Fig 1.
Cinchona alkaloids.
Fig 2.
Structures of cinchonidine (CD) and cinchonine (CN) compounds.
Absolute configurations, opposite in pseudo-enantiomers at positions 8 and 9, are marked with an asterisk and noted; (8S,9R) in cinchonidine and (8R,9S) in cinchonine.
Fig 3.
Representative inhibition experiment of BChE inhibited by CN-Bzl and AChE inhibited by CD-(mCl).
Points indicate the average apparent enzyme-inhibitor constant (Ki,app) at a given substrate (acetylthiocholine; ATCh) concentration according to the Hunter-Downs equation. The lines derived from linear regression analysis and y-intercept represent the enzyme-inhibitor dissociation constant Ki. The concentrations of CN-Bzl and CD-(mCl) used in experiments were 2–10 μM and 10–40 μM, respectively. For BChE and CN-Bzl determined enzyme-inhibitor dissociation constant (Ki) and enzyme-substrate dissociation constant (Ks) were 2.9±0.3 μM and 0.29±0.04 mM, respectively. For AChE and CD-(mCl) determined Ki and Ks constants were 23±1 μM and 0.74±0.08 mM.
Table 1.
Inhibition of human BChE and AChE by the tested compounds.
Table 2.
Stereoselectivity of BChE and AChE.
Fig 4.
CD-(pBr) (thicker stick model) and CN-(pBr) (slimmer stick model) in the active site of BChE (yellow carbon atoms) and AChE (grey carbon atoms) obtained by ONIOM calculations.
A) overlay of CD-(pBr) bioactive conformers; B) overlay of CN-(pBr) bioactive conformers; C) overlay of CD-(pBr) and CN-(pBr) bioactive conformers from AChE; D) overlay of CD-(pBr) and CN-(pBr) bioactive conformers from BChE.
Fig 5.
CD-(pBr) (stick model) and CN-(pBr) (yellow stick model) in the active site of BChE obtained by ONIOM calculations.
The hydroxyl group hydrogen bond is marked with a green line and the values are given in Å. Only amino acids in the vicinity (up to 5 Å) of the compounds are displayed. Hydrogen atoms of the amino acid are omitted for clarity.
Fig 6.
CD-(pBr) (stick model) and CN-(pBr) (yellow stick model) in the active site of AChE obtained by ONIOM calculations.
The hydroxyl group hydrogen bond is marked with a green line and the values are given in Å. Only amino acids in the vicinity (up to 4 Å) of the compounds are displayed. Hydrogen atoms of amino acid are omitted for clarity.