Inhibition of Monoamine Oxidase by C5-substituted Phthalimide Analogues

Bioorg Med Chem. 2011 Aug 15;19(16):4829-40. doi: 10.1016/j.bmc.2011.06.070. Epub 2011 Jun 29.


Literature reports that isatin as well as C5- and C6-substituted isatin analogues are reversible inhibitors of human monoamine oxidase (MAO) A and B. In general, C5- and C6-substitution of isatin leads to enhanced binding affinity to both MAO isozymes compared to isatin and in most instances result in selective binding to the MAO-B isoform. Crystallographic and modeling studies suggest that the isatin ring binds to the substrate cavities of MAO-A and -B and is stabilized by hydrogen bond interactions between the NH and the C2 carbonyl oxygen of the dioxoindolyl moiety and water molecules present in the substrate cavities of MAO-A and -B. Based on these observations and the close structural resemblances between isatin and its phthalimide isomer, a series of phthalimide analogues were synthesized and evaluated as MAO inhibitors. While phthalimide and N-aryl-substituted phthalimides were found to be weak MAO inhibitors, phthalimide homologues containing C5 substituents were potent reversible inhibitors of recombinant human MAO-B with IC(50) values ranging from 0.007 to 2.5 μM and moderately potent reversible inhibitors of recombinant human MAO-A with IC(50) values ranging from 0.22 to 9.0 μM. By employing molecular docking the importance of hydrogen bonding between the active sites of MAO-A and -B and the phthalimide inhibitors are highlighted.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Drug Evaluation, Preclinical
  • Humans
  • Insecta
  • Isatin / analogs & derivatives
  • Isatin / chemistry*
  • Isatin / pharmacology
  • Models, Molecular
  • Molecular Conformation
  • Monoamine Oxidase / chemistry*
  • Monoamine Oxidase / metabolism
  • Monoamine Oxidase Inhibitors / analysis
  • Monoamine Oxidase Inhibitors / chemical synthesis*
  • Monoamine Oxidase Inhibitors / chemistry
  • Monoamine Oxidase Inhibitors / pharmacology
  • Phthalimides / chemistry*
  • Phthalimides / pharmacology
  • Protein Binding
  • Structure-Activity Relationship
  • Time Factors


  • Monoamine Oxidase Inhibitors
  • Phthalimides
  • Isatin
  • Monoamine Oxidase