A compound of the formula: or a pharmaceutically acceptable salt thereof, wherein L is -NHC -, -C NH-, -OC - or -C O-; n is and integer from 1 to 4 and is unsubstituted or substituted with one or more substituents independently chosen from halogen, hydroxyl, amino, cyano, C 1 -C 4 alkyl, C 1 -C 4 alkoxy, C 1 -C 2 haloalkyl, or C 1 -C 2 haloalkoxy; R 1 is hydrogen, C 1 -C 6 alkyl, C 2 -C 6 alkenyl, (C 3 -C 7 cycloalkyl)C 0 -C 2 alkyl, (mono- or di-C 1 -C 4 alkylamino)C 1 -C 4 alkyl, or (mono- or di-C 1 -C 4 alkylamino)C 1 -C 4 alkoxy; R 2 is mono-, bi-, or tricyclic carbocyclic or heterocylic group, a (mono- or di-C 1 -C 4 alkylamino)C 2 -C 4 alkyl group, or C 4 -C 8 alkyl, each of which R 2 is unsubstituted or substituted with one more substituents independently chosen from halogen, hydroxyl, amino, nitro, cyano, C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, -OR 11, -(CH 2) 0-4 C R 11, -(CH 2) 0-4 NR 11 R 12, -(CH 2) 0-4 C NR 11 R 12, -(CH 2) 0-4 N(R 11)C (R 12), -(CH 2) 0-4 C OR 11, -(CH 2) 0-4 OC R 11, -(CH 2) 0-4 C R 11, -(CH 2) 0-4 S a R 11, -(CH 2) 0-4 S b NR 11 R 12, -(CH 2) 0-4 N(R 11)S b R 12, and (phenyl)C 0 -C 2 alkyl, where a is 0, 1, or 2, and b is 1 or 2, R 11, R 12, and R 13 are independently chosen at each occurrence from hydrogen and a C 1 -C 6 aliphatic group; each of R 11, R 12, and R 13 is unsubstituted or substituted with one or more substituents independently chosen from: halogen, hydroxyl, vinyl, allenyl, oxo, cyano, amino, -COOH, C 1 -C 6 alkyl, C 1 -C 6 alkoxy, (mono- and di-C 1 -C 6 alkylamino)C 0 -C 2 alkyl, C 1 -C 6 alkylester, C 1 -C 6 alkylthio, C 1 -C 2 haloalkyl, and C 1 -C 2 haloalkoxy; R 3 and R 4 are 0 or 1 or more substituents independently chosen from halogen, hydroxyl, amino, cyano, C 1 -C 4 alkyl, C 1 -C 4 alkoxy, C 2 -C 4 alkanoyl, (mono- and di-C 1 -C 4 alkylamino)C 0 -C 2 alkyl, C 1 -C 2 haloalkyl, and C 1 -C 2 haloalkoxy; with the proviso that when R 1 is ethyl, the group is not 4-methoxybenzyl-NHC -, pyridin-2-ylmethyl-NHC -, 3-(morpholin-1-yl)propyl-NHC -, 3-(azepan-1-yl)propyl-NHC -, 3-(azepan-1-yl)ethyl-NHC -, 3-(pyrrolidin-1-yl)propyl-NHC -, 3-(4-methylpiperazin-1-yl)propyl-NHC -, 3-(piperidin-1-yl)propyl-NHC -, di-isopropylaminopropyl-NHC -, di-propylaminopropyl-NHC -, di-butylaminopropyl-NHC -, or 3-(butyl(ethyl)amino)propyl-NHC -. L is -NHC -, -C NH-, -OC - or -C O-; n is and integer from 1 to 4 and is unsubstituted or substituted with one or more substituents independently chosen from halogen, hydroxyl, amino, cyano, C 1 -C 4 alkyl, C 1 -C 4 alkoxy, C 1 -C 2 haloalkyl, or C 1 -C 2 haloalkoxy; R 1 is hydrogen, C 1 -C 6 alkyl, C 2 -C 6 alkenyl, (C 3 -C 7 cycloalkyl)C 0 -C 2 alkyl, (mono- or di-C 1 -C 4 alkylamino)C 1 -C 4 alkyl, or (mono- or di-C 1 -C 4 alkylamino)C 1 -C 4 alkoxy; R 2 is mono-, bi-, or tricyclic carbocyclic or heterocylic group, a (mono- or di-C 1 -C 4 alkylamino)C 2 -C 4 alkyl group, or C 4 -C 8 alkyl, each of which R 2 is unsubstituted or substituted with one more substituents independently chosen from halogen, hydroxyl, amino, nitro, cyano, C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, -OR 11, -(CH 2) 0-4 C R 11, -(CH 2) 0-4 NR 11 R 12, -(CH 2) 0-4 C NR 11 R 12, -(CH 2) 0-4 N(R 11)C (R 12), -(CH 2) 0-4 C OR 11, -(CH 2) 0-4 OC R 11, -(CH 2) 0-4 C R 11, -(CH 2) 0-4 S a R 11, -(CH 2) 0-4 S b NR 11 R 12, -(CH 2) 0-4 N(R 11)S b R 12, and (phenyl)C 0 -C 2 alkyl, where a is 0, 1, or 2, and b is 1 or 2, R 11, R 12, and R 13 are independently chosen at each occurrence from hydrogen and a C 1 -C 6 aliphatic group; each of R 11, R 12, and R 13 is unsubstituted or substituted with one or more substituents independently chosen from: halogen, hydroxyl, vinyl, allenyl, oxo, cyano, amino, -COOH, C 1 -C 6 alkyl, C 1 -C 6 alkoxy, (mono- and di-C 1 -C 6 alkylamino)C 0 -C 2 alkyl, C 1 -C 6 alkylester, C 1 -C 6 alkylthio, C 1 -C 2 haloalkyl, and C 1 -C 2 haloalkoxy; R 3 and R 4 are 0 or 1 or more substituents independently chosen from halogen, hydroxyl, amino, cyano, C 1 -C 4 alkyl, C 1 -C 4 alkoxy, C 2 -C 4 alkanoyl, (mono- and di-C 1 -C 4 alkylamino)C 0 -C 2 alkyl, C 1 -C 2 haloalkyl, and C 1 -C 2 haloalkoxy; with the proviso that when R 1 is ethyl, the group is not 4-methoxybenzyl-NHC -, pyridin-2-ylmethyl-NHC -, 3-(morpholin-1-yl)propyl-NHC -, 3-(azepan-1-yl)propyl-NHC -, 3-(azepan-1-yl)ethyl-NHC -, 3-(pyrrolidin-1-yl)propyl-NHC -, 3-(4-methylpiperazin-1-yl)propyl-NHC -, 3-(piperidin-1-yl)propyl-NHC -, di-isopropylaminopropyl-NHC -, di-propylaminopropyl-NHC -, di-butylaminopropyl-NHC -, or 3-(butyl(ethyl)amino)propyl-NHC -.