Therapeutic compounds and compositions

A compound of formula (II):

• or a pharmaceutically acceptable salt thereof, wherein
• R1 is hydrogen or —NR8R9;
• Ra is C1-6 alkyl, C1-6 haloalkyl, halo, cyano, or —OR6;
• Rb is hydrogen or C1-6 alkyl;
• R2 is optionally substituted 5-membered heteroaryl or optionally substituted 5-membered heterocyclyl;
• R3 is hydrogen, C1-6 alkyl, or C1-6 haloalkyl;
• R4 is C1-6 alkyl, C1-6 haloalkyl, cycloalkyl, heterocyclyl, aryl, or heteroaryl, wherein the cycloalkyl, heterocyclyl, aryl, or heteroaryl is optionally substituted with one, two, or three independent occurrences of halo, C1-6 alkyl, C1-6 haloalkyl, cyano, or —OR6;
• R5 is hydrogen, C1-6 alkyl, C1-6 haloalkyl, cycloalkyl, or aryl, wherein the cycloalkyl or aryl is optionally substituted with one, two, or three independent occurrences of halo, C1-6 alkyl, C1-6 haloalkyl, cyano, or —OR6 or
• R4 and R5, taken together with the carbon atom to which they are attached form a ring;
• R6 is hydrogen, C1-6 alkyl, or C1-6 haloalkyl;
• each R8 and R9 is independently hydrogen, C1-6 alkyl, —C(O)R10, or —C(O)OR10;
• R10 is C1-6 alkyl or C1-6 haloalkyl;
• Rx is —O or absent, wherein when Rx is —O, the nitrogen atom of the pyridyl ring is positively charged and Rx is negatively charged, thereby forming a pyridyl N-oxide;
• m is 0, 1, 2, or, 3;
• and
• n is 0 or 1, wherein if n is 0, then R5 is hydrogen and R4 is absent.