Antiparasitic agents

1. A compound of the formula

or a pharmaceutically acceptable salt of said compound, wherein:

X is O or S;

R 1 , R 2 , R 3 and R 4 are each independently selected from H, halo, CN, (C 1 -C 4 )alkyl (C 1 -C 4 )haloalkyl, O—(C 1 -C 4 )alkyl, and O—(C 1 -C 4 ) haloalkyl;

R 5 , R 6 , R 7 , R 8 and R 9 are each independently selected from H, halo, (C 1 -C 4 )alkyl, (C 3 -C 6 )cycloalkyl, (C 1 -C 4 )haloalkyl, O—(C 1 -C 4 )alkyl, O—(C 3 -C 6 )cycloalkyl, O—(C 1 -C 4 )haloalkyl, SF 5 , S(O) m —(C 1 -C 4 )alkyl, S(O) m —(C 3 -C 6 )cycloalkyl and S(O) m —(C 1 -C 4 )haloalkyl;

R 10 is H or (C 1 -C 4 )alkyl;

R 11 is H or (C 1 -C 4 )alkyl;

and m is 0, 1 or 2.

2. A compound according to claim 1 wherein at least one of R 1 , R 2 , R 3 and R 4 is CN and at least two of R 1 , R 2 , R 3 and R 4 are H.

3. A compound according to claim 2 wherein one of R 1 and R 4 is H and the other is selected from H, F, Cl, Br and CF 3 , and one of R 2 and R 3 is H and the other is CN.

4. A compound according to claim 1 wherein one of R 5 , R 6 , R 7 , R 8 and R 9 is selected from halo, (C 1 -C 4 )haloalkyl, O—(C 1 -C 4 )haloalkyl, SF 5 and S(O) m —(C 1 -C 4 )haloalkyl and the others are H.

5. A compound according to claim 4 wherein one of R 6 and R 7 is CF 3 , OCF 3 , SF 5 , SCF 3 or S(O) 2 CF 3 , and the other is H.

6. A compound according to claim 5 wherein R 7 is CF 3 , OCF 3 , SF 5 , SCF 3 or S(O) 2 CF 3 and R 7 , R 8 , R 10 and R 11 are H.

7. A compound according to claim 1 wherein R 10 is (C 1 -C 4 )alkyl.

8. A compound according to claim 1 wherein R 10 is methyl.

9. A compound according to claim 1 wherein R 11 is H.

10. A compound according to claim 1 wherein X is O.

11. A compound according to claim 1 wherein R 1 and R 4 are each independently selected from H, Cl, Br and CF 3 , R 7 is CF 3 , OCF 3 , SF 5 , SCF 3 or S(O) 2 CF 3 , and R 8 is H.

12. A compound according to claim 11 wherein X is O.

13. A compound according to claim 12 wherein R 1 is selected from H, Cl, Br and CF 3 , R 2 is H, R 3 is CN, and R 4 is H.

14. A compound according to claim 1 selected from:

N-[1-cyano-1-(5-cyano-2,3-dihydro-1-benzofuran-2-yl)ethyl]-4-[(trifluoromethyl)thio]benzamide,

N-{(1R*)-1-cyano-1-[(2R*)-5-cyano-2,3-dihydro-1-benzofuran-2-yl]ethyl}-4-[(trifluoromethyl)thio]benzamide,

N-{(1R)-1-cyano-1-[(2R)-5-cyano-2,3-dihydro-1-benzofuran-2-yl]ethyl}-4-[(trifluoromethyl)thio]benzamide,

N-{(1S)-1-cyano-1-[(2S)-5-cyano-2,3-dihydro-1-benzofuran-2-yl]ethyl}-4-[(trifluoromethyl)thio]benzamide,

N-{(1R*)-1-cyano-1-[(2S*)-5-cyano-2,3-dihydro-1-benzofuran-2-yl]ethyl}-4-[(trifluoromethyl)thio]benzamide,

N-{(1R)-1-cyano-1-[(2S)-5-cyano-2,3-dihydro-1-benzofuran-2-yl]ethyl}-4-[(trifluoromethyl)thio]benzamide,

N-{(1S)-1-cyano-1-[(2R)-5-cyano-2,3-dihydro-1-benzofuran-2-yl]ethyl}-4-[(trifluoromethyl)thio]benzamide,

N-[1-cyano-1-(5-cyano-2,3-dihydro-1-benzofuran-2-yl)ethyl]-4-(trifluoromethoxy)benzamide,

N-{(1R*)-1-cyano-1-[(2R*)-5-cyano-2,3-dihydro-1-benzofuran-2-yl]ethyl}-4-(trifluoromethoxy)benzamide,

N-{(1R)-1-cyano-1-[(2R)-5-cyano-2,3-dihydro-1-benzofuran-2-yl]ethyl}-4-(trifluoromethoxy)benzamide,

N-{(1S)-1-cyano-1-[(2S)-5-cyano-2,3-dihydro-1-benzofuran-2-yl]ethyl}-4-(trifluoromethoxy)benzamide

N-{(1R*)-1-cyano-1-[(2S*)-5-cyano-2,3-dihydro-1-benzofuran-2-yl]ethyl}-4-(trifluoromethoxy)benzamide,

N-{(1R)-1-cyano-1-[(2S)-5-cyano-2,3-dihydro-1-benzofuran-2-yl]ethyl}-4-(trifluoromethoxy)benzamide,

N-{(1S)-1-cyano-1-[(2R)-5-cyano-2,3-dihydro-1-benzofuran-2-yl]ethyl}-4-(trifluoromethoxy)benzamide,

N-[1-(7-chloro-5-cyano-2,3-dihydro-1-benzofuran-2-yl)-1-cyanoethyl]-4-(trifluoromethoxy)benzamide,

N-{(1R*)-1-[(2R*)-7-chloro-5-cyano-2,3-dihydro-1-benzofuran-2-yl)-1-cyanoethyl]-4-(trifluoromethoxy)benzamide,

N-{(1R)-1-[(2R)-7-chloro-5-cyano-2,3-dihydro-1-benzofuran-2-yl)-1-cyanoethyl]-4-(trifluoromethoxy)benzamide,

N-{(1S)-1-[(2S)-7-chloro-5-cyano-2,3-dihydro-1-benzofuran-2-yl)-1-cyanoethyl]-4-(trifluoromethoxy)benzamide,

N-{(1R*)-1-[(2S*)-7-chloro-5-cyano-2,3-dihydro-1-benzofuran-2-yl)-1-cyanoethyl]-4-(trifluoromethoxy)benzamide,

N-{(1R)-1-[(2S)-7-chloro-5-cyano-2,3-dihydro-1-benzofuran-2-yl)-1-cyanoethyl]-4-(trifluoromethoxy)benzamide,

N-{(1S)-1-[(2R)-7-chloro-5-cyano-2,3-dihydro-1-benzofuran-2-yl)-1-cyanoethyl]-4-(trifluoromethoxy)benzamide,

N-[1-(7-chloro-5-cyano-2,3-dihydro-1-benzofuran-2-yl)-1-cyanoethyl]-4-(pentafluorothio)benzamide,

N-{(1R*)-1-[(2R*)-7-chloro-5-cyano-2,3-dihydro-1-benzofuran-2-yl]-1-cyanoethyl]-4-(pentafluorothio)benzamide,

N-{(1R)-1-[(2R)-7-chloro-5-cyano-2,3-dihydro-1-benzofuran-2-yl]-1-cyanoethyl]-4-pentafluorothiobenzamide,

N-{(1S)-1-[(2S)-7-chloro-5-cyano-2,3-dihydro-1-benzofuran-2-yl]-1-cyanoethyl]-4-(pentafluorothio)benzamide,

N-{(1R*)-1-[(2S*)-7-chloro-5-cyano-2,3-dihydro-1-benzofuran-2-yl]-1-cyanoethyl]-4-(pentafluorothio)benzamide,

N-{(1R)-1-[(2S)-7-chloro-5-cyano-2,3-dihydro-1-benzofuran-2-yl]-1-cyanoethyl]-4-(pentafluorothio)benzamide, and

N-{(1S)-1-[(2R)-7-chloro-5-cyano-2,3-dihydro-1-benzofuran-2-yl]-1-cyanoethyl]-4-(pentafluorothio)benzamide, or a pharmaceutically acceptable salt thereof.

15. A method of treatment of a parasitic infestation in a host animal, comprising treating said host animal with an effective amount of a compound as defined in claim 1 or a pharmaceutically acceptable salt thereof.

16. The method according to claim 15 wherein the host animal is a non-human animal.

17. The method according to claim 15 wherein the parasite is a nematode.

18. A pharmaceutical composition comprising a compound according to claim 1 , or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable carrier.

19. The pharmaceutical composition according to claim 18 further comprising a second therapeutic agent.

20. The pharmaceutical composition according to claim 19 wherein the second therapeutic agent is selected from ivermectin, avermectin, abamectin, emamectin, eprinomectin, doramectin, selamectin, moxidectin, nemadectin and milbemycin oxime.

21. The pharmaceutical composition according to claim 19 wherein the second therapeutic agent is selected from albendazole, cambendazole, fenbendazole, flubendazole, mebendazole, oxfendazole, oxibendazole and parbendazole.

22. The pharmaceutical composition according to claim 19 wherein the second therapeutic agent is selected from tetramisole, levamisole, pyrantel pamoate, oxantel and morantel.

23. The pharmaceutical composition according to claim 19 wherein the second therapeutic agent is selected from closantel, triclabendazole, clorsulon, rafoxanide, niclosamide, praziquantel and epsiprantel.

24. The pharmaceutical composition according to claim 19 wherein the second therapeutic agent is selected from fipronil, lufenuron, tebufenozide, spinosad and imidacloprid.