4-Aryl Pyrrolidines as Novel Orally Efficacious Antimalarial Agents. Part 2: 2-Aryl- N-(4-arylpyrrolidin-3-yl)acetamides

Article abstract of DOI:10.1021/acsmedchemlett.9b00123

Malaria is caused by infection from the Plasmodium parasite and kills hundreds of thousands of people every year. Emergence of new drug resistant strains of Plasmodium demands identification of new drugs with novel chemotypes and mechanisms of action. As

Full text of DOI:10.1021/acsmedchemlett.9b00123

Letter
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Cite This: ACS Med. Chem. Lett. XXXX, XXX, XXX−XXX
4‑Aryl Pyrrolidines as Novel Orally Efficacious Antimalarial Agents.
Part 2: 2‑Aryl‑N‑(4-arylpyrrolidin-3-yl)acetamides
Marvin J. Meyers,*,† Jianguang Liu,‡ Zhijun Liu,‡ Hongwei Ma,‡ Linglin Dai,§ Dickson Adah,§,∥
Siting Zhao,§ Xiaofen Li,§ Xiaorong Liu,‡ Yongzhi Lu,‡ Yanhui Huang,‡ Zhengchao Tu,‡
Xiaoping Chen,*,§ and Micky D. Tortorella*,‡,⊥
†Department of Chemistry, Saint Louis University, Saint Louis, Missouri 63103, United States
‡Drug Discovery Pipeline at the Guangzhou Institutes for Biomedicine and Health, Chinese Academy of Sciences, Guangzhou
510530, China
§Laboratory of Pathogen Biology, State Key Laboratory of Respiratory Disease, Center of Infection and Immunity, Guangzhou
Institutes of Biomedicine and Health, Chinese Academy of Sciences, Guangzhou 510530, China
∥University of Chinese Academy of Sciences, Beijing 100049, China
⊥Legion Pharma Co Ltd., Guangzhou 510530, China
S
* Supporting Information
ABSTRACT: Malaria is caused by infection from the
Plasmodium parasite and kills hundreds of thousands of
people every year. Emergence of new drug resistant strains of
Plasmodium demands identification of new drugs with novel
chemotypes and mechanisms of action. As a follow up to our
evaluation of 4-aryl-N-benzylpyrrolidine-3-carboxamides as
novel pyrrolidine-based antimalarial agents, we describe herein
the structure−activity relationships of the reversed amide
homologues 2-aryl-N-(4-arylpyrrolidin-3-yl)acetamides. Un-
like their carboxamide homologues, acetamide pyrrolidines do not require a third chiral center to be potent inhibitors of P.
falciparum and have good pharmacokinetic properties and improved oral efficacy in a mouse model of malaria. Compound
(−)-32a (CWHM-1552) has an in vitro IC50 of 51 nM in the P. falciparum 3D7 assay and an in vivo ED90 of <10 mg/kg/day
and ED99 of 30 mg/kg/day in a murine P. chabaudi model. Remarkably, the absolute stereochemical preference for this
acetamide series (3S,4R) is opposite of that determined for the homologous carboxamide series. Lead compounds for this class
have modest affinities for the hERG channel and inhibit CYP 3A4. Additional optimization is needed in order to eliminate these
undesired properties from this otherwise promising series of antimalarial compounds.
KEYWORDS: Aspartic protease inhibitors, pyrrolidines, antiplasmodial, antimalarial
he World Health Organization reports that there were
approximately ∼219 million new cases of malaria
T
resulting in an estimated 435,000 deaths in 2017.1 Given the
persistent emergence of drug resistant strains of Plasmodium
falciparum, the most deadly of the species causing malaria,
there is an ongoing need to identify novel chemotypes for new
antimalarial drugs. In the preceding paper,2 we described the
evaluation of pyrrolidine carboxamides as a novel class of
antimalarial compounds with the potential for optimization as
drug candidates (Figure 1). That work led to the discovery of
CWHM-1008 (1), which is a potent inhibitor of P. falciparum
growth in both the drug sensitive 3D7 and resistant Dd2
strains and is orally efficacious in a mouse model of malaria
(ED99 ≈ 30 mg/kg/day, p.o., q.d.).
Figure 1. Evaluation of 4-aryl pyrrolidines as novel antimalarials.
In our quest to identify related aryl pyrrolidines with an
improved oral efficacy, we synthesized a set of pyrrolidine
acetamides in which the carboxamide from the previous work
is “reversed” (Figure 1). Prototypical compounds from our
previous work included ( )-2 and ( )-3. These compounds
Received: March 20, 2019
Accepted: May 28, 2019
Published: May 28, 2019
© XXXX American Chemical Society
A
DOI: 10.1021/acsmedchemlett.9b00123
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have respective IC50 potency values in a SYBR Green Pf 3D7
assay3 of 190 and 250 nM, highlighting the need for a third
chiral center for good potency. Herein, we describe the
synthesis and structure−activity relationship (SAR) studies for
4-aryl pyrrolidine acetamides that do not rely on a third chiral
center for good potency and in vivo efficacy and pharmaco-
kinetic (PK) properties.
Table 1. Acetamide Aryl Ring SAR
Results and Discussion. Synthesis. Direct acetamide
analogs of ( )-2 were synthesized as racemic mixtures
according to the route illustrated in Scheme 1. Aldehyde 4
a
Scheme 1. Synthesis of Racemic Acetamide Analogs
a
Reagents and conditions: (a) nitromethane, NaOH, EtOH; (b)
Ac 2 O , D M AP , D C M ; ( c) N - ( me t h o x y m e th y l) -N -
(trimethylsilylmethyl)benzylamine, TFA, DCM; (d) Fe, NH4Cl,
EtOH, H2O; (e) 2-(4-(dimethylamino)phenyl)acetic acid, HATU,
TEA, DCM; (f) Pd/C, ammonium formate, MeOH.
a
was then condensed with nitromethane and NaOH followed
by dehydration with acetic anhydride to give the nitro olefin 5.
The azomethine ylide generated from N-(methoxymethyl)-N-
(trimethylsilylmethyl)benzylamine was reacted with the nitro
olefin 5 to stereoselectively give the trans-3 + 2 cycloaddition
product4,5 pyrrolidine intermediate ( )-6. The nitro group
was reduced with iron to furnish the 3,4-trans-pyrrolidinyl-
amine intermediate ( )-7a. Amide coupling followed by
deprotection of the N-benzylpyrrolidine using transfer hydro-
genation conditions with ammonium formate and Pd/C
provided the target analog ( )-9 as a racemic mixture.
Additional analogs ( )-10−23 were synthesized in the same
manner from their corresponding aryl aldehydes and aryl acetic
acids (see Supporting Information).
IC50 values are given as average potency values in the Pf 3D7 assay
SD (n ≥ 3). Standards chloroquine and artemesinin have IC50 values
of 54 0.4 and 33 0.6 nM, respectively.
phenyl ring with a pyridine (20−23) resulted in larger
reductions in potency.
Synthesis of Single Enantiomers. Single enantiomers were
prepared as illustrated in Scheme 2. Intermediate ( )-7 was
coupled with naproxen (24) to provide diastereoisomers that
were resolved by silica gel chromatography as (−)-25a and
(+)-25b. Independently, the diastereomers were hydrolyzed in
a three-step process by first acylation to the Boc amide 26a
followed by displacement of naproxen with hydrazine and
finally deprotection of the Boc group with trifluoroacetic acid
to give the aminopyrrolidine as a single enantiomer (28a).
Amide coupling and deprotection then furnished the target
pyrrolidines as single enantiomers (−)-30a and (+)-30b.
Analogs 31−44 were prepared by the analogous procedure.
Absolute stereochemistry was determined as (3S,4R)-config-
uration by small molecule X-ray powder diffraction with
(−)-32a (see Supporting Information). Absolute stereo-
chemical assignment was made for remaining analogs based
on their optical rotations with negative rotations being
assigned the (3S,4R)-configuration and positive rotations
being assigned the (3R,4S)-configuration.
Acetamide Aryl Ring SAR. The SAR for the terminal
acetamide aryl ring is shown in Table 1. The reversed amide
tended to be equipotent to slightly more potent than the direct
amide comparators (e.g., compare 9 to 2 and 10 to 3). The
SAR for the acetamides was similar to the carboxamides in our
previous work.2 Unadorned phenyl (11) was 20-fold less active
than dimethylaniline 9. Methoxy 12 and methyl 13 analogs
were modestly less potent than the dimethyl amine analog 9.
Removing the methyl groups from the aniline moiety led to a
30-fold loss in potency (14). Replacement of the aniline N
atom with CH resulted in a 6-fold loss in potency (15).
Extension of the dimethylaniline ring by one methylene led to
a 14-fold loss in potency (16). Moving the dimethylamino,
methoxy, and methyl groups to the meta position gave more
modest 2-fold losses in potency (17−19). Replacing the
Stereochemistry and 4-Aryl Ring SAR. The (+)- and
(−)-single enantiomers of 30−44 were assayed in the Pf 3D7
assay (Table 2). In our previous work with the carboxamide
B
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a
Scheme 2. Synthesis of single enantiomers.
a
Reagents and conditions: (a) HATU, TEA, DCM; (b) silica gel chromatography; (c) Boc2O, DMAP, THF; (d) hydrazine hydrate, MeOH; (e)
TFA, DCM; (f) 2-(4-(dimethylamino)phenyl)acetic acid, HATU, TEA, DCM; (g) Pd/C, ammonium formate, MeOH.
pyrrolidines, we had found that halo- and haloalkyl- phenyl and
pyridyl groups tended to be favored aryl groups in the 4-
position. In particular, CF3 and CF2CH3 were optimal
substituents. As illustrated with 30−32, the (−)-enantiomers
are 7- to 13-fold more potent than the (+)-enantiomers. This is
particularly remarkable since the preferred (3S,4R)-config-
uration for these acetamide pyrrolidines is the opposite of the
(+)-(3R,4S)-configuration that is preferred for the carbox-
amide pyrrolidines in our previous work.2
Since the (−)-enantiomer was clearly more potent than the
(+)-enantiomer, we focused our SAR studies on the
(−)-enantiomer (Table 2). In this series of compounds, 4-
SF5 (31a) was equipotent to 4-CF3 (30a) and only modestly
less potent than the CF2CH3 (32a), which was the most
potent compound we identified at 51 nM. CF2CF3, t-Bu, and
Br (33−35) were all potent in the 120−140 nM range.
Increasing the size of the 4-substituent to Ph, however, led to
large drops in potency (36). Similar to the carboxamide series,
3-substitution with Cl and SF5 was tolerated with no
detrimental effects (37−38). It is notable that SF5 is ∼5-fold
more potent in this acetamide series than the carboxamide
series.
As observed in the carboxamide series, heterocycles such as
pyridines, benzothiophenes, and benzofurans are tolerated. Di-
and pentafluoro ethylpyridines (39−40) are among the most
potent compounds we have assayed (IC50 = 60 and 63 nM,
respectively). Unsubstituted benzothiophene and -furan were
potent (41−42; IC50 = 140−150 nM), but substitution with
small halogens led to reductions in potency (43−44).
We also evaluated methylation of both the amide (45) and
pyrrolidine (46) (Figure 2). Methylation of the amide led to
less than 2-fold reduction in potency (compare 45 to 30a).
However, methylation of the pyrrolidine led to a more
substantial 6-fold reduction of potency (compare 46 to 10).
Potency against the Drug-Resistant Dd2 Strain of P.
falciparum. Lead compounds 30a, 31a, and 32a were profiled
in extensive side-by-side studies in the multidrug resistant Dd2
strain of P. falciparum (Table 3). All three compounds have
equivalent potency against the Pf 3D7 strain and the multidrug
resistant Dd2.
compounds for inhibition of human β-secretase (BACE1), Pf
plasmepsin II (PM-II), and Pf plasmepsin IV (PM-IV)
enzymes. However, none of the three compounds inhibited
these aspartic proteases (data not shown). To date, we have
not identified a biomolecular target for these pyrrolidines, and
we cannot rule out inhibition of other Plasmodium aspartic
proteases.
In Vitro Safety Profiling. In our previous work, we identified
the potential for binding the hERG channel.2 To address this
potential safety concern, we evaluated three lead compounds in
this series for hERG binding in a competitive binding assay
(Table 4). Compounds tested have binding affinities for hERG
ranging from 2 to 5 μM, giving modest 28- to 55-fold hERG/
3D7 selectivity ratios. We also evaluated these same three
compounds for inhibition of a panel of five human CYPs.
While the three compounds had minimal to no inhibition of
CYPs 1A2, 2D6, 2C9, and 2C19, they did moderately inhibit
CYP 3A4 with IC50 values from 871 to 2500 nM. Cytotoxicity
in HepG2 cells indicated no cytotoxicity at 5 μM (see
Supporting Information). Compound 32a was nontoxic at 50
μM, a selectivity index of nearly 1000-fold. However,
additional optimization work will need to be done in order
to reduce hERG binding and CYP 3A4 inhibition.
In Vivo Pharmacokinetics. Compounds 30a, 31a, and 32a
were selected for mouse PK studies. The compounds were
dosed as a single cassette by i.v. administration. All three
compounds were found to have respectable half-lives (2.7 to
7.0 h) and low clearance in mice (Table 5).
32a Is Orally Efficacious in a Mouse Model of Malaria. In
order to determine if the acetamides were orally efficacious,
lead compounds 30a, 31a, and 32a were evaluated in the P.
chabaudi murine Peters 4-day suppressive test.3,6 NIH mice
were inoculated with parasitized red blood cells. After 4 h, the
compounds were dosed orally once daily for 4 days.
Parasitemia levels were determined 24 h after the last
treatment (Table 6 and Figure S2). We initially tested all
three compounds at 30 mg/kg/day alongside CQ and
carboxamide 1 and found all three compounds to fully inhibit
parasitemia at 99.9% at 30 mg/kg/day, while carboxamide 1
exhibited 92.2% inhibition in this experiment (see Supporting
Information). Since our target ED99 was 10 mg/kg/day, we
elected to evaluate all three compounds at 10 and 32a at 3, 10,
and 30 mg/kg/day. Only the 30 mg/kg/day dose of 32a gave
Inhibition of Aspartic Proteases. Since our original
hypothesis was that these pyrrolidines might be aspartic
protease inhibitors,2 we profiled a select set of three
C
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day and an ED99 of 30 mg/kg/day. Compounds 30a and 31a
did reduce parasitemia at 10 mg/kg/day, but not to the same
level as 32a.
Table 2. Pyrrolidine Aryl Ring SAR
Compound concentrations in the plasma were determined at
1, 6, and 24 h post dose on the last day of treatment.
Compound concentrations of 32a in the plasma at 24 h
remained within 2-fold of the Pf 3D7 IC50 (51 nM) only for
the most fully efficacious dose of 30 mg/kg/day. At 10 mg/kg/
day, compound concentrations at 24 h post dose were 6- to 30-
fold lower than their respective Pf 3D7 IC50 values. Compound
32a narrowly misses our goal of in vitro EC50 < 10 nM but
satisfies our goal of in vivo ED90 < 10 mg/kg/day.
Conclusions. 4-Aryl 3-acetamide pyrrolidines are potent
inhibitors of P. falciparum and have good pharmacokinetic
properties and oral efficacy in a mouse model of malaria.
Compound 32a (CWHM-1552) has an in vitro IC50 of 51 nM
in the Pf 3D7 assay and an in vivo ED90 of <10 mg/kg/day and
ED99 of 30 mg/kg/day. Surprisingly, the absolute stereo-
chemical preference for this acetamide series is opposite of that
for the related carboxamide series we previously described.
Unfortunately, the lead compounds for this class have modest
affinities for the hERG channel (single digit micromolar) and
inhibit CYP 3A4 at submicromolar levels. Additional
optimization is needed in order to eliminate these undesired
properties from this otherwise promising series of antimalarial
compounds.
EXPERIMENTAL SECTION
■
(
)-(3R,4S)-1-Benzyl-3-nitro-4-(4-(trifluoromethyl)phenyl)-
pyrrolidine (6). To a stirred solution of 5 (3.06 g, 14.1 mmol) in
dichloromethane (50 mL) was added N-(methoxymethyl)-N-
(trimethylsilymethyl)-benzylamine (4.01 g, 16.9 mmol). The resulting
mixture was cooled to 0 °C, and a solution of TFA (0.001 mL, 0.1
equiv) in dichloromethane (1.0 mL) was added dropwise. The
reaction mixture was allowed to warm to room temp and stirred for
16 h. The solvent was removed by evaporation in vacuo, and the
resulting oil was purified by flash column chromatography (petroleum
ether/ethyl acetate: 80/20) to give the title compound (3.5 g, 72%
yield). 1H NMR (400 MHz, CDCl3) δ ppm 7.60 (d, J = 8.0, 2H), 7.45
(d, J = 8.0, 2H), 7.35 (m, 5H), 4.94 (br.s, 1H), 4.06 (br.s, 1H), 3.77
(s, 2H), 3.40 (br.s, 1H), 3.29 (m, 2H), 2.77 (br.s, 1H).
a
(
)-(3R,4S)-1-Benzyl-4-(4-(trifluoromethyl)phenyl)-
IC50 values are given as average potency values in the Pf 3D7 assay
pyrrolidin-3-amine (7). To a flask was added ( )-6 (3.5 g, 10
mmol), ammonium chloride (5.35 g, 100 mmol), iron (0.9 g, 50
mmol), EtOH (40 mL), and water (10 mL). The reaction flask was
replaced with argon three times and then heated at 80 °C for 4 h. The
reaction was cooled to room temp and filtered through Celite, rinsing
with ethyl acetate. The ethyl acetate layer was washed using additional
water, then brine, dried over sodium sulfate, and concentrated under
vacuum to give 2.56 g (80% yield) of the title compound as a brown
solid. The product was then used in the next step without further
purification. MS: m + 1 = 321.5.
SD (n ≥ 3).
(−)-(S)-N-((3S,4R)-1-Benzyl-4-(4-(trifluoromethyl)phenyl)-
pyrrolidin-3-yl)-2-(6-methoxynaphthalen-2-yl)propanamide
(25a) and (+)-(S)-N-((3R,4S)-1-Benzyl-4-(4-(trifluoromethyl)-
phenyl)pyrrolidin-3-yl)-2-(6-methoxynaphthalen-2-yl)-
propanamide (25b). To a suspension of ( )-7 (2.56 g, 8.0 mmol),
naproxen (1.7 g, 9.6 mmol), and HATU (3.65 g, 9.6 mmol) in
dichloromethane (50 mL) was added triethylamine (2.0 mL, 16.0
mmol). The reaction mixture was stirred at room temperature for 16
h. The mixture was diluted with dichloromethane (50 mL) and
washed with sat. sodium carbonate solution then brine, dried over
sodium sulfate, filtered, mixed with silica gel, and concentrated. The
residue was purified by flash column chromatography (DCM/ethyl
acetate: 20/1).
Figure 2. Methylated analogs. IC50 values are given as average
potency values in the Pf 3D7 assay (n ≥ 3).
Table 3. In Vitro Potency against Pf Dd2 Strain
Compound
Pf 3D7 IC50, nM (n)
Pf Dd2 IC50, nM (n)
30a
31a
32a
120 20 (3)
91 7 (6)
51 8 (7)
78 9 (5)
89 9 (5)
53 4 (5)
99.9% inhibition and 94% at 10 mg/kg/day. The dose−
response data allow us to approximate an ED90 of <10 mg/kg/
The first eluting compound was (−)-(S)-N-((3S,4R)-1-benzyl-4-
(4-(trifluoromethyl)phenyl)pyrrolidin-3-yl)-2-(6-methoxynaphthalen-
D
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Letter
a
Table 4. In Vitro Safety Profiling Data
Pf 3D7 IC50,
hERG IC50,
nM
hERG/3D7
Ratio
CYP 3A4 IC50,
nM
CYP 1A2 IC50,
nM
CYP 2D6 IC50,
nM
CYP 2C9 IC50,
nM
CYP 2C19 IC50,
nM
Compound
nM
30a
31a
32a
120
91
51
5,910
2,572
2,809
49
28
55
871
159
2,500
>100,000
>100,000
>100,000
24,500
90,020
40,600
98,100
36,600
>100,000
45,400
29,400
49,700
a
Pf = P. falciparum; IC50 = inhibitory concentration at 50%.
a
was stirred at room temp for 2 h. The solvent was removed in vacuo.
The residue was taken up in dichloromethane and washed with
saturated sodium carbonate solution followed by saturated sodium
chloride. The organic phase was dried over sodium sulfate, filtered,
and concentrated under vacuum to give 430 mg (95% yield) of the
title compound as a colorless oil. The product was then used in the
next step without further purification. MS: m + 1 = 321.5.
Table 5. Mouse Pharmacokinetic Data
Compound
t1/2, h
CLz, mL/min/kg
Vz, L/kg
30a
31a
32a
5.6
7.0
2.7
7.9
10.5
13.8
4.2
6.2
2.1
a
Compounds were dosed by IV cassette at 2 mg/kg/day to male KM
N-((3S,4R)-1-Benzyl-4-(4-(trifluoromethyl)phenyl)-
pyrrolidin-3-yl)-2-(4-(dimethylamino)phenyl)acetamide (29a).
To a suspension of 28a (430 mg, 1.34 mmol), 2-(4-(dimethylamino)-
phenyl)acetic acid (288 mg, 1.61 mmol), and HATU (611 mg, 1.61
mmol) in dichloromethane (10 mL) was added triethylamine (0.37
mL, 2.68 mmol). The reaction mixture was stirred at room temp for
16 h. The mixture was diluted with dichloromethane (50 mL) and
washed with saturated sodium carbonate solution then brine, dried
over sodium sulfate, filtered, and concentrated. The residue was
purified by flash column chromatography (petroleum ether/ethyl
acetate: 1/1) to give 483 mg (75% yield) of the title compound as a
white solid. MS: m + 1 = 482.2.
mice (n = 6). CLz = apparent rate of clearance; Vz = apparent volume
of distribution.
2-yl)propanamide (25a), which was obtained as a white solid (1.1 g,
27% yield). TLC Rf = 0.55 (DCM/ethyl acetate: 10/1). [α]D20 −42.1
(c 0.58, MeOH). MS: m + 1 = 533.1. 1H NMR (500 MHz, CDCl3) δ
ppm 7.71−7.67 (m, 3H), 7.50 (d, J = 7.05, 2H), 7.32 (m,8H), 7.16
(dd, J = 9.0, 2.0, 1H), 7.12 (s, 1H), 4.60 (br.s, 1H), 3.93 (s, 3H), 3.88
(br.s, 1H), 3.83 (br.s, 1H), 3.67 (q, J = 7.0, 1H), 3.44 (br.s, 2H), 3.05
(br.s, 1H), 2.91 (br.s, 1H), 2.69 (br.s, 1H), 1.54 (d, J = 7.5, 3H).
The second eluting compound was diastereomer (+)-(S)-N-
((3R,4S)-1-benzyl-4-(4-(trifluoromethyl)phenyl)pyrrolidin-3-yl)-2-
(6-methoxynaphthalen-2-yl)propanamide (25b), which was obtained
as a white solid (1.3 g, 31% yield). TLC Rf = 0.45 (DCM/ethyl
acetate: 10/1). [α]D20 +99.1 (c 0.21, MeOH). MS: m + 1 = 533.2. 1H
NMR (500 MHz, CDCl3) δ ppm 7.65 (dd, J = 8.5, 4.5, 2H), 7.60(s,
1H), 7.38 (d, J = 8.0, 2H), 7.32 (m, 6H), 7.12 (m, 4H), 4.58 (br, 1H),
3.92 (s, 3H), 3.78 (br, 2H), 3.65 (q, J = 7.0, 1H), 3.26 (t, J = 8.5, 1H),
3.15 (br, 1H), 3.04 (t, J = 9.0, 1H), 2.90 (br, 1H), 2.60 (t, J = 9.0,
1H), 1.51 (d, J = 7.0, 3H).
tert-Butyl (3S,4R)-1-Benzyl-4-(4-(trifluoromethyl)phenyl)-
pyrrolidin-3-ylcarbamate (27a). To a suspension of (−)-25a
(1.1 g, 2.1 mmol) and DMAP (303 mg, 2.5 mmol) in THF (25 mL)
was added di-tert-butyl dicarbonate (1.5 mL, 6.3 mmol). The reaction
mixture was heated to reflux for 4 h. After the solution was cooled to
room temp, MeOH (25 mL) and hydrazine (0.32 mL, 10.5 mmol)
were added, and the mixture was stirred at room temp for 12 h. The
solvent was removed by evaporation in vacuo, and the resulting oil
was purified by flash column chromatography (petroleum ether/ethyl
acetate: 60/40) to give the title compound (600 mg, 68% yield). MS:
m + 1 = 421.3. 1H NMR (400 MHz, CDCl3) δ ppm 7.39 (d, J = 4.4, 2
H), 7.33 (d, J = 4.4, 2H), 7.28 (m, 5H), 4.93 (br.s, 1H), 4.21 (br.s,
1H), 3.65 (s, 2H), 3.16 (br.s, 2H), 2.97 (t, J = 8.4, 1H), 2.69 (br.s,
1H), 2.50 (br.s, 1H), 1.41 (br.s, 9H).
(−)-2-(4-(Dimethylamino)phenyl)-N-((3S,4R)-4-(4-
(trifluoromethyl)phenyl)pyrrolidin-3-yl)acetamide (30a). To a
flask was added 29a (483 mg,1.0 mmol), ammonium formate (315
mg, 5.0 mmol), Pd/C (50 mg, 10%), and MeOH (10 mL). The
reaction flask was flushed with argon three times and then heated at
70 °C for 30 min. The reaction was cooled to room temp and filtered
through Celite, rinsing with MeOH. The solvent was removed by
evaporation in vacuo, and the residue was purified by flash column
chromatography (DCM/NH3 in MeOH: 20/1) to give the title
20
compound 234 mg (60% yield). [α]D −58.2 (c 0.22, MeOH). MS:
1
m + 1 = 392.6. H NMR (500 MHz, DMSO-d6) δ ppm 8.19 (d, J =
7.5, 1H), 7.62 (d, J = 8.0, 2H), 7.47 (d, J = 8.0, 2H), 6.97 (d, J = 8.5,
2H), 6.61 (d, J = 9.0, 2H), 4.16 (m, 1H), 3.21 (d, J = 3.0, 2H), 3.15
(m, 3H), 2.84 (s, 6H), 2.80 (dd, J = 11.2, 8.0, 1H), 2.60 (dd, J = 10.8,
6.4, 1H). 13C NMR (125 MHz, DMSO-d6) δ 171.0, 149.6, 148.1,
129.7, 128.7, 127.4 (q, J = 31.3), 125.5 (t, J = 3.8), 124.9 (q, J =
270.0), 124.4, 112.8, 58.4, 53.9, 53.5, 51.6, 42.0, 40.7. HRMS (ESI)
m/z: [M + H]+ Calcd for C21H25F3N3O 392.1944; found 392.1962.
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acsmedchem-
lett.9b00123.
(3S,4R)-1-Benzyl-4-(4-(trifluoromethyl)phenyl)pyrrolidin-3-
amine (28a). To a suspension of 27a (600 mg, 1.42 mmol) in
dichloromethane (2.0 mL) was added TFA (2.0 mL), and the mixture
Table 6. In Vivo Efficacy of Acetamide Pyrrolidines in P. chabaudi ASS Infected Mice
b
Plasma Compound Concentration (nM)
a
Oral Dose (qd)
% Inh. of Growth
1 h
6 h
24 h
30a, 10 mg/kg/day
31a, 10 mg/kg/day
32a, 3 mg/kg/day
32a, 10 mg/kg/day
32a, 30 mg/kg/day
CQ, 10 mg/kg/day
61.2 6.6
65.3 11.3
34.0 16.7
94.1 1.5
99.9 0.0
99.9 1.1
255 60
129 22
114 21
389 148
1310 420
80.7 9.6
181 55
119 56
34.1 5.0
48.9 4.0
1150 500
83.4 8.9
7.4 4.2
14.9 7.0
6.6 2.0
1.7 0.3
28.5 20.4
68.6 12.0
a
b
Inhibition of parasitemia after 4 days of qd oral dosing. Plasma compound concentrations were determined at the designated hour post dosing on
day 4. n = 6 animals/group. nd = not determined.
E
DOI: 10.1021/acsmedchemlett.9b00123
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ACS Medicinal Chemistry Letters
Letter
Tortorella, M. D. 4-Aryl pyrrolidines as a novel class of orally
efficacious antimalarial agents. Part 1: Evaluation of 4-aryl-N-
benzylpyrrolidine-3-carboxamides. J. Med. Chem. 2019, 62, 3503.
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Qin, L.; Chen, X. Synergy of the antiretroviral protease inhibitor
indinavir and chloroquine against malaria parasites in vitro and in
vivo. Parasitol. Res. 2011, 109, 1519−1524.
(4) Hosomi, A.; Sakata, Y.; Sakurai, H. Chemistry of organosilicon
compounds. 195. N-(Trimethylsilylmethyl)aminomethyl ethers as
azomethine ylide synthons. A new and convenient access to
pyrrolidine derivatives. Chem. Lett. 1984, 13, 1117−1120.
(5) Terao, Y.; Kotaki, H.; Imai, N.; Achiwa, K. Trifluoroacetic acid-
catalyzed 1,3-cycloaddition of the simplest iminium ylide leading to 3-
or 3,4-substituted pyrrolidines and 2,5-dihydropyrroles. Chem. Pharm.
Bull. 1985, 33, 2762−2766.
(6) He, Z.; Qin, L.; Chen, L.; Peng, N.; You, J.; Chen, X. Synergy of
human immunodeficiency virus protease inhibitors with chloroquine
against Plasmodium falciparum in vitro and Plasmodium chabaudi in
vivo. Antimicrob. Agents Chemother. 2008, 52, 2653−2656.
Synthetic procedures and characterization data for
compounds 5, 8−23, 30b, and 31−46, 1H NMR spectra
for (−)-30a, (−)-31a, and (−)-32a, X-ray crystallo-
graphic data for 32a, and biological assays (PDF)
AUTHOR INFORMATION
Corresponding Authors
*(M.J.M.) E-mail: marvin.j.meyers@slu.edu. Phone: 1-314-
977-5197.
*(X.C.) E-mail: chen_xiaoping@gibh.ac.cn.
*(M.D.T.) E-mail: m.tortorella@gibh.org.
ORCID
Marvin J. Meyers: 0000-0001-5484-619X
Author Contributions
M.J.M. designed compounds. J.L., Z.L., and H.M. synthesized
compounds. L.D., D.A., S.Z., and X.Li tested compounds for
antimalarial activity. X.Liu determined PK of compounds. Y.L.
determined absolute stereochemistry of compounds. Y.H. and
Z.T. determined the hERG, CYP, and cytotoxicity of
compounds. M.J.M., X.C., and M.D.T. designed and directed
the experiments. M.J.M. and J.L. wrote the manuscript. All
authors have approved of the final version of the manuscript.
All authors have given approval to the final version of the
manuscript.
■
Funding
Research reported in this publication conducted at Saint Louis
University was supported by Saint Louis University and the
National Institute of Allergy and Infectious Diseases of the
National Institutes of Health under Award Number
R01AI106498. Research reported in this publication con-
ducted at the Guangzhou Institutes of Biomedicine and
Health, Chinese Academy of Sciences, was supported by
Bureau of Science and Information Technology of Guangzhou
Municipality Grant number 2009Z1-E841 and Natural Science
Foundation of China (NSFC) and by the Ministry of Sciences
and Technology Key Program (No. 2016YFE0107300). The
content is solely the responsibility of the authors and does not
necessarily represent the official views of Saint Louis
University, the Guangzhou Institutes of Biomedicine and
Health, Chinese Academy of Sciences, the Natural Science
Foundation of China, or the National Institutes of Health.
Notes
The authors declare the following competing financial
interest(s): X.C., L.D., J.L., H.M., M.D.T., and M.J.M. are
inventors on a patent application filed by Legion Pharma
claiming compounds in this manuscript. M.D.T. owns stock in
Legion Pharma.
ACKNOWLEDGMENTS
The authors would like to thank Dr. Bryan Yeung for helpful
discussions.
■
ABBREVIATIONS
Pf, Plasmodium falciparum; PM, plasmepsin; SI, selectivity
index; CQ, chloroquine; mg/kg/day, milligrams per kilogram
■
REFERENCES
■
(1) World Malaria Report 2018; World Health Organization:
Geneva, 2018.
(2) Meyers, M. J.; Liu, J.; Xu, J.; Leng, F.; Guan, J.; Liu, Z.; McNitt,
S. A.; Qin, L.; Dai, L.; Ma, H.; Adah, D.; Zhao, S.; Li, X.; Polino, A. J.;
Nasamu, A. S.; Goldberg, D. E.; Liu, X.; Lu, Y.; Tu, Z.-C.; Chen, X.;
F
DOI: 10.1021/acsmedchemlett.9b00123
ACS Med. Chem. Lett. XXXX, XXX, XXX−XXX