Bridged tricyclic gaba derivatives as calcium channel modulators, methods of making and methods of using thereof

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

• R1, R2, R3, R3′, R4, R5, R6, R7, and R8 are each independently selected from hydrogen, deuterium, halogen, substituted or unsubstituted C1-C6 alkyl, and substituted or unsubstituted C3-C6 cycloalkyl, wherein the substituted C1-C6 alkyl and substituted C3-C6 cycloalkyl are optionally further substituted with 0 to 6 substituents selected from halogen, hydroxyl, carboxyl, amino, cyano, C1-C3 alkyl, and C3-C6 cycloalkyl;
• and
• R9 is selected from carboxylic acid (—COOH),