Subtle relationships between the structures of some aspirin derivatives

Gabapentin (GBP) is an API used against epilepsy, neuropathic pain and in the treatment of limb tremor [1].Several polymorphs of GBP have been reported and characterized, but only SCX of Form II was known until very recently.Our group managed to obtain two new SCX structures of different polymorphs [2,3].These new forms are not as stable as Form II, proved by several experiments.Form IV can even be considered a disappearing polymorph [3] because it readily transforms into another form.New crystal forms of GBP were obtained on acidifying the solution.We obtained GBP chloride hemihydrate, an ethyl ester of GBP and a co-crystal of GBP-lactam and benzoic acid [Fig.1] in different crystallization conditions.All these structures were determined by SCXRD, presenting different physicochemical properties and supramolecular arrangements [5].Intramolecular interactions are only observed in Form IV and GBP Cl hemi-hydrate.[1]

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