Parasiticidal 2-alkoxy- and 2-aryloxyiminoalkyl trifluoromethanesulfonanilides

Article abstract of DOI:10.1016/j.bmcl.2007.10.090

A series of novel 2-alkoxy- and 2-aryloxyiminoalkyl trifluoromethanesulfonanilide derivatives have shown significant in vitro parasiticidal activity against the ectoparasites Ctenocephalides felis and Rhipicephalus sanguineus. A number of these compounds also displayed significant in vitro endoparasite activity against the nematode Haemonchus contortus. Crown Copyright

Full text of DOI:10.1016/j.bmcl.2007.10.090

Available online at www.sciencedirect.com
Bioorganic & Medicinal Chemistry Letters 18 (2008) 252–255
Parasiticidal 2-alkoxy- and 2-aryloxyiminoalkyl
trifluoromethanesulfonanilides
Abdelselam Ali,a Timothy M. Altamore,a Marianne Bliese,a Petr Fisara,b Andris J. Liepa,a
Adam G. Meyer,a,* Oahn Nguyen,a Roger M. Sargent,b David G. Sawutz,c
David A. Winkler,a Kevin N. Winzenberga and Angela Ziebella
aCSIRO Molecular and Health Technologies, Bag 10, Clayton South, Vic. 3169, Australia
bSchering-Plough Pty. Ltd, 11 Gibbon Road, Baulkham Hills, NSW 2153, Australia
cSchering-Plough Research Institute, 2015 Galloping Hill Road, Kenilworth, NJ 07033-1300, USA
Received 7 September 2007; revised 22 October 2007; accepted 25 October 2007
Available online 30 October 2007
Abstract—A series of novel 2-alkoxy- and 2-aryloxyiminoalkyl trifluoromethanesulfonanilide derivatives have shown significant
in vitro parasiticidal activity against the ectoparasites Ctenocephalides felis and Rhipicephalus sanguineus. A number of these com-
pounds also displayed significant in vitro endoparasite activity against the nematode Haemonchus contortus.
Crown copyright Ó 2007 Published by Elsevier Ltd. All rights reserved.
The cat flea, Ctenocephalides felis, and the brown dog
CF3SO2HN
R
CF3SO2HN R1
tick, Rhipicephalus sanguineus, are prevalent nuisance
ectoparasite species afflicting companion animals.1,2
These pests cause blood loss anemia, allergic dermatitis,
and are vectors for infectious pathogens.3 Although the
introduction of the topical insecticides fipronil, imida-
cloprid, and selamectin has revolutionized flea control
on cats and dogs, of these, only fipronil and selamectin
are known to be efficacious as acaricides. Moreover,
since development of resistance to these parasiticides is
a distinct possibility,4 new agents to control fleas and
ticks must continue to be discovered.
O
N
R2
1
2
R
2a R = 4-Cl, R1 = Et,
1a R = 4-Cl, 2-CO2Me
1b R = 4-OCF3
R2 = -CH2-cyclohexyl
1c R = 4-OCF2CHF2
Figure 1.
known to act as uncouplers of oxidative phosphoryla-
tion in mitochondria.6
Trifluoromethanesulfonanilide (TFMS) derivatives 1 are
reported to display potent insecticidal, acaricidal, and
nematicidal properties.5,6 For example, 4-chloro-2-
methoxycarbonyl TFMS 1a (amidoflumet) is under
development for use against house dust mites,5 whereas
the 4-fluoroalkoxy TFMS compounds 1b, 1c control
Haemonchus contortus in sheep at low dosages6
(Fig. 1). Compounds containing the TFMS moiety are
As part of a program to discover new drugs to control
important ectoparasites afflicting companion animals,
a set of novel 2-alkoxyiminoalkyl TFMS compounds 2
were screened in a commercial, single-dose (1.26 lg/
cm2) cat flea assay.7 An O-alkyloxime ether, 4-chloro-
2-[1-(cyclohexylmethoxyimino)propyl] TFMS 2a, gave
100% mortality in the cat flea assay, with a correspond-
ing LC50 = 29 ng/cm2 for C. felis. This compound subse-
quently gave 100% mortality in a single-dose (10 lg/tick)
brown dog tick assay and an LD50 = 3.4 lg/tick for
R. sanguineus,7 demonstrating that the 2-alkoxyimi-
noalkyl TFMS template may deliver significant insecti-
cidal and acaricidal activity. Furthermore, 2a showed
activity against the endoparasite H. contortus
Keywords: Trifluoromethanesulfonanilide; Oxime ether; Parasiticide;
Ctenocephalides felis (cat flea); Rhipicephalus sanguineus (brown dog
tick); Haemonchus contortus.
*
Corresponding author. Tel.: +61 3 9545 2476; fax: +61 3 9545
2376; e-mail: adam.meyer@csiro.au
0960-894X/$ - see front matter Crown copyright Ó 2007 Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2007.10.090

A. Ali et al. / Bioorg. Med. Chem. Lett. 18 (2008) 252–255
253
CF3SO2HN R1
CF3SO2HN R1
the reaction of 2-keto TFMS precursors 3 with O-alkyl-
oxyamines 4 (Scheme 1 and Table 1).10,11
O
N
R2
i)
O
H2NOR2
R
R
As shown in Table 1, most O-alkyloxime ethers 2 dis-
played excellent activity against cat flea, although none
were as potent as the commercial flea control drug fipro-
nil. The best activity was obtained with an electron-
withdrawing moiety on the TFMS ring (preferably
R = 4-Cl), R1 as a small alkyl group (methyl or ethyl),
and R2 as a small hydrophobic group.12 For example,
the O-(cyclopropylmethyl) derivative 11 gave an
LC50 = 5 ng/cm2. Significantly, most O-alkyloxime
ethers highly active against C. felis were also similarly
active against R. sanguineus, with some derivatives hav-
3
4
2
Scheme 1. Reagents: (i) N-(R2O)phthalimide, (CH3)2N(CH2)2NH2,
EtOH then AcOH to pH 4 or HClÆH2NOR2, NaOAc, EtOH.
(LD99 = 3 lM),8 indicative of important broad-spec-
trum endectoparasiticidal activity.
To probe SAR associated with compound 2a, a library
of O-alkyloxime ether analogs 2 was prepared from
Table 1. Activity of compounds 2a, 5–39 against C. felis (C.f.), R. sanguineus (R.s.), and H. contortus (H.c)a
CF3SO2HN R1
O
N
R2
2a, 5-39
R
Compound
R
R1
R2
C.f. % Mortalityb
C.f. LC50
(ng/cm2)
R.s. %
Mortalityb
R.s. LD50
(lg/tick)
H.c. LD99
(lM)
2a
5
4-Cl
4-Cl
4-Cl
4-Cl
5-CF3
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
5-CF3
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Br
5-F
Et
–CH2-cyclohexyl
–CH2-cyclohexyl
-CH2-cyclohexyl
-CH2-cyclohexyl
–CH2-cyclohexyl
–CH2-cyclopentyl
–CH2-cyclopentyl
–CH2-cyclopropyl
–CH2-cyclopropyl
Cyclohexyl
Cyclohexyl
Cyclohexyl
Cyclohexyl
Cyclohexyl
Cyclopentyl
Cyclopentyl
Me
100
96
29
100
100
3.4
7
Me
n-Pr
Ph
Et
6
70
11
7
8
97
52
17
8
9
10
Me
Et
97
97
18
100
90
2.2
7.5
36
11
12
Me
Et
100
100
100
100
43
5
8
100
100
100
100
1.0
1.2
13
14
Me
Et
5.7
15
16
n-Pr
Ph
Me
Me
Et
12
4
45
17
18
100
100
100
100
100
100
100
45
100
100
93
19
20
21
15
11
1.5
25
Me
Et
21
22
Me
Et
95
85
0.89
1.2
16
Me
Me
Me
Me
Me
Me
Et
>15
>13
>15
>15
>16
23
24
Et
Et
100
8
25
26
6-OMe
H
Et
Et
92
90
95
27
28
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
i-Pr
i-Pr
100
100
100
100
100
100
100
100
100
100
100
100
100
100
92
29
30
Me
Et
t-Bu
t-Bu
41
43
6
1.4
1.5
16
18
90
82
31
32
Me
Et
–CH2CF3
–CH2CF3
–(CH2)2OMe
–(CH2)2OMe
Allyl
0.94
80
33
34
Me
Et
12
100
95
0.71
35
36
Me
Et
100
100
100
100
70
Allyl
21
11
0.67
0.99
0.86
2.5
32
37
38
Me
Et
Propargyl
Propargyl
–CH2-20-thienyl
27
20
35
39
Et
7
0.1–0.2
Fipronil
Permethrin
Ivermectin
Levamisole
0.14–0.22
0.006–0.007
0.71–1.3
a No entry indicates that the compound was not assayed.
b Measured at 24 h.

254
A. Ali et al. / Bioorg. Med. Chem. Lett. 18 (2008) 252–255
ing levels of dog tick activity comparable to the com-
mercial ectoparasiticide permethrin: for example, com-
pound 36 gave an LD50 = 0.67 lg/tick for R. sanguineus.
(Scheme 1 and Table 2).10,11 A number of these deriva-
tives displayed high mortality in a single-dose cat flea as-
say, with some having LC50 values comparable to the
best O-alkyloxime ether TFMS compounds. Good
activity was observed for analogs where R1 was a methyl
or ethyl group,13 and where the O-benzyl moiety con-
tained at least one electron-withdrawing group: for
example, compounds 40 and 45. Two 5-trifluoromethyl
TFMS derivatives, compounds 61 and 62, were also
The high activity against C. felis of compound 39,
an O-(20-thienylmethyl) derivative (LC50 = 7 ng/cm2),
prompted the preparation of a set of isosteric O-ben-
zyloxime ether analogs 40–62 from the reaction of 2-car-
bonyl TFMS precursors 3 with O-benzyloxyamines 4
Table 2. Activity of compounds 40–80 against C. felis (C.f.), R. sanguineus (R.s.), and H. contortus (H.c.)a
CF3SO2HN R1
O
N
40-80
R3
n
R
Compound
R
R1
n
R3
C.f. % Mortalityb
C.f. LC50
(ng/cm2)
R.s. %
Mortalityb
R.s. LD50
(lg/tick)
H.c. LD99
(lM)
40
41
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
5-CF3
5-CF3
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
5-CF3
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
Et
Et
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
4-Cl
4-Br
100
78
12
17
83
58
90
2.5
1.7
1.8
0.84
6.9
2.7
0.56
0.84
0.63
1.3
7.2
3
42
43
Et
Et
4-CF3
4-t-Bu
2-CF3
2,4-DiCF3
2,4-DiCl
2,3-DiCl
3,4-DiCl
2,4-DiF
4-Cl
98
8c
2.7
44
45
Et
Et
96
36
19
31
88
100c
94c
63
46
47
Et
Et
48
49
Et
Et
100
95c
100
2c
36c
79c
88
12c
10c
10c
12c
42
21c
100
100
100
100
78
50
51
Me
Me
n-Pr
n-Pr
n-Pr
i-Pr
i-Pr
H
72
2,4-DiCF3
4-CF3
2,4-DiCF3
2,4-DiCl
4-CF3
2,4-DiCF3
2,4-DiCF3
2,4-DiCl
3,4-DiCl
2,4-DiCF3
4-Cl
0.22
3.2
2.5
3.6
2.6
1.5
0.59
2
52
53
54
55
56
57
58
59
H
H
1.4
3.1
60
61
Ph
Me
Et
27
25
95
92
62
63
4-Cl
4-Cl
Et
Et
51
35
1
64
65
4-F
4-Br
1.5
3.5
3.7
3.6
2
Et
Et
66
67
3-Cl
100
71
Et
Et
3-CF3
3,4-Cl
4-Cl
68
69
99
6
1.9
Et
100
90
17
100
47
70
71
Me
Me
Me
Me
Me
Me
Me
n-Pr
i-Pr
i-Pr
Ph
4-Cl
4-F
1
100
91
10
1.3
4.6
0.87
3.8
0.83
1.6
14
72
73
4-Br
3-Cl
100
96
74
75
3-CF3
3,4-Cl
H
71
76
77
6c
36
4-F
4-Cl
78
79
100
100
21
71
65
42
1.7
11
4-F
4-F
80
Fipronil
Permethrin
Ivermectin
Levamisole
0.1–0.2
0.14
0.006–0.031
0.71–1.6
a No entry indicates that the compound was not assayed.
b Measured at 24 h.
c Measured at 8 h.

A. Ali et al. / Bioorg. Med. Chem. Lett. 18 (2008) 252–255
255
highly active against C. felis. Several O-benzyloxime
ether derivatives were also active against R. sanguineus,
although their levels of activity were generally less than
the best O-alkyloxime ether TFMS compounds.
best balance of activity against these ectoparasites was
generally exhibited by O-alkyloxime ether derivatives.
Furthermore, O-benzyl- and O-aryloxime ether TFMS
derivatives often displayed high in vitro activity against
the endoparasite H. contortus. The best endectoparasiti-
cidal activity was shown by O-benzyl- and O-aryloxime
ether derivatives such as compounds 42 and 64, respec-
tively. Further research to explore the parasiticidal
activity associated with the 2-alkoxy- and 2-aryl-
oxyiminoalkyl TFMS template is ongoing.
A number of O-benzyloxime ether TFMS compounds
also displayed excellent activity against H. contortus
when screened in a high-throughput H. contortus larval
development assay.8 Many derivatives showed levels of
activity comparable to the commercial endoparasiticide
drug levamisole, although none was as potent as iver-
mectin. Good activity was obtained for ketoxime ethers
where R1 was a methyl or ethyl group and R3 consisted
of at least one electron-withdrawing group: for example,
compounds 42 and 51. Aldoxime ethers such as com-
pound 57 were also highly active in the nematode assay.
It is apparent from SAR that the optimal O-benzyl moiety
for activity against H. contortus was the 2,4-bis(trifluoro-
methyl)benzyl group. Significantly, the most active O-
benzyloxime derivative (compound 51, LD99 = 0.22 lM)
maintained activity against resistant strains of H. contor-
tus: LD99 = 0.53 lM for the benzimidazole- and levam-
isole-resistant Lawes strain and LD99 = 0.53 lM for the
avermectin-resistant CAVR strain. Furthermore, com-
pound 51 was active against the McMaster strains of
Ostertagia circumcinta, LD99 = 1.1 lM, and Trichostron-
gylus colubriformis, LD99 = 2.2 lM.
Supplementary data
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/
j.bmcl.2007.10.090.
References and notes
1. Rust, M. K.; Dryden, M. W. Annu. Rev. Entomol. 1997,
42, 451.
2. Sonenshine, D. E. Biology of Ticks; Oxford University:
New York, 1991, Vol. 1, and 1993; Vol. 2.
3. Moriello, K. A. Anim. Health Res. Rev. 2003, 4, 157.
4. Payne, P. A.; Dryden, M. W.; Smith, V.; Ridley, R. K.
Vet. Parasitol. 2001, 102, 331.
5. Mori, T.; Takada, Y.; Hatakoshi, M.; Matsuo, N. Biosci.
Biotechnol. Biochem. 2004, 68, 425, and references cited
therein.
To further probe SAR associated with the 2-alkoxyimi-
noalkyl TFMS template, the O-benzyl moiety was re-
placed with an O-aryl unit. This structural change
eliminates a potential site of metabolic and/or chemical
degradation. Thus, a set of O-aryloxime ethers 63–80
were prepared from the reaction of a 2-keto TFMS 3
with an O-aryloxyamine 4 (Scheme 1 and Table 2).10,11
A number of these derivatives gave high mortality in a
cat flea assay, with some displaying levels of activity
comparable to the best O-alkyloxime ether TFMS com-
pounds. The most active derivatives had R1 as a methyl,
ethyl or i-propyl group, and R3 as a mono- or di-halo
substituent: for example, compounds 68, 71, and 78.
Several O-aryloxime ether derivatives were also highly
active in the dog tick assay, although these compounds
had LD50 values significantly greater than permethrin.
In some cases an O-aryloxime ether derivative was
highly active against both ectoparasites: for example,
compound 71 (LC50 = 10 ng/cm2 for C. felis, and
LD50 = 1.3 lg/tick for R. sanguineus). In contrast, a 5-
trifluoromethyl TFMS derivative (compound 69) highly
active against C. felis was inactive against dog tick.
Many O-aryloxime ether derivatives also displayed good
activity when screened in a H. contortus larval assay: for
example, compound 74 (LD99 = 0.83 lM).
6. McCracken, R. O.; Carr, A. W.; Stillwell, W. H.;
Lipkowitz, K. B.; Boisvenue, R.; O’Doherty, G. O. P.;
Wickiser, D. I. Biochem. Pharm. 1993, 45, 1873.
7. C. felis and R. sanguineus assays were conducted by the
Centre for Entomological Research and Insecticide Tech-
nology, UNSW, Randwick, NSW, Australia, or by
Agrisearch Services Pty. Ltd, 50 Leewood Drive, Orange,
NSW, Australia. Representative in vitro C. felis and R.
sanguineus single-dose assays and LC50/LD50 measure-
ment protocols are described in Supplementary data.
8. Nematocide assays were conducted by Microbial Screen-
ing Technologies Pty. Ltd, Smithfield, NSW, Australia.
H. contortus LD99 values were determined using the larval
development assay described in Ref. 9.
9. Gill, J. H.; Redwing, J. M.; Van Wyk, J. A.; Lacey, E. Int.
J. Parasitol. 1995, 25, 463.
10. Meyer, A. G.; Winzenberg, K. N.; Sawutz, D. G.; Liepa,
A. J. US Pat. Appl. Publ. US 2006063841 A1, 2006; Chem.
Abstr. 2006, 144, 331134.
11. Representative procedures describing the preparation of 2-
alkoxy- and 2-aryloxyiminoalkyl TFMS compounds, and
O-alkyl-, O-benzyl-, and O-aryloxyamines are given in
Supplementary data.
12. Mitochondrial uncoupling activity is primarily a function
of acidity (pKa) and lipophilicity (logP), see: Terada, H.
Biochim. Biophys. Acta 1981, 639, 225.
In summary, a number of novel 2-alkoxy- and 2-aryl-
oxyiminoalkyl TFMS derivatives displayed excellent
in vitro activity against C. felis and R. sanguineus. The
13. The low C. felis mortality observed for compound 51
probably reflects measurement of mortality at 8 h rather
than 24 h.