title: Crystal structures of a new polymorphic form of gabapentin monohydrate and the e and z isomers of 4-tertiarybutylgabapentin.
abstract: Gabapentin, a widely used antiepileptic drug, crystallizes in multiple polymorphic forms. A new crystal form of gabapentin monohydrate in the space group Pbca is reported and the packing arrangement compared with that of a previously reported polymorph in the space group P2(1)/c [Ibers, J.A. (2001) Acta Crystallogr; C57:641]. Gabapentin polymorphs can also occur from a selection of one of the two distinct chair forms of the 1,1-disubstituted cyclohexane. Crystal structures of the E and Z isomers of 4-tert-butylgabapentin provide models for analyzing anticipated packing modes in the conformational isomers of gabapentin. The E isomer crystallized in the space group Pca2(1), while the Z isomer crystallized in the space group P2(1)/c. The crystal structure of E-4-tert-butylgabapentin provides the only example of a structure in a non-centrosymmetric space group. Crystal structures of the hydrochloride and hydrobromide salts of 4-tert-butyl derivatives are reported. The results suggest that for gabapentin, a large 'polymorph-space' may be anticipated, in view of the multiple conformational states that are accessible to the molecule.
authors.affiliation: Department of Physics, Indian Institute of Science, Bangalore 560012, India.
authors.forename: Prema G
authors.initials: PG
authors.lastname: Vasudev
authors.forename: Subrayashastry
authors.initials: S
authors.lastname: Aravinda
authors.forename: Kuppanna
authors.initials: K
authors.lastname: Ananda
authors.forename: Shettykere Dayananda
authors.initials: SD
authors.lastname: Veena
authors.forename: Kuppuswamy
authors.initials: K
authors.lastname: Nagarajan
authors.forename: Narayanaswamy
authors.initials: N
authors.lastname: Shamala
authors.forename: Padmanabhan
authors.initials: P
authors.lastname: Balaram
mesh_terms: D000588:Amines / Q000737:chemistry*; D000927:Anticonvulsants / Q000737:chemistry*; D003460:Crystallization; D018360:Crystallography, X-Ray; D003509:Cyclohexanecarboxylic Acids / Q000737:chemistry*; D000077206:Gabapentin; D006860:Hydrogen Bonding; D007536:Isomerism; D008958:Models, Molecular; D015394:Molecular Structure; D005680:gamma-Aminobutyric Acid / Q000737:chemistry*
chemical_list: D000588:Amines; D000927:Anticonvulsants; D003509:Cyclohexanecarboxylic Acids; D005680:gamma-Aminobutyric Acid; D000077206:Gabapentin