,2,4,5-tetraoxanes: Structure determination and their antimalarial
activity. Steroids 1996, 61, 688−696. (b) Opsenica, D.; Pocsfalvi, G.;
Juranic, Z.; Tinant, B.; Declercq, J. P.; Kyle, D. E.; Milhous, W. K.;
Solaja, B. A. Cholic acid derivatives as 1,2,4,5-tetraoxane carriers:
Structure and antimalarial and antiproliferative activity. J. Med. Chem.
2000, 43, 3274−3282. (c) Solaja, B. A.; Terzic, N.; Pocsfalvi, G.;
Gerena, L.; Tinant, B.; Opsenica, D.; Milhous, W. K. Mixed steroidal
1,2,4,5-tetraoxanes: antimalarial and antimycobacterial activity. J. Med.
Chem. 2002, 45, 3331−3336. (d) Opsenica, D.; Angelovski, G.;
Pocsfalvi, G.; Juranic, Z.; Zizak, Z.; Kyle, D.; Milhous, W. K.; Solaja, B.
A. Antimalarial and antiproliferative evaluation of bis-steroidal
tetraoxanes. Bioorg. Med. Chem. 2003, 11, 2761−2768. (e) Opsenica,
D.; Kyle, E.; Milhous, W. K.; Solaja, B. A. Antimalarial,
antimycobacterial and antiproliferative activity of phenyl substituted
mixed tetraoxanes. J. Serb. Chem. Soc. 2003, 68, 291−302. (f) Terzic,
N.; Opsenica, D.; Milic, D.; Tinant, B.; Smith, K. S.; Milhous, W. K.;
Solaja, B. A. Deoxycholic acid-derived tetraoxane antimalarials and
antiproliferatives. J. Med. Chem. 2007, 50, 5118−5127.
Trioxane (26d, More Polar Isomer). This was obtained as a
1
white solid; mp 178−180 °C. IR (KBr, cm−1) 2928, 3426. H NMR
(300 Hz, CDCl3) δ 0.72 (s, 3H), 0.96 (s, 3H), 0.99−2.65 (m, 23H),
3.62 (t, 1H, J = 8.4 Hz), 3.73 (dd, 1H, J = 11.8 and 2.8 Hz), 4.01 (dd,
1H, J = 11.8 and 10.7 Hz), 5.16 (dd, 1H, J = 10.7 and 2.8 Hz), 5.33 (s,
1H), 5.49 (s, 1H), 7.25 (d, 2H, J = 8.3 Hz), 7.46 (d, 2H, J = 8.3 Hz).
13C NMR (75 MHz, CDCl3) δ 11.31 (CH3), 20.82 (CH2), 23.16
(CH3), 23.58 (CH2), 24.25 (CH2), 25.71 (CH2), 26.27 (CH2), 30.81
(CH2), 33.01 (CH2), 35.21 (C), 35.77 (CH2), 35.88 (CH), 37.12
(CH2), 39.40 (CH), 40.30 (CH), 43.29 (C), 51.28 (CH), 62.80
(CH2), 80.23 (CH), 82.13 (CH), 103.86 (C), 117.35 (CH2), 122.53
(C), 128.29 (2 × CH), 131.92 (2 × CH), 137.75 (C), 142.59 (C).
ESMS (m/z) 553 [M + Na]+. Anal. Calcd for C29H39BrO4: C, 65.53%,
H, 7.40%. Found: C, 65.03%, H, 7.77%.
ASSOCIATED CONTENT
■
S
* Supporting Information
1H NMR and 13C NMR Spectra of bile acid-based trioxanes
23a−d, 24a−d, 25a−d, 26a, 26b and 26d. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*Phone: +91 0522 2624273. Fax: +91 0522 2623405. E-mail:
chandancdri@yahoo.com.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
M.H., V.P.V., A.S.S., and N.K.N. are thankful to University
Grant commission (UGC) and Council of Scientific and
Industrial Research (CSIR), New Delhi, for the awards of
Senior Research Fellowship. P.R.M. thanks CSIR, New Delhi,
for an Emeritus Scientistship.
ABBREVIATIONS USED
■
SAR, structure−activity relationship; TLC, thin-layer chroma-
tography; Rf, retention factor; EtOAc, ethyl acetate; p-TSA,
para-toluenesulfonic acid; m-CPBA, meta-chloroperoxybenzoic
acid
REFERENCES
(1) CSIR−CDRI Communication No. 7561.
(2) W.H.O.: 10 Facts on Malaria.www.who.int/features/factfiles/
malaria. (b) Wahlgren, M.; Bejarano, M. T. A blueprint of ‘bad air’.
Nature 1999, 400, 506−507.
■
(3) (a) Wellems, T. E.; Plowe, C. V. Chloroquine-Resistant Malaria.
J. Infect. Dis 2001, 184, 770−776. (b) Hastings, I. M. The origins of
antimalarial drug resistance. Trends Parasitol. 2004, 20, 512−518.
(c) Ginsburg, H. Should chloroquine be laid to rest? Acta Trop. 2005,
96, 16−23.
(8) For earlier publication on trioxanes from our laboratory see:
(a) Singh, C.; Misra, D.; Saxena, G.; Chandra, S. Synthesis of in vivo
potent antimalarial 1,2,4-trioxanes. Bioorg. Med. Chem. Lett. 1992, 2,
497−500. (b) Singh, C.; Misra, D.; Saxena, G.; Chandra, S. In vivo
potent antimalarial 1,2,4-trioxanes: Synthesis and activity of 8-(α-
arylvinyl)-6,7,10-trioxaspiro[4,5]decanes and 3-(α-arylvinyl)-1,2,5-
trioxaspiro[5,5] undecanes against Plasmodium berghei in mice.
(4) For reviews on artemisinin and its analogues see: (a) Klayman, D.
L. Qinghaosu (artemisinin): An antimalarial drug from China. Science
1985, 228, 1049−1055. (b) Luo, X. D.; Shen, C. C. The chemistry,
pharmacology and clinical applications of qinghaosu (artemisinin) and
its derivatives. Med. Res. Rev. 1987, 7, 29−52. (c) Meshnick, S. R.;
Taylor, T. E.; Kamchonwongpaisan, S. Artemisinin and the
antimalarial endoperoxides: From herbal remedy to targeted chemo-
K
dx.doi.org/10.1021/jm301323k | J. Med. Chem. XXXX, XXX, XXX−XXX

Journal of Medicinal Chemistry
Article
Bioorg. Med. Chem. Lett. 1995, 5, 1913−1916. (c) Singh, C.; Gupta, N.;
Puri, S. K. Geraniol-derived 1,2,4-trioxanes with potent in vivo
antimalarial activity. Bioorg. Med. Chem. Lett. 2003, 13, 3447−3450.
(d) Singh, C.; Malik, H.; Puri, S. K. Synthesis and antimalarial activity
of a new series of trioxaquines. Bioorg. Med. Chem. 2004, 12, 1177−
1182. (e) Singh, C.; Gupta, N.; Puri, S. K. Synthesis of new 6-
alkylvinyl/arylalkylvinyl substituted 1,2,4-trioxanes active against
multidrugresistant malaria in mice. Bioorg. Med. Chem. 2004, 12,
5553−5562. (f) Singh, C.; Srivastava, N. C.; Puri, S. K. Synthesis and
antimalarial activity of 6-cycloalkylvinyl substituted 1,2,4-trioxanes.
Bioorg. Med. Chem. 2004, 12, 5745−5752. (g) Singh, C.; Malik, H.;
Puri, S. K. New orally active spiro 1,2,4-trioxanes with high antimalarial
potency. Bioorg. Med. Chem. Lett. 2005, 15, 4484−4487. (h) Singh, C.;
Malik, H.; Puri, S. K. Orally active 1,2,4-trioxanes: synthesis and
antimalarial assessment of a new series of 9-functionalized 3-(1-
arylvinyl)-1,2,5-trioxaspiro[5,5]undecanes against multidrug-resistant
Plasmodium yoelii nigeriensis in mice. J. Med. Chem. 2006, 49, 2794−
2803. (i) Singh, C.; Verma, V. P.; Naikade, N. K.; Singh, A. S.; Hassam,
M.; Puri, S. K. Novel bis- and tris-1,2,4-trioxanes: synthesis and
antimalarial activity against multidrug-resistant Plasmodium yoelii in
Swiss mice. J. Med. Chem. 2008, 51, 7581−7592. (j) Singh, C.;
Hassam, M.; Naikade, N. K.; Verma, V. P.; Singh, A. S.; Puri, S. K. J.
Med. Chem. 2010, 53, 7587−7598.
(c) Lemos, T. L. G.; McChesney, J. D. Utilization of common natural
products as synthons: Preparation of progesterone from lithocholic
acid. J. Nat. Prod. 1990, 53, 152−156.
(11) Combe, M. G.; Henbest, H. B.; Jackson, W. R. Aspects of
stereochemistry. Part XXI. Hydrogenation of 3-Oxo-Δ4-steroids over a
palladium-calcium carbonate catalyst. J. Chem. Soc.(C) 1967, 2467−
2469.
(12) (a) Singh, C. Preparation of β−hydroxyhydroperoxides by
photooxygenation of allylic alcohols and their elaboration into 1,2,4−
trioxanes. Tetrahedron Lett. 1990, 31, 6901−6902. (b) Singh, C.;
Gupta, N.; Puri, S. K. Photooxygenation of 3−aryl−2−cyclohexenols:
Synthesis of a new series of antimalarial 1,2,4−trioxanes. Tetrahedron
Lett. 2005, 46, 205−207.
(13) Note for alternative views of X-ray of 26a please see Supporting
Information.
(14) (a) Peters, W. Techniques for the study of drug response in
experimental malaria. In Chemotherapy and drug resistance in malaria;
Academic Press: London, 1970; pp 64−136. (b) In vivo antimalarial
efficacy test: The blood schizonticidal activity of the test compounds
was evaluated in rodent model using multidrug−resistant (MDR)
strain of Plasmodium yoelii nigeriensis. The colony bred Swiss mice of
either sex (20 2 g) were inoculated intraperitoneally with 1 × 106 P.
yoelii nigeriensis (MDR) parasites 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 23a−d,
24a−d, 25a−d, 26a, 26b and 26d were prepared in groundnut oil 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, 0.3 mg for a dose of 24 mg/kg
and 0.15 mg for a dose of 12 mg/kg) in 0.1 mL and administered
orally for each dose. Parasitaemia level were recorded from thin blood
smears on day 4 and subsequently twice a week till day 28. The
animals which did not develop patent infection till day 28 were
recorded as cured.17 Mice treated with β−arteether served as positive
control.
(15) (a) 100% protection means none of the treated mice developed
patent infection during the 28 days observation period and hence were
recorded as cured. Similarly, 20% protection means only one out of
five mice was cured. (b) 100% suppression of parasitemia means no
parasites were detected in 50 oil immersion microscopic fields
(parasites if at all present are below the detection limit). The parasites
present below the detection limit can multiply and eventually can be
detected during observation on subsequent days. In such cases,
though, the drug is providing near 100% suppression of the
parasitaemia on day 4 but will not provide full protection to the
treated mice in the 28 day survival assay. Multidrug−resistant
Plasmodium yoelii nigeriensis used in this study is resistant to
chloroquine, mefloquine, and halofantrine.
(9) For important publication on 1,2,4-trioxane from other
laboratories see: (a) Payne, G. B. Tungstic acid catalyzed
hydroxylation of cyclohexene in nonaqueous media. J. Org. Chem.
1957, 22, 1682−1685. (b) Jefford, C. W.; Jaggi, D.; Boukouvalas, J.;
Kohmoto, S. Reaction of bicyclic endoperoxides with carbonyl
compounds. A new approach to 1,2,4-trioxanes. J. Am. Chem. Soc.
1983, 105, 6497−6498. (c) Kepler, J. A.; Philip, A.; Lee, Y. W.; Morey,
M. C.; Caroll, F. I. 1,2,4- Trioxanes as potential antimalarial agents. J.
Med. Chem. 1988, 31, 713−716. (d) Avery, M. A.; Chong, W. K. M.;
Detre, G. Synthesis of (+)-8a, 9-secoartemisinin and related analogues.
Tetrahedron Lett. 1990, 31, 1799−1802. (e) Bunnelle, W. H.; Isbell, T.
A.; Barnes, C. L.; Qualls, S. Cationic ring expansion of an ozonide to a
1,2,4-trioxane. J. Am. Chem. Soc. 1991, 113, 8168−8169. (f) Posner, G.
H.; Milhous, W. K. Olefin oxidative cleavage and dioxetane formation
using triethylsilyl hydrotrioxide: applications to preparation of
potential antimalarial 1,2,4-trioxanes. Tetrahedron Lett. 1991, 32,
4235−4238. (g) Bloodworth, A. J.; Shah, A. Synthesis of 1,2,4-
trioxanes via intramolecular oxymercuration. J. Chem. Soc., Chem.
Commun. 1991, 947−948. (h) Bloodwarth, A. J.; Johnson, K. A. 6-
Hydroxymethyl-1,2,4-trioxanes and derivatives: an alternative 1,2,4-
trioxane synthesis from β’γ’-unsaturated β-hydroxyhydroperoxides.
Tetrahedron Lett. 1994, 35, 8057−8060. (i) O’Neill, P. M.; Pugh, M.;
Davies, J.; Ward, S. A.; Park, B. K. Regioselective Mukaiyama
hydroperoxysilylation of 2-alkyl-or 2-aryl-prop-2-en-1-ols: application
to a new synthesis of 1,2,4-trioxanes. Tetrahedron Lett. 2001, 42,
4569−4571. (j) O’Neill, P. M.; Mukhtar, A.; Ward, S. A.; Bickley, J. F.;
Davies, J.; Bachi, M. D.; Stocks, P. A. Application of thiol-olefin co-
oxygenation methodology to a new synthesis of the 1,2,4-trioxane
pharmacophore. Org. Lett. 2004, 6, 3035−3038. (k) Bartoschek, A.; El-
(16) The wide difference in activities of the two fractions is
surprising. It appears that the trioxanes formed from only one of the
two enantiomeric hydroxyhydroperoxides show significant activity.
(17) Puri, S. K.; Singh, N. Azithromycin: antimalarial profile against
blood and sporozoite−induced infections in mice and monkeys. Expl.
Parasitol. 2000, 94, 8−14.
Idreesy, T. T.; Griesbeck, A. G.; Hoinck, L.; Lex, J.; Miara, C.;
̈
Neudorfl, J. M. A family of new 1,2,4-trioxanes by photooxygenation of
̈
allylic alcohols in sensitizerdoped polymers and secondary reactions.
Synthesis 2005, 2433−2444. (l) Griesbeck, A. G.; Blunk, D.; El-Idreesy,
T.; Raabe, A. Bicyclic peroxides and perorthoester with 1,2,4-trioxane
structures. Angew. Chem., Int. Ed. 2007, 46, 8883−8886. (m) Ramirez,
A. P.; Thomas, A. M.; Woerpel, K. A. Preparation of bicyclic 1,2,4-
trioxanes from γ, δ-unsaturated ketones. Org. Lett. 2009, 11, 507−510.
(n) Griesbeck, A. G.; Neudorfl, J.; Horauf, A.; Specht, S.; Raabe, A.
̈
̈
Antimalarial peroxide dyads from natural artemisinin and hydrox-
yalkylated 1,2,4-trioxanes. J. Med. Chem. 2009, 52, 3420−3423.
(10) (a) Putz, G.; Schmider, W.; Nitschke, R.; Kurz, G.; Blum, H. E.
Synthesis of phospholipid-conjugated bile salts and interaction of bile
salt-coated liposomes with cultured hepatocytes. J. Lipid Res. 2005, 46,
2325−2338. (b) Tochtrop, G. P.; Dekoster, G. T.; Cistola, D. P.;
Covey, D. F. Synthesis of [3,4-13C2]-enriched bile salts as NMR probes
of protein-ligand interaction. J. Org. Chem. 2002, 67, 6764−6771.
L
dx.doi.org/10.1021/jm301323k | J. Med. Chem. XXXX, XXX, XXX−XXX