Solid‐state structure of orphenadrine hydrochloride and conformational comparisons with diphenhydramine hydrochloride and nefopam hydrochloride

Robert Glaser, David Donnell, Knut Maartmann‐Moe

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Abstract

The solid‐state structure of (±)‐orphenadrine hydrochloride [(CH3)2NCH2CH2OCH(o‐CH3C6H4)(Ph) · HCl], a skeletal muscle relaxant drug, was determined by single‐crystal X‐ray diffraction analysis. Orphenadrine hydrochloride gave crystals belonging to the monoclinic P21/n space group, and at low temperature (92 K), the following parameters were found: a = 6.923 (4), b = 7.508 (5), c = 33.22 (3) Å, V = 1720 (3) Å3, Z = 4, R(F) = 0.109, and RW(F) = 0.131. Data were collected from poor crystalline material because of the low volume of the needle‐shaped crystals (0.025 × 0.025 × 0.15 mm3). A molecular mechanics model was calculated by using an input structure based on atomic coordinates of the crystallographically determined molecular structure. The resulting molecular mechanics model and the structure determined by X‐ray crystallography have the same molecular conformation. Whereas both solid‐state (±)‐orphenadrine hydrochloride and diphenhydramine hydrochloride [(CH3)2NCH2CH2OCH(Ph)2 · HCl] have synclinal NCCO and antiperiplanar NCCOCAr2 torsion angles, the former has a helical arrangement for Ar2CH, as expected, and the phenyl rings in the latter are disposed in a nonhelical, “open‐book” arrangement.

Original languageEnglish
Pages (from-to)858-862
Number of pages5
JournalJournal of Pharmaceutical Sciences
Volume81
Issue number9
DOIs
StatePublished - 1 Jan 1992

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