Synthesis and anthelmintic properties of arylquinolines with activity against drug-resistant nematodes

Article abstract of DOI:10.1016/j.bmcl.2005.07.044

2,4-Disubstituted quinolines with additional substituents in positions 5-8 have been found to have anthelmintic properties. A number of 2,4-dimethoxy-6- or 8-arylquinolines have potent activity against the sheep nematode Haemonchus contortus, with LD

Full text of DOI:10.1016/j.bmcl.2005.07.044

Bioorganic & Medicinal Chemistry Letters 15 (2005) 4806–4808
Synthesis and anthelmintic properties of arylquinolines with
activity against drug-resistant nematodes
a
Sharon Rossiter, Jean-Marie Peron, Philip J. Whitfield and Keith Jones
b
c
a,b,
*
´
aDepartment of Chemistry, KingÕs College London, Strand, London WC2R 2LS, UK
bSchool of Chemical and Pharmaceutical Sciences, Kingston University, Penrhyn Road, Kingston-upon-Thames, Surrey KT1 2EE, UK
cDivision of Life Sciences, Franklin-Wilkins Building, KingÕs College London, 150 Stamford Street, London SE1 9NN, UK
Received 27 May 2005; revised 14 July 2005; accepted 14 July 2005
Available online 13 September 2005
Abstract—2,4-Disubstituted quinolines with additional substituents in positions 5–8 have been found to have anthelmintic proper-
ties. A number of 2,4-dimethoxy-6- or 8-arylquinolines have potent activity against the sheep nematode Haemonchus contortus, with
LD99 values of the same order of magnitude as levamisole. These arylquinolines maintain their activity against levamisole-, ivermec-
tin- and thiabendazole-resistant strains of H. contortus.
ꢀ 2005 Elsevier Ltd. All rights reserved.
Parasitic nematode infections are a continuing threat in
both human and animal medicine. The most commonly
used classes of drugs to treat such infections are the
benzimidazoles, such as thiabendazole 1, imidazo-thiaz-
oles, such as levamisole 2, and avermectins (obtained
from the fermentation products of Streptomyces avermi-
tilis). There is evidence of emerging resistance to some
drugs in the developing world,1 and in some areas with
high agricultural dependence multiple resistance to all
major drug classes is appearing in livestock.2 Alterna-
tives to these classes of drug are now being sought (see
Fig. 1).
H
N
N
S
S
N
N
N
thiabendazole 1
levamisole 2
Figure 1.
OMe
N
H
O
We have recently published a concise synthesis of the
phenylquinoline alkaloid atanine, 3,3 shown to be active
against larval stages of the trematode parasite Schistoso-
ma mansoni, the cause of schistosomiasis (bilharzia), a
major health issue in developing countries (see Fig. 2).4
3
Figure 2.
stages and the model nematode Caenorhabditis elegans
revealed that some of these intermediates exhibited
anti-nematode activity, differing from the pattern of
activity against schistosomes.5
As part of our programme of synthesis and testing of
novel atanine analogues, we synthesized a number of
intermediate trisubstituted quinolines with substituents
in ring positions 5–8. Tests against Sc. mansoni larval
From these early biological results, we became interest-
ed in aryl-substituted quinolines, and so we set out to
investigate the synthesis of these novel 2,4-dimethoxy
aryl-substituted quinolines by exploring the Suzuki cou-
pling of 5-, 6-, 7- and 8-bromoquinoline intermediates.
Keywords: Quinolines; Suzuki coupling; Anthelmintics.
*
Corresponding author at present address: CR-UK Centre for Cancer
Therapeutics, The Institute of Cancer Research Haddow Laborato-
ries, 15 Cotswold Road, Belmont, Sutton, Surrey SM2 5NG, UK.
Tel.: +44 0 208 722 4334; fax: +44 0 208 722 4324; e-mail:
keith.jones@icr.ac.uk
Substituted 2,4-dimethoxyquinolines were synthesized by
condensation/cyclization of the appropriately substituted
0960-894X/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.07.044

S. Rossiter et al. / Bioorg. Med. Chem. Lett. 15 (2005) 4806–4808
4807
aniline 4 with malonic acid and phosphoryl chloride to
give the 2,4-dichloroquinolines 5, followed by displace-
ment by methoxide ion to give the required quinolines
6 (Scheme 1).6
The bromo-2,4-dimethoxyquinolines 7 were then cou-
pled to the required aryl groups under Suzuki condi-
tions7 to yield the arylquinolines 8 (Scheme 2). They
proceeded in good yield, although it was observed that
8-bromoquinolines were much more sensitive, requiring
careful purification of substrate, reagents and solvent
along with strictly oxygen-free reaction conditions to
give consistent yields.8
For our proposed synthesis of arylquinolines, the
bromoquinoline precursors were required. The reaction
of 3-bromoaniline gave a mixture of 5- and 7-bromo-
quinolines, which were separable by column chromatog-
raphy (Table 1).
A number of 2,4-disubstituted quinolines (ca. 80) were
tested against the agriculturally important parasitic
nematode Haemonchus contortus, using the commer-
cial NemaTox larval development screen used for
determining drug susceptibility.9 It was observed that
greater than 40% of these compounds exhibited
Cl
HO2C
CO2H
nematocidal
activity
(LD99 < 100 lg/mL),
with
those exhibiting LD99 better than 25 lg/mL shown
in Table 2.
NH2
POCl3, 5h, reflux
R
N
Cl
R
4
5
In particular, it appeared that 6- and 8-substituted
2,4-dimethoxyquinolines showed the greatest activity
against H. contortus. Five compounds, including the
arylquinolines 13–16, had LD99 of 12.5 lg/mL or lower
in this first screen, showing potential for useful anti-
nematode activity. The LD99 of compounds 15 and 16,
3.1 lg/mL, was of the same order as the commercial
nematocides, levamisole and closantel. These five most
active compounds were resynthesized in gram quantities
for further investigation (see Fig. 3).
NaOMe, MeOH
48h, reflux
OMe
N
OMe
R
6
Scheme 1. Synthesis of substituted 2,4-dimethoxyquinolines.
Table 1. Yields of bromoquinolines 5 and 6 in Scheme 1
Entry
4
5 (yield %)
6 (yield %)
OMe
N
OMe
N
OMe
N
1
R = 2-Br
R = 3-Br
R = 8-Br (31)
R = 5-Br (6)
R = 7-Br (11)
R = 6-Br (28)
R = 8-Br (64)
R = 5-Br (82)
R = 7-Br (76)
R = 6-Br (93)
2a
Cl
OMe
OMe
OMe
3
R = 4-Br
12
a 3-Bromoaniline led to a mixture of 5- and 7-bromoquinolines 5.
Yields refer to isolated, purified material.
14
13
OMe
MeO
OMe
N
OMe
N
OMe
OMe
N
ArB(OH)2, Pd(PPh3)4
PhMe, Na2CO3
80˚C, 48h
68-90%
OMe
OMe
Ar
N
OMe
Br
OMe
8
16
7
15
Scheme 2. Synthesis of arylquinolines via Suzuki coupling.
Figure 3.
Table 2. LD99 values for compounds 9–16 (substituted at positions 2–8) against H. contortus
Compound
C-2
C-3
C-4
C-5
C-6
C-7
C-8
LD99 (lg/mL)
9a
10
11b
12
13
14
15
16
OMe
OMe
Cl
Ph
H
H
H
H
H
H
H
OMe
OMe
OMe
OMe
OMe
OMe
OMe
OMe
H
Me
H
H
H
H
H
H
H
H
Me
H
H
H
H
H
H
H
H
H
H
Ph
25
25
H
H
Cl
25
OMe
OMe
OMe
OMe
OMe
12.5
12.5
12.5
3.1
3.1
H
H
Ph
4-MeO-C6H4
H
H
4-MeO-C6H4
a Synthesized from 2,4-dimethoxyquinoline by bromination at position 3 and subsequent Suzuki coupling.5,10
b Product of incomplete substitution of 2,4-dichloroquinoline by methoxide.

4808
S. Rossiter et al. / Bioorg. Med. Chem. Lett. 15 (2005) 4806–4808
Table 3. LD99 values of compounds 12–16 against susceptible and drug-resistant nematodes
Compound
LD99 (lg/mL)
H. contortus H. contortus VSRG,
susceptible
H. contortus Lawes,
H. contortus CAVR, T. colubriformis O. circumcincta
ivermectin resistant
benzimidazole resistant levamisole and
benzimidazole resistant
12
13
14
15
16
1
13
13
4.4
8.8
6.3
6.3
3.1
25
50
13
6.3
6.3
6.3
3.1
3.1
0.16
1.6
6.3
3.1
2.2
5
3.1
3.1
3.1
3.1
6.3
3.1
3.1
3.1
6.3
3.1
1.6
1.6
5
>100
0.16
0.78
nt
nt
nt
nt
2
1.6
nt, not tested.
3. Jones, K.; Roset, X.; Rossiter, S.; Whitfield, P. J. Org.
Biomol. Chem. 2003, 1, 4380.
Compounds 12–16 were tested against susceptible
strains of H. contortus, strains resistant to benzothiaz-
oles (VSRG strain), ivermectin (CAVR strain) or both
benzothiazoles and levamisole (Lawes strain) plus sus-
ceptible strains of Trichostrongylus colubriformis and
Ostertagia circumcincta. Results are shown in Table 3,
with activities of thiabendazole 1 and levamisole 2 for
comparison.
4. Perrett, S.; Whitfield, P. J. Planta Med. 1995, 61, 276.
5. Rossiter, S. Ph.D. thesis, University of London, 1999.
6. Ziegler, E.; Gelfert, K. Monatsh. Chem. 1959, 90, 822.
7. Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457.
8. Synthesis of arylquinolines: typical procedure: 8-bromo-
2,4-dimethoxyquinoline (0.4 g, 1.5 mmol) was dissolved
in toluene (10 mL) under argon. Tetrakis-(triphenylphos-
phine)palladium (0) (52 mg, 3 mol%) and aqueous sodi-
um carbonate (2 mL of a 2 M solution) were added, and
the mixture was stirred for 5 min. Benzeneboronic acid
(0.20 g, 1.7 mmol) in ethanol (1 mL) was added, and the
mixture was then heated under reflux for 48 h. After
cooling, the mixture was poured into a separating funnel,
and the reaction flask was washed with water (20 mL)
and ether (20 mL); the washings being added to the
separating funnel. The aqueous layer was extracted with
ether (3 · 20 mL), and the combined organic layers were
dried over magnesium sulfate before removal of the
solvent under reduced pressure. The crude product was
purified by column chromatography (9:1 hexane–EtOAc)
to yield 90% of 2,4-dimethoxy-8-phenylquinoline as white
plates, mp (CH2Cl2/MeOH) 110–112 ꢁC; found M+:
265.1105, C17H15NO2 requires 265.1103; 1H NMR
(CDCl3): d 8.16 (1H, dd, J 8.2, 1.5 Hz, H5), 7.90 (2H,
dd, J 8.3, 1.5 Hz, H20, H60), 7.77 (1H, dd, J 7.2, 1.5 Hz,
H7), 7.54 (2H, m, H6 and H40), 7.47 (2H, dd, J 8.3,
7.2 Hz, H30, H50), 6.29 (1H, s, H3), 4.01 (3H, s, OMe),
3.99 (3H, s, OMe); 13C NMR (CDCl3): d 164.5, 163.4
(C2, C4), 144.7, 140.4, 138.5 (C10, C8, C8a), 131.3, 131.1,
127.9, 127.2, 123.5, 121.8 (C5, C6, C7, C20–60), 120.1
(C4a), 90.7 (C3), 56.2 (OMe), 53.8 (OMe); Anal. Calcd
for C17H15NO2: C, 76.96; H, 5.70; N, 5.28. Found: C,
76.91; H, 5.65; N, 5.19.
Of these compounds, 15 and 16 exhibited the greatest
activity against susceptible strains of H. contortus
(3.1 lg/mL), comparable in potency to levamisole. Com-
pounds 15 and 16 were also active against the various
drug-resistant strains of H. contortus, with 16 proving
to be even more potent (LD99 1.6 lg/mL) against both
the multiple-resistant Lawes strain and the ivermectin-
resistant CAVR strain. There is also evidence of activity
against the important parasitic nematodes T. colubrifor-
mis and O. circumcincta.
In summary, we have prepared novel arylquinolines in
good yield via Suzuki coupling of substituted bromo-
quinolines. We have demonstrated that a number of
these quinolines, in particular the 6-arylquinolines 15
and 16, show promising potency against susceptible
and drug-resistant strains of an important nematode tar-
get and represent a new class of anthelmintic compounds.
There is obvious potential for lead optimization and fur-
ther development to offer a new line of defence against
drug-resistant parasitic nematode infections.
9. (a) Lacey, E.; Redwin, J. M.; Gill, J. H.; Demargheriti,
V. M.; Waller, P. J. In Resistance of Parasites to
Antiparasitic Drugs; MSD AGVET: Rahway, NJ, USA,
p 177; (b) NemaTox assay: 80–100 nematode eggs were
added to each well of a multiwell plate containing the
compound under investigation (at a range of concentra-
tions from 100 lg/mL downwards in sequential twofold
dilutions) in an agar matrix. The wells were supplement-
ed with nutrient medium and incubated at 26 ꢁC until
larvae in the control wells had developed to the 1.3 larval
stage. On Day 5, a qualitative assessment of the larvae
was performed to determine the lowest concentration at
which development was inhibited in 99% of the larvae
present.
Acknowledgments
This work was supported by a Wellcome Trust student-
ship (S.R.). The authors thank Schering-Plough Animal
Health for arranging the biological testing.
References and notes
1. Albonico, M.; Bickle, Q.; Ramsan, M.; Montresor, A.;
Savioli, L.; Taylor, M. Bull. World Health Organ. 2003,
81, 343.
2. (a) Besier, R. B.; Love, S. C. J. Aust. J. Exp. Agr. 2003, 43,
1383; (b) Thomaz-Soccol, V.; de Souza, F. P.; Sotomaior,
C.; Castro, E. A.; Milczewski, V.; Mocelin, G.; Silva, M.
D. C. P. E. Braz. Arch. Biol. Technol. 2004, 47, 41.
10. Stavenuier, J.; Hamzink, M.; van der Hulst, R.;
Zomer, G.; Westra, G.; Kriek, E. Heterocycles 1987,
10, 2711.