A compound of formula I: where: R 1 is -OR 10 or -NR 60 R 70; R 2 is H or -OR 20; R 3 is selected from Cl, F, -CH 3, and -CF 3; () a represents (CH 2) a and a is 0 or an integer from 1 to 3; R 4 is selected from -C 1-6 alkyl; -C 3-7 cycloalkyl; -C 0-2 alkylene-COOR 40; -NR 41 R 42; -NHC O-C 1-6 alkyl; -NHC R 43; -NHC NH-R 44; phenyl substituted with one or two groups independently selected from halo, -O-C 1-6 alkyl, -C 0-1 alkylene-COOR 40, -SO 2 NH 2, -C NR 41 R 42, and tetrazole; and -C 0-2 alkylene-C 1-9 heteroaryl or a partially unsaturated -C 0-2 alkylene-C 3-5 heterocycle both optionally substituted with 1-3 groups independently selected from halo, -OH, =O, -CHO, -C 1-6 alkyl, -CF 3, and -COOR 40; R 5 is selected from H, halo, -OH, -C 1-6 alkyl, -O-C 1-6 alkyl, phenyl, and morpholine; R 6 is H or halo; R 10 and R 40 are independently selected from H, -C 1-6 alkyl, -C 1-3 alkylene-C 6-10 aryl, -C 1-3 alkylene-C 1-9 heteroaryl, -C 3-7 cycloalkyl, -[(CH 2) 2 O] 1-3 CH 3, -C 1-6 alkylene-OC R 13, -C 1-6 alkylene-NR 14 R 15, -C 1-6 alkylene-C R 17, -C 0-6 alkylenemorpholine, -C 1-6 alkylene-SO 2 -C 1-6 alkyl, R 13 is selected from -C 1-6 alkyl, -O-C 1-6 alkyl, -C 3-7 cycloalkyl, -O-C 3-7 cycloalkyl, phenyl, -O-phenyl, -NR 14 R 15, and -CH(NH 2)CH 2 COOCH 3; R 14 and R 15 are independently selected from H, -C 1-6 alkyl, and benzyl, or R 14 and R 15 are taken together as -(CH 2) 3-6 -, -C -(CH 2) 3 -, or -(CH 2) 2 O(CH 2) 2 -; R 16 is -C 1-6 alkyl or -C 0-6 alkylene-C 6-10 aryl; R 17 is selected from -O-C 1-6 alkyl, -O-benzyl, and -NR 14 R 15; R 20 is H or is taken together with R 10 to form -CR 21 R 22 - or is taken together with R 60 to form -C -; R 21 and R 22 are independently selected from H, -C 1-6 alkyl, and -O-C 3-7 cycloalkyl, or R 21 and R 22 are taken together to form =O; R 43 is selected from -C 1-6 alkyl, -C 1-3 alkylene-COOR 40, phenyl, and pyridine; R 44 is selected from -C 1-6 alkyl, -C 1-6 alkylene-COOR 40, phenyl, and thiophene-COOR 40, where thiophene is optionally substituted with CH 3; R 60 is selected from H, -OH, -OC R 61, -CH 2 COOH, -O-benzyl, pyridyl, and -OC NR 62 R 63; R 61 is selected from H, -C 1-6 alkyl, -C 6-10 aryl, -OCH 2 -C 6-10 aryl, -CH 2 O-C 6-10 aryl, and -NR 62 R 63; R 70 is selected from H, -C 1-6 alkyl, and -C R 71; R 71 is selected from H, -C 1-6 alkyl, -C 3-7 cycloalkyl, -C 6-10 aryl, and -C 1-9 heteroaryl; R 41, R 42, R 62, and R 63 are independently H or -C 1-4 alkyl; or a pharmaceutically acceptable salt thereof. R 1 is -OR 10 or -NR 60 R 70; R 2 is H or -OR 20; R 3 is selected from Cl, F, -CH 3, and -CF 3; () a represents (CH 2) a and a is 0 or an integer from 1 to 3; R 4 is selected from -C 1-6 alkyl; -C 3-7 cycloalkyl; -C 0-2 alkylene-COOR 40; -NR 41 R 42; -NHC O-C 1-6 alkyl; -NHC R 43; -NHC NH-R 44; phenyl substituted with one or two groups independently selected from halo, -O-C 1-6 alkyl, -C 0-1 alkylene-COOR 40, -SO 2 NH 2, -C NR 41 R 42, and tetrazole; and -C 0-2 alkylene-C 1-9 heteroaryl or a partially unsaturated -C 0-2 alkylene-C 3-5 heterocycle both optionally substituted with 1-3 groups independently selected from halo, -OH, =O, -CHO, -C 1-6 alkyl, -CF 3, and -COOR 40; R 5 is selected from H, halo, -OH, -C 1-6 alkyl, -O-C 1-6 alkyl, phenyl, and morpholine; R 6 is H or halo; R 10 and R 40 are independently selected from H, -C 1-6 alkyl, -C 1-3 alkylene-C 6-10 aryl, -C 1-3 alkylene-C 1-9 heteroaryl, -C 3-7 cycloalkyl, -[(CH 2) 2 O] 1-3 CH 3, -C 1-6 alkylene-OC R 13, -C 1-6 alkylene-NR 14 R 15, -C 1-6 alkylene-C R 17, -C 0-6 alkylenemorpholine, -C 1-6 alkylene-SO 2 -C 1-6 alkyl, R 13 is selected from -C 1-6 alkyl, -O-C 1-6 alkyl, -C 3-7 cycloalkyl, -O-C 3-7 cycloalkyl, phenyl, -O-phenyl, -NR 14 R 15, and -CH(NH 2)CH 2 COOCH 3; R 14 and R 15 are independently selected from H, -C 1-6 alkyl, and benzyl, or R 14 and R 15 are taken together as -(CH 2) 3-6 -, -C -(CH 2) 3 -, or -(CH 2) 2 O(CH 2) 2 -; R 16 is -C 1-6 alkyl or -C 0-6 alkylene-C 6-10 aryl; R 17 is selected from -O-C 1-6 alkyl, -O-benzyl, and -NR 14 R 15; R 20 is H or is taken together with R 10 to form -CR 21 R 22 - or is taken together with R 60 to form -C -; R 21 and R 22 are independently selected from H, -C 1-6 alkyl, and -O-C 3-7 cycloalkyl, or R 21 and R 22 are taken together to form =O; R 43 is selected from -C 1-6 alkyl, -C 1-3 alkylene-COOR 40, phenyl, and pyridine; R 44 is selected from -C 1-6 alkyl, -C 1-6 alkylene-COOR 40, phenyl, and thiophene-COOR 40, where thiophene is optionally substituted with CH 3; R 60 is selected from H, -OH, -OC R 61, -CH 2 COOH, -O-benzyl, pyridyl, and -OC NR 62 R 63; R 61 is selected from H, -C 1-6 alkyl, -C 6-10 aryl, -OCH 2 -C 6-10 aryl, -CH 2 O-C 6-10 aryl, and -NR 62 R 63; R 70 is selected from H, -C 1-6 alkyl, and -C R 71; R 71 is selected from H, -C 1-6 alkyl, -C 3-7 cycloalkyl, -C 6-10 aryl, and -C 1-9 heteroaryl; R 41, R 42, R 62, and R 63 are independently H or -C 1-4 alkyl; or a pharmaceutically acceptable salt thereof.