A compound of structural Formula: or a salt thereof, wherein: R 1 is selected from aryl, heteroaryl, C 3-10 cycloalkyl, C 6-11 bridged cycloalkyl, C 6-11 spirocycloalkyl, C 3-10 heterocycloalkyl, C 6-11 bridged heterocycloalkyl, and C 6-11 spiroheterocycloalkyl, and is optionally substituted with one or more R 4 groups; R 2a is selected from H, C 1-3 alkyl, and C 1-3 haloalkyl; R 2b is selected from H, C 1-3 alkyl, and C 1-3 haloalkyl; R 3 is selected from purinyl, pyrrolopyridinyl, pyrazolopyridinyl, pyrazolopyrimidinyl and pyrrolopyrimidinyl, and is optionally substituted with one or two R 5 groups; each R 4 is independently selected from amino, halo, cyano, hydroxy, oxo, alkyl, haloakyl, C 3-10 cycloalkyl, C 3-10 heterocycloalkyl, hydroxyalkyl, NR 6 C NR 7 R 8, NR 6 C R 7, =N-R 7, NR 6 C OR 7, OC NR 7 R 8, OC R 7, S R 7, S 2 R 7, S 2 OR 7, S NR 7 R 8, S 2 NR 7 R 8, S (NR 7)R 8, NR 6 S R 7, NR 6 S 2 R 7, C OR 7, C R 7, C NR 7 R 8, and OR 7; each R 5 is independently selected from amino, halo, cyano, hydroxy, oxo, alkyl, haloalkyl, C 3-10 cycloalkyl, C 3-10 heterocycloalkyl, alkoxy, haloalkoxy, NR 9 C NR 10 R 11, NR 9 C R 10, C NR 10 R 11, NR 9 C OR 10, OC NR 10 R 11, S R 10, S 2 R 10, S 2 OR 10, S NR 10 R 11, S 2 NR 10 R 11, S (NR 10)R 11, and C OR 10; each R 6, R 7, and R 8 is independently selected from hydrogen, alkyl, haloalkyl, C 3-7 cycloalkyl, and C 3-7 heterocycloalkyl, any of which, excluding hydrogen, is optionally substituted with one or more R 12 groups, R 7 and R 8, together with the atom to which they are both attached, can optionally form a 3-7 membered saturated or unsaturated ring optionally containing 1 or 2 heteroatoms, and R 1, together with R 6, R 7, or R 8, can optionally form a ring; each R 9, R 10, and R 11 is independently selected from hydrogen, alkyl, haloalkyl, C 3-7 cycloalkyl, and C 3-7 heterocycloalkyl, R 10 and R 11, together with the atom to which they are both attached, can optionally form a 3-7 membered saturated or unsaturated ring optionally containing 1 or 2 heteroatoms, and R 3, together with R 9, R 10, or R 11, can optionally form a ring; and each R 12 is independently selected from halo, hydroxy, C 1-3 alkyl, C 1-3 haloalkyl, and alkoxy; wherein cannot be 6-[4-(morpholin-4-yl)-5H, 6H, 7H, 8H-pyrido[4,3-d]pyrimidin-6-yl]pyridine-3-carbonitrile. R 1 is selected from aryl, heteroaryl, C 3-10 cycloalkyl, C 6-11 bridged cycloalkyl, C 6-11 spirocycloalkyl, C 3-10 heterocycloalkyl, C 6-11 bridged heterocycloalkyl, and C 6-11 spiroheterocycloalkyl, and is optionally substituted with one or more R 4 groups; R 2a is selected from H, C 1-3 alkyl, and C 1-3 haloalkyl; R 2b is selected from H, C 1-3 alkyl, and C 1-3 haloalkyl; R 3 is selected from purinyl, pyrrolopyridinyl, pyrazolopyridinyl, pyrazolopyrimidinyl and pyrrolopyrimidinyl, and is optionally substituted with one or two R 5 groups; each R 4 is independently selected from amino, halo, cyano, hydroxy, oxo, alkyl, haloakyl, C 3-10 cycloalkyl, C 3-10 heterocycloalkyl, hydroxyalkyl, NR 6 C NR 7 R 8, NR 6 C R 7, =N-R 7, NR 6 C OR 7, OC NR 7 R 8, OC R 7, S R 7, S 2 R 7, S 2 OR 7, S NR 7 R 8, S 2 NR 7 R 8, S (NR 7)R 8, NR 6 S R 7, NR 6 S 2 R 7, C OR 7, C R 7, C NR 7 R 8, and OR 7; each R 5 is independently selected from amino, halo, cyano, hydroxy, oxo, alkyl, haloalkyl, C 3-10 cycloalkyl, C 3-10 heterocycloalkyl, alkoxy, haloalkoxy, NR 9 C NR 10 R 11, NR 9 C R 10, C NR 10 R 11, NR 9 C OR 10, OC NR 10 R 11, S R 10, S 2 R 10, S 2 OR 10, S NR 10 R 11, S 2 NR 10 R 11, S (NR 10)R 11, and C OR 10; each R 6, R 7, and R 8 is independently selected from hydrogen, alkyl, haloalkyl, C 3-7 cycloalkyl, and C 3-7 heterocycloalkyl, any of which, excluding hydrogen, is optionally substituted with one or more R 12 groups, R 7 and R 8, together with the atom to which they are both attached, can optionally form a 3-7 membered saturated or unsaturated ring optionally containing 1 or 2 heteroatoms, and R 1, together with R 6, R 7, or R 8, can optionally form a ring; each R 9, R 10, and R 11 is independently selected from hydrogen, alkyl, haloalkyl, C 3-7 cycloalkyl, and C 3-7 heterocycloalkyl, R 10 and R 11, together with the atom to which they are both attached, can optionally form a 3-7 membered saturated or unsaturated ring optionally containing 1 or 2 heteroatoms, and R 3, together with R 9, R 10, or R 11, can optionally form a ring; and each R 12 is independently selected from halo, hydroxy, C 1-3 alkyl, C 1-3 haloalkyl, and alkoxy; wherein cannot be 6-[4-(morpholin-4-yl)-5H, 6H, 7H, 8H-pyrido[4,3-d]pyrimidin-6-yl]pyridine-3-carbonitrile.