Structure investigations of agonists of the natural neurotransmitter acetylcholine II [1]. X-ray structure analysis of trimethyl(4-oxopentyl)ammonium-chloride.

The crystal structure of Trimethyl(4-oxopentyl)ammonium-chloride ([(CH3)3N--(CH2)3COCH3]Cl-) (1) was determined by an X-ray structure analysis. 1 crystallizes in the orthorhombic space group P2(1)2(1)2(1) with a = 10.440 (3), b = 14.600 (9), c = 6.804 (9) A and with four formula units per unit cell. The structure was solved by a Patterson and a successive Fourier synthesis. The least squares refinement yielded an R-value of 0.064 for 1077 observed reflections. The cation of 1 is derived from acetylcholine by replacement of the ester oxygen with a CH2 group. It shows a potent nicotinic activity and a significant difference in conformation as compared with acetylcholine. In the crystal structure the anions are oriented stereospecifically with respect to the tetrahedron of the quaternary ammonium group. The geometry of two triangles formed by the quaternary nitrogen atom, the oxygen atom of the carbonyl group, and by either of the two anions nearest to the quaternary ammonium group is characteristic for the nicotinic activity of 1.