Protease inhibitors and methods of use

A compound of formula (I):

• or a pharmaceutically acceptable salt thereof, wherein:
• R1 is selected from:
• (i) aryl, which is substituted with 1 or 2 substituents independently selected from halo, C1-C3 alkyl, C1-C3 alkoxy, C1-C3 hydroxyalkyl, C1-C3 haloalkyl, C1-C3 haloalkoxy, and cyano;
• and (ii) a monocyclic 6-membered heteroaryl having 1 or 2 nitrogen atoms, which is substituted with 1 or 2 substituents independently selected from halo, C1-C3 alkyl, C1-C3 alkoxy, C1-C3 hydroxyalkyl, C1-C3 haloalkyl, C1-C3 haloalkoxy, and cyano;
• R1a and R1b are each independently selected from hydrogen and C1-C3 alkyl;
• B is a monocyclic heteroaryl, bicyclic heteroaryl, or a bicyclic heterocyclyl, wherein B is linked to the remainder of the molecule via a carbon atom, and wherein the monocyclic heteroaryl, bicyclic heteroaryl, and bicyclic heterocyclyl are independently unsubstituted or substituted with 1, 2, or 3 substituents independently selected from C1-C3 alkyl, C1-C3 alkoxy, C1-C3 hydroxyalkyl, halo, C1-C3 haloalkyl, C1-C3 haloalkoxy, C3-C6 cycloalkyl, aryl, arylalkyl, amino, hydroxy, cyano, oxo, and thioxo;
• R2 is hydrogen or C1-C3 alkyl;
• X1 is CR3a or N, X2 is CR3b or N, X3 is CR3c or N, and X4 is CR3d or N;
• R3a, R3b, R3c, and R3d are each independently selected from hydrogen, C1-C3 alkyl, C1-C3 alkoxy, halo, C1-C3 haloalkyl, C1-C3 haloalkoxy, C1-C3 hydroxyalkyl, cyano, —OR3e, —COOR3f, —CON(R3g)(R3h), and —(CH2)n3-G3, wherein R3e, R3f, R3g, and R3h are each independently selected from hydrogen and C1-C3 alkyl, wherein n3 is 0, 1, or 2, and wherein G3 is selected from C3-C6 cycloalkyl and a 4- to 6-membered monocyclic heterocycle;
• R4 is selected from:
• a 5-membered monocyclic heteroaryl having 1, 2, 3, or 4 heteroatoms independently selected from N, O, and S;
• a 5- or 6-membered heterocyclyl having 1, 2, or 3 heteroatoms independently selected from N, O, and S;
• cyano;
• —CR4cR4d—NR4aR4b;
• and —C(O)NR4aR4b;
• wherein the heteroaryl and heterocyclyl are independently unsubstituted or substituted with 1, 2, or 3 substituents independently selected from C1-C3 alkyl, C1-C3 alkoxy, C1-C3 hydroxyalkyl, halo, C1-C3 haloalkyl, C1-C3 haloalkoxy, C3-C6 cycloalkyl, aryl, arylalkyl, amino, hydroxy, cyano, oxo, and thioxo;
• R4a and R4b are each independently selected from hydrogen and C1-C3 alkyl;
• and
• R4c and R4d are each independently selected from hydrogen, C1-C3 alkyl, C1-C3 haloalkyl, and C3-C6 cycloalkyl, or R4c and R4d, together with the carbon atom to which they are attached, are taken together to form a 3- to 6-membered ring.