Preparation and Characterization of Carboxylic Acid Adducts of Gabapentin

Gabapentin, C9H17NO2, 2-[1-(aminomethyl) cyclohexyl] acetic acid, is used as an anticonvulsant drug to help control partial seizures in the treatment of epilepsy and to manage postherpetic neuralgia after 'shingles'. Cocrystals of gabapentin with a series of hydroxyl carboxylic acids and a cocrystal of gabapentin with oxalic acid were previously reported. The adduct with salicylic acid was prepared, along with adducts of two dicarboxylic acids, succinic acid and adipic acid, and an adduct with 1,2,4,5benzenetetracarboxylic acid. Formation of new materials is demonstrated by new unique physical properties, including lower melting points (102.8-105.1 degrees C, 90.0- 93.0 degrees C, and 152.4-154.8 degrees C for succinic acid, adipic acid, and 1,2,4,5-benzenetetracarboxylic acid products, respectively) than those of the individual starting materials. Shifts in infrared bands for nu(O-H), nu(N-H), and nu(C=O) bands confirm adduct formation and indicate the nature of the interactions between the two components in the lattice.