A compound of Formula I: wherein: R 1 and R 3 each independently is selected from among hydrogen, C 1 -C 4 alkyl, a heteroalkyl selected from among CH 3 C(=O)CH 2 -, CH 3 C(=O)CH 2 CH 2 -, CH 3 CH 2 C(=O)CH 2 CH 2 -, CH 3 C(=O)CH 2 CH 2 CH 2 -, CH 3 OCH 2 CH 2 -, CH 3 OC(=O)CH 2 -, and CH 3 NHCH 2 -, C 1 -C 4 haloalkyl, a heteroaryl containing three to nine atoms and optionally substituted with a substituent selected from among halo, hydroxy, cyano, O-C 1 -C 6 -alkyl, C 1 -C 6 -alkyl, hydroxy-C 1 -C 6 -alkyl and amino-C 1 -C 6 -alkyl, where at least one atom is a heteroatom selected from among oxygen, sulfur, nitrogen and phosphorus, and a C 3 -C 9 aryl optionally substituted with a group selected from among cycloalkyl, aryl, heteroaryl, non-aromatic heterocycle, hydroxy, alkoxy, aryloxy, mercapto, alkylthio, arylthio, cyano, halo, carbonyl, thiocarbonyl, O-carbamyl, N-carbamyl, O-thiocarbamyl, N-thiocarbamyl, C-amido, N-amido, S-sulfonamido, N-sulfonamido, C-carboxy, O-carboxy, isocyanato, thiocyanato, isothiocyanato, nitro, silyl, trihalomethanesulfonyl, and amino; or R 1 and R 3 taken together form a C 3 -C 8 carbocyclic ring; R 2 and R 4 are each hydrogen; or R 2 and R 4 taken together form a bond; R 5 is selected from among hydrogen, C 1 -C 8 alkyl, C 1 -C 8 haloalkyl, a heteroalkyl selected from among CH 3 C(=O)CH 2 -, CH 3 C(=O)CH 2 CH 2 -, CH 3 CH 2 C(=O)CH 2 CH 2 -, CH 3 C(=O)CH 2 CH 2 CH 2 -, CH 3 OCH 2 CH 2 -, CH 3 OC(=O)CH 2 -, CH 3 NHCH 2 -, C 7 -C 10 arylalkyl, and C 2 -C 8 heteroarylalkyl containing at least one heteroatom selected from among oxygen, sulfur, nitrogen and phosphorus; and R 6 is hydrogen or F; or a pharmaceutically acceptable salt thereof. R 1 and R 3 each independently is selected from among hydrogen, C 1 -C 4 alkyl, a heteroalkyl selected from among CH 3 C(=O)CH 2 -, CH 3 C(=O)CH 2 CH 2 -, CH 3 CH 2 C(=O)CH 2 CH 2 -, CH 3 C(=O)CH 2 CH 2 CH 2 -, CH 3 OCH 2 CH 2 -, CH 3 OC(=O)CH 2 -, and CH 3 NHCH 2 -, C 1 -C 4 haloalkyl, a heteroaryl containing three to nine atoms and optionally substituted with a substituent selected from among halo, hydroxy, cyano, O-C 1 -C 6 -alkyl, C 1 -C 6 -alkyl, hydroxy-C 1 -C 6 -alkyl and amino-C 1 -C 6 -alkyl, where at least one atom is a heteroatom selected from among oxygen, sulfur, nitrogen and phosphorus, and a C 3 -C 9 aryl optionally substituted with a group selected from among cycloalkyl, aryl, heteroaryl, non-aromatic heterocycle, hydroxy, alkoxy, aryloxy, mercapto, alkylthio, arylthio, cyano, halo, carbonyl, thiocarbonyl, O-carbamyl, N-carbamyl, O-thiocarbamyl, N-thiocarbamyl, C-amido, N-amido, S-sulfonamido, N-sulfonamido, C-carboxy, O-carboxy, isocyanato, thiocyanato, isothiocyanato, nitro, silyl, trihalomethanesulfonyl, and amino; or R 1 and R 3 taken together form a C 3 -C 8 carbocyclic ring; R 2 and R 4 are each hydrogen; or R 2 and R 4 taken together form a bond; R 5 is selected from among hydrogen, C 1 -C 8 alkyl, C 1 -C 8 haloalkyl, a heteroalkyl selected from among CH 3 C(=O)CH 2 -, CH 3 C(=O)CH 2 CH 2 -, CH 3 CH 2 C(=O)CH 2 CH 2 -, CH 3 C(=O)CH 2 CH 2 CH 2 -, CH 3 OCH 2 CH 2 -, CH 3 OC(=O)CH 2 -, CH 3 NHCH 2 -, C 7 -C 10 arylalkyl, and C 2 -C 8 heteroarylalkyl containing at least one heteroatom selected from among oxygen, sulfur, nitrogen and phosphorus; and R 6 is hydrogen or F;