Structure investigations of agonists of the natural neurotransmitter acetylcholine, IV. X-ray structure analyses of trimethylpentylammonium-chloride and (4-acetoxybutyl)trimethylammonium-iodide.

The crystal structures of the title compounds which display cholinergic activity at the ganglionic receptor have been determined by X-ray structure analysis. [(CH3)3N+C5H11]Cl- (1) crystallizes in the orthorhombic space group Pbnm with half a formula unit per asymmetric unit, a = 11.381(14), b = 12.871(17), c = 7.316(4) A. The intensities of 1106 independent reflections were collected with an automatic diffractometer. The structure refinement converged at R = 0.133 for the 355 observed reflections. The cation of 1 is disordered. [(CH3)3N+ (CH2)4-O-C(O)-CH3]I- (2) crystallizes in the orthorhombic space group P2(1)2(1)2(1) with four formula units per unit cell, a = 16.783(8), b = 10.276(6), c = 7.427(10) A. The intensities of 1469 independent reflections were collected. The structure refinement converged at R = 0.071 for 1383 observed reflections. In both compounds the trimethylammonio methyl groups are coordinated nearly tetrahedrally by four anions in the first coordination sphere. Anions which occupy a special face type (B) of the tetrahedron of the (CH3)3N+ -CH2-group may be treated as a "model binding site" of the receptor. In the crystal structure of 2 the anions occupying B-type faces form together with the ammonium nitrogen and the carbonyl oxygen so called "Activity triangles". The almost equal geometries of these activity triangles are correlated with the mode of pharmacological action.