A compound of formula I for use in the prophylaxis or treatment of malaria, in which R 1 and R 2 are independently selected from H, aryl and heteroaryl, or R 1 and R 2 together form a C 5 -C 7 ring, R 3 -R 7 are independently selected from H, halogen, alkyl and alkoxy, X is (CH 2) n in which n is 0-5, Y is selected from CH 2, NR 8, O or S in which R 8 is H or alkyl, salts thereof and stereoisomers thereof, in which "alkyl" means a group selected from C 1 -C 7 straight chain alkyl groups, optionally substituted with one or more F, Cl, Br, and C 1 -C 7 branched alkyl groups optionally substituted with one or more F, Cl, Br, "aryl" means a group selected from phenyl, and phenyl substituted with one or more F, Cl, Br, S, N, C 1 -C 7 alkoxy, nitrile, trifluoromethyl, C 1 -C 7 straight chain alkyl groups and C 1 -C 7 branched alkyl groups, the alkyl groups being optionally substituted with one or more F, Cl, Br, "heteroaryl" means a group selected from thiophenyl, furyl, pyridinyl, isoxazolinyl, pyrrolinyl, oxazolinyl, thiazolinyl, imidazolyl which is optionally substituted with one or more F, Cl, Br, S, N, C 1 -C 7 alkoxy, nitrile, trifluoromethyl, C 1 -C 7 straight chain alkyl groups and C 1 -C 7 branched alkyl groups, the alkyl groups being optionally substituted with one or more F, Cl, Br, "halogen" means F, Cl or Br, and "alkoxy" means a C 1 -C 7 alkoxy group provided that: when R 1 and R 2 are independently selected from H, phenyl, 4-fluorophenyl, 4-chlorophenyl, 4-methylthiophenyl or R 1 and R 2 together form-(CH 2) 2 CH(CH 3)-(CH 2) 2 -, X is (CH 2) n, n is 0-3 and Y is CH 2, then R 3 -R 7 are not all H. R 1 and R 2 are independently selected from H, aryl and heteroaryl, or R 1 and R 2 together form a C 5 -C 7 ring, R 3 -R 7 are independently selected from H, halogen, alkyl and alkoxy, X is (CH 2) n in which n is 0-5, Y is selected from CH 2, NR 8, O or S in which R 8 is H or alkyl, salts thereof and stereoisomers thereof, "alkyl" means a group selected from C 1 -C 7 straight chain alkyl groups, optionally substituted with one or more F, Cl, Br, and C 1 -C 7 branched alkyl groups optionally substituted with one or more F, Cl, Br, C 1 -C 7 straight chain alkyl groups, optionally substituted with one or more F, Cl, Br, and C 1 -C 7 branched alkyl groups optionally substituted with one or more F, Cl, Br, "aryl" means a group selected from phenyl, and phenyl substituted with one or more F, Cl, Br, S, N, C 1 -C 7 alkoxy, nitrile, trifluoromethyl, C 1 -C 7 straight chain alkyl groups and C 1 -C 7 branched alkyl groups, the alkyl groups being optionally substituted with one or more F, Cl, Br, phenyl, and phenyl substituted with one or more F, Cl, Br, S, N, C 1 -C 7 alkoxy, nitrile, trifluoromethyl, C 1 -C 7 straight chain alkyl groups and C 1 -C 7 branched alkyl groups, the alkyl groups being optionally substituted with one or more F, Cl, Br, "heteroaryl" means a group selected from thiophenyl, furyl, pyridinyl, isoxazolinyl, pyrrolinyl, oxazolinyl, thiazolinyl, imidazolyl which is optionally substituted with one or more F, Cl, Br, S, N, C 1 -C 7 alkoxy, nitrile, trifluoromethyl, C 1 -C 7 straight chain alkyl groups and C 1 -C 7 branched alkyl groups, the alkyl groups being optionally substituted with one or more F, Cl, Br, "halogen" means F, Cl or Br, and "alkoxy" means a C 1 -C 7 alkoxy group when R 1 and R 2 are independently selected from H, phenyl, 4-fluorophenyl, 4-chlorophenyl, 4-methylthiophenyl or R 1 and R 2 together form-(CH 2) 2 CH(CH 3)-(CH 2) 2 -, X is (CH 2) n, n is 0-3 and Y is CH 2, then R 3 -R 7 are not all H.