Structural requisites of 2-(p-chlorophenoxy)propionic acid analogues for activity on native rat skeletal muscle chloride conductance and on heterologously expressed CLC-1

Br J Pharmacol. 2003 Aug;139(7):1255-64. doi: 10.1038/sj.bjp.0705364.


(1) The 2-(p-chlorophenoxy)propionic acid (CPP) modulates in a stereoselective manner the macroscopic chloride conductance (gCl), the electrical parameter sustained by the CLC-1 channel, of skeletal muscle. In order to determine the structural requirements for modulating native gCl and to identify high-affinity ligands, the effects of newly synthesised CPP analogues have been evaluated on gCl of rat EDL muscle fibres by means of the two-microelectrode current-clamp technique. (2) Each type of the following independent modification of CPP structure led to a three- to 10-fold decrease or to a complete lack of gCl-blocking activity: replacement of the electron-attractive chlorine atom of the aromatic ring, substitution of the oxygen atom of the phenoxy group, modification at the chiral centre and substitution of the carboxylic function with a phosphonate one. (3) The analogues bearing a second chlorophenoxy group on the asymmetric carbon atom showed a significant gCl-blocking activity. Similar to racemate CPP, the analogue with this group, spaced by an alkyl chain formed by three methylenic groups, blocked gCl by 45% at 100 micro M. (4) These latter derivatives were tested on heterelogously expressed CLC-1 performing inside-out patch-clamp recordings to further define how interaction between drug and channel protein could take place. Depending on the exact chemical nature of modification, these derivatives strongly blocked CLC-1 with K(D) values at -140 mV ranging from about 4 to 180 micro M. (5) In conclusion, we identified four molecular determinants pivotal for the interaction with the binding site on muscle CLC-1 channels: (a) the carboxylic group that confers the optimal acidity and the negative charge; (b) the chlorophenoxy moiety that might interact with a hydrophobic pocket; (c) the chiral centre that allows the proper spatial disposition of the molecule; (d) an additional phenoxy group that remarkably stabilises the binding by interacting with a second hydrophobic pocket.

MeSH terms

  • 2-Methyl-4-chlorophenoxyacetic Acid / analogs & derivatives*
  • 2-Methyl-4-chlorophenoxyacetic Acid / chemistry*
  • 2-Methyl-4-chlorophenoxyacetic Acid / pharmacology*
  • Animals
  • Binding Sites
  • Chloride Channels / biosynthesis*
  • Chloride Channels / drug effects
  • Chloride Channels / genetics
  • Humans
  • Male
  • Muscle, Skeletal / drug effects*
  • Muscle, Skeletal / physiology
  • Oocytes / drug effects
  • Oocytes / metabolism
  • Quantitative Structure-Activity Relationship*
  • Rats
  • Rats, Wistar
  • Stereoisomerism*
  • Xenopus laevis


  • Chloride Channels
  • 2-(4-chlorophenoxy)propionic acid
  • 2-Methyl-4-chlorophenoxyacetic Acid