Inhibition of acetylcholinesterase by hemicholiniums, conformationally constrained choline analogs. Evaluation of aryl and alkyl substituents. Comparisons with choline and (3-hydroxyphenyl)trimethylammonium

Abstract

2-Substituted-2-hydroxy-4,4-dimethylmorpholiniums (hemicholiniums) inhibit acetylcholinesterase (EC 3.1.1.7)-catalyzed hydrolysis of acetylthiocholine (ATCh). The 4-substituted arenes [NH2, NHC(O)CH3, Cl, CN, and NO2] have values of inhibition constants (Ki) that range from 220 to 3690 microM, which correlate with Hammett sigma, rho approximately 0.8. The alkyl compounds, hydrogen, methyl, tert-butyl, and trifluoromethyl, have values of Ki of 550, 560, 1200, and 1200 microM, respectively. These values compare favorably with Ki = 960 microM for choline. The conformation of AChE-bound choline must be gauche to support our suggestion that hemicholiniums are conformationally constrained analogues of choline. (3-Hydroxyphenyl)trimethylammonium (5) inhibits most strongly, Ki = 0.21 microM, of the compounds examined in this study. The solvent isotope effect (H2OKi/D2OKi = 0.83 +/- 0.04) suggests that inhibition by 5 involves hydrogen bonding. The binding by AChE of the hemicholiniums of various sizes and the strong binding of 5 support an earlier proposal [Schowen, K. B., Smissman, E. E., and Stephen, W. F., Jr. (1975) J. Med. Chem. 18, 292-300] that the active site of AChE has ample space for rotation about the C-C bond in choline. Compound 5, which has one more carbon between the hydroxy and trimethylammonium than does choline, inhibits much more potently than either choline or the hemicholiniums. Compound 5 provides a correct spacer to span the trimethylammonium recognition site and the esteratic site of AChE. This aromatic spacer interacts favorably with the hydrophobic active site, and the phenolic hydroxyl probably hydrogen bonds to the histidine in the esteratic site. Choline in any conformation and the hemicholiniums are too short to make a strong hydrogen bond.

Metabolic and Bioactivity Insights into Brassica oleracea var.acephala

“…Thus, due to the closely related structure of sinapine with ACh, it may act as a competitive inhibitor for the enzyme . Sinapine has a quaternary nitrogen that probably binds reversibly to the site on the enzyme where the quaternary ammonium of AChE binds .…”

“…Thus, due to the closely related structure of sinapine with ACh, it may act as a competitive inhibitor for the enzyme (24). Sinapine has a quaternary nitrogen that probably binds reversibly to the site on the enzyme where the quaternary ammonium of AChE binds (25). 16), the insect was revealed to be able to selectively sequester, metabolize, and excrete phenolic compounds from its feeding material and exhibited stronger antioxidant potential than its host plant; the AChE inhibitory capacity of the insect material, as well as that of host kale leaves, was also evaluated for the first time, to be compared with that of B. oleracea seeds.…”

Structure-Based Alignment and Comparative Molecular Field Analysis of Acetylcholinesterase Inhibitors

“…Furthermore, the K i values for the same compounds measured by different authors agreed with each other very closely. For example, the K i values of choline reported in refs and were 9.3 × 10 -4 and 9.6 × 10 -4 M, respectively, and K i values of (3-hydroxyphenyl)trimethylammonium in refs and were 2.10 × 10 -7 and 3.10 × 10 -7 M, respectively. Thus, we felt confident that all the data are compatible with each other.…”

“…Biological Activity Data. For this work we have selected 60 chemically diverse inhibitors of AChE (Table ) whose activity was measured by four different research groups. − This data set included two of the three inhibitors (THA and EDR) whose complexes with AChE were characterized by X-ray crystallography . The inhibitory activity of the compounds was expressed as IC 50 values (Table ); the data were either presented in this form in the original publication 31 or calculated from the originally reported K i values 28-30 using the Cheng−Prusoff equation where K i is the dissociation constant of the enzyme−inhibitor complex, S is the substrate concentration, and K m is the Michaelis constant of the substrate.…”

Change in the Mode of Inhibition of Acetylcholinesterase by (4-Nitrophenyl)sulfonoxyl Derivatives of Conformationally Constrained Choline Analogues

“…AChE activity was measured at 25.0 ( 0.1EC by the coupled assay method described by Ellman et al (19). Time courses were followed at 412 nm and were fit to the integrated Michaelis-Menten equation to obtain values of Km and Vmax, as described by Lee et al (8). The initial substrate concentration was 0.5 mM.…”