Negative allosteric modulators of metabotropic glutamate receptor 2

A compound of formula (I), or a pharmaceutically acceptable salt thereof,

• wherein:
• R1a and R1b are independently hydrogen or C1-4alkyl;
• R2 is hydrogen or C1-6alkyl;
• R3 is a 6- to 12-membered aryl, C5-7carbocyclyl, 5- to 12-membered heterocyclyl containing 1-3 heteroatoms, or 5- to 6-membered heteroaryl containing 1-3 heteroatoms, the heteroatoms being independently selected from the group consisting of N, O, and S, wherein R3 is unsubstituted or substituted with 1, 2, 3, or 4 substituents independently selected from the group consisting of C1-4alkyl, halogen, cyano, C1-2haloalkyl, —OR3a, and C(O)R3a;
• R3a, at each occurrence, is independently hydrogen, C1-4alkyl, C1-2haloalkyl, or C3-4cycloalkyl;
• R4 and R5 are each independently hydrogen, C1-4alkyl, halogen, cyano, C1-2haloalkyl, —OC1-4alkyl, or —OC1-2haloalkyl;
• R6 is G6 or —C1-4alkylene-G6;
• G6 is a 5- to 12-membered heteroaryl, 4- to 12-membered heterocyclyl, or phenyl, the heteroaryl and heterocyclyl containing 1-3 heteroatoms independently selected from the group consisting of O, N, and S, wherein G6 is unsubstituted or substituted with a first substituent selected from the group consisting of C1-4alkyl, halogen, cyano, C1-2haloalkyl, oxo, —OR6a, —N(R6a)2, —SR6a, —N(R6a)C(O)R6a, —C(O)OR6a, —C(O)N(R6a)2, —SO2N(R6a)2, —SO2R6, —C1-6alkylene-OH, G6a, and —C1-4alkylene-G6a, and optionally further substituted with 1-3 substituents independently selected from the group consisting of C1-4alkyl, halogen, cyano, C1-2haloalkyl, oxo, —OC1-4alkyl, and —OC1-2haloalkyl;
• R6a, at each occurrence, is independently hydrogen, C1-4alkyl, C1-2haloalkyl, C3-4cycloalkyl, or —C1-4alkylene-C3-4cycloalkyl;
• R6b, at each occurrence, is independently C1-4alkyl, C1-2haloalkyl, C34cycloalkyl, or —C1-4alkylene-C3-4cycloalkyl;
• and
• G6a is a phenyl, C3-6cycloalkyl, 5- to 6-membered heteroaryl containing 1-3 heteroatoms, or 4- to 6-membered heterocyclyl containing 1-2 heteroatoms, the heteroatoms in the heteroaryl and heterocyclyl being independently selected from the group consisting of O, N, and S, wherein G6a is optionally substituted with 1-4 substituents independently selected from the group consisting of C1-4alkyl, C1-2fluoroalkyl, halogen, cyano, oxo, OH, and —OC1-4alkyl;
• provided the compound is not:
• 4,6-bis[4-(1,1-dimethylethyl)phenyl]-2,3-dihydro-2-methyl-1H-isoindol-1-one;
• or
• 4-(3-fluoro-5-hydroxyphenyl)-6-(3-fluorophenyl)-2,3-dihydro-1H-isoindol-1-one.