Stereochemistry of anticholinergic agents. Part IV. Crystal and molecular structure of penthienate bromide [diethyl-(2-hydroxyethyl)-methylammonium bromide α-cyclopentyl-2-thienylglycolate]: some stereochemical correlations

Abstract

Crystals of the title compound are triclinic, space group P with Z= 2 in a unit cell of dimensions a= 7·14 ± 0·01, b= 8·32 ± 0·01, c= 17·31 ± 0·01 Å, α= 90·7 ± 0·05, β= 83·9 ± 0·05, γ= 97·5 ± 0·05°. The structure was determined by Patterson and Fourier methods by use of three-dimensional X-ray counter data, and refined by least-squares to R 7·1% for 2219 structure amplitudes. The thienyl ring is planar and is oriented nearly perpendicular to the mean plane of the ester group. The cyclopentyl ring is in the envelope conformation. The acetylcholine-like system adopts a conformation similar to that of acetylcholine in crystals of the chloride salt. The molecular geometry is compared with those of certain related anticholinergic cations as determined in the solid state by X-ray crystallography. A common feature is that the previously defined ‘methyl side’ of the acetylcholine system is partially blocked by ring substituents in the acyl group and by a large cationic head.