Orally active, water-soluble antimalarial 3-aryltrioxanes: Short synthesis and preclinical efficacy testing in rodents

Article abstract of DOI:10.1021/jm020210h

Short chemical syntheses of four new antimalarial trioxanes are presented, starting with inexpensive and commercially available cyclohexanone. Almost exclusive formation of the trioxane 12α-stereoisomers simplifies product purification. Carboxyphenyltrioxanes 3 and 5 are thermally stable in air even at 60°C for 24 h. When administered orally, these new carboxyphenyltrioxanes are highly efficacious in curing malaria-infected mice. Important for their practical in vivo administration, these new synthetic antimalarial trioxanes 3 and 5 are 14-20 times more soluble in water at pH 7.4 than is artelinic acid (1), a leading semisynthetic, herb-derived antimalarial trioxane drug candidate.

Full text of DOI:10.1021/jm020210h

3824
J . Med. Chem. 2002, 45, 3824-3828
Expedited Articles
Or a lly Active, Wa ter -Solu ble An tim a la r ia l 3-Ar yltr ioxa n es: Sh or t Syn th esis a n d
P r eclin ica l Effica cy Testin g in Rod en ts
Gary H. Posner,*,† Heung Bae J eon,† Poonsakdi Ploypradith,†,‡ Ik-Hyeon Paik,† Kristina Borstnik,† Suji Xie,§ and
Theresa A. Shapiro§
Department of Chemistry, School of Arts and Sciences, The J ohns Hopkins University, 3400 N. Charles Street,
Baltimore, Maryland 21218-2685, Division of Clinical Pharmacology, Department of Medicine, School of Medicine,
The J ohns Hopkins University, Baltimore, Maryland 21205, and Malaria Research Institute,
Bloomberg School of Public Health, The J ohns Hopkins University, Baltimore, Maryland 21205
Received May 15, 2002
Short chemical syntheses of four new antimalarial trioxanes are presented, starting with
inexpensive and commercially available cyclohexanone. Almost exclusive formation of the
trioxane 12R-stereoisomers simplifies product purification. Carboxyphenyltrioxanes 3 and 5
are thermally stable in air even at 60 °C for 24 h. When administered orally, these new
carboxyphenyltrioxanes are highly efficacious in curing malaria-infected mice. Important for
their practical in vivo administration, these new synthetic antimalarial trioxanes 3 and 5 are
14-20 times more soluble in water at pH 7.4 than is artelinic acid (1), a leading semisynthetic,
herb-derived antimalarial trioxane drug candidate.
In tr od u ction
Starting from cyclohexanone, we recently developed a
five-step total synthesis of water-soluble simplified
3-carboxyphenyltrioxane 2 that has at least as good a
therapeutic index (efficacy/toxicity) as that of nature-
derived artelinic acid (1) in rodents.10 Now we report
on second-generation water-soluble synthetic carbox-
yphenyltrioxanes 3 and 5, in which the design of
trioxane 5 was inspired by the pioneering work of Oh
and colleagues.11 Noteworthy characteristics of these
new chemical entities 3 and 5, as described in detail
below, include especially their high solubility in water
and their high chemotherapeutic efficacy upon oral
administration to malaria-infected mice.
About 40% of the world’s population is currently at
risk for contracting the infectious parasitic disease
malaria.1 On the basis of ancient Chinese folk herbal
medicine,2-4 several derivatives of the natural 1,2,4-
trioxane artemisinin are now used as fast-acting che-
motherapeutic drugs to cure individuals who have
malaria.5-7 One such artemisinin derivative is water-
soluble trioxane artelinic acid (1), designed by the U.S.
Ch em istr y
Short syntheses of simplified trioxanes 3 and 5, as
well as of their corresponding 3-fluorophenyl analogue
4 and 3-phenyl analogue 6, are shown in Schemes 1 and
2. Noteworthy features of these synthetic routes are as
follows: (1) in Scheme 1, use of 4-bromobenzyl alcohol
in the form of its dianion 7 to produce benzylic alcohol
ketone 8 directly (i.e., without alcohol protection-
deprotection) in 70% yield; (2) air photooxygenation
without protecting the benzylic hydroxyl group; (3)
almost exclusive formation of the 12R-benzyloxy product
9 (with only a trace of the easily separable 12â-
benzyloxy diastereomer); (4) in Scheme 2, intramolecu-
lar formation and effective use of cyclic vinyl ether 10
to form keto vinyl ether 11; (5) successful photooxygen-
ation of keto ether 11 into styryltrioxane 12 with
exclusive formation of only the 12R-pyran stereoisomer.
Walter Reed Army Institute of Research, and it is a
leading candidate for antimalarial drug development.8,9
The 12R-stereochemistry of new trioxanes 3-6 was
established by a combination of their NMR spectroscopic
characteristics12 and chromatographic polarities. As we
have seen previously in similar trioxanes,10 the 12R-
stereoisomers are more polar than the corresponding
12â-isomers upon TLC and HPLC chromatography.
* To whom correspondence should be addressed. Phone: 410-516-
4670. Fax: 410-516-8420. E-mail: gposner1@jhem.jhu.edu.
† School of Arts and Sciences.
‡ Current address: Laboratory of Medicinal Chemistry, Chulabhorn
Research Institute, Vipavadee-Rangsit Highway, Bangkok, Thailand.
§ School of Medicine and Bloomberg School of Public Health.
10.1021/jm020210h CCC: $22.00 © 2002 American Chemical Society
Published on Web 07/30/2002

3-Aryltrioxanes
J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 18 3825
Sch em e 1
Sch em e 2
Like MHP-34a (2), 12R-benzyloxytrioxanes 3 and 4 have
characteristic 1H NMR peaks at δ 2.3 and at δ 2.5,
respectively, and also characteristic 13C NMR peaks for
the C12-acetal carbon atom at δ 94 and δ 98, respectively
(in contrast to δ 104-105 for the 12â-diastereomers; see
Experimental Section). Likewise, the R-pyrans 5 and 6
Biology
Because in vitro antimalarial testing generally indi-
cates only very low activity for water-soluble trioxanes,
we evaluated carboxyphenyltrioxanes 3 and 5 directly
via in vivo testing in mice following an established
protocol.13 Efficacy against P. berghei malaria parasites
was studied using oral administration as the most
challenging mode of drug delivery. Results are sum-
marized in Table 1. Whereas first-generation carboxy-
phenyltrioxane 2 is about 5 times less efficacious than
artelinic acid (1),10 carboxyphenyltrioxanes 3 and 5 both
are about only 2 times less efficacious than artelinic
acid. Importantly, however, these two new trioxanes are
considerably more soluble in pH 7.4 buffered water than
is 1; trioxane 3 is about 14 times more soluble (7 mg/
mL) than 1, and trioxane 5 is about 20 times more
soluble (10 mg/mL). This relatively high water solubility
1
have characteristic C12-H H NMR singlets at δ 5.5 and
δ 5.4, respectively.
The thermal stability of new synthetic trioxanes 3 and
5 is very good. Heating crystalline trioxanes 3 and 5 in
air at 60 °C for 24 h caused less than 5% decomposition,
1
as judged by H NMR spectroscopy. Also, heating a pH
7.4 phosphate-buffered 0.1 N NaCl solution of trioxane
3 at 40 °C for 7 days caused less than 5% decomposition,
as judged by 1H NMR spectroscopy. Under these pH 7.4
buffered conditions, trioxane 5 showed approximately
20% decomposition.

3826 J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 18
Ta ble 1. Antimalarial Efficacy in Mice Against P. berghei
Posner et al.
saturated aqueous NaHCO3, and the mixture was poured into
a separatory funnel containing 50 mL of ether and 30 mL of
water. The organic layer was further washed with 20 mL of
saturated aqueous NaCl, dried over MgSO4, and concentrated.
The residue was subjected to column chromatography with
EtOAc/hexanes (1:10) as eluent to give the p-fluorophenyl
ketone intermediate (0.60 g, 92%) as a pale-yellow oil. 1H NMR
(400 MHz, CDCl3): δ 7.87-7.91 (m, 2H), 7.26-7.34 (m, 5H),
7.04-7.12 (m, 2H), 5.97 (d, J ) 2.0 Hz), and 5.84 (s) (1H total),
4.59-4.76 (m, 2H), 2.77-3.01 (m), and 2.40 (dt, J d)14.0 Hz,
J t)4.4 Hz) (3H total), 1.95-2.06 (m, 3H), 1.78-1.85 (m, 1H),
1.49-1.76 (m, 5H), 1.14-1.40 (m, 1H). 13C NMR (100 MHz,
CDCl3): δ 199.3, 199.0, 165.5 (d, J C-F ) 252 Hz), 165.4 (d, J C-F
) 252 Hz), 138.8, 137.99, 137.96, 137.88, 133.6 (d, J C-F ) 3.1
Hz), 133.5 (d, J C-F ) 3.1 Hz), 130.58 (d, J C-F ) 9.1 Hz), 130.56
(d, J C-F ) 9.1 Hz), 128.35, 128.34, 127.7, 127.6, 127.3, 127.2,
121.0, 119.9, 115.5 (d, J C-F ) 21.9 Hz), 115.4 (d, J C-F ) 21.9
Hz), 73.4, 73.3, 38.6, 36.9, 36.7, 33.6, 32.8, 31.8, 28.3, 27.2,
26.5, 25.9, 25.8, 22.9, 22.8, 21.6. HRMS (EI, M+) calcd
352.1839, found 352.1844.
a
a
compd
ED50
,
mg/kg
ED90, mg/kg
1
3
5
9.6
17.0
15.0
29.0
59.0
51.0
a
Four different doses were administered each day for 4 days
to five mice per dose regimen to establish the ED values indicated
here using a previously described protocol.13
of new trioxanes 3 and 5 means that they can be
administered in vivo orally or intravenously in consider-
ably more concentrated aqueous solutions than can 1.
No overt signs of toxicity were observed in these in vivo
antimalarial experiments.
For comparison with hydrophilic trioxane 3, the
corresponding but hydrophobic 3-p-fluorophenyltrioxane
4 was prepared (Scheme 1) and was evaluated for in
vitro antimalarial activity following an established
protocol.14 Relative to artemisinin with an IC50 of 9.4
nM, water-insoluble fluorophenyltrioxane 4 has an IC50
of 31 nM. Also, for comparison with hydrophilic trioxane
5, hydrophobic 3-phenyltrioxane 6 was prepared; it has
an in vitro antimalarial IC50 of 1.3 nM. Although
hydrophobic 3-fluorophenyl 4 and especially 3-phenyl-
trioxanes 6 have high in vitro antimalarial activities,
they could not be easily administered in vivo intrave-
nously or orally because of their insolubility in water.
In conclusion, new structurally simple, synthetic
3-carboxyphenyltrioxanes 3 and 5 are highly water-
soluble and orally efficacious antimalarial compounds
that deserve further preclinical evaluation as potential
drugs for malaria chemotherapy.15-18
A flame-dried 250 mL three-necked round-bottom flask was
charged with triphenyl phosphite (1.02 g, 3.29 mmol) in dry
CH2Cl2 (55 mL) at room temperature. The mixture was cooled
to -78 °C, and ozone generated from UHP oxygen was bubbled
through the solution until saturation was indicated by a deep-
blue color of the solution. The mixture was then purged with
Ar until the mixture was colorless. To this mixture was slowly
added a precooled (-78 °C) solution of the p-fluorophenyl
ketone intermediate (Z/E ) 1/1, 0.58 g, 1.65 mmol) in dry CH2-
Cl2 (30 mL) via cannula. The reaction mixture was stirred at
-78 °C and monitored continuously by TLC. TLC after 30 min
showed no starting material. To this mixture at -78 °C was
added dropwise a precooled (-78 °C) solution of Me3SiOTf
(TMSOTf, 0.33 mL, 1.82 mmol) in CH2Cl2 (5 mL) via cannula
for 2 min. The resulting mixture was stirred at -78 °C until
all dioxetane intermediate was consumed as indicated by TLC.
At that time, the reaction mixture was treated with a 25 wt
% solution of sodium methoxide in MeOH (3.3 equiv), and the
reaction mixture was warmed to room temperature. The
mixture was diluted with H2O and CHCl3. The organic layer
was separated, washed with brine, dried over MgSO4, and
concentrated. The residue was subjected to column chroma-
tography with EtOAc/hexanes (1:10) as eluent to give 12R-
benzyloxytrioxane 4 (0.18 g, 29%) and 12â-benzyloxytrioxane
(0.17 g, 27%). Further purification of 12R-benzyloxytrioxane
4 by HPLC (silica, 3% EtOAc/hexanes, 3.0 mL/min, 254 nm,
Rt ) 14.5 min) afforded a white solid: mp 116-117 °C. 1H
NMR (400 MHz, CDCl3): δ 7.54 (m, 2H), 7.30-7.52 (m, 5H),
7.04 (m, 2H), 5.28 (s, 1H), 5.00 (d, J ) 12.6 Hz, 1H), 4.78 (d,
J ) 12.6 Hz, 1H), 2.83 (ddd, J d ) 14.4, 13.2, 4.0 Hz, 1H), 2.47
(m, 1H), 2.26 (ddd, J d ) 14.4, 4.8, 2.8 Hz, 1H), 1.69-1.84 (m,
3H), 1.54-1.64 (m, 3H), 1.06-1.26 (m, 3H), 0.93 (qt, J q ) 13.6
Hz, J t ) 3.2 Hz, 1H). 13C NMR (100 MHz, CDCl3): δ 162.9 (d,
J C-F ) 247 Hz), 137.4, 136.5 (d, J C-F ) 3.2 Hz), 128.39, 128.36,
127.9, 127.5 (d, J C-F ) 8.6 Hz), 115.1 (d, J C-F ) 21.8 Hz), 103.8,
98.4, 83.7, 69.5, 45.5, 37.6, 33.4, 32.5, 27.1, 25.1, 22.7. HRMS
(CI, M + H+) calcd 385.1815, found 385.1820. Further puri-
fication of 12â-benzyloxytrioxane by HPLC (silica, 3% EtOAc/
hexanes, 3.0 mL/min, 254 nm, Rt ) 9.0 min) afforded a white
Exp er im en ta l Section 19
P r ep a r a tion of 2-(2′-Cya n oeth yl)-1-(ben zyloxym eth -
ylen e)cycloh exa n e. A solution of (benzyloxymethyl)triph-
enylphosphonium chloride20 (2.19 g, 5.23 mmol) in THF (40
mL) was put in a methanol bath fixed at -43 °C. To this
solution was added n-BuLi (1.6 M in hexanes, 3.3 mL, 5.28
mmol) slowly by syringe. The solution turned red and was
stirred for 30 min. To the resultant ylide solution was added
a solution of 2-cyanoethylcyclohexanone21 (0.40 g, 2.65 mmol)
in THF (4 mL) via cannula, and then it was stirred for 20 h at
-43 °C. The reaction mixture was quenched with water and
extracted with ether. The organic layer was separated, dried
over MgSO4, and concentrated. The residue was subjected to
column chromatography with EtOAc/hexanes (1:10) as eluent
to give the product (0.57 g, 84%, Z/ E ) 1/3) as a colorless oil.
1H NMR (400 MHz, CDCl3): δ 7.25-7.36 (m, 5H), 5.98 (s), and
5.89 (s) (1H total), 4.68-4.77 (m, 2H), 2.93 (m), and 2.49 (dt,
J d)14.0 Hz, J t)4.0 Hz) (1H total), 1.98-2.20 (m, 3H), 1.76-
1.92 (m, 2H), 1.43-1.72 (m, 6H), 1.13-1.32 (m, 1H). 13C NMR
(100 MHz, CDCl3): δ 139.4, 138.5, 137.5, 137.3, 128.24, 128.21,
127.7, 127.6, 127.4, 127.3, 120.4, 119.8, 118.7, 117.8, 105.9,
73.4, 73.3, 37.4, 32.5, 31.1, 27.8, 27.4, 26.8, 26.7, 26.2, 22.2,
21.9, 21.5, 15.0. HRMS (M + Na) calcd 278.1515, found
278.1511.
P r ep a r a tion of p-F lu or op h en yltr ioxa n e 4. To a solution
of p-bromofluorobenzene (0.49 g, 2.80 mmol) in ether (30 mL)
at -78 °C was added t-BuLi (1.6 M in pentane, 2.9 mL, 4.64
mmol) via syringe over 1 min. The resulting solution was
stirred at -78 °C for 30 min. A precooled (-78 °C) solution of
2-(2′-cyanoethyl)-1-(benzyloxymethylene)cyclohexane (0.48 g,
1.68 mmol) in ether (20 mL) was then added dropwise via
cannula for 2 min. The resulting mixture was stirred at -78
°C for 30 min, then the cooling bath was removed, and the
reaction mixture was allowed to reach room temperature. At
this point, TLC analysis indicated full consumption of the
starting material. The reaction was quenched with 5 mL of
1
solid: mp 59-60 °C. H NMR (400 MHz, CDCl3): δ 7.50 (m,
2H), 7.30-7.43 (m, 5H), 7.04 (m, 2H), 5.34 (d, J ) 1.2 Hz, 1H),
5.10 (d, J ) 12.0 Hz, 1H), 4.74 (d, J ) 12.0 Hz, 1H), 2.79 (ddd,
J d ) 14.6, 13.4, 3.6 Hz, 1H), 2.31 (ddd, J d ) 14.6, 4.2, 3.2 Hz,
1H), 2.05 (m, 1H), 1.72-1.88 (m, 4H), 1.60-1.72 (m, 4H), 1.29
(m, 1H), 1.19 (m, 1H). 13C NMR (100 MHz, CDCl3): δ 162.9
(d, J C-F ) 247 Hz), 137.3, 136.7 (d, J C-F ) 3.7 Hz), 128.4, 127.9,
127.8, 127.3 (d, J C-F ) 8.2 Hz), 115.1 (d, J C-F ) 21.4 Hz), 104.8,
102.7, 83.9, 71.2, 47.5, 39.1, 35.5, 30.9, 26.8, 25.0, 24.0.
P r ep a r a tion of p-(Hyd r oxym eth yl)p h en yl Keton e 8. To
a solution of p-bromobenzyl alcohol (0.22 g, 1.18 mmol) in ether
(20 mL) at -78 °C was added t-BuLi (1.4 M in pentane, 2.5
mL, 3.60 mmol, 3 equiv) via syringe over 1 min. The resulting
solution was stirred at -78 °C for 30 min. A precooled (-78
°C) solution of 2-(2′-cyanoethyl)-1-(benzyloxymethylene)cyclo-

3-Aryltrioxanes
J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 18 3827
hexane (0.20 g, 0.78 mmol) in ether (10 mL) was then added
dropwise via cannula for 2 min. The resulting mixture was
warmed to room temperature slowly and stirred overnight. The
reaction was quenched with 3 mL of saturated aqueous
NaHCO3, and the mixture was poured into a separatory funnel
containing 50 mL of ether and 20 mL of water. The aqueous
layer was further extracted with 30 mL of ether. The organic
layer was collected, dried over MgSO4, and concentrated. The
residue was subjected to column chromatography with EtOAc/
hexanes (1:2) as eluent to give the ketone 8 (0.20 g, 70%) as a
pale-yellow oil. 1H NMR (400 MHz, CDCl3): δ 7.86 (m, 2H),
7.26-7.42 (m, 7H), 5.97 (d, J ) 1.2 Hz), and 5.86 (s) (1H total),
4.61-4.74 (m, 2H), 2.77-3.01 (m), and 2.40 (dt, J d)13.6 Hz,
J t)4.8 Hz) (3H total), 2.51 (br s, 1H), 1.91-2.08 (m, 3H), 1.49-
1.85 (m, 6H), 1.18-1.40 (m, 1H). 13C NMR (100 MHz, CDCl3):
δ 200.8, 200.5, 146.0, 145.8, 138.7, 137.90, 137.86, 136.3, 136.1,
128.3, 128.2, 127.6, 127.2, 126.5, 126.4, 121.0, 120.0, 73.3, 73.2,
64.5, 64.4, 38.6, 37.0, 36.8, 33.5, 32.8, 31.7, 28.2, 27.1, 26.4,
26.0, 25.8, 22.9, 22.7, 21.5. HRMS (M + Na) calcd 387.1931,
found 387.1934.
45.1, 37.2, 33.2, 31.6, 26.7, 24.8, 22.2. HRMS (M + Na) calcd
433.1622, found 433.1600. Anal. Calcd for C24H26O6: C, 70.23;
H, 6.38. Found: C, 69.94; H, 6.22.
1
For the 12â-stereoisomer. H NMR (400 MHz, CD3OD): δ
8.01-8.04 (m, 2H), 7.59-7.62 (m, 2H), 7.31-7.47 (m, 5H), 5.34
(s, 1H), 5.08 (d, J ) 12.0 Hz, 1H), 4.78 (d, J ) 12.0 Hz, 1H),
2.80 (ddd, J d)14.4, 12.0, 3.6 Hz, 1H), 2.25 (ddd, J d)14.8, 4.4,
3.2 Hz, 1H), 2.06 (m, 1H), 1.65-1.89 (m, 8H), 1.22-1.30 (m,
2H). 13C NMR (100 MHz, CD3OD): δ 169.5, 147.0, 139.0, 132.4,
130.9, 129.6, 129.5, 129.1, 126.6, 106.3, 104.3, 85.2, 72.7, 49.1,
40.4, 36.7, 32.2, 28.1, 26.3, 25.2.
P r ep a r a tion of Cyclic En ol Eth er 10. A solution of 0.90
g (4.03 mmol) of 2-(2′-cyanoethyl)-6-(2′-hydroxyethyl)-1-(meth-
oxymethylene)cyclohexane19 and 60 mg of p-TsOH in toluene
(60 mL) was heated to reflux under Dean-Stark conditions
for 4 h. The reaction mixture was cooled to room temperature,
a few of drops of triethylamine were added to the solution,
and then it was concentrated. The residue was subjected to
column chromatography quickly with CH2Cl2 as eluent to give
0.63 g (83%) of 10 as a yellow oil. 1H NMR (400 MHz, CDCl3):
δ 6.08 (s, 1H), 3.74-3.88 (m, 2H), 2.33-2.48 (m, 2H), 1.88-
2.03 (m, 4H), 1.75-1.83 (m, 3H), 1.35-1.59 (m, 3H), 1.09 (m,
1H), 0.90 (m, 1H). 13C NMR (100 MHz, CDCl3): δ 136.1, 119.8,
119.1, 63.8, 38.6, 34.8, 33.3, 33.0, 30.5, 27.1, 25.6, 15.0. HRMS
(M + Na) calcd 214.1202, found 214.1194.
P r ep a r a tion of 3-P h en yltr ioxa n e 6. A solution of 0.45 g
(2.4 mmol) of 10 in Et2O (40 mL) was cooled to -78 °C. In a
separate flask, 12 mL of PhLi (1.0 M in ether/cyclohexane) was
precooled to -78 °C and cannulated to the solution. The
resulting solution was stirred at -78 °C for 1 h, then at room
temperature for 1 h. The reaction mixture was cooled to 0 °C
and slowly quenched with saturated NaHCO3. The aqueous
layer was extracted with Et2O, and the organic layer was
separated, dried over MgSO4, and concentrated. The residue
was subjected to column chromatography with CH2Cl2 as
eluent to give 0.46 g (71%) of phenyl ketone intermediate as a
pale-yellow solid: mp 72.5-73.5 °C. 1H NMR (CDCl3): δ 7.98-
7.95 (m, 2H), 7.56-7.46 (m, 3H), 6.22 (s, 1H), 3.91-3.76 (m,
2H), 3.13-2.98 (m, 2H), 2.04-1.63 (m, 8H), 1.56-1.35 (m, 2H),
1.26-0.94 (m, 2H). 13C NMR (CDCl3): δ 200.37, 136.96, 136.27,
132.91, 128.53, 128.00, 120.11, 63.77, 39.61, 36.40, 35.15,
34.22, 33.20, 30.64, 25.98, 25.63.
P r ep a r a tion of p-(Hyd r oxym eth yl)p h en yltr ioxa n e 9.
A 100 mL three-necked round-bottom flask equipped with
dispersion bubbler gas inlet, gas outlet, and a septum was
charged with p-(hydroxymethyl)phenyl ketone 8 (Z/E ) 1/3,
104 mg, 0.29 mmol) in dry CH2Cl2 (30 mL), and about 1 mg of
methylene blue was added. To the solution maintained at -78
°C was bubbled dry air at a flow rate of ∼240 mL/min.
Irradiation was achieved via a 250 W IR lamp (General
Electric) at 1 in distance from the reaction flask. TLC analysis
after 20 min showed no starting material, at which time the
IR lamp was removed. The air bubbler and outlet also were
removed, and the reaction mixture was placed under an Ar
atmosphere. A precooled (-78 °C) solution of Me3SiOTf (0.13
mL, 0.72 mmol, 2.5 equiv) in CH2Cl2 (3 mL) was added slowly
via cannula for 2 min. The reaction was stirred for 1 h at -78
°C, then quenched with 1-ethylpiperidine (0.16 mL, 4 equiv)
by syringe. The reaction mixture was allowed to warm to room
temperature and then concentrated. To the residue was added
dry THF (10 mL), and 1.5 mL of 1 M TBAF (tetra-n-
butylammonium fluoride) in THF was added to the solution
at 0 °C. The resulting solution was stirred for 1 h at room
temperature. The reaction mixture was quenched with 3 mL
of water and poured into a separatory funnel containing 20
mL of EtOAc and 10 mL of water. The aqueous layer was
further extracted with 20 mL of EtOAc. The organic layer was
collected, washed with saturated NaCl solution, dried over
MgSO4, and concentrated. The residue was subjected to column
chromatography with EtOAc/hexanes (1:3) as eluent to give
the R-benzyltrioxane 9 (38 mg, 33%) as a colorless oil. 1H NMR
(400 MHz, CDCl3): δ 7.56 (m, 2H), 7.30-7.42 (m, 7H), 5.29
(s, 1H), 5.00 (d, J ) 12.0 Hz, 1H), 4.77 (d, J ) 12.0 Hz, 1H),
4.71 (s, 2H), 2.84 (ddd, J d)14.8, 12.8, 4.0 Hz, 1H), 2.48 (dm,
J d ) 13.2 Hz, 1H), 2.28 (dm, J d ) 14.8 Hz, 1H), 1.69-1.84 (m,
4H), 1.55-1.64 (m, 3H), 1.07-1.26 (m, 3H), 0.94 (m, 1H). 13C
NMR (100 MHz, CDCl3): δ 141.4, 140.0, 137.4, 128.4, 127.8,
126.7, 125.7, 104.0, 93.2, 83.7, 69.3, 64.9, 45.5, 37.6, 33.4, 32.5,
27.1, 25.1, 22.7. HRMS (M + Na) calcd 419.1829, found
419.1843.
A 100 mL three-necked round-bottom flask equipped with
dispersion bubbler gas inlet, gas outlet, and a septum was
charged with the phenyl ketone intermediate (0.12 g, 0.44
mmol) in dry CH2Cl2 (25 mL), and about 1 mg of methylene
blue was added. To the solution at -78 °C was bubbled dry
air at a flow rate of ∼240 mL/min. Irradiation was achieved
via a 250 W IR lamp at 1 in. distance from the reaction flask.
The reaction was monitored continuously by TLC. TLC after
1 h showed no starting material, and then the IR lamp was
removed. The air bubbler and outlet were removed, and the
reaction was placed under an Ar atmosphere. A precooled (-78
°C) solution of TBSOTf (0.15 mL, 0.66 mmol) in CH2Cl2 (7 mL)
was added slowly via cannula. The reaction mixture was
stirred for 2 h at -78 °C, and then the reaction was quenched
with NEt3 (0.18 mL) by syringe. The reaction mixture was
allowed to warm to room temperature and then concentrated.
The residue was subjected to column chromatography with
EtOAc/petroleum ether (1:9) as eluent to give the trioxane 6
(30 mg, 23%). Further purification of trioxane 6 by HPLC
(silica, 10% EtOAc/hexanes, 2.0 mL/min, 254 nm, Rt ) 19.3
P r ep a r a tion of p-Ca r boxyp h en yltr ioxa n e 3. A solution
of p-benzyltrioxane 9 (25 mg, 0.063 mmol) and KMnO4 (30 mg)
in acetone (5 mL) was stirred for 4 h (no starting material by
TLC) at room temperature, generating a precipitate. The
precipitate was filtered and washed with more acetone, and
then it was dissolved in H2O (5 mL). The filtrate was acidified
with aqueous 0.5 N HCl solution to pH 2, generating a white
solid, which was filtered and recrystallized from MeOH/H2O
at room temperature to give 12 mg (46%) of 3 as a white
1
min) afforded a white solid: mp 81-82 °C. H NMR (CDCl3):
δ 7.60-7.58 (m, 2H), 7.36-7.30 (m, 3H), 5.44 (s, 1H), 3.97 (m,
1H), 3.81 (m, 1H), 2.88 (m, 1H), 2.47 (m, 1H), 2.32 (m, 1H),
1.87 (m, 1H), 1.80-1.59 (m, 7H), 1.42-1.25 (m, 2H), 1.15 (m,
1H). 13C NMR (CDCl3): δ 139.80, 128.90, 128.27, 125.68,
104.26, 92.22, 80.18, 61.36, 46.10, 39.85, 37.50, 32.60, 28.30,
26.95, 26.52, 25.01. HRMS calcd (M + Na) 325.1416, found
325.1414.
1
solid: mp 192.5-193.5 °C. H NMR (400 MHz, DMSO-d6): δ
7.96 (d, J ) 7.2 Hz, 2H), 7.64 (d, J ) 8.0 Hz, 2H), 7.30-7.37
(m, 5H), 5.52 (s, 1H), 4.96 (d, J ) 12.0 Hz, 1H), 4.75 (d, J )
12.0 Hz, 1H), 2.75 (t, J ) 13.6 Hz, 1H), 2.28 (d, J ) 11.6 Hz,
1H), 2.18 (d, J ) 13.6 Hz, 1H), 1.49-1.79 (m, 6H), 1.06-1.28
(m, 4H). 13C NMR (100 MHz, DMSO-d6): δ 166.8, 144.5, 137.9,
131.1, 129.4, 128.3, 127.9, 127.7, 125.7, 103.1, 93.8, 83.4, 69.5,
P r ep a r a tion of p-Stylyl Keton e 11. To a solution of
p-styryl bromide (0.22 g, 1.68 mmol) in ether (30 mL) at -78
°C was added t-BuLi (1.5 M in pentane, 2.2 mL, 3.20 mmol)
via syringe over 1 min. The resulting dark-red solution was

3828 J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 18
Posner et al.
stirred at -78 °C for 20 min. A precooled (-78 °C) solution of
the nitrile 10 (0.22 g, 1.15 mmol) in ether (20 mL) was then
added dropwise via cannula for 2 min. The resulting mixture
was stirred at -78 °C for 30 min, then the cooling bath was
removed, and the reaction mixture was allowed to reach room
temperature. At this point, TLC analysis indicated full con-
sumption of the starting material. The reaction was quenched
with 5 mL of saturated aqueous NaHCO3, and the mixture
was poured into a separatory funnel containing 50 mL of ether
and 30 mL of water. The organic layer was further washed
with 20 mL of saturated aqueous NaCl, dried over MgSO4, and
concentrated. The residue was subjected to column chroma-
tography with EtOAc/hexanes (1:12) as eluent to give the
ketone 11 (0.245 g, 72%) as a sticky white solid. 1H NMR (400
MHz, CDCl3): δ 7.91-7.94 (m, 2H), 7.46-7.49 (m, 2H), 6.75
(dd, J d)17.6, 10.8 Hz, 1H), 6.22 (s, 1H), 5.87 (dd, J d)17.6, 0.8
Hz, 1H), 5.39 (dd, J d ) 10.8, 0.8 Hz, 1H), 3.77-3.91 (m, 2H),
2.96-3.11 (m, 2H), 1.86-2.04 (m, 5H), 1.75-1.84 (m, 2H), 1.67
(m, 1H), 1.36-1.59 (m, 2H), 1.14 (m, 1H), 0.99 (m, 1H). 13C
NMR (100 MHz, CDCl3): δ 199.7, 141.8, 136.2, 136.1, 135.9,
128.4, 126.2, 120.0, 116.5, 63.7, 39.6, 36.3, 35.1, 34.2, 33.2, 30.6,
25.9, 25.7.
P r ep a r a tion of p-Stylyltr ioxa n e 12. A 100 mL three-
necked round-bottom flask equipped with dispersion bubbler
gas inlet, gas outlet, and a septum was charged with the
ketone 11 (0.22 g, 0.74 mmol) in dry CH2Cl2 (75 mL), and about
1.5 mg of methylene blue was added. To the solution at -78
°C was bubbled dry air at a flow rate of ∼240 mL/min.
Irradiation was achieved via a 250 W IR lamp at 1 in. distance
from the reaction flask. The reaction was monitored continu-
ously by TLC. TLC after 1 h showed no starting material, and
then the IR lamp was removed. The air bubbler and outlet
were removed, and the reaction mixture was placed under an
Ar atmosphere. A precooled (-78 °C) solution of TMSOTf (0.27
mL, 1.48 mmol) in CH2Cl2 (7 mL) was added slowly via
cannula. The reaction mixture was stirred for 2 h at -78 °C,
and then the reaction was quenched with 1-ethylpiperidine
(0.31 mL) by syringe. The reaction mixture was allowed to
warm to room temperature and then concentrated. The residue
was subjected to column chromatography with EtOAc/hexanes
(1:10) as eluent to give the trioxane 12 (79 mg, 33%) as a sticky
white solid. 1H NMR (400 MHz, CDCl3): δ 7.54 (d, J ) 8.4
Hz, 2H), 7.37 (d, J ) 8.4 Hz, 2H), 6.68 (dd, J d ) 17.6, 10.8 Hz,
1H), 5.74 (d, J ) 17.6 Hz, 1H), 5.43 (s, 1H), 5.24 (d, J ) 10.8
Hz, 1H), 3.97 (dd, J d ) 11.6, 4.0 Hz, 1H), 3.81 (m, 1H), 2.87
(m, 1H), 2.46 (tt, J t ) 13.2, 4.8 Hz, 1H), 2.31 (dm, J d ) 14.4
Hz, 1H), 1.86 (dt, J d ) 13.2 Hz, J t ) 2.4 Hz, 1H), 1.58-1.82
(m, 7H), 1.23-1.43 (m, 2H), 1.15 (d, J ) 13.2 Hz, 1H). 13C NMR
(100 MHz, CDCl3): δ 139.2, 138.1, 136.3, 126.1, 126.0, 114.5,
104.2, 92.2, 80.2, 61.4, 46.1, 39.4, 37.5, 32.6, 28.3, 26.9, 26.5,
25.0. HRMS (M + Na) calcd 351.1567, found 351.1571.
Fund for generous financial support, and Professor
Wallace Peters and Mr. Brian Robinson for the efficacy
testing.
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P r ep a r a tion of p-Ca r boxyp h en yltr ioxa n e 5. A solution
of p-styryltrioxane 12 (61 mg, 0.19 mmol) and KMnO4 (118
mg) in acetone (6 mL) was stirred for 2 h (no starting material
by TLC) at room temperature, generating a precipitate. The
precipitate was filtered and washed with more acetone, and
then it was dissolved in MeOH (20 mL). The filtrate was
rotary-evaporated, and the residue was dissolved in water (4
mL). The aqueous solution was acidified with aqueous 0.5 N
HCl solution to pH 2, generating a white solid, which was
filtered and recrystallized from MeOH/i-PrOH at room tem-
perature to give 33 mg (50%) of 5: mp 153-154 °C (white
1
solid). H NMR (400 MHz, CD3OD): δ 7.93 (dm, J d ) 8.4 Hz,
2H), 7.56 (dm, J d ) 8.4 Hz, 2H), 5.51 (s, 1H), 3.80-3.96 (m,
2H), 2.86 (m, 1H), 2.27-2.40 (m, 2H), 1.59-1.91 (m, 8H), 1.32-
1.47 (m, 2H), 1.19 (d, J ) 14.0 Hz, 1H). 13C NMR (100 MHz,
CD3OD): δ 175.0, 143.3, 140.0, 130.2, 126.5, 105.7, 93.7, 81.8,
62.3, 47.7, 41.0, 38.8, 33.7, 29.4, 28.2, 27.8, 26.4. HRMS (M +
Na) calcd 369.1309, found 369.1321. Anal. Calcd for
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and Antimalarial Activities of Structurally Simplified 1,2,4-
Trioxanes Related to Artemisinin. Heteroat. Chem. 1995, 6,
105-116.
C
19H22O6: C, 65.88; H, 6.40. Found: C, 65.29; H, 6.23.
Ack n ow led gm en t. We thank the NIH (Grants AI-
34885 and RR-00052) and the Burroughs Wellcome
J M020210H